Ask Pinkbike - Single Pivot vs Four Bar and Internal Routing vs Water
Here at Pinkbike we get inundated with all kinds of questions, ranging from the basic "Can I have stickers" to more in-depth, soul searching types of queries like if you should pop the question or what to name your first child. Ask Pinkbike is an occasional column where we'll be hand picking and answering questions that have been keeping readers up at night, although we'll likely steer clear of those last two and keep it more tech oriented.
Single-Pivot Swingarm or Four-Bar Suspension?
Question: JacobSpera asks in the All-Mountain and Cross-Country Forum: Currently, I am looking into getting an "all-mountain" bike. Something with 160mm of travel up front. I really have my eye set on the Santa Cruz Heckler. The simplicity of the single pivot swingarm is really interesting, yet the more research I do, the less I can find on single-pivot designs. What are the pros and cons of the single pivot?
 | While most bicycle designers are convinced that four-bar linkages are the best solution for mountain bike rear suspension, the simple single-pivot swingarm type has persisted, even flourished, right under their noses. Trek's entire off-road range uses it, as does Devinci and Cannondale, and your pick, the Santa Cruz Heckler, has been a high ranking member of the single-pivot swingarm club which has survived in spite of the fact that SC has invested heavily in its four-bar VPP System. The staying power of the single-pivot swingarm hinges on its simplicity. It has fewer moving parts and that means it can either be made stronger, lighter, or more reliable - or a combination of all three. Technically, the single-pivot swingarm's long lever arm can be used to minimize leverage rate changes as the suspension compresses, which suspension tuners love, especially in the case of longer travel bikes. Efficient pedaling is equally important, and the exact placement of the forward swingarm pivot largely determines how firm or mushy the suspension will feel under power. Magically, this secret spot has evolved to be somewhere at or in front of the bottom bracket centerline and aligned with the chain pretty close to where it intersects the top of a 30-tooth front sprocket. A single-pivot-type suspension configured as such, and designed to drive the shock with a slight rising leverage rate is tough to beat. Four-bar suspensions can offer marginal improvements because their forward pivot locations are not fixed. As the suspension compresses, the point that the wheel pivots around migrates. Clever designers can manipulate the various lengths and pivot locations of each suspension member to control or enhance the way the suspension affects braking, pedaling firmness and suspension sensitivity. The possible combinations are limitless and thus, four-bar cycling suspension has spawned a zillion patents along with a never-ending spiel of marketing claims. In real life, however, four-bar suspensions are nearly as limited as the old fashion single-pivot types, because manipulating the linkage geometry to achieve gains in one arena, like uncoupled braking or pedaling firmness, for example, erodes the suspension's performance somewhere else. It should come as no surprise then, that the best performing four-bar suspensions today are compromises - careful blends of the positive and negative attributes that come with migrating pivot locations and leverage rates. And it also should come as no surprise, given the fact that the customer wants the same things from both systems - efficient pedaling, bottomless suspension action and accurate braking - that the performance of the better four-bar and single-pivot bikes available today varies by only a few percentage points. So, if you like simple and the Heckler floats your boat, I'd recommend it. - RC |
The Heckler's single-pivot swingarm and simple suspension design doesn't require a Ph.D. to tune and rest assured, Santa Cruz wouldn't sell it unless it pedaled well and descended faster than an aging rap star. Santa Cruz photo
Does Internal Cable Routing Let Water In?
Question: PB user sorenwrang asked the following in the Bikes, Parts, and Gear forum: I have often considered the pros and cons of inner cable routing, and what I am most concerned about is getting water inside the frame. I guess there is some sort of rubber washer sealing the entrance of the cable into the frame - but I guess it can't keep the water out in all situations? Isn't this a pretty significant disadvantage? I am thinking of waiting for the new Scott Voltage FR 710, which has inner cable routing - but I am really not sure if I like it. What do you think of inner cable routing with regards to water in the frame?
| The past few seasons have seen internal cable routing come back in fashion, for no real reason other than achieving the clean, sleek look that hiding shift and brake lines inside the frame allows. Luckily, most bike manufacturers are using some sort of internal guide or sleeve to make housing installation and replacement easier, a welcome change from the earlier attempts at internal routing that required the hand and eye coordination of a bomb squad technician to deal with. While it is easier slightly easier for water to get into the frame with this design, I wouldn't say it's that much of a detriment. As you mentioned, many bikes use a rubber grommet of some kind to help keep moisture out, as well as to prevent the housing from rattling against the frame. Also, there's often a drain point located on the bottom bracket shell that will give water a place to exit. If you do happen to go on an extremely wet ride, or got a little zesty with the pressure washer, removing the seatpost and turning your bike upside down will allow most of the water that entered the frame to drain out. Even here in the Pacific Northwest, where riding in wet weather is a fact of life, I haven't run into any major problems with water collecting in frames due to the internal routing. As far as Scott's new Voltage FR 710 goes, the amount of internal routing on that bike is fairly minimal - the housing is routed externally on the downtube, with only the rear derailleur housing entering the frame briefly on the driveside seatstay. - Mike Kazimer |
It might not look like it from this angle, but the majority of the Voltage 710's housing is routed externally.
