Tested: How Much Slower Are Idler Bikes For Climbing?

Aug 18, 2021
by Seb Stott  
03.06.21. Pinkbike BikePark Wales Rider Seb Stott. PIC Andy Lloyd www.andylloyd.photography andylloyder

Bikes with a high pivot and an idler pulley are nothing new, but until recently were pretty much confined to downhill and freeride rigs. Now though, following huge success in downhill racing, they're making their way into the enduro and trail bike categories. In fact, a pretty high percentage of the enduro and trail bikes released lately use high pivot suspension.

With their rearward axle paths and minimal pedal-kickback, they have advantages when riding down hill, particularly when it comes to reducing harshness over square-edge bumps. But what about climbing? The idler pulley must create some amount of drag, not just to turn the bearing in the pulley, but also to articulate the chain pins as the chain (which is under tension) bends around the idler wheel. Many high-pivot bikes also require a lower guide pulley on the lower chain span to reduce the chain growth there, which could add a little more drag. The question is: how much drag, exactly? And how much slower (if at all) is an idler bike uphill?

Crunching The Numbers From Levy's Efficiency Test

The first thing that got me intrigued about this question was Mike Levy's Efficiency test from last year's field test. Levy rode all ten bikes - five from the trail bike test and five from the enduro category - up the same hill at an impressive 300W. What struck me is the fact that the two idler bikes (the Actofive P-Train and the Norco Shore) came dead last. The P-Train, which was in the trail bike category and so had faster-rolling control tires, was slower than all the non-idler enduro bikes.

Norco Shore review
Tom Richards photo
The Norco Shore and Actofive P-Train were the two slowest-climbing bikes from last year's field test by some margin.

You could be forgiven for chalking that up to the fact that these bikes were the heaviest on test. But climbing speed on a reasonably steep, non-technical climb has a very simple linear relationship with total system weight (the system weight is the total weight of the bike plus the rider, which in this case was Mike Levy, at 70Kg). So, if the system weight went up by 1%, all else being equal, we'd expect the time to go up by 1%. If the climb was less steep, we'd expect the time to go up by less than this because aerodynamic drag would become a factor irrespective of the weight. Check out bikecalculator.com or this video to go deeper on this.

The thing is, the system weight of Levy on the P-Train was 3% heavier than the next slowest trail bike (Ibis Mojo), but the time was 9% slower. Similarly, with the Norco Shore the system weight was 2.7% heavier than with the next slowest enduro bike (Trek Slash) but the time was over 9% slower. In both cases, there's about a 6% discrepancy in climbing speed compared to what we'd expect based on the weight difference alone.

Now, I think Mike would be the first to admit that these tests weren't the most scientific. For one thing, he only did one climb on each bike so we can't be sure if the results were repeatable and consistent. It also doesn't prove that it was the idlers making those two bikes go slower up hill; it could also be suspension bob, which robs power by oscillating the shock. But high pivot bikes can be designed to have very little pedal bob if the pivot and idler locations give the right amount of anti-squat. So what would happen if you took pedal bob out of the equation and just focused on the drivetrain losses?

Forbidden Dreadnought vs Privateer 161 Climbing Test

To try and find some answers, I did my own testing on a Forbidden Dreadnought, which has relatively little in the way of pedal-bob. I rode up the same 10% tarmac climb four times at 300W (I couldn't face being out-done by Levy). I did the exact same thing on a bike without an idler (Privateer 161) with the same wheels and tires, set to the same pressures. Both bikes had clean and freshly-lubed chains, using the same chain lube. I used the same SRM power meter pedals for both bikes, and used the lockout on both bikes to minimize the effect of pedal bob, making it more of a test of drivetrain efficiency than overall efficiency including pedal bob.

On average, the Forbidden was just 0.8% slower than the Privateer in this test. However, the Privateer weighed 0.66 kg more than the Forbidden (16.46 kg vs 15.8 kg, with pedals, respectively) so if we want to know about drivetrain efficiency, we should account for that.

Bike Calculator tells us that with a 10% gradient and my 86 kg weight, the Forbidden would go 0.66% slower if it weighed as much as the Privateer (this is the same as the percentage difference in system weight). If we increase the Forbidden's times by 0.66% to account for its lighter weight, the average difference grows to 1.5%.

This is just a crude real-world test, not real science. The error bars on the 1.5% figure are pretty wide, so it's not a precise measurement. But it does suggest the Dreadnought is less efficient than the Privateer once you take weight into account, though the discrepancy is a lot smaller than it was for the two idler bikes in the field test. Maybe those two bikes had a lot of suspension bob, or perhaps something about their idlers was less efficient.


Power Meter Efficiency Test


To get a more accurate and reliable idea of the amount of drag in the idler, I set up another experiment. I borrowed a Wahoo Kickr smart turbo trainer, which has a built-in power-meter, to measure the power being transmitted to the cassette. I first mounted the Forbidden to this, then the Privateer, and used the same SRM pedals to measure my input into the drivetrain. I used the same crank on both bikes so I didn't have to re-calibrate the pedals when I swapped bikes, and I used the same chain too (with a few links removed for the Privateer) to ensure no difference in chain efficiency. I warmed up the power meters before taking any measurements. The Wahoo can self-adjust to provide a consistent amount of resistance, which I set to a realistic 230W. This meant that the output power from the drivetrain was exactly the same each run, whereas if I had aimed for a certain input power at the pedals, this is harder to keep consistent. I pedaled at a consistent 90 rpm, and measured the average power at the pedals required to maintain that 230W at the cassette. I measured the average power over two minutes of steady pedaling; it took around one minute for the average power numbers to settle down to a consistent value.

On the Forbidden, the average power at the cassette was 230W, and the average power at the pedals was 264W. On the Privateer, my average power at the cassette was again 230W and the average power measured by the pedals was 258W. I repeated this test and got the exact same result.

So, to have the same 230W output power at the wheel, you need six more watts at the crank on the Forbidden. That's 2.3% more power required from the rider to go the same speed on the Forbidden; alternatively, you'd go about the same percentage slower uphill at the same power output. This is slightly higher than the figure I came to from the real-world test, but it's in the same ballpark given the error bars, and the indoor test is more likely to be accurate. This test probably isn't precise enough to go into decimal places, so it's more reasonable to say the Dreadnought is about 2% less efficient.

Caveats

This test isn't meant to be the last word on idler efficiency. You could do this test with a whole range of different cadences, power outputs, chain lubes and conditions of drivetrain wear. The chain in this test was new, clean and well-lubricated; otherwise, the power losses at the idler might be higher than they were in this test. Different bikes with different idler designs might have different amounts of drag, too. Despite all those variables, I'm still scratching my head as to why the field test bikes were so much slower.

Conclusion

In the conditions of this test, the idler bike's drivetrain was six watts, or around 2%, less efficient. So if all else was equal, you'd have to pedal 2% harder to go the same speed, or go about 2% slower for the same effort. By "if all else was equal" I mean ignoring any differences in pedal bob (another source of inefficiency) or weight. Some idler bikes may have more pedal bob and more weight than non-idler bikes in the same category, but this isn't always the case.

Is that a big deal? Having to put down 2% more watts isn't something you're likely to immediately notice in the real world or in a blind test. Having done a lot of pedaling on the Dreadnought before taking these measurements, it's not as if the bike feels markedly slower than other enduro bikes. On the other hand, if you could consistently go 2% faster for the same effort, that's a relatively big deal as far as the differences between modern bikes go. To get the same benefit in terms of climbing speed, you'd have to drop 2% of the system weight (bike + rider) - for an average 75 kg cyclist and 15 kg bike, that's about 1.8 kg. And unlike a weight penalty, the power loss will significantly affect riding on the flat as well as up hill. So, is a 2% difference in efficiency a big deal to you?

Assuming this test is accurate, how significant is a 2% loss in efficiency (climbing speed) to you?




