chainstay length growth?

THATmanMANNY

Well-Known Member
I'm reading some review for single pivot bikes. One review said that that certain bike design sucks and he would never ride one again because a single pivot in front of BB, means chainstay length growth. He then added ask your local shop and they can tell you like it's left from right.

I've always read about it in the past but never really understood it. I'm assuming that when bike is compressed the chainstay length grows but how does this affect your riding? Can anyone elaborate on this?

Also, speaking of single pivot and multi pivot bikes (i.e. fsr, vpp)... for those who went from single to multi do you really notice the differences of brake jack, better contact with ground, etc...?
 

stb222

Love Drunk
Jerk Squad
Also, speaking of single pivot and multi pivot bikes (i.e. fsr, vpp)... for those who went from single to multi do you really notice the differences of brake jack, better contact with ground, etc...?

I went from a mutil-pivot (trance) to a single-pivot(rush) and there are noticble differences between the the two. I have not experienced brake jack on either bike. The trance did have better ground contact since the suspension is more active and sensitive and the rear wheel always stays on the ground, with the single pivot, sometimes you get some "skipping" on long sections of rocks and roots at higher speeds since the suspension compresses and rebounds at a slower rate, however, I have never encountered where this has been a problem. I went with a single pivot because of less maintenance and stiffer rear end of the bike. On the trance, I always had a flexy feel from the rear wheel when cornering. It felt like my hub was loose or my rim was flexing alot, but they weren't. Over time the pivots developed some play (even after replaced the bearings), which caused this sensation. It was especially noticable at 6 mile. The rush is twice as stiff when it comes to the rear end, not even a comparison.
 

stb222

Love Drunk
Jerk Squad
:hmmm: does this sound stupid... so where does the chainstay length growth come into play?

i am no expert, but based on the pivot location, the chain may loose enough tension when the supsension compresses that it causes problems with pedal feedback and such. I am sure mtbjeff or jbonger knows the ins and outs
 

Maurice

New Member
:hmmm: does this sound stupid... so where does the chainstay length growth come into play?

When climbing, the force that puts tension on the chain (your legs) will fight the force that tries to compress the suspension (terrain). The ride is less compliant that way.

When considering single-pivot, also take into account brake jack...
 

NJ-XC-Justin

KY-DH-Freddy
Ever see a test of a bike's rear wheel being squeezed with and without a floating brake caliper like Kona's DOPE system? Pretty interesting to see how much is going on there.
 

syadasti

Wet Rag
This depends on the pivot location (or virtual pivot location in multipivot bikes) the original outland and first generation SC/Intense VPP had lots of chaingrowth too which is why they are so annoying to some people (not much better in this regard than their high single pivot bikes but gives SC a reason for premium pricing). Their latest bikes were designed by an different engineer who knows what he's doing so that was one of the things he focused on so you wouldn't get a ton of growth/feedback when you were riding.

When you have lots of chain/wheelbase growth the suspension in some gears isn't as active, cornering is less optimal, and the rear seems to hang up on obstacles (particular in the high single pivot designs). As a positive it does not bob as much with the chain pulling the wheel into the ground but on the other hand you get feedback through the pedals at times.

BTW, almost no modern bikes have brack jack (extension). Some of the old lawhill had it but thats about it off the top of my head. Almost all bikes have brake squat these days. A little squat is good as the rear sinks and stabilizes you.
 
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Ian F

Well-Known Member
I'm curious about what review you're reading and when it was written.

Most single-pivot bikes made today for XC use have pivot locations designed to minimize chain growth during compression. The Rize and XC Foes models come to mind... however, there is generally a limit on how much travel you can get out of such designs before the arc of the travel becomes an issue. Most DH/FR single-pivot models have a pivot location farther forward and usually a bit higher - most often placed as close to the chain line as possible - assuming a chain guide and single-front in the 38t-42t range.

My current FS bike is a '98 Yeti Lawwill DH-6 which I have been riding since I purchased it new, so I am quite familiar with it. All of the DH-oriented Lawwills made by Yeti/Schwinn (and currently Rotec) are equiped with floating brakes. Needless to say, the rear brake has no influence on the suspension action whatsoever. The XC oriented Schwinns as well as the 1st gen Tomac DH frame were not equiped with floating links... For Tomes, this wasn't an issue ("Brake? Why would I do that?"), but is what a complaint for those with less than optimal braking technique (the other 99.9% of riders...). Some of it could be "dailed out" by setting up the suspension soft in the rear and stiffer in the fork...

Anyway, my FS frame previous to the Yeti was a Foes Weasel - a high-forward single pivot design. Not a bad frame all things considered, and while the chain growth wasn't an issue during climbing (helped push the rear wheel into the ground), it was annoying with pedaling through rough stuff and on descents, the suspension would stiffen a bit under braking. To this day, some C-dales, Santa Cruz, and Foes models still use a similar pivot location to the Weasel.

There are trade-offs with any design.
 

brybry57

Member
think of a motorcycle.... they have a single pivot for the swingarm when the suspension is depressed the chain tightens this occurs not only under landings and bumps but under acceleration too so on a mtb you can see that depending on the pivot location this will all be a factor. I ride a rush and love it, but I have never ridden a multi link setup long enough to get used to the feel, my preference is the swingarm style setup.
 
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