The Tuesday Tune Ep 12: Leverage Rates

Jan 31, 2017
by Vorsprung Suspension  
Views: 5,981    Faves: 30    Comments: 1


Mountain bike frames have various forms of what we broadly refer to as suspension design, but more specifically could be termed kinematic design. Kinematic design refers to the ways which each member of the suspension linkage move, particularly relative to one another. In other words, the suspension kinematics are the geometric motions of the linkage, before we start introducing force or mass to our considerations.

Anyone who's ridden more than a couple of different mountain bikes is well aware of how different the rear end of the bike can feel, even with the same travel and when using the same shock. Variations in leverage rate, among other things, are a very large factor in determining how the suspension performs, so this week in the Vorsprung Suspension workshop, we're looking at the ways in which variations in the leverage ratio can affect the feel of the bike, and why small changes can result in fairly large differences.

Leverage ratio is typically defined as the ratio of mechanical advantage that the axle has over the shock. This can be an instantaneous leverage ratio at a single point in the travel, or an average leverage ratio obtained by dividing wheel travel by shock stroke. Plotting the instantaneous leverage ratio against travel gives us a leverage rate curve. The difference between ratio and rate is that the rate describes how the ratio is changing throughout the travel. In the motorsports world it is more common to use the term motion ratio, which is the same thing but inverse - it is obtained by dividing shock stroke by wheel travel.

When considering the overall wheel rates - that is, the spring rate and the damping rate when measured at the wheel - it is necessary to understand the spring and damping characteristics of your shock as well as the leverage rate characteristic of your linkage. Some frames work really well with the linearity of coil shocks and relatively poorly with progressive air shocks, and vice versa, and it is this interaction between the leverage rate and the shock's spring characteristics that is primarily responsible for this. An in-depth discussion of how air springs, particularly those of our own products, interact with various leverage rate curves can be found here.

Please note a few things here:
1. As usual, the devil is absolutely in the details. Generalisations, including some of the things we refer to in the video, are not applicable to every variant of any particular linkage design, and this is a long long way from being a comprehensive breakdown of leverage rates.
2. A certain acronym or name for a linkage type does not mean all frames of that type perform or feel the same. They can vary hugely.
3. We're not here to tell you what system is "best". There is really no objective way to assess that - everyone's preferences and priorities vary, and what works well for someone who likes a super firm feel doesn't necessarily work well for someone who wants the plushest thing out there.
4. If you'd like to see what your own bike's leverage rate is like, download a program called Linkage and measure up your own bike to see how it stacks up. Note on using this program: there are a great many existing files out there and a lot of them are a fair way off the mark, particularly on bikes with very short links. Don't rely on clicking on points on a photo for accurate inputs - that can be accurate enough for singlepivot bikes with no linkage, but on anything else it's more than likely going to be misleading. Use a measuring tape to verify distances between points on your suspension if you want accurate results.

Terminology worth knowing:
Linear leverage rate: this would be better termed "constant leverage ratio", as this is what delivers a linear force vs displacement curve at the wheel (if using a linear spring).
Progressive leverage rate: also known as a "rising rate", this creates a force vs displacement curve at the wheel that is progressive, ie an increasing wheel spring rate even if using a linear spring.
Digressive leverage rate: the opposite of the progressive leverage rate.


MENTIONS: @VorsprungSuspension



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80 Comments

  • 16 2
 So the spring is the bit that makes the bike bounce, right?

Cool, got it.
  • 28 0
 That's the one. The dampener is the bit that makes it wet.
  • 2 0
 @VorsprungSuspension: rebound is how quick you can get back up after falling off...
  • 1 0
 Thanks Guys..

This is all great stuff, but please FFS! one thing at a time... I'm still getting to grips with the whole spring/bouncy theory Wink
  • 9 2
 Haha I get the first comment cause everyone else is watching for the third time trying to understand
  • 4 0
 @VorsprungSuspension great video as usual! On the topic of leverage ratios. Was at a Giant dealer a couple days ago... The Reign has a 57mm stroke shock for 160mm of rear wheel travel.... Why oooh why!!??