322 Comments

  • 764 21
 First to comment...probably gonna screw this up. Idle means doing nothing therefore idler pullys do nothing to impact climbing efficiency. Did not read article first.
  • 122 3
 I'll give you an upvote to support your goal of getting some upvotes.
  • 59 21
 Idle is actually french for heavy, so it does impact climbing.
  • 25 2
 Here, have an upvote.
  • 5 2
 Nailed it.
  • 31 0
 @rokokong: idle is not heavy in french idle means nothing in French, in my french anyway.
  • 160 1
 @ybsurf: Excuse my French but there's nothing worse than American Idle
  • 13 1
 Hard to argue with that. Case closed. hire this guy pinkbike, would have saved you all that trouble.
  • 12 3
 Idle means putting out no power, “idlER” means even beyond this i.e. consuming power therefore idlers consume power. That’s just science.
  • 6 0
 @Drew-O: i didn't say it was scientific
  • 6 0
 Idle means running without throttle applied. I idle all the time. Some might say I'm idlely or "The Idler"
  • 2 0
 @mi-bike: not enough upvotes here...
  • 6 0
 @pugafi: I take it as a complement that Simon Cowell logged in to downvote me though
  • 2 0
 Every 60 seconds....nah never mind.
  • 1 0
 Love it XD Big Grin
  • 3 0
 @rokokong: in Latin it could mean chainless , so would have no impact whatsoever !
  • 2 0
 Without purpose or effect; pointless, or a pulley that transmits no power but guides or stretches a belt or rope.
  • 2 38
flag PDXooo (Aug 18, 2021 at 12:02) (Below Threshold)
 lol Please Read Articles First as you're Obviously inexperienced with matters of drivetrain efficiency... ANYTHING on the rotating assembly of a bike(or car, or fan) - ANYTHING with a mass, requires more energy to move(rotate in this case)... This article just goes into 'by how much', in order to ascertain 'how much it may matter' & in the end 'how much might it matter to you as a rider'... =]
  • 7 0
 @PDXooo: Thank you very much for adding 2 very impotant and entertaining percent of basic physics background information to my knowledge.
  • 1 0
 @rokokong: only in france
  • 1 3
 more scientific than the formulas used in the article
  • 3 0
 @ybsurf: in my French either ... maybe Belgian, Luxembourg or some other Francophone country dialect ?
  • 2 0
 Eric Idle is a funny mother&#$#
  • 5 0
 @seb-stott spend countless hours putting together this article, you stole the spotlight with a one minute comment- how is that for climbing efficiency?
  • 2 0
 how????????????????????????????????????????????? GG
  • 1 0
 Gold
  • 2 0
 @rokokong: Idle isn't french and there's not word sounding or wrote like that in french
  • 1 0
 Sounds about right
  • 3 0
 @Supergirl56: He didn't read the article...or your username.
  • 1 0
 @Drew-O: You know what you can do with your science....Only thing worse are facts.
  • 1 0
 @rokokong: yeah but only in France.
  • 1 0
 @PDXooo: your friends must find you boring for sure.
  • 2 3
 @inonyme: You'll be happy to know, that I Don't Have ANY Friends... -.- #YouJERK
  • 2 0
 Spoiled gutless mommas boys cannot climb any bike no matter how modern...Shut up and ride!!
  • 1 0
 @curendero: ebikers don't need no mommas!
  • 1 0
 @nicolassherbrooke: what do you know about french huh? mr maple leaf ..
  • 1 0
 @rokokong: what do you know about French huh ? Mr masonry ...
  • 1 0
 @Balgaroth: That idle means heavy, like my first comment
  • 1 0
 @rokokong: time to go back to French class boy
  • 2 0
 you didnt even have to cause the writer is a complete idiot.Everyone that owns a Dreadnought knows they are the best.
  • 97 1
 Damn. That's German level thought experiments with well enumerated caveats. Well done for the gedanken.
  • 13 1
 *Gedanken
FTFY.
  • 5 0
 This makes sense if you compare a geared bike (2 jockey wheels) and a single speed. IIRC you lose a few percent with a mech which doesn't bend the chain as much as an idler. The straighter the chain the more efficient it is.
  • 5 0
 @fartymarty: you can even tell the difference between a vertical frame dropout ss with tensioner (even the decent dmr one) and adjustable dropouts without tensioner (i've had both). Pretty subtle but still there.
  • 2 0
 @fartymarty: Same with larger vs smaller jockey wheels. Ideally the idler should be bigger to minimise the losses which mostly come from the chain bending.
  • 2 0
 @tremeer023: yeah proper single speed feels super efficient compared to a mech. I've not had a tensioner on for a while so can't really comment. It makes sense and idler is less efficient.
  • 1 0
 @fartymarty: idler adds only another bending point for the chain, compared to standard derailuer drivetrains.
I think the longer chain on idlered bike elongates more and idler also makes the chain work in improper angles most of the time.
  • 2 0
 @fluider: does it actually add another bending point thought? Without an islet, the chain wraps 180 degrees around the chainring. With an older the chain wraps 90 degrees on the chainring and 90 degrees on the idler. All you’re adding is another bearing.
  • 2 0
 @BrianColes: Chain running on and off the teeth of chainring also adds drag. You can see the rollers rotating.
  • 2 0
 @fartymarty: mechs bend the chain more than the idler, look at the pictures above
I think the difference is the tension on the chain on the wheel
  • 2 0
 @fartymarty: straighter chains are more efficient indeed but the main thing difference between the idler and a mech/derailleur is that the idler is in the loaded part of the chain. The energy loss in a chain drive mainly happens at the contacts between the rings/sprockets and the chain and the more force at these contacts the more losses. The mech is in the unloaded part of the chain so very little energy is lost at that point.
  • 68 0
 That indoor test is really well thought out. Science props.
  • 149 3
 It's a good thing this is on a MTB website... If they publish this test on cyclingtips, every roadie on the internet will run out to buy a smart trainer and some power meter pedals so they can run their own tests to see which chamois creme is more efficient.
  • 45 0
 @srjacobs: you see few months ago I'd say that's a nice joke but now I moved to a different country and heard some conversations between some roadies and THEY LITERALLY were discussing which chamois creme is more efficient for pedalling
  • 12 0
 @theoskar57: was it the one made from graphene?
  • 55 4
 @theoskar57: Hahaha! That's hilarious. Stupid roadies.

Sooooo... which cream did they say is the most efficient?
  • 13 1
 Keep in mind the error bars here. Kickr is +/- 1%, SRM pedals are +/-1.5%. Theoretically up to 2.5% could be just the margin of error from the devices. Now granted that's more likely between devices, and did a good job with setup to ensure less issues.

Two other things: Shocks can absorb energy, would like to see them fully locked out or replaced with wood blocks. Additionally the forbidden has a chain guide, the privateer doesn't appear to. I imagine that and not the idler itself is responsible for the loss. Granted guide seems likely to be more needed with an idler since there is less chain wrap on the chainring, but the shore and ptrain get away without it.

I suspect this is largely down to design priorities for the bikes. I suspect the forbidden sans guide would fair much better.
  • 9 12
 @jordanaustino: lower pulley is required for an idler bike. Upper guide does not affect anything since it should not touch the chain in normal pedaling.

Regarding the margin of error on the Kickr/Pedals, I believe that is stating they could be off by that percentage consistently. As long as the measurements are repeatable it is a valid test. Getting the same results twice says it should be fairly accurate. A few more repeats would have been better though.
  • 6 2
 @salespunk: loads of high pivot bikes don’t have a lower guide/roller wut u talking about
  • 5 1
 @salespunk: Idler bikes don't need a lower guide. Mine doesn't have one and it does just fine.
  • 4 0
 @salespunk: my kavenz certainly does not require anything else than the idler. 0 chain drops so far.
  • 16 1
 @jordanaustino: the error in the power meters is measured v true power, which should be repeatable. Therefore, since the same pedals and trainer were used the comparison should be accurate. Had a different set of pedals and a different trainer been used the compounding error would cast doubt on the results.
  • 2 0
 @Mr-Gilsch: Mine too. I might throw one on if I was riding purely bike park but no issues so far.
  • 4 0
 @srjacobs: And then they would blurt "chapeau", the roadie equivalent of "namaste".
  • 4 1
 @jordanaustino: ... not sure about the +/- thing. When you test on the same kickr and with the same set off pedals, they might be off, compared to the accurate measurement of the power output, but since he uses the same kickr/SRM pedals the +/- accuracy doesn‘t matter.
  • 1 0
 @jordanaustino: do shocks absorb energy that would otherwise be used in forward motion on a hardtail? When stood next to my bikes, I can't apply any force to my FS that compresses the shock that would result in my hardtail moving forward. I would genuinely like an explanation so I can stop thinking about it.
  • 1 0
 @kevinturner12: Yes, or at least they can.

Obvious example would be a bike with low anti-squat. You apply power to the pedals and instead of that moving your center of mass forward, the bike "squats" into its suspension. Energy that would otherwise go to moving you forward is instead absorbed by the shock and dissipated by its damper. On a HT this doesn't happen, obviously.
  • 2 0
 @mechaNICK: No it is not. If it were repeatable the calibration would solve for it. They have taken steps to minimize it though of course.
  • 1 0
 @kevinturner12: In theory if you "locked" the suspension you could still lose energy through frame flex in the pivots and such. Locked suspensions also aren't fully locked.

With a true hardtail? No there are still system losses through the frame and drivetrain of course. Power lost to flex can also be returned to the system, like a spring. Socks are very purposefully bad springs that absorb energy though.
  • 1 0
 @Drew-O: I get that a ht doesn't squat but isn't that vertical force just absorbed by the frame and tyres. Pushing down on a FS compresses the shock but doing the same to a ht doesn't move it forward. That vertical force is just used to compress the frame and tires.
  • 1 0
 @jordanaustino: I'm struggling to see how a vertical force can be converted to a horizontal force. Using your spring analogy, the return force is in exactly in the opposite direction to the applied force so wouldn't contribute to forward motion.
  • 1 0
 @kevinturner12: Don't think of it as vertical vs. horizontal. Think of it as: when you're sitting on a bike, there's an imaginary line between the contact patch of the rear tire and your center of mass. You move forward by having the tire's contact patch push on you center of mass. On a HT this connection is direct (tire to frame to your ass) but on a FS with low anti-squat, the connection has a shock in the middle of it. So every time the contact patch pushes, it does so via a shock, which contains a damper whose job is to make sure the shock doesn't return all the energy put into it. So the contact patch (watts in) is losing energy to the shock as it tries to push your center of mass up a hill (energy out).
  • 1 0
 @kevinturner12: Squat is driven by the chain the torque of the chain pulling the wheel either compresses to extends the suspension based on the kinematics of a given bike (anti squat). In theory it can do neither but that's not particularly realistic. (This is what 100% anti-squat is, but there are also oscillating forces involved that might be the "vertical" force you talk about and it doesn't matter that much). If the frame drive force doesn't compress or extend the frame, that force can instead drive the wheel forward.