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10 10th letter in the alphabet, J
210=BJ
So the more choice the better I reckon (so long as you understand what you are buying other than hype)
Needs of the one outweigh the needs of the many as a famous captain once said
-What every bike company that specs remote shock lockouts thinks their customers do
Its pivot placement has a very light pedal stroke and climbs great.
Beings as its direct you can also dial in the suspension easily for big drops and jumps.
You can feel the suspension working directly so, you do adapt to how it reacts allowing you use it to your benefit.
Example; doing a bunny hop on a hard-tail, single pivot, 4bar and VPP are all different.
You have to change your timing and preload the suspension a little differently but once acclimated you can hop just as good on any bike.
I personally love the feeling of a FSR 4-bar. My current bikes both have a FSR link and they pedal and take rough trials greatly with very little trouble like brake jack or squatting.
However, I rode a 2004 heckler and felt on top of the world.
I also rode a bullet and both bikes were perfect correlating great times on the trails.
Like anything in life personal preference differs from one to another and you can't pass judgement to someone who honestly believes what they are doing or in this case riding, is the best!
hahahahah
I hope that makes sense!
RideOn!
"earlier attempts at internal routing that required the hand and eye coordination of a bomb squad technician to deal with"
I remember 1992 trying to redo the internal cable routing in a Klein and feeling a bit like a bomb technician. Great information keep it up!
Ever tried routing a mo darker summum
OK, rant over, carry on
GT idrive is a single pivot but absolutely does not suffer from this due to pivoting BB. I have a distortion and rides up/down better than anything I have tried..
The one time you really, really need your rear tire gripping the dirt is when you are braking - you can go faster as a result (brake later, brake harder, spend less time going slow, spend less time in the bushes).
Foes ftw !!! Kona have it ????really?
I read about this bike when I recently heard Ghost bikes would be sold in the U.S. And this conversation made me think of how they attach the brake mount directly to the axle, not the frame. What are the pros and cons of this?
In response to RC, I'm not entirely sure how much playing with the position of the main pivot can control these braking issues. Effect them maybe, but only within a very small range where the problem is still quite noticeable. I have owned quite a few SP bikes, including a Santa Cruz Bullit for a few years, and they all kicked my arse braking through washboard sections. I have owned APB's since then and have ridden a number of FSR designs and with both the difference is very noticeable. They simply buck less than any bike where the brake caliper is bolted to the main swing arm. Yes there is the "then brake less" argument, but having a bike that can brake anywhere can allow you to brake less. So yes the better single pivot designs do come close to eliminating this problem, but I don't think this is true for the Heckler. Don't get me wrong, I loved my Bullit, I was just aware that it got a bit wild braking in the rough.
I have wondered myself about the funny things pro racers do (choosing not to run a torque arm, or in Barels case running one set up to actually increase brake squat) but can only conclude that it has something to do with the differing conditions they ride in. Namely a WC race track tends not to have 50ft of brake bumps before every single corner (and quite often other quite ridiculous places like half way round a berm, or in the middle of a long straight). Sadly many of the tracks I frequent are fairly torn up by the time I get there.
www.liteville.de/t/22_29.html
www.pinkbike.com/news/Liteville-301-MK10-Tested.html
How?
If you attach the brake caliper to the swingarm, no matter where you put the main pivot, applying the brake is going to cause the swingarm to rotate around its pivot. There is no physical way this won't happen.
Take the shock off the Entourage with the front triangle firmly secured in a stand. Spin the rear wheel up and slam the brake on. All the inertia of the wheel is going to be transferred directly into the swing arm, causing it to rotate around the main pivot. essentially the suspension will "compress". Do the same on a bike where the brake is mounted on a non-rotating member (eg fsr, split pivot or a single pivot with a torque arm) and do the same. As long as the front triangle is firmly secured nothing much is going to happen as the inertia will be transferred into the front triangle, trying to spin the whole frame forward, rather than just the swingarm.
In normal use it is not the inertia of the wheel that causes this effect, but the ground trying to force the wheel to keep rotating against the opposing force of the brake, so the forces involved are quite massive.
It would actually be fascinating to perform the test you're talking about on a variety of suspension designs, to see the real life effects.