Seems like even 63mm would have been a better option and that's not even all that much bigger.
  • 17 0
 Higher leverage ratios do have some advantages - more leverage over the friction of the seals in the shock means less stiction, smaller shock means less weight, and making the shock smaller usually makes it easier to package. Specialized also run relatively high leverage ratios on a few of their most popular bikes. The downsides of the higher leverage ratios though are more stress on the shock, requiring higher damping force, which in turn has to dissipate energy in a smaller amount of oil/aluminium, and therefore reduces the thermal mass and the thermal stability of the system as a whole as a result. In theory, you can achieve identical spring curves and damping curves at the wheel with almost any leverage ratio, but in practice it becomes more and more difficult as you go to one extreme or the other (ie very high or very low leverage ratios). Back in the day it seemed to be commonly accepted that around 3:1 was a good number to work with, nowadays we are seeing numbers usually somewhere around the 2.5:1 mark. Companies tried shocks with leverage ratios as low as 2:1 (eg the Foes 2:1, and the Morewood Makulu got fairly close to that as well) but at that point the weight of the shock, the space it was taking up in the frame, and the difficulty valving existing damper architectures lightly enough seemed to push designers back to higher leverage ratios.
  • 1 0
 @VorsprungSuspension: Interesting indeed. My Enduro has close to a 3:1 leverage ratio I see.
  • 4 0
 This is the perfect video to watch since i just picked up a 27.5 nomad and threw on a fox float x2. I was thinking i was gonna be blown away by the performance right off the bat but so far it hasnt been quite the experience i thought it was gonna be. I heard Float x2's from the factory had a pretty heavy compression tune from the fatory and paired with SC's VPP design made it feel even stiffer. I have the option of getting the X2 re valved for my body weight or just say screw it and throw the coil version on there. This video def made me get a better understanding of the different designs out there and how they feel.
  • 2 1
 I spent over a year attempting to get settings perfect - I found that that HSR plays a really imporant role in managing your compression use - send me a PM and I can send you all of my settings. I also had 4 volume reducers to acheive bottom out resistance and small bump compliance - I ran about my body weight in air pressure. I also ran a coil and it tracked much better but the wieght difference feels awk to me...it's a great climbing platform but it's really difficult to get mid support and bottom out resistance while still maintaining high speed small bump sensitivity. I heard that the engineers designed the Nomad to be run with a coil and that's what a bunch of the factory guys were doing here at the CA races...
  • 2 0
 @VorsprungSuspension So, to help digest - I have a 2017 slash 9.8 29er and I came off a SC Nomad 27.5. Based on the only public information I can find (linkagedesign.blogspot.de/2016/09/trek-slash-29-2017.html) and it may be junk but since the manufacturers don't provide this info it's all I have...it appears that the slash has a near linear compression ratio starting ration 2.95mm/mm with a 1:1 negative slope until the end of the stroke where it slightly increases (assuming to be more progressive to avoid bottom out when combined with Fox X2). How might I expect the climbing platform, mid-stroke support and progressiveness to be in comparison to VPP and what type of shock is most suitable coil or air spring. It seems insane that the industry can't optimize leverage data with shocks to acheive the goal of their specific bikes purpose and category....l astly, for racing applications (assuming sag =) and that you want to have the bestsmall bump compliance (assuming at cost of climbing platform), mid level support and full stroke progressiveness how does any consumer know what frame design is the 'best' for their application - design wise not quality, maintenance etc.? Lastly, is this a relaible resource to work from (www.i-tracksuspension.com/suspensiontheory2.html#antirise) or can you provide some good introductory to mid-level text given some physics experince. Thanks for killing it!
  • 6 0
 @Loamhuck if you already have the Slash, I'd recommend riding it and comparing it with your experience with the Nomad, just trying to notice all the subtle differences. Your questions are fairly broad and therefore difficult to answer - it's not really possible for me to answer "how does a consumer know what's best". Even the designers don't agree on what's best, and these are people who spend all day every day thinking about it and studying it!

The industry can't optimise leverage rates as such because there is no optimal rate - everything is a compromise to some degree, and the industry as a whole is constantly learning and refining. There are advantages and disadvantages to everything, and a lot of the time it's more useful to minimise a disadvantage than to maximise an advantage, if that makes sense.