As for the return of energy to the system with hard tails: www.renehersecycles.com/the-biomechanics-of-planing is fairly well written albeit by a guy who is a bit nutty. cyclingtips.com/2017/06/cyclingtips-podcast-does-frame-stiffness-matter contains an interview with a long time bicycle engineer who tried in vain to prove that frame flex affected drivetrain efficiency (can affect other things though!). Remember we aren't generating vertical and horizontal forces into our bicycles, we are generating torque. Deflection is just storing that up and then pushing it back at us.
  • 2 0
 @toast2266: when roadies talk about anti squat they’re actually talking about testing chamois cream
  • 1 0
 @jordanaustino: yes, I can see how squat happens. What I can't see is that just because you can't see the compression of a ht doesn't mean it isn't happening. If it is just the torque of the chain causing compression you would be able to see it by turning the pedals on a workstand. Ok you would need to put a lot of energy in but it doesn't seem to me that that would happen. The weight and movement of the rider is also needed for the suspension to compress.
  • 2 0
 @Drew-O: at the contact patch the forces operating are gravity which is cancelled out by resistance from the ground and friction which drives you forward. There is no net force pushing towards your centre of gravity.
  • 1 0
 @kevinturner12: JFC dude, you’ve made this way more complicated than it really is. Based on your description there is no way a bicycle can move forward. And yet it does! I don’t think I can explain this to you within the bizarre set of mental constraints you’ve constructed.
  • 1 0
 @Drew-O: sorry, not trying to be awkward. Just your explanation seemed to assume that if there is no movement as in the frame of a ht then no energy is absorbed. There is nothing in my description that would stop a bike moving forward.
  • 1 0
 @kevinturner12: You can see the relation between the drivetrain and the suspension simply by slamming the rear wheel on the ground. On most bikes, the pedals will spin backwards. That's pedal kickback, which almost every bike exhibits to some extent or another. So in reverse, you spin the pedals forward and it'll compress the suspension.

It's seems like everything you're talking about is simplifying forces into vertical and horizontal. But in reality, all of the forces (regardless of the direction they're pointing to start with) get turned into rotational torque. Drivetrain forces are torque around the BB and rear axle, and impact forces are rotational torque around the various pivot points / instant center of the suspension. And that's all exactly the same on a hardtail, the only difference being that impact forces are rotating around whatever the flex points of the frame are (and obviously the amount of movement in a hardtail is super minimal. But it's not zero).
  • 1 0
 @toast2266: How does MVDP and Tom Pidcock find the time to geeky out about chamois cream AND anti-squat curves???

Or do you think Pidcock is racing the Vuelta Espana and saying "all of you are a bunch of stupid roadies?"
  • 1 0
 @toast2266: yes, I realise I was over simplifying. My question really is whether that super minimal movement in a hardtail uses as much energy as is needed to compress a shock by a more visible amount. Whatever torque or forces are generated are presumably the same in a ht and FS so why would those forces compress a FS frame but not a ht.
  • 2 0
 @kevinturner12: Of course not. A hardtail frame flexes by some minimal amount, and a minimal amount of energy is lost in that system. A suspension frame has that same amount of minimal movement associated with frame flex, but it also has a shock, the entire purpose of which is to absorb energy and convert it into heat. Some of the energy put into the system via the pedals goes into moving the suspension, which in turn moves the shock, which in turn converts that energy into heat. A hardtail doesn't have that, so the only energy that the frame loses (again, by converting it into heat) is from the nominal amount of frame flex. Just like if a shock is locked out, it moves less, converts less energy into heat, and therefore is more efficient.

In other words, any given bike will transfer some amount of the energy you put into the pedals into torque at the rear axle, which drives the wheel. Every bike will have some amount of inefficiency in that transfer of energy. Energy is lost to friction in the chain, energy is lost to friction in the bearings, energy is lost to flex in the frame, energy is lost to movement of the shock, etc. All of that lost energy is converted to heat, which does nothing to propel you forward. The more stuff you add to the system, (like an idler) the more energy is going to be lost to heat along the way. Shocks are just a bit unique because their entire purpose is to convert energy into heat, whereas all of the other components are trying to convert as little energy into heat as possible (i.e. they try to minimize friction).
  • 1 0
 @toast2266: this goes back to my original point. If I push down on an FS some of that energy is used to compress the shock but for a hardtail it is all used to flex the frame. Both systems can use the same amount of energy but in different ways. Just because the shock compresses doesn't mean it uses more energy just that it uses it in a different way. A FS frame will flex less than a ht. In effect all frames have a shock just in a hardtail it is the flex of the frame.
  • 1 0
 @kevinturner12: if you just slowly push down on a HT and a full suspension bike once, most of that energy is being transferred through the bike into the ground. The bikes aren't converting much of it into heat. But if you repeatedly bounce on the bikes, the hardtail is still going to transfer most of that energy to the ground (and convert some nominal amount of it into heat via frame flex) whereas the full suspension will convert a non-nominal amount of that energy into heat via the shock.
  • 1 0
 @toast2266: if you push down with the same force then resistance from the ground will be the same because the weight of rider plus bike will be the same. Even if not, how is the energy transferred into the ground converted to forward motion?
  • 1 0
 @kevinturner12: Huh? You're trying to push down on the bike and get forward motion? I have no idea what you're talking about.
  • 1 0
 @toast2266: that is entirely my point. To compress the shock you need to push down so how can compressing the shock reduce pedaling efficiency? I just want an example of what you could do to a FS bike that would compress the shock but would make a ht move forward. Even if it's a thought experiment.
  • 2 0
 @kevinturner12: You turn the pedals. That creates torque. Some percentage of that energy turns the wheel, and some percentage of it is lost to inefficiencies. Force in the drivetrain compresses the suspension on most FS bikes. Compressing the suspension is one of the inefficiencies that converts drivetrain energy into heat. On a HT, it's the exact same thing except there's no shock so that inefficiency is removed, and therefore a higher percentage of your pedaling energy becomes rotational torque at the rear wheel.

This really isn't that complicated.
  • 1 1
 @toast2266: ok, the only thing I don't get is how to compress the shock without effectively applying a vertical force. Once you apply a vertical force then any inefficiencies are irrelevant because you can't convert the vertical force into forward motion.
  • 1 0
 @kevinturner12: Your premise is incorrect. You can absolutely convert vertical force into forward motion. That's what happens every time you push down on the pedals. And that same vertical force that pushes straight down on the pedals to produce forward motion also gets translated (in part) into torque that rotates the suspension around the linkage and thus compresses the shock.

Both a bike's drivetrain and a bike's suspension are all about taking force that's going in one direction and converting it into force that's going in another direction.
  • 1 0
 @toast2266: there is no mechanism though for the downward force on the shock or on the frame of a hardtail to be converted into forward motion is there?
  • 1 0
 @kevinturner12: On an FS, yes. That's what anti-squat is. On a HT, not really unless the downward force is applied to the pedals.
  • 1 0
 @toast2266: but that means that a ht would be less efficient than a FS.
  • 1 0
 @kevinturner12: Sure, if you completely ignore where the forces that actually move a bike forward are coming from and instead try to drive the bike forward via an inefficiency inherent to a full suspension design, then yes, hardtails are less efficient.
  • 1 1
 @toast2266: an FS doesn't move forward if you push down on it anymore than a ht does. All I want to know is how you can compress the shock without applying a vertical force. A shock is a piston so needs a force to compress it not torque. Or a reason why you apply a vertical force to a FS and not a ht.
  • 1 0
 @kevinturner12: A FS will move forward if you hold the pedals in place to resist the pedal kickback that occurs when the suspension compresses. A HT will not, because there's no pedal kickback to speak of.
  • 1 0
 @toast2266: holding the pedals in place introduces another force into the system though.
  • 2 0
 @kevinturner12: at this point you're just being willfully stupid.
  • 1 0
 @toast2266: not trying to be. If you hold the pedals in place it is that energy that causes the bike to move forward not pushing down on it. You are effectively putting in a small pedal stroke. Thanks for your patience.
  • 41 0
 Great test written up in a great article, easy to understand and it seems like a good methodology. It would be interesting to make the same test of a pinion gearbox.
  • 22 0
 People far more competent than me have tested the efficiency of the Pinion and other gearboxes (Andreas Oehler from FahrradZukunft). This article gives a good explanation of the results (and in English):

www.cyclingabout.com/speed-difference-testing-gearbox-systems
  • 1 0
 ^Seconded!
  • 3 0
 @seb-stott: interesting, thanks for the response
  • 1 0
 @seb-stott:
Interesting data. It suggests a traditional derailleur drivetrain (I think it was Ultegra) would be around 2% more efficient than a Rohloff hub. If you took into account how dirty/worn an mtb drivetrain might be compared to a road one in a lab test, the Rohloff may not lose anything.
  • 2 0
 @DC1988: Add chain skew and inefficency of a 10T cog (polygon effect) and the Rohloff might be more efficient. Something the bike industry doesn't want you to know. Remember im referring only to the fastest gear.
  • 54 20
 who cares climbing sucks
  • 18 43
flag stumphumper92 (Aug 18, 2021 at 9:19) (Below Threshold)
 Exactly why i bought an ebike. I don't have to worry about sh*t like this
  • 4 3
 100%
  • 3 0
 Let's do some times downhill laps against the privateer next
  • 5 0
 With more efficiency it's over sooner so less sucky.
  • 26 0
 If you're testing the idler only, maybe you should put a lower guide on the Privateer as well or remove the lower guide on the Dreadnought, I think that could definitely bring the test closer. I know alot of people running the Forbiddens with no lower guide.
  • 5 3
 It could even be more efficient than privateer without the lower guide.
  • 18 1
 Yes it would be cool to do another test with and without the roller (also with dirty or dry chain), but I wanted to test the bikes how I would actually ride them (there's a good reason the Dreadnought is fitted with the roller guide - it has a lot more lower chain growth without it.)