Not sure how you'd simulate pedalbob though, as it is a far more complex motion.
If you want an in-depth look at some of these systems and how they compare, then download the demo from www.bikechecker.com
IMO suspension design comes quite low on the list of things that will help me become a better rider.
1. Ability - Two arm, Two legs and torso movement will produce significantly more suspension to the system as a whole. Add to that line choice and pre-loading, unloading bike in the right places.
2. Bike setup/Geo - Bars, Stem, head angle, chainstay length, BB height, and frame size (reach). Tyre psi!
3. Shock/Spring setup. Correct Spring/Pressure and correct LS and HS compression setup for my bike, ability, style and terrain.
4. Suspension Design.
So IMO, the first 3 three need to be dialed before being too concerned on suspension design. This can only be achieved by riding lots of different bikes and setups. Most modern bikes are awesome!
To decide on what's suspension is best to you, everything comes down to Axle path (dictated by IC and movement of IC) and shock leverage. Read up on how these change characteristics and pick bike with best match, along with weight, stiffness, price, athestics……….
Simples.
Oh and can we please loose the "brake jack" terminology. The Heckler (and most EVERY) bike out there does not jack it squats. if your rear end feels like its lifting its because your front end is diving (your weight is shifting forward) it has nothing to do with the rear suspensions reaction to braking!
I've been spoilt, as I got my first fully rigid in 1988, so had to learn good body English to be able to ride anything at a reasonable speed offroad! Done wrong resulted in painful wrists or worse. Many people have only ridden full suspension aggressively, and hence a more difficult learning curve and bad habits.
This year my local bike shop supplied me a 29er Superfly FS 7 with ABP: Active Braking Pivot, they say: "Other full suspension systems firm up under braking, reducing your control when you need it most. Trek’s patented Active Braking Pivot solves that by keeping your suspension active whether you're on the brakes or off"
well let 's see i am already scared
Single pivots are fine but in my opinion Split Pivot is better and may be the best suspension design out there (depending on execution) because the pedalling and braking effects are separated and can be tuned separately which is not the case in single pivot or FSR or VPP or DW link or other true 4 bar designs.
In fact the accelerative forces are so low in bicycles that anti-squat % difference between a Trek single pivot and a Specialized 4-bar are practically zero.
Other factors like IC and leverage ratio are far more critical to suspension performance IMO.
Squeeze the rear brake on rough terrain and all designs will stiffen.
Actuated = it has a linkage driven shock, which allows you to tune the leverage rate through the suspension cycle more easily than on a shock with a fixed mount on the swing arm
Floating brake = the brake mount is separated from the suspension bar linking the wheel to the frame. Easier described in action: when you pull on the rear brake the rear wheel digs in and tried to drive the suspension. By moving the brake off the swing arm you're meant to isolate this effect to some extent.
And yes it's a single pivot because the wheel is on one bar (bar 1) which directly connects to the frame (bar 2). Hence all single pivots are two bar, irrespective of what other bars are floating around the place driving the shock/ mounting the brake.
A four bar linkage is one where there are four connected bars with the frame as one and the wheel on another which is NOT directly connected to the frame. As the article states, this allows the suspension designer to address stuff like chain growth and brake jack in a more sophisticated way. However when you look at the performance of split pivot in DH (Trek Session, Devinci Wilson) and Enduro (TMo's Trek Remedy & Otons Devinci Spartan) it's clear the differences are fine.
My Rush has the shock mounted to the toptube, like the Heckler, whereas an Orange 5 has it mounted to the downtube.
Bear in mind that my opinion about internal cable routing could cause troubles. Everyone knows how the brake hose rubs the fork crown or the frame, how aggressive it could be, so make sure you wrap the hose with some scotch insulation or so before install it inside i consider that rubbing can reduce the frame life or may be im wrong prove it if so
Six hundred thousand dollars. That's not stealing.
Years ago Giant payed Renault F1 suspension gurus to come up with the NRS suspension design, which Specialized promptly stomped on and it cost Giant a fortune including lost future revenue AND they now had to come up with a new suspension platform. Why would they then deliberately risk a similar outcome by stealing Maestro from Dave Weagle?
I guy a new Giant every year. They work great, ride great, and the price is great.
BTW, you might still be able to find a post online where DW admits he was mightily inspired by a Turner DH (a VPP bike). DW-Link is very, very close to that Turner. And that Turner was a descendent of the Outland VPP, which may have come fror something else, who knows. People in glass houses...
THIS... yoda.densan.ca/kmr/bikes/profloat1.jpg ... for example is a late production (about 1995) Mantis ProFloater, designed and build by RC before he sold his brand (to some morons who'd later run it into bankruptcy) and before he took over Editor-in-chief duties at Mountain Bike Action.