The i-Track website is solid, Hugh knows what he's talking about. That page is one of if not the the best text you'll find.
  • 8 0
 @VorsprungSuspension: I like how diplomatic you are about the VPP's leverage ratio! ;-)
  • 1 0
 @Happymtbfr: not our place to judge really. There's a lot of people who love their VPP bikes' suspension, particularly the DH bikes that drive the shock off the lower link.
  • 1 0
 @VorsprungSuspension: yes you are right and sorry for my "sarcastic" comment!
To be honest, I like Santa Cruz, they make good looking bikes and know how to build quality carbon frames. I just wish they could build a shorter travel version of their V10
  • 1 0
 @VorsprungSuspension: thanks for the response. The nomads initial travel was firm which could be overcome by LSC adj but the mid stroke in big hits was too linear and even with max vol reducers in X2 it would bottom out. Fast chunk was the strength in my opinion but but the traction and small bump sensitivity just never felt right. It was a tradeoff. Running a coil helped the initial part of the stroke and felt like it tracked great on climbs but it felt heavy. Haven't had a chance to get in the slash due to injury but would like to hear how you might expect it to compare given the change in frame design.
  • 1 0
 @nicolai12: your experiences mirror ours... I think you'll like what you're on now Smile
  • 2 0
 Excellent video, thank you, I've always glazed over "leverage ratios" before because, well what the heck were they Big Grin
I have a Knolly Delirium at the moment with the wrong coil on it for me, before i source a new one, do you know if the Delirium is better suited to a coil or an air shock?
  • 2 0
 The Delirium is fairly progressive and should work well with a coil shock, but not so progressive that an air shock is going to be ridiculous either.
  • 1 0
 @VorsprungSuspension: Good to know, thanks Steve!
  • 2 0
 Great stuff again, who'd have thought Tuesday would become my favorite day of the week Smile

Question -- in theory, I can get very similar results at the end of travel either with a strictly progressive rate and a coil spring, or a progressive/digressive rate and an air spring. The damping rates (given the same damper) would be quite different. Will this difference be obviously noticeable?
  • 5 0
 This is gold guys... NERD out.
  • 9 8
 Can I just the ride the bike and tell you whether or not I like the way it rides?

I have way too many non-engineer friends who spend hours on Wikipedia soaking up information about this stuff just so they can have the proper words to justify why they're selling Bike A and buying Bike X, even though they've thoroughly enjoyed Bike A for 10 years.

For reference, look up the nocebo effect (it's related to placebo).

In short, it means that once you think you have an ailment, your body/mind will in turn actually give you that ailment.

Thus, if your buddy suddenly reads about "Bike A's suspension is regressive," then he'll show up the next day, alarmed, and say, "Braaah, dude, my linkage is 2.3 to 1, not 2.29 to 1; no wonder I've been going OTB on that one g-out by our house! I need to get Bike X, because its ratio is 2.31 to 1, which is waaaay better, braaah!"

See, a monster was just unnecessarily created.
  • 46 0
 Welcome to the internet. Here you'll find that the bike you're riding is the wrong one, that your suspension setup is wrong, your political views are wrong and that your riding technique is clearly more wrong than any of the above. The only solution to these is to change everything you do, everything you buy and everything you say until you're just as wrong in the opposite direction Smile

I 100% support the notion of riding stuff and deciding for yourself whether it works for you - theory has to fit reality, not the other way around. But if it happens that you decide you don't like it or that something could be better, understanding how it works helps you work out what the best course of action might be to improve things. For example, if you have Bike A and there's one particular characteristic about it that annoys you, chances are you won't be too stoked if you end up replacing it with Bike B that actually still has that same annoying characteristic.
  • 1 0
 so true. but, if you get this and relate it to the feel of riding a particular bike, you start to be able to fine tune your suspension properly, that is of course, if you actually can notice little changes in setup...
  • 6 0
 @VorsprungSuspension: So you're telling me, go buy a Bronson?
  • 2 15
flag likeittacky (Jan 31, 2017 at 17:35) (Below Threshold)
 @VorsprungSuspension: Dude, you could use a better classroom, maybe outside or a closed office with better acoustics for video clarity. "Just saying", good stuff though!
  • 20 0
 @likeittacky: haha, duly noted. I'll see if I can find some kind of better microphone setup. Currently I have to yell at the camera from 4 metres away, which I think translates to 1/463 of a league or however you measure that in imperial.
  • 1 0
 @vorsprungsuspension