Also, because the chain is under much more tension in the upper span, I think that's where most of the extra drag comes from (though I can't be sure). It's also worth noting the two field test bikes had no lower guide.
  • 6 1
 @seb-stott: frankly, I'm surprised how many high pivot idler bikes don't have a lower roller, as the lower span chain growth can be huge, presumably doesn't do the clutch any good, maybe holds back suspension performance and wears the chainring faster. I guess it's too avoid *more* friction and needing longer than standard chains
  • 4 0
 Dave beat me to it but yes, the obvious test would be to remove the lower pulley, and compare with and without. Next article hopefully.
  • 2 0
 @seb-stott: considering roadies spend some fortunes in ridiculously oversized derailleur pulley to save Watts, its fair to say that even the slack side of the chain has some impact on efficiency. But if I remember well it is 1 or 2 watts saved by these gimmicks so probably negligeable in a offroad setup with heavy chain contamination going on during each spin.
  • 2 0
 @seb-stott: My understanding is that power loss from idler pulleys is proportional to rotation speed, and that the load applied plays only a very small role.
This is certainly true as far as the drag contributed by the bearings, but may be less so once engagement between the chain and the teeth of the idler gear is also factored in.

The way to test this would be to keep the gear combination and power output the same, but vary the chain speed (cadence).

For a given gear combination and final drive, a lighter rider would pay a larger proportional penalty, because their power output to maintain the same speed on a climb is lower, but the drivetrain loss is fixed.
  • 1 0
 Would a test on back pedal resistance sort this out ?
  • 20 0
 Seb is killing it with his reviews & articles. Great addition to PB team.
  • 15 0
 interesting test. As a druid owner I find this interesting in the way that I know my bike has more traction on tech climbs than any other bike I have owned or ridding up a hill. SO at a possible 2% power loss at the wheel, the gain i get from better traction on tech climbs will always get me to the top faster than ever before. With less mistakes on the climb I burn less energy which is the point of the test in the first place.
It also descends so much better too.
  • 5 0
 This is the exact experience I had when I went from a hardtail to full suspension. Yes, the hardtail is going to be more efficient as a machine, but the traction I got from the full suspension allowed me to ride up steeper grades without slipping on loose gravel or having me get hung up on a water bar. So even though the machine itself was less efficient and heavier, the system allowed me to climb better.
  • 16 9
 As an ex-Druid owner I will disagree. I sold the Druid because it was slower climbing, the rearweard axle path bogged me down on tech, and made the bike feel far less lively pooping off natural features. I found that I needed significantly more speed to perform the same maneuvers on the Druid as I needed on a non high pivot. The long-gets longer, rear center is not helpful for anything but going straight.
  • 4 0
 @nurseben: Not the guy you replied to... but I've heard similar from another guy... but also heard from another few guys (hard charging rippers/jumpers) that, ya it was a little different but they've gotten used to it and don't notice the downsides while the upsides are so good. All anecdotal stories from riders (I live near the area so there are quite a few bikes and I see one on almost every ride these days).

But, your comment makes me wonder if that's why we're seeing some of the newer idler bikes as rather than pure high pivots... but as four bar bikes mixed with a mid-high pivot. Reduce the full on rearward axle path and make it start rearward, then more up and even a little forward at the top. Perhaps that's a better "all-round" solution than the the pure rear-ward path?
  • 7 0
 @nurseben: pooping off features…. Despite you now being my hero i know you need to be lively and wuick when doing this kind of shit
  • 5 0
 @Compositepro: that's right, pooping as I'm popping, just gotta watch that tire rub Wink
  • 3 1
 @islandforlife: Spec Enduro does that. It's a good compromise but there are situations it can get hung up more like a single pivot... big repeated square edge hits. No bike is perfect though, the Enduro is amazing through chatter and corners really well.
  • 2 1
 @themouse77 Except that the real-world field tests found the opposite regarding climbing speed.
  • 13 0
 My beer gut costs me 17% loss in climbing efficiency but instead of quitting drinking i will not buy a bike that loses 2% on the climbs.
  • 13 0
 Clear. Science-y. Interesting. Nice one!!
  • 8 0
 It would be interesting to see how that power loss changed at different power outputs. Is it really 2% or is it always a 6W difference or does it scale with input? To a big rider who puts out a ton of power the loss in watts is going to sting a little less then a smaller guy with a lower output.

Awesome test though, I've wanted someone to do this for awhile.
  • 10 0
 From what I understand, chain friction scales linearly with power. So in that case the 2% figure would be similar for different power outputs. On the other hand, whatever drag is in the lower pulley is probably constant no matter how much power you put in. I think that's a small component, however, given the idler pulley is under far more tension.
  • 1 0
 @seb-stott: ahhh that's good to know!
  • 2 2
 @seb-stott: If Idlers are under so much tension, would putting them on some kind of spring or clutch-like device (similar to a derailleur but smaller/simpler) help with the power losses? If so, I know the idler position is quite important to the suspension kinematics, but would moving it a few mm's either way during big tension moments actually affect performance?

Side note... ran into a guy at my local enduro race last weekend on a Norco Shore. Asked him how he was liking it... said it performed amazingly well but living with it was a pain in the ass... among other things he said the chain would skip off the idler and jam between the idler and guide fairly often. I was surprised...
  • 4 0
 @seb-stott: According to multiple studies shown in the book Cycling Science by David Gordon Wilson chain drive power transmission efficiency actually increases as wattage goes up. From a 1983 study by 'Keller' the efficiency of chain drive at 100W is 97.3%, 200W is 98.1% and 400W is 99.0%. Its a very interesting book and well worth a read.
  • 2 0
 @islandforlife: Dood, removing tension IS removing power.
  • 2 0
 @Eatsdirt: Ya, I was kinda thinking after my comment that I'd probably just make it worse than better, ha!
  • 1 0
 @seb-stott: the overall efficiency may scale linearly with power, but even it if does, the intercept is non-zero, and the slope of the line is not 1:1. The lower the power output, the more significant the fixed component is, so smaller riders are inevitably disadvantaged more.

This paper compared theoretical and measured chain drive efficiency, carefully excluding the efficiency losses from the bearings:
www.mdpi.com/2076-3417/10/21/7729/pdf

In brief, efficiency decreases with increase in power as you say, and also with increased rotational speed and offset angle between drive and driven gears. But if you look at Fig 7, the effect of increasing torque is actually much smaller than a change in offset angle (cross chaining), and also much smaller than the fixed component modelled by changing the damping coefficient of the chain.

Notably bearings also have a significant component of efficiency loss which is not proportional to power, namely seal drag.https://www.skf.com/binaries/pub12/Images/0901d1968065e9e7-The-SKF-model-for-calculating-the-frictional-moment_tcm_12-299767.pdf
  • 2 0
 @Eatsdirt: physics says no.

Wikipedia even handily explains it in relation to bikes.

You can remove tension and keep the same power simply by changing to an easier gear and pedalling faster.

Or you can apply plenty of tension by cranking down on the pedals while keeping the rear brake locked, generating no power at all.
  • 2 0
 @dsut4392: Context. FFS.
  • 1 0
 @Eatsdirt: Sorry about that, didn't read the post you were replying to...in the case of your post, two wrongs did make a right Smile
  • 1 0
 @seb-stott: I'd be interested whether pulley size, tooth profile, or stiffness of the idler mount might explain part of the difference between the Norco and Actofive, and the Forbidden. There's a lot of power going through the pulley, I imagine details might end up mattering a lot.
  • 1 0
 ...also you looked to be in a taller gear on the trainer than Levy was IRL. This might increase losses in the rest of the drivetrain, obscuring the relative effect of the idler.
  • 12 0
 NICE TEST SON !
  • 9 1
 Yes, finally its worth to buy an 499€ cheap OSPW system to save those 2Watts.

Link: www.ceramicspeed.com/en/cycling/shop/oversized-pulley-wheel-systems/ospw-x-for-sram-eagle-axs


Thank me later...
  • 7 0
 There is a slight increase in drag for sure, but when climbing tech, the increase in traction from the HSP on my Druid has allowed me to clean climbs I have never cleaned, keeps me on the bike etc...which seems faster than walking. Almost all my climbing best have come on the Druid. With that said, if you don't keep your drivetrain clean, and lubed, you will experience more drag/power loss from the idler
  • 12 5
 This article says "...Having to put down 2% more watts isn't something you're likely to immediately notice in the real world or in a blind test..." and from the Dreadnought review "...That's (2%) is too small a difference to justify anyone claiming that they can "feel" the extra drag, even if the slight noise of the idler gives a psychological sense of inefficiency"...

