Suspension Tech Thread

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Suspension Tech Thread
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Posted: Jan 8, 2012 at 1:49 Quote
By popular request in the Homemade Bikes thread I'm starting a new thread to discuss suspension technology and theory. The effects of axle path, pivot placement, leverage ratio, etc on ride.

Can anyone explain how short-link 4 bars like vpp supposedly offer less brake jack/squat? I can't exactly see how it deals with those forces.

Posted: Jan 8, 2012 at 1:52 Quote
Cool, was thinking about doing this myself.

Posted: Jan 8, 2012 at 3:48 Quote
Good idea, will post up some links ive been using for my dissertaion etc so ppl at least have a basic understanding before the torrent of silly questions arises. I'd clarify its for discussing design etc, rather than 'how fast should the rebound eb on my dj pro forks' before that starts!

Posted: Jan 8, 2012 at 6:36 Quote
Here are some great resources:

http://www.eibach.com/eibach/img/ers-14suspensionworksheet.pdf

Simple explanation made by Eibach about how springs work and basic suspension leverage mechanics. It explains car suspensions but those concepts can easily be adapted to 2 wheels. *Keep in mind that "Motion Ratio" is referred in the montainbike industry as" Leverage Ratio".

Also there's a great book called Motorcycle Handling and Chassis Design by Tony Foale. It lacks info on linkage design but has a great chapter on Anti-Squat/Dive and chain induced torque. It is mostly dedicated to motorcycles but again, it can be applied to bicycles too.

Posted: Jan 8, 2012 at 15:19 Quote
aceospades1250 wrote:
By popular request in the Homemade Bikes thread I'm starting a new thread to discuss suspension technology and theory. The effects of axle path, pivot placement, leverage ratio, etc on ride.

Can anyone explain how short-link 4 bars like vpp supposedly offer less brake jack/squat? I can't exactly see how it deals with those forces.

well it makes the rear triangle rotate less
it appears to me like it rotates more earlier in the travel tho... hmm

Posted: Jan 8, 2012 at 15:52 Quote
cedrico wrote:
aceospades1250 wrote:
By popular request in the Homemade Bikes thread I'm starting a new thread to discuss suspension technology and theory. The effects of axle path, pivot placement, leverage ratio, etc on ride.

Can anyone explain how short-link 4 bars like vpp supposedly offer less brake jack/squat? I can't exactly see how it deals with those forces.

well it makes the rear triangle rotate less
it appears to me like it rotates more earlier in the travel tho... hmm

the rear triangle rotates forwards as it moves through the travel, in much the same way a floating brake arm does, no?

Posted: Jan 9, 2012 at 9:56 Quote
aceospades1250 wrote:
"snip"

Can anyone explain how short-link 4 bars like vpp supposedly offer less brake jack/squat? I can't exactly see how it deals with those forces.

The easiest way to eplain, the easiest way to achieve this is to make a model of the rear triangle with the presumed links, them have a rear wheel in the rear triangle locked from rotating(simulating as if the brake was appied), and with the shock attached(but no spring), compress the shock to the presumed sag point, then try to rotate the locked wheel(which in turn trys to rotate the triangle)... depending where the links are in their rotation, they will cause the rotaitional force to the triangle to transferr into up/downwards travle(squat/jack)... This can then be accessed to change the angle of one of the links to counter react this, so that at that sagpoint, will be the point when the suspension is impervious to the brakes input...BUT as soon as the suspension moves either direction away from that point, it loses the imperviousness...

The one difference(and where VPP differs and gets part of it's pattent) is since the links rotate different directions, they can be configured so that the rotational force of the triangle is pulling on both of them, they both rear their "Bottom point" of thier swing(like a swing when it come to rest at bottom due to gravity...), and they are stabil at that point, as where a DW-link style set-up has one link being pulled, and the other being pushed against, the one being pushed is a unstabil "Tipping point" which they try to ballence the suspension at that point for the countering effect... This is what sets the VPP appart and if that "Bottoming point" is right at the sag point, then this can possibly result in a set-up that when the brake is appllied, it pulls the suspension to that pont and trys to hold it there, but this can also be construed as brake jack... It depends how they set it up to determine how much a hold the brake force has on the suspension, or how easy it can break away from this hold...

I hope this helps you understand it better! tup

Posted: Jan 9, 2012 at 10:00 Quote
*reach their "Bottom point"

Posted: Jan 12, 2012 at 13:34 Quote
BUMP

This thread ain't gettin' much hits! lol

Posted: Jan 12, 2012 at 13:38 Quote
Thanks man I didn't read this first time around but it makes some more sense...Funny that this thread doesn't get many hits when this topic was on fire in the HMB thread!

Posted: Jan 12, 2012 at 13:44 Quote
A rearwards axle path is not the holy grail of rear suspension technology....Discuss

Posted: Jan 12, 2012 at 13:49 Quote
I'd say its worth considering, but firstly your leverage curve, antisquat should be optimized. A rearward axle path cannot really harm bump absorbrion ability, the theory is sound. It can creat peculiar ride feel though, as the bikes changing in length constantly.

I got my avalanche cart in my boxxer sorted today and new bearings for the 303, still needs a new upper rail but the supension feels niiiiiiice

Posted: Jan 12, 2012 at 13:50 Quote
don't worry, I'll get it going again Razz

on the hmb thread, somebody talked about how on the santacruz website, joe corner or watever was saying that the axle path is not important as things like the leverage ratio and the rest because the rear wheel is restricted by the chain, he said that.

now if you have two chains, one that goes to the pivot point and one from the pivot point to the rear cog, what he said doesn't mean much anymore... Leverage ratio is obviously super important, but this doesn't mean that axle path isn't.

what do u guys think?

Posted: Jan 12, 2012 at 13:51 Quote
mozz wrote:
A rearwards axle path is not the holy grail of rear suspension technology....Discuss
IMO there is no holy grail, UNTIL you have an entire world that would all agree on it, and since riders style, needs, and prefferances differ, there will never be one "Holy Grail"...

Posted: Jan 12, 2012 at 13:51 Quote
cedrico wrote:
don't worry, I'll get it going again Razz

on the hmb thread, somebody talked about how on the santacruz website, joe corner or watever was saying that the axle path is not important as things like the leverage ratio and the rest because the rear wheel is restricted by the chain, he said that.

now if you have two chains, one that goes to the pivot point and one from the pivot point to the rear cog, what he said doesn't mean much anymore... Leverage ratio is obviously super important, but this doesn't mean that axle path isn't.

what do u guys think?


Agreed. One of the biggest flaws in a lot of supension design (IMO) is they design around the current chain line and are restricted by it. but if you use idlers or a jackshaft style set up, you are free to design your supension system to act however you want and then reroute the chain to give the best parameters.

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