At about 9:00 you draw attention to the similar curves
Of a VPP system (which are similar to meastro and Dw, or somwhat anyhow yes?) and an air shock can "exacerbate" or double up the "stiff-soft-stiff" quality of the curve.
Is this why a coil shock seems transforms the ride so significantly beyond the inherent linear nature of the coil shock itself?
By that I mean it does a linear shock let the bike express it's own mechanical leverage curve design more clearly?

Thanks again for another great Tuesday night brain bleed!
  • 5 0
 Thanks for the kind words @joeyrotundo! VPP bikes with the shock driven off the top link have an inherent tendency towards the falling-linear-rising rate type curve, or at least some portion of that curve. DW-link typically runs the inverse on air-sprung bikes, and different altogether on coil-sprung variants.

However, yes, linearising the first 2/3 of a shock's spring curve (either with a coil spring or a more linear air sleeve such as our Corsets) makes a very noticeable improvement on any frames with that leverage rate curve type basically because you're no longer doubling up on the spring rate variations to the same degree, so you don't get such an extreme swing between firm/soft/firm.
  • 2 0
 @VorsprungSuspension:
Thank you much for the reply,
More to learn about the various suspension types apparently!
At least on the right track with latter, thankfully.

I can see the merit in the architecture of the vorsprung corset more clearly now. It seems another rather large suspension company has since evolved their air cans as well since the corset's release.
  • 1 0
 How about measuring sag based on leverage ratio. I read from Banshee Keith, we aren't supposed to measure sag based on the shock stroke only but the leverage ratio as well. According to him measuring sag based on rockshox shock stanchion number is inaccurate.
  • 3 0
 That is correct in a technical sense - to measure sag precisely you have to be doing it at the wheel not the shock. However, exact sag percentages are not necessarily something to chase on a mountain bike anyway, spring rate relative to rider weight/requirements is the dominant factor there, sag is simply an easily measurable parameter to get you in the right ballpark and allow frame manufacturers to give you a good starting point.
  • 1 0
 @VorsprungSuspension, Thank you very much for your Tuesday tunes, I love what you guys are doing, you are answering a lot of questions I was asking myself (and even some I was not thinking about).
I have a question about my bike setup: I have a capra which is very progressive with a float X2, and I find that it is hard to hit full travel. Would there be any disadvantages of removing spacer to decrease the shock ramp up? Another way of putting it would be: will the float X2 with few volume spacers behave like a coil shox?
Also, what is the impact of a very progressive linkage like this on riding? Obviously you have little damping at the beginning of the stroke and a lot at the end of the stroke, but I have trouble guessing whether it is actually a good thing or a bad thing. (I guess it is good for small bumps absorption but the rebound will be slower at the end of the stroke so it will maybe have trouble to recover from big repeated hits. But other than that…?)
  • 1 0
 You could lower the pressure in your X2 which will increase your sag or you can also remove some spacers and keep the same pressure which will give you the same sag and less ramp up.
The X2 has a wide range of comp/reb adjustments so that you are likely to find someyhing that fits you.

As I understand highly progressive linkage can lead to either too much sensitivity at the beginning of the stroke or difficulties for using full travel.
  • 1 0
 Taking spacers out is the right move if you're largely happy with the ride qualities but struggling to use full travel. Very progressive linkages tend to be very soft at the start of the travel, run quite a bit of sag and be fairly hard to bottom out. If done correctly they can provide an amazingly forgiving ride with a lot of traction, but taken to extremes you end up with something that is prone to harshness and rides too low in its travel. Rebound at the end of stroke is typically faster rather than slower on a progressive bike.
  • 1 0
 Hi,

so theoretically, on my Giant Glory 2016 which has a slighlty progressive ratio the first 2/3 of the travel and then a regressive ratio I should more likely use an air shock? You probably got some experience with this pretty popular bike, any advice?