I think both of these are wrong. If you're anywhere close to your limit you could tell 2% easily. When you're further from the limit I reckon you'd still get a sense of it. After all no-one really feels the first 150W or so, but they'll be quite sensitive to the upper 30 or so of their sustainable power....so here a difference of 5 or 6 W will totally be noticeable in the real world.
  • 13 1
 Maybe you can notice 2% more power if you're already at or near your FTP, but can you notice going (roughly) 2% slower? In the real world, I think you mostly pedal at a comfortable power rather than a certain speed, and so you'll just go a little slower for the same power.
  • 5 0
 It's ironic because I rode a prototype idler bike with and without earphones and what you hear really affects how you feel about efficiency
  • 2 0
 @seb-stott: Easy to notice when your chain is dirty how much slower your bike is?
Not 2% slower that you notice, it is 2% more resistance that you notice!
If only there was a solution to that?
  • 2 0
 @seb-stott: I've been running a Highlander all year and there is a BIG difference in my speed between that bike and my SB5.5 on climbs (on the descents, the Highlander crushes extra hard). Admittedly, the Highlander weighs a few pounds more AND has the idler (although I took out the extra idler bearing seals and the drag on the pedals is noticeably less), which has got me thinking that it might have something to do with the anti-squat.

Do you think that it is possible that the changes in anti-squat are more pronounced on a high pivot bike? Could it be that the anti-squat value is very high when the bike is level (manufacturers provide the value in this way) but then dramatically decreases when the trail pitches up? I don't know enough about the way anti-squat is calculated to know one way or the other but the change in character is so dramatic, I thought it might be something like that contributing to the perceived effort.
  • 9 1
 @seb-stott: on a 1 hour climb 2% is 1.2 minutes. Imagine riding with equally matched friends and being a full 1.2 minutes behind- that's enough to make you feel bad for holding up the group. That's enough that if you were on your non-idler bike and you were waiting for your friend you'd just be starting to wonder if you need to start riding back down to see if they had a heart attack.

I doubt if there is a real way to test it going downhill, but is it likely that its 2% faster going down? MAYBE on rough enough terrain (like double black or red).
  • 1 0
 @twonsarelli: You could try sealing your chain in a box or bag or casings to keep your chain/drive clean, which will make more difference than 2%
Can make you up something if you would like to test?
You could see difference in anti-squat by using idler or re routeing chain normally without idler?
Would be interested in results!
  • 2 0
 @ICKYBOD: That's where I noticed it. I go on a group ride with friends at the normal local trails. We ride together all the time, and I know their pace. Then I get on a bike with a less efficient drivetrain, and all of a sudden I'm either off the back or having to put out a noticeable increase in effort. I can't tell you what the numeric difference is, but I know it's there and I know it's noticeable.
  • 1 0
 @ICKYBOD: Yup, the riding I do includes a lot of climbing. I'm a decent climbing but not the lightest dude so I need as much help as I can get. Admittedly, I'm not buying one of these tanks anyway.
  • 1 0
 @aljoburr: The shape of the real triangle doesn't allow the chain to go directly from the cassette to the chainring, so no way to compare how it feels in that sense. Also, that would result in massive pedal kickback, seeing as how the idler is there for exactly that purpose. The seals had a lot of drag but I don't ride in wet conditions, so it hasn't really been an issue to remove them. It actually allows the idler a bit of side-to-side play, which I think helps it maintain better alignment as the chain shifts across the cassette.
  • 1 0
 Anybody have a good power meter here? We need to do testing with a lightweight tire like the Ardent and compare it to DH casing minions. I wouldn't be surprised if the efficiency loss is comparable to a clean idler.
  • 1 0
 @seb-stott: hmmm I don't know, when you frame it like that maybe you're right.... if you were cruising easily up a fireroad at 8mph and someone pressed a magic button so you were suddenly doing 7.84 would you notice the moment it happened? I kinda think you might,..possibly, maybe not! I think the presentation of the 2% is interesting,...it seems like such a little amount, but I'd argue the range of perceptible power is a good chunk smaller than absolute power, and the significance of the '2%' becomes greater the closer you get to your limit, I'd guess it's perceptible a fair way from FTP.
  • 1 0
 @tb927: if my ongoing high pivot vs switch infinity experiment is anything to go on, i would kill to have the difference be just 2%. It feels more like 50.. (again, surely not all due to the existence of the idler)
  • 7 1
 Was hoping this would go a bit deeper and include tests of idler bikes without the e13 chain guide like the Cannondale or Acto. People running the Forbidden's without the e13 guide and with something like a MRP guide notice a perceived reduction in friction. Interested to see if this is correlates with increased efficiency.
  • 1 0
 ^This
  • 2 0
 A buddy of mine removed the guide on his Druid and noticed maybe a tiny amount of friction reduction, but also dropped a bunch of chains,,,,,That (and for the reasons mentioned in another comment above), he put it back on:

"I'm surprised how many high pivot idler bikes don't have a lower roller, as the lower span chain growth can be huge, presumably doesn't do the clutch any good, maybe holds back suspension performance and wears the chainring faster."
  • 1 0
 @Marky771: Most people that ride a Druid with the clutch off for that very reason. Reduces tension on the chain and allows the suspension to move more freely.
  • 6 0
 I've had an idler bike and I can say confidently that it defenitly felt like more work on the climbs wether this is precived or actual fact (2%???) it's enough for me to not want an idler bike as my "trail bike" or "one bike to do it all".
  • 6 0
 Can the chain get to the cassette on the forbidden without the idler? for the wahoo test, that would be the best test for the exact difference, locked out on a trainer, the chain won't grow enough to be an issue.
  • 1 0
 This would be the best test, but I do appreciate the effort seb has gone to with this test.
  • 1 0
 Exactly what I was thinking.
  • 16 11
 Having owned and ridden a Druid, I can attest to the impact of the idler: You can feel the resistance when riding as well as hear it.

Of course there is something that remains unaccounted for and that is the affect of the rear suspension on forward momentum, esp. when climbing tech.

Yes, in theory a high pivot suspension softens/absorbs a square impact by moving the rear wheel backwards, but by absorbing the impact it also absorbs forward momentum.

This ^ is the five hundred pound gorilla that no one wants to talk about with these high pivot bikes.

Yes, the high pivots seems to be faster and better for certain downhill applications, but not so much for all mountain riding.
  • 3 0
 If the suspension is absorbing an impact then that is not being transmitted to the body of the rider. Moving the rider absorbs and eats up energy. I don't know which is more efficient exactly; moving the shock or moving the rider, but less force into the rider should mean less fatigue. Isolating the rider from vibrations and heaving due to transmissions of force from the surface are something that has lead to efficiency gains in the road world over the last few years.
  • 5 0
 I think your physics are wrong here, but I'm sure we have a physicist, or worse, a bunch of engineers in the crowd somewhere, unless PB is only read by (fake) lawyers and (fake) doctors. The rear axle moving (slightly) backwards reduces the force absorbed by the wheel vs a standard axle path and the bike and rider maintain greater forward inertia as a whole. If you wanted to, you could view the entire bike and rider as a single mass; if the rear wheel can get over an object with a lower impact, that mass should maintain a higher speed.
  • 2 0
 And this was not tested neither on tarmac nor on the trainer.
  • 4 0
 @shredddr: I'm a fake engineer and yes, backward axle path means fewer forces so, for the same size of bump, fewer kinetic energy lost. So you keep your momentum better. The energy moving the shock would be lost anyway, moving the shock less and raising the rider's height more so it doesn't count.
  • 1 4
 @faul: ... and yet, it didn't feel that way to me or to anyone of my riding buddies. We all felt like the bike bogged down when it hit objects, and though the impacts seemed muted, the loss of energy was palpable. The loss of "activity" was most obvious when hitting square edged features that engaged the rear suspension.
  • 4 0
 @nurseben High pivot bikes carry more momentum on rough terrain, not less, and this applies to going both uphill and downhill. Here's a nice explanation: youtu.be/zHt1TCFvMV4?t=368
  • 6 0
 I had a Druid and now a Dreadnought and this was not my experience at all, I had a coil on both bikes. What shock did you have on it?

Climbing, I will give you, I definitely feel slower on flat rolling stuff compared to my previous bike. But through technical climbing I keep up fine and clean stuff I was not doing on other bikes (could just be me getting better).

Downhill, this is anecdotal, but everyone I ride with says I pull away in the rough and given that it feels like I am holding on to a freight train when I am off the brakes, I would say that adds up. I rode it back to back with an SB150 and its not close in regards to stability. I tried hard to not drink the koolaid...but its delicious
  • 1 0
 @nurseben: What was the bike? what shock?
I think your feeling is unrelated to the "high" pivot/idler itself.
Sounds more like a rebound issue, maybe due to shock internal settings or really low kickback of the frame. Or the opposite, a too soft spring rate.
  • 1 2
 @faul: I rode a Druid with multiple shocks. I'm competent with suspension set up, so it was definitely a suspension design issue.

I'm riding CBF and Four Link now, but I have ridden DW, Split Pivot, a bunch of single pivots, Trek, Specialized, etc...

I tend to prefer a more active suspension, so the Druid was not my cup of tea.

I ride a lot of very technical terrain, rocky, chunder, sand, ledges, steps, big climbs, etc... and the Druid felt like it was slowing me down and throwing off my game.

On the down, the Druid was interesting, it really did suck up landings, but at the same time it sucked up take offs, so everything felt muted.

What turned me off most to the Druid and high pivot design was that it took more energy to get the same pop.
  • 5 0
 I owned a Druid for a period of time. It has this unique muted efficiency, which when you got use to it, was one of the fastest "trail" climbers. Trail being relatively flat, non-technical single track . Instead of experiencing the small bounces, it would motor up normal trails very fast. It never felt fast, but my fastest climbs to date were on the Druid.
  • 5 0
 I own a Forbidden Druid and a Transition Carbon Sentinel.

While I can't speak to Watts/Powermeters and the scientific side of testing, I can tell you: I run the same tires and tire pressure on both bikes. Both bikes have a Push 11/6 coil shock. After 1,000kms on the Druid I'm consistently faster on the same climbs with the Druid. I believe this is due to the better traction the Druid gets me. The Sentinel is the more playful bike (after installing a Cascade link), but I do prefer riding the Druid. It's a fabulous bike and the idler is a non-issue for me. I service my own bikes and don't mind giving the idler wheel some love from time to time.
  • 3 0
 the dude who s done the reviwes is a complete idiot. I own a Dreadnought a Stumpy evo and a Bronson V3 ( 201Cool , the Dreadnought is the best bike ever.Like I dont get his f*cking review.
  • 4 0
 I would like to see this compared to say an EFFI gear bike where the output shaft is already up and you wouldn't need an extra idler pulley. How would the extra resistance of the EFFI gearbox stack up against this 2% of the idler pulley? Of course the EFFI bike could have an chain tensioning device as well.
  • 2 0
 There's some good info on gearbox efficiency in here:

www.cyclingabout.com/speed-difference-testing-gearbox-systems

"In the test, a Shimano Ultegra 2X drivetrain achieved an average of 96.2% drivetrain efficiency, while a SRAM Force 1X drivetrain averaged out at 95.1% efficient. This means that a Rohloff hub likely runs 1-2% less efficient, while a Pinion gearbox or Shimano internal gear hub is 5-6% less efficient, on average."
  • 1 1
 @seb-stott: The gear you are in also matters. Those figures are an average of efficiency loss over the range of the cassette. Because 11 and 12 speed cassettes are so freaking wide, you get a poor chainline in the extreme gears on either end, with "The [SRAM] 1X drivetrain is as efficient as 96.0% and as inefficient as 92.4%", and this with 11 speed, 12 speed would be worse.
  • 2 0
 @seb-stott: I specifically ask about the EFFI gear because unlike the Pinion it has a high output shaft. With the current trend of high pivot designs, the Pinion would need an idler pulley on top of the weight and drag of the gearbox.

So say an EFFI gear box would be a bit closer to a Rohloff in terms of efficiency and be like 4% draggier than a geared bike. Then substract 2% of the idler pulley and then consider the extra drag of a slushed up with mud idler and it could become quite interesting for a EFFI geared high pivot design riding a lot in muddy conditions (UK for instance).
  • 2 0
 @CS645: if only someone made an effigear, high pivot bike specifically designed for British winters....


www.starlingcycles.com/bikes/spur
  • 2 0
 @hamncheez:

Thanks, that one makes sense!

I hope we'll see a proper review of the Cavalerie Blackbird as well some time: www.cavalerie-bikes.com/blackbird

In general I'm a bit surprised we don't see more attention for the EFFI gearbox with it's high output shaft in the current High pivot trend.
  • 2 0
 @CS645: it is rather curious that Pinion gets all the attention....
  • 5 1
 This test was with the lockout. Levy's test was without the lockout. I have not ridden these particular bikes, but lockouts can make a huge difference on some bikes. IMO that was an error on Levy's test, I think most people use their lockouts most of the time climbing.
  • 5 0
 I'm no engineer, so this might be nonsense:

Wouldn't a more accurate test to see how much an idler saps power be to compare the dreadnought to itself, but bypass the idler on one of the tests?
  • 1 1
 You'd have to replace the shock with a rod.
  • 3 0
 I'd like to see a more direct comparison review of a bike that previously did not have a idler but now does, with a similar component build and weight. As an example, the new GT Force vs the old GT force or the new Trek DH bikes vs the old design (I realize even these are not a perfect comparison)......another thought, idler's are old news and were used 20 years ago, and frankly, if the industry is bringing back old tech, I want to see the industry bring back, and evolve (lighten and perfect), floating brake adapters. Those make a huge difference on certain suspension designs that are still used today.
  • 6 2
 my norco shore is the best bike i've ever had, i could care less about climbing, it climbs fine, if anything it's just making me stronger. going downhill on the shore though.. a friggin dream come true. it's a beast.
  • 3 0
 Question for you... I ran into a guy at my local enduro who was on a Shore... said the same as you about the downhill performance. But he had quite a couple of negative things to say about living with the bike day to day... cable routing around the middle of the bike, the "soft as cheese" ethirteen wheels and cranks (as he put it). But his comment about the idler was interesting.. he said it was crazy how often the chain would drop off the idler and get stuck between the pulley and the guide. Wondering if you've seen similar issues?
  • 2 0
 @islandforlife: that's interesting! so i had mine built from the frame, i don't have the eThirteen components but i did hear about the routing being a real B to get sorted.
i've been riding the shore.. hard for about half a year now, i've never had the chain come off the idler. i do have a friend who just got the range that was having a similar problem though. He changed his bottom chainring from a 28 to a 30 and said it's working better? *i have close to zero mechanical bike knowledge though* so take what i'm saying with a grain of salt.
  • 8 3
 Idler pulleys are the automotive-sport-lowering-springs of the bike world. They:

-Look Cool
-Improve performance in theory
-Don't do much of anything.
  • 6 0
 kinda seems like everyone should just ride downhill bikes, that seems to be all anyone cares about anymore anyways.
  • 3 0
 Yeah, sometimes I wonder if some guys just walk up the hills.
  • 3 0
 On the Forbidden nearly all the drag is from the lower E13 guide. It’s horrible, makes loud noises, chain jams the roller, sucks power and looks ugly. I removed it on my Druid and the bike improved in all aspects. The upper idler will use power but it’s very small, I’d suspect way less than 6 watts. Maybe 2.
  • 2 0
 But then an idler in theory will tame the downhills more and therefore give you more energy in reserve to tackle the climbs? I know I’ve definitely felt less fatigued than riding buddies from just better suspension, that’s going to transfer to more power on the climbs over a normal ride?
  • 2 0
 What am I missing? Doesn't this all depend on the antisquat of the suspension in the climbing gear? Or is this really just about the extra drag due to the extra pulleys and way longer chain? If it's just about the extra drag, then that 2% would be a penalty everywhere and not just in climbing.
  • 1 0
 Never ridden one, but supposedly there's actually quite a bit of tension on that idler pulley. So I think it's about how much drag is added by driving that tension up, over and around another pulley.
  • 1 0
 @islandforlife: So it would be the overall efficiency vs just "does it climb slower?"
  • 4 0
 The Poll needs a caveat: for an enduro/ all mountain type bike: 2% doesn’t bother me.

For a lightweight trail bike/ marathon bike/ XC bike: 2% means a lot.
  • 1 0
 100%
  • 2 0
 This is awesome and we need more tests like this, but it should be noted that 2% more power doesn't mean 2% slower or faster. It's not a linear relationship between watts and time. For instance, if a climb takes 100 minutes on a standard bike, and then you do the same climb and lose 2% to the idler, the time up the climb will not be 98 minutes. It will be slower, but by exactly how much probably needs to be calculated on an algebraic curve taking into account grade of climb and wind speed.
  • 5 4
 It's not quite a deal-breaker, but its a strong factor. I bought a new bike this year, and the Forbidden was very close to being the bike that I bought. But the complications of the high pivot design (poor efficiency, extra maintenance) were one of the factors that lead me to go in a different direction.
  • 2 0
 I'm skeptical it's much more maintenance, though maybe that depends where you live and riding conditions. Yeti's switch infinity's need a little extra labor, Santa Cruz have bearing life issues, loads of Horst main pivots seem to have a short life, I've seen people bitching about the sheer number of Evil Delta bearings. I think the guys riding in moondust have had their share of complaints, but I'd be interested to see if the new solid lube bearing alleviates this. Along with the teased stainless idler...
  • 2 0
 I'd be interested in seeing what the results are without the lower guide. I know some folks with Forbidden bikes run them without that, or switch the stock one for the MRP SXg and (anecdotally) report feeling less drag.
  • 1 1
 A buddy of mine ran his Druid without the lower guide and dropped chains quite a lot. Not worth it for him to get a hair less drag (he said it wasn’t that noticeable after removing anyway).
  • 4 0
 I bet the 2% less efficiency comes less from the idler and more from the chain guide on the Forbidden...
  • 3 0
 Soooo what you are saying is I am 2% fitter than my mates? lol Been riding a Druid for 3 years now and honestly 2% is negligible compared to the benefits on the downhill.
  • 1 0
 Without the lower guide, I bet the drag in the drivetrain is significantly lower. I think it would be easy to optimise the idler mechanism to minimise impact. Bearing to shaft alignments etc. Some of that roadie derailleur pulley magic would help too.
  • 1 0
 Some of my hobby work includes creating precise mechanisms for astronomy. Sprocket bearing alignment makes a huge difference to the operation of those. Especially the sprockets that are on a cantilevered shaft.
  • 4 0
 I find I climb better on my idler equipped high pivot bike. Particularly on technical climbs.
  • 2 0
 Same. I find the rear end doesn't get hung up on ledgy parts of a climb. Even better, I don't have to hump the bike (for lack of a better description) over those ledges, saving me even more energy.
  • 2 0
 Where’s Orange? They got bullied out of using idler wheels about 15 years ago after campaigning for them for ages and now they’re in trend they’ve seemed to have gone missing.
  • 2 0
 My high pivot bike (Kavenz) is set up to smash things going downhill, I'm unconcerned with a minor loss in drivetrain efficiency on my enduro bike. I have an XC bike for those kinds of concerns!
  • 1 0
 Anyone know roughly what the difference in watts is between pedals and cassette on non-idler bikes similar to the Dreadnought and 161? I understand that there are tons of factors affecting this but in general how do idler designs compare to others?
  • 2 0
 @seb-stott could you do a similar test where you compare different compounds/casings/tread patterns on some tyres, so we can get a feel for what 2% difference makes in the real world?
  • 1 0
 @seb-stott Great article. I'd like to see the results of the same testing for the new Norco Range, which doesn't have a lower roller and has a larger idler pulley (18t instead of 16t for the Dreadnought). Both of these differences should increase efficiency. Also, in which gears did you do the testing described in the article? Did you measure efficiency for the whole range of gears for both bikes?
  • 1 0
 Why didn't you just do one test on the dreadnought with the idler disengaged and a shorter chain? If the shock is locked out, you do t need the idler. Would have saved you a lot of work. Also, the privateer may have more frame flex or other variables Making it less efficient so the difference between the bikes may be minimized by these variables.
  • 1 0
 @seb-stott: Interesting test but we can't quite make sure the loss of efficiency comes from the idler with different setups. A bearing spinning less freely or too much grease here and there could explain that 6W loss.