Thanks for those vids they're super instructive. Waiting for them each week.
  • 2 0
 The Glory is pretty progressive overall, and works well with a coil shock for most people (unless you need a LOT of bottoming resistance, ie your name is Remy). Check out the highest and lowest leverage ratios on the curve - there's a big drop. Also, don't necessarily assume that curves you can find online are 100% accurate - some of them are quite a way off the mark.
  • 1 0
 @VorsprungSuspension: Thanks a lot!

I did find the curves on Youtube indeed... and I honestly don't have the level to need a lot of bottoming resistance (27% to 30% SAG) ha ha!
I was hesitating cause of what I read here and there and also interested in a little weight loss (a SAR spring could be a solution) but bike works well I was just curious to hear from someone who knows better. Make things clearer.

Rémy? Giant? Good old days or...? @sillyseason
  • 1 0
 @VorsprungSuspension: great videos - thank you. A couple of questions about sag and leverage rates, a lot of progressive systems, are very progressive up to the sag of 30%, which than become relatively linear to the end of the stroke, designed for an air shock. You explained it well and it makes sense - to overcome the initial air shock seal friction. How important is the initial 30% of travel considering when we are on the bike and we are hovering around 30% sag? Is the initial progression designed solely around the seals or is there important qualities for this initial range. What happens when you reduce this initial friction (Corset, EVOL, etc), how do you compensate for this - more air pressure or compression? This reduction in seal friction, is similar to the coil your AM/Trail bike trend. For system that is progressive and than linear, how well do coils work on these systems. It seems like you need a higher spring to handle the initial progressive for sag and does this help with post-sag part of the suspension that is linear?
  • 2 0
 The part of the travel before sag is really important actually. The wheels leave the ground (and suspension reaches full extension even with the wheels on the ground) a lot more frequently than you might expect when descending, meaning the suspension is very active in that part of the travel quite frequently.

If you take the initial progression too far, you can end up with something that sags too far and/or runs into a wall of force at some point, but initial progression is not necessarily incompatible with coil shocks. How suitable a coil shock is for any given bike is, in our experience, more determined by the ending stroke ramp up of the leverage rate rather than the first half of the travel. Lacking ending stroke ramp up in the leverage rate means you need either a suitably progressive spring (and/or damper) curve from the shock, or you need to basically overspring the bike to prevent it bouncing off the bottom out bumper all the time.
  • 1 0
 Kudos for being so polite on VPP-just doesn't make sense... I don't see why bike designers wouldn't agree that you need to mitigate the negative effects at the beginning of an air shock's stroke for small bump and take advantage of the ramp up without over-doing it. Climb switch/pedal modes can be used for the uphills, no? Great video, very interesting as I have just changed my fox dps for a monarch plus on specialized turbo levo to have a more progressive ride and it's looking good.
  • 1 0
 Not all VPP bikes have that curve - the DH bikes that drive the shock off the lower link are quite different, and even the 951 is basically entirely progressive (enormously so!). However, it's very difficult to avoid that shape leverage rate on the VPP bikes if driving the shock off the top link, and changing the locations of the pivots of that link would make substantial alterations to the pedaling and braking characteristics so there are limitations to what changes can be made there.
  • 1 0
 @VorsprungSuspension: Makes sense yeah, I had a banshee rune that didn't seem to follow that curve? Sorry VPP is probably a bit too general, but I think I can probably guess at some well known VPP bikes that have these "querks", I think I recall seeing their strange curves in another article or post somewhere
  • 4 0
 @supermike306: The Rune is pretty much the opposite to VPP bikes (VPP as a trademarked term refers to bikes like those made by Santa Cruz and Intense, with two links that rotate in opposite directions and the upper link attached somewhere near the top tube/seat tube junction).
  • 1 0
 @VorsprungSuspension Can you comment on the trend of replacing air shocks for coil on AM bikes? I just can't see the linear coils working well with a frame designed around an air shock which would ramp up-you're gonna end up with a hard shock or a lot of bottom out's right?
  • 4 0
 In many cases that is correct. In a lot of cases frames kind of split the difference and have leverage rates that work reasonably well with either air or coil shocks. The big difference though is that coil shocks typically have DH-oriented dampers whereas not all air shocks do, and even with potential disadvantages in the form of spring curves on some frames, DH dampers are typically better suited to aggressive descending than the kind of dampers you typically find in inline or lightweight piggyback air shocks.
  • 1 0
 @VorsprungSuspension: Thanks great info
  • 1 0
 @VorsprungSuspension