Testing the Forbidden with the chain running through the idler and then bypassing the idler would definitely help with isolating the tested variable.
  • 1 0
 My input is quite irrelevant since I only ride hardtails... but I think I really wouldn't mind the power penalty if I preferred the idler bike's descending capability. I recently rode a test loop with my trail and enduro bikes in identical conditions and came out 5% faster on the trail bike, with climbing and descending combined. My conclusion was - subjectively the climb wasn't any more tedious on the enduro, I simply chose a lower gear more often. But the descent was just way more fun
  • 1 0
 I'd care if they start making XC and short travel trail bikes with idlers and I was racing them in a format where climbing mattered.

For the categories of these bikes it means nothing if (IF) the bike performs better on the downs, which is their main purpose.

I wouldn't mind getting to the trailhead after a 30min climb 30s after my buddies as long as I'm first back to the parking lot.
  • 1 0
 If I sit on the can right before my ride, I can drop my body weight by 0.5%, which means my climbing efficiency increases immediately. That will make up for some of the inefficiency the idler pulley I put on my steel hardtail to improve traction creates. The pulley is on a clamp attached to the seat tube so I can adjust its height. I’ll share my power data for different idler positions in a different post.
  • 1 0
 2% less efficient is not a big deal if your aim is to go fast downhill. Would still prefer to forget the complexity and go for a Pinion bike which from the article stats has the same efficiency as an idler bike with a new chain.
  • 1 0
 Well thought out test...
Apart from. Climbs are not on the flat, you should angle the bike to simulate a climb and ensure that the forces are going in the right direction. Also, a hysteresis brake of any type is only a basic simulation of a constant load that will vary with input power and heat dissipation. Better control is needed to evaluate power output (constant current source to real hysteresis brake), that's from my limited experience motor drives and hysteresis brakes, ATE for motor drives too.
  • 2 1
 For total number of required Watts you are right, but...
Power-loss in drivetrain for idler-bike was 34W, compared to 28W.
That is massive.
It all depends how you sell the numbers!
I do think, that idler-bikes are massively overrated(for normal riding, with some climbing), but worth for all the shuttlers and flat-pedallers.
  • 1 0
 More mass probably does not equal slower, it equals less acceleration- practically negligible for a long, constant grade climb. This is assuming force is constant and considering that force= mass * acceleration. The effect of chain length should probably also be considered, as rotational energy is dependent on the inertial energy storage which is dependent on radius squared. Furthermore, speed is not linear with power. Newtonian drag is Force = drag constant * velocity, and power is force * velocity. So power should be proportional to the velocity squared.

With that in mind, it seems that the power loss is mostly coming form the inertial effects of the extra long and more massive chain (as well as the idler bearing drag). This would result in slower acceleration of the drivetrain over each pedal stoke, equating to less linear velocity of the bike. Now its also interesting to note that more drivetrain inertial energy storage is advantageous in rough terrain, where it will allow for torque smoothing and more average torque transmission.

The chain friction should be negligible, as the chain still completes the same angular displacement, but at a lower angular velocity - thus we have opposing affects of lower kinetic friction per link, but more links. That only leaves the drag of the idler bearing itself.

Seems to me that pedaling ability is more than justified by the speed that will come form pumping on a proper rearward axle path design. Just my 2 cents. Cool to see somebody actually measuring these differences
  • 4 1
 Beta got about 1% in their tests FWIW on the Dreadnaught compared to a Scott Ransom.
  • 1 1
 Have you got a link for that?
  • 1 0
 @seb-stott: you re f*cked up dude,the Dreadnought is the best bike ever. Like seriusly you re dumb
  • 4 0
 So, are high pivots faster downhill?
  • 2 0
 Asking the real questions!
  • 5 1
 There’s definitely something going on. When you get off the brakes they accelerate through impacts better than non-HP bikes.
  • 4 7
 -2% faster downhill
+2% slower uphill
+100% more maintenance
  • 4 5
 @jclnv: No they don't, that's the koolaide talking
  • 2 0
 @nurseben: Which models have you ridden and what is reasoning for saying otherwise.
  • 1 0
 @jclnv: Druid
  • 1 0
 @nurseben: Maybe shock set-up related? I needed a different shock tune on the Druid. There is definitely something going with acceleration. When you point it down chunk it gets up to speed quickly. The other aspects people say like feeling like they have more travel I haven’t noticed.
  • 4 0
 2.3% !! OMG thats why im always last!
  • 1 0
 by chance are you related to Towelie?
  • 4 0
 Efficiency will drop by a lot more when chain gets dirty?
  • 2 0
 The real question is... can you spend $2,000 on ceramic bearings in the idler, hubs, pulley wheels, and BB to overcome that 2%?

If PB gives me the money, I can do the test.
  • 2 1
 I’m putting ceramic bearings on my Deviate Highlander build. The idler is the main culprit. Just replacing those with hybrid ceramic is cheap, like $60.
  • 5 0
 i've seen a couple roadie tests that indicate most of the power loss comes from chain frictional losses (being wrapped around small tooth count cogs) rather than the bearings (on pulleys). similarly, going from a 10t cassette cog to 11t (with chainrings adjusted to match gear inches) nets measurable wattage benefit.

so - seems like increasing the idler pulley size (like deviate) would benefit efficiency more than anything (and perhaps reduce drivetrain loss to negligible levels).
  • 1 0
 @xy9ine: interesting. Good point
  • 1 0
 @xy9ine: that makes sense. Will be interesting to see if Forbidden embraces that thinking.
  • 2 2
 Alright, so let's make this "2%" change mean something and provide some context. Because as a number by itself, it's about as useful as tits on a bull.

What is the power difference on a normal drivetrain between having a new chain and a worn chain? A clean chain and a dirty chain? What is the power difference between two gears in the middle of your cassette cluster? How about a straight derailleur hanger and a bent one? Are all of those things that we're all familiar with the feel of >>2%? or 2%?
  • 3 1
 Does anyone have any information on wear items like the chain and the idler pulley? How much more do you spend on two chains and replacement idlers?
  • 1 0
 Well you only need two chains once, if you have a large or XL Druid at least. A full single chain fits medium or lower. And for the larger frames you only need a few links. Just buy two chains once and then you'll have a donor for years to come where you can grab the extra links from.
  • 1 0
 @PTyliszczak: Or get to know you LBS... They will always have a few extra links lying around from other chain installs. Likely just give them to you.
  • 1 0
 Not that much, for riding for fun. but if you put it in perspective in a race, on a 10min run, 2% would be 12s, that s huge based on the last few races won within the same second after 2 days of racing.
  • 1 1
 But this is an enduro bike, and the climbing in enduro races is untimed (and you can push your bike up without pedaling). 2% less efficient on climbs doesn't mean it's also 2% less efficient downhill (which is the direction this thing is built to race).
  • 1 0
 @charliewentoutside: there is still a good amount of pedaling depending on the race, but yeah I agree. Now we need to know how much faster, if any, they are downhill!
  • 3 0
 Yo dawg, I heard you like power meters, so we put a power meter on your power meter so you can get power with your meter.
  • 4 0
 if you're even concerned, buy an XC bike you nerd.
  • 1 0
 And do more squats
  • 2 0
 @CSharp: Take a dump before riding. Weight loss will account for the lost watts.
  • 2 0
 @PTyliszczak: LOL, warming up by squatting in the woods with the bike on the back and expelling a bit of weight while you're at it does help!
  • 1 1
 and dump your water bottle, wussy.
  • 1 0
 I would be interested to hear the effects of high pivot on drivetrain wear as there is less link engagement at both ends. Also does a standard chain contain enough links for replacement?
  • 1 1
 1) Fellow Autist unite, cause I just love these sort of tests! Thanks for doing it.

2) The way I see it if a standard drivetrain is our standard and we call that 100% efficient, the actual losses going to an idler is basically 21% from the standard, which is a HELL of a lot. That's why these bikes feel so draggy. I don't think anyone could feel 2%, at least not as easily as most riders indicate. Yet nearly everyone comments on HP drag after riding them.

There are a few ways to do the math but in it's most basic form 28/230 = gives up 12.2% drivetrain efficiency where-as 34/ 230 = gives up 14.8% drivetrain efficiency. Ultimately the INCREASE in drivetrain efficiency loss increases a full 21% over the standard. (14.8-12.2)/ 12.2 = 21.3

That represents a pretty notable efficiency loss. In an attempt to try and quantify what that would feel like to the average rider I went to the bicycletirerollingresistance website where they measure the rolling resistance of tires, unfortunately they are highly focused on the XC/ light trail side of the equation so there aren't a ton of modern tires listed that most here would have experience with. However 5 watts is the difference between a '21 Schwalbe Racing Ralph Super Race & a Maxxis Rekon Exo. A 6 watt difference can be found between the same Racing Ralph and the Continental Cross King Protection. For example. The RR differences between these tires is very notable to pretty much any rider.

Seb, consider designing a truly accurate tire rolling resistance stand. It should mimic rocky ground and not be a smooth roller which is flawed.
  • 2 0
 No one rides these bikes on pavement or a trainer - is there no efficiency gained by having a rearward axle path over roots and rocks on a typical single track climb?
  • 1 0
 Very valid point. Harder to test for, but I’m sure it could be done. Almost need a treadmill with 2x4s rotating around to control for it.
  • 1 1
 It makes sense that the indoor losses were higher than the outdoors losses. Outdoors, with the shock locked out, your losses are mainly comprised of drag, rolling resistance from the tyres and drivetrain losses, whereas indoors the drag and rolling resistance from the tyres disappear. It is reasonable to assume, that with the shock locked out, and the same tyres and tyre pressures, outdoors there is not much difference between the two bikes for their drag and rolling resistance figures. The idler appears to add 2.3% to the drivetrain resistance but drivetrain resistance is only one factor in the total losses that you experience while pedalling and therefore the affect on the total losses will be less than 2.3%.

In this case, it will vary depending on speed and other factors, it would appear that drivetrain losses accounted for about 65% of the total losses: 2.3 x 0.65 = 1.5. The other 35% of the losses didn't change significantly between the bikes for the outside tests and this is why the drop in performance is more pronounced in the indoor, as the 35% of unchanging losses have been removed from the test.
  • 1 1
 Just sold my Druid. The drag is noticeable, but not a deal breaker. I tired it without the lower guide and it was better, however the lack of chain wrap caused excessive noise from the main chain ring, it annoyed me so I reinstalled it. Mainly you feel the drag because you hear it! And it gets significantly louder as condition worsens. The idler bear is under load, and doesn’t last well. Having to use extra links is a pain and there are quirks with setting up shifting. I have no doubt that if I was mainly descending, I’d be keeping it, but as a do everything bike in my location, I’m going back to a conventional setup.
  • 1 0
 I am always wondering why no one is using bigger idler wheels. Friction is reduced almost linearly with A bigger pulley. On the other hand, friction will go up a lot with a dirty chain.
  • 2 0
 If you own a druid or dreadnought lose the lower guide thats were the drag is coming from , i done that an now ther is no resistance at all
  • 1 0
 I am going to lose more sleep at the cost of two XX1 chains to run on an idler pulley style bike than the 1.2s per minute lost on a climb that isn’t even part of an normal timed enduro stage.
  • 1 0
 My bike has a front freewheel, a draggy rear hub, a cut up old plastic derailleur pulley zip tied as a tensioner, a rubbing chain guide and two rubbing brakes. Do people really care about efficiency of one idler this much?
  • 3 0
 Eeny, meeny, miny, moe...
  • 2 1
 When my car is in idle it pretty much does nothing except wasting gas in exchange of blowing AC to make me comfy, idler pully does things similarly I guess?
  • 2 3
 So today's dish, is high pivot.
Yesterday was virtual pivot
Previously FSR
And the day before single pivot...
Last week we had floating... as like Y bikes from Trek and Slighshot bikes

We're so lost in the suspension department...man!!!!


At leats the 29/27.5 wheel combo is gaining some speed, and we stopped asking/searching for new wheel sizes!
Now...if we could only go back to 26 in the rear, everyone would gain some manoverability

Cheers from the under ground
  • 1 0
 I'm curious if the idler bikes are more than 2% faster on the DH. If they're more than 2% faster down, then there faster over all, and that's what I care about
  • 1 2
 I sold my Forbidden Druid because the idler pulley felt like it had a lot of drag. I don’t know if it was psychological because I could always hear it or if it was simply the 2% but when I changed bikes it felt free again.
  • 1 0
 Back when bikes had more than one chainring I always thought I was a bit nuts for thinking the bike felt better in the big ring. Maybe I wasn't nuts after all.
  • 2 0
 After reading this, the word "Idle" is starting to sound so weird
  • 3 0
 im 230lb so....
2% is 2%
  • 3 0
 2%... yup im around 260lb and to me the climb is decided by will on the given day... Either i climb or the car does the work.
  • 1 0
 It would be easier to understand the numbers if they were in fractions vs decimals and percents.
1/100 % sarcasm.
  • 1 0
 Didn’t read yet, but let me guess — not slow enough to make a difference for most of our purposes.
  • 1 0
 The short of it is: drivetrain efficiency loss can be countered by reduced weight, so if you want a bike with a high idler pulley- get a really light one.
  • 2 0
 @bvd453: That, or lose weight.

But I guess my point is, why does it matter? These clearly weren’t made with climbing in mind. And I don’t think the type of rider buying them have climbing in mind beyond it being a necessary evil before the descent. They’ll still get you to the top, though. Climb up things a little slower, then enjoy it for the purpose for which it was built.
  • 1 0
 Why the wouldn't you read it? Too much information a bit scary ?
  • 1 0
 @TheR: The point is that if you can quantify the loss, then each person can determine whether its relevant to them or not. For me it wouldn't be (although the added complexity and need for additional chain links is a turn off), but for those who race enduro that 2% loss in a transfer or a "pedally" stage might be a deal breaker
  • 1 0
 @NZRalphy: Operative word in my original comment was “yet,” Mr. Wizard.
  • 1 0
 @bvd453: I get your point, but first, do you think most of us are racing? Also, in the case that you are in an enduro race, you also need to ask the question if the 2% loss on the ups outweigh the potential gains on downs and tech.
  • 1 0
 @TheR: Most? No. Many? Yes.
  • 1 0
 I’m putting hybrid ceramic bearings on the idler of my upcoming Deviate Highlander build. About $60-80. Problem solved.
  • 1 0
 Doing quick math
You will be 24 seconds slower on a 20 minute climb
2% difference is like running a 50 gear vs 51 gear
  • 2 0
 Idler, the Poorman's eBike.
  • 1 0
 It should have been: It's a deal-breaker. I want to get to the top as EASY as possible.
  • 1 0
 Where is the vote option for, it’s a bike, go ride it and forget about watts and half percentages…
  • 1 0
 @seb-stott, What would happen if you used the Forbidden with running the chain over the idler for the test?
  • 1 0
 Just went from a non HP Session to a HP one. Rides in my local bike park clearly show faster runs and smoother rides.
  • 1 0
 The voting proves PB users are like sheep they all follow each other with the latest trends
  • 1 1
 To make this test fair, they need to put a power drill into the crankset and power it like that. Then there would be no difference between test riders.
  • 2 0
 If it CLIMBS* better, I really don't care.
  • 1 0
 Just knowing it is less efficient will probably the thing that affects people more than the actual loss of efficiency...
  • 2 0
 Seems about right
  • 1 0
 Nrrrrrgh...the house is so 70's.
  • 1 0
 Gna be really nice for E bikes.
  • 1 0
 Why not just use a jackshaft
  • 1 0
 (even more) added weight & frictional losses, limited crank options (LHD), inability to tune antisquat through drive cog placement (as it's concentric with pivot). they DO look rad, though. envisioning a modern superco-like smashy enduro machine...
  • 1 0
 Always good thought out content from Seb
  • 1 0
 How much do u lose on a chairlift again?
  • 1 0
 exactly what HP was designed for.. Downhill/lift access bikes.
  • 1 0
 Idler E-bike.
340% - 2% = +338% for climping!
  • 1 0
 Let's grab an idler puller and be dick about it.
  • 1 0
 Put into context, 2% slower in 4 minutes is 7 seconds.
  • 1 0
 Would be interesting to see how much worse it is with a dirty drive chain.
  • 13 16
 These test are all so unscientific, that there really is no conclusion that can be drawn by any of them. I appreciate the idea behind them, but in real world riding, no one out there is going to notice this.
  • 3 4
 Are you shore, boy?
  • 6 0
 I agree that 300 watts ridden by 2 different riders can equal drastic changes in times. The body movement changes everything as well.
  • 1 1
 They are really slow because they destroy derraileurs
  • 1 0
 Eat %2 less
  • 2 4
 Does anyone buy 160mm bikes to pedal efficiently up the hill?
  • 5 0
 Yes, otherwise I'd be riding a downhill bike.
  • 2 0
 well yes and no, also depends how you define efficiently, if I put a 28 or 30t chainring(an locked out) on a heavy bike and im not absolutely buggerd at the top I would consider that efficient, I dont buy a bike for how it pedals but how comfy the seated geo is, at 95kg i always drop to 28 or 30t chainring from the stock 32/34, at higher speeds where you would top out a 30/11 tucking is more efficient anyway.

In the end, you could define my opinion is no, but seated geo makes more of a difference as i lock the shock everytime anyway.

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