Since you mentioned the Yeti SB series, I have a nagging question about that bike's suspension design (and perhaps others).

The idea, as I understand the marketing material Smile , is that the chainstay distance increases in order to stretch the upper part of the chain. The stretched chain acts like a spring, resisting initial motion of the suspension and preventing the rear damper from moving. There is some critical point in the motion of the rear wheel at which the chainstay measurement decreases and this spring force is essentially relieved.

I have batted this idea around with an engineer friend of mine and neither of us can decide from thought experiment alone whether this "chain as a stiff spring" concept is actually correct. For example there are a few degrees of play in the ratcheting mechanism of the rear hub which could allow slack in the chain, and tension in the chain can be relieved by accelerating the rear wheel's rotation.

I would love to hear your thoughts on this design feature and whether it really works as intended.
  • 4 0
 You seem to be referring to anti squat which is "active" only when pedalling. Check the i-track suspension website for more info/explanation
  • 2 0
 @Happymtbfr: That is a very interesting reference. Thanks!

Their analysis, at first glance, seems to take place on a bike that isn't moving. Since chain tension can be relieved by rotating the rear wheel, I'm still not clear on how effective a design paradigm it is in practice.
  • 3 0
 @WaterBear it all comes down to whether you're pedalling or coasting. If you're pedalling, the chain tension does oppose compression of the suspension to a specific extent (exactly how much is a result of the rate of anti-squat generated). If you're coasting, the rear wheel can release chain slack at a substantial rate, and so in almost all circumstances it has no bearing on bump absorption.
  • 3 0
 @WaterBear: Should also mention that anti-squat does not necessarily impede bump absorption even when pedalling. In fact, when pedalling, if you have an anti-squat rate that balances the pedalling-induced extensive forces precisely against the acceleration-induced compressive forces, but the rate of anti-squat drops off beyond the current dynamic sag point, you can achieve an effectively superior ability to absorb bumps than while coasting. This is because you have acceleration induced compressive force (let's call it C1 and say it's a positive number) balanced against the pedalling induced extensive force (let's call that E1, and it's a negative number because it's acting in the opposite direction), so that C1 + E1 = 0 when on smooth ground, which can be transposed as C1 = -E1. However, if you then introduce a bump force called C2, you have C1 + C2 + E1 = X, but since C1 and E1 cancel out, C2 = X, which is now your net compressive force. However, if E1 actually decreases in magnitude (for ease of explanation, let's say it disappears entirely) as C2 occurs, then all of a sudden the net force available to compress the suspension is C1 + C2 + 0 = X, which is clearly higher than C1, until such time as the suspension extends again to the point where E1 is back to its original value.

Sounds like magic or some kind of lifting-yourself-up-by-your-ears, I realise, but it is possible because it's a purely transient dynamic effect opposed by the rider's mass, not a static force balance. Funnily enough this is one of the major tenets of the DW-link design, and is outlined in the patents.
  • 3 0
 @Happymtbfr: That's one of them, there's at least one other one.
  • 1 0
 @VorsprungSuspension Any thoughts on the new DB Air IL? Supposedly the spring rate is more linear and requires more force to bottom out than on the older DB Inline. Seems like an improvement to me, if true.

www.canecreek.com/resources/DBair_IL/Reliability_graphics/LinEair_Airsping_Comparisson.jpg
  • 2 0
 Should be an improvement for sure, to what degree we have not yet analysed.
  • 1 0
 I love this series - it is awesome.

Now if I could just figure our why Scott decided to go with a digressive - linear - digressive leverage ratio on my Genius 720. I've been battling this since I got the bike and would not have bought it originally if I had known about it. I've maxed out the recommended number of volume spacers in two different air shocks I've tried (the stock fox float nude 2 and a DB Inline) and I'm still bottoming more than I like unless I run less than 20% sag or take my chances with more volume spacers than recommended.
  • 2 0
 Thanks for the kind words. It kind of says something about the degree to which the bike industry disagrees on things that the leverage rate on one bike can be the exact opposite of the leverage rate curve shape on another frame designed for the same type of thing. While it's not really our place to cast judgment on frame design, I can't say I would disagree with your synopsis.
  • 1 0
 I've got a Genius 710 and recently swapped out the stock air can on my Nude shock for a Corset. Small bump compliance in the initial stroke is noticeably better as is the resistance to wallowing and improved traction in the middle of the travel. There was also an increase in the progressiveness at the end stroke, I had to remove the volume spacer that came in the stock can when I put the Corset on in order to use all of the bike's travel. Just my two cents, I don't have alot of time with the new air can, but the Corset is a huge improvement.
  • 1 0
 Not sure if anybody's still paying attention to this (very helpful) video, but I've heard that heavier riders should generally look for bikes with a lower average leverage ratio, as they can run lower pressures in air shocks (lower spring rates on coil) without worrying about having too much sag. Is the inverse true for lighter riders (should we look for bikes with a higher average leverage ratio)? I'm probably around 60-61 kg, but I don't know if either the mechanical advantage of a higher leverage ratio would effectively offset the increased spring rate, which would be most important to me in the initial portion of the travel, or if I would even need to increase my spring rate at all because I still wouldn't bottom out easily (assuming a slightly progressive leverage rate).
  • 2 0
 +1 for mentioning those old Manitou frames! Saw one hanging in the shop back in 1993 when I got my first true mountain bike. Remember being both blown away and confused Wink
  • 3 0
 Sorry to digress @VorsprungSuspension but your linkage design is THIS: mombat.org/MOMBAT/Bikes/1992_Trek_9000.html
Wink
  • 2 0
 These videos are great! Thanks a lot...I'm going from a air shock to a coil and found this informative.
  • 4 1
 OMG... I love my hardtail so so so so so very much.

Beer
  • 6 0
 Unmatched pedalling efficiency and bottoming resistance! Smile
  • 3 0
 This info is nothing but gold.
  • 1 0
 Can you explain the physics of why force on the shock is proportional to (leverage ratio)^2?
  • 4 0
 Not force on the shock, but spring rate at the wheel vs spring rate at the shock. Because spring rate is defined as [units of force] divided by [units of distance], if you increase the leverage ratio then you simultaneously require more force from the shock (for any given displacement of the wheel), but because the shock has been compressed less far, you're also having to generate that higher force at a lower displacement of the spring. Some sample numbers for an 8"/200mm travel DH bike:

2:1 leverage ratio with a 200lbs/in spring rate at the shock would mean that to compress the spring halfway through its travel (total travel, given the 2:1 overall leverage ratio, is 4"/100mm), you need to compress it 2" which is 400lbs at the spring, or 200lbs at the wheel. The wheel has moved 4" for that 200lbs, which means (200/4) = 50lbs/in wheel spring rate.

Let's say the leverage ratio now becomes 4:1 but you want the same stiffness at the wheel (50lbs/in), we reverse the order of calculations:
50lbs/in at the wheel means 200lbs to move the wheel 4" again, but now the shock is only moving 1" (4:1 leverage ratio). In addition to only moving 1", it has half as much leverage over the swingarm, so it needs to be able to generate 4x the force that the wheel is seeing (instead of 2x - ie twice as much force as before). So now we have twice the units of force, over half the distance, meaning a 4x higher spring rate.
  • 4 0
 @VorsprungSuspension: Thanks for clarifying, and for the example. That now makes sense.
  • 1 0
 @VorsprungSuspension: What determines the use/need of a low volume can vs a big volume air can?
  • 3 1
 Oh look, a high pivot...
  • 2 0
 Very interesting. Thanks
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