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DH bike with two shocks.

scott43

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Not so long ago, someone, can't remember who, was advocating a modern motorcycle race bike with old-school dual shocks..the logic being less stress on the shocks. Which kinda makes sense..but there are other drawbacks obviously. So I wouldn't discount it..it might be easier to tune or package that way. Having said that, most modern motocross bikes make do with a single shock. Maybe the shock they need just isn't manufactured yet...
 
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Erik Timmerman

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Did you watch the video Scott? I think it's potentially really cool that once you have separated the damper from the spring they can have two different leverage ratios.
 

cantunamunch

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Did you watch the video Scott? I think it's potentially really cool that once you have separated the damper from the spring they can have two different leverage ratios.

The scene you're probably referring to is that shot from underneath the frame. Is there anything in the actual riding we're supposed to notice?
 

crgildart

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Ahh so their shock absorbers need a shock absorber?
 

scott43

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Did you watch the video Scott? I think it's potentially really cool that once you have separated the damper from the spring they can have two different leverage ratios.
It looked like spring and damper plus damper? Could be wrong. And yeah I suppose you could change the ratio of the second damper to alter the curve. More at the end of the stroke.
 

Tom K.

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Interesting. I'd love to see a tech write up and suspension curves for the design.

Otherwise, between progressive and straight-wound springs, plus tuning of high and low-speed compression and rebound shim stacks, and end of stroke ramp up adjustment via various mechanical and/or hydraulic methods, I'm having a hard time imagining the advantage of two shocks.
 

scott43

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Yeah, I mean, I'm not sure what they're trying to solve? I know stiction can be an issue and maybe they're trying to lower pressure in the shock to make it more compliant. Maybe they're able to more finely tune the damping because they can use a "longer" travel damper.
 
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Erik Timmerman

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Since the two shocks are in two different places, connected to the bike in two different ays, you can have totally different leverage ratios. I tried to find a decent chart showing the rate curves of a few different bikes. Falling rate, rising, rising then falling and falling then rising. Each of these bikes has different characteristics because of these curves. They also play better with certain shocks because of this. For example, you don't want to put a linear rate coil shock on the Ibis, it needs the end stroke progression of an air shock. What the Cannonade does is it lets you pick the ratio the spring is working at and have a different rate for the damper. It's probably not accurate to say the big has two "shocks", the one with the spring on probably doesn't have a damper in it at all. You could choose a spring location that gives you the spring rate of the Santa Cruz, and a damper location that lets you have the linear rate of the Trek.
ffshockleveragecomparegraph1.jpg
 
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Erik Timmerman

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Maybe they're able to more finely tune the damping because they can use a "longer" travel damper.

That is probably part of it, longer shock with less leverage has slower shaft speeds and doesn't blow up as much.
 

CalG

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Having the damper unit geometry such that there is a relatively long damper stroke relative to wheel movement is always a good thing. (the term is wheel rate)
Hydraulic damping does not do well with small movements. Motion reversals are a significant source of "uncontrolled" damping. Such weakness nibbles away at traction.

Some high end front fork systems put the compression damping in one unit, and the rebound damping in the other.

Perhaps the biggest advantage of a multi damper design is "simplicity".
 
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Erik Timmerman

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That's what I'm talking about. Of course without Dave Weagle to explain that to me...
 

Josh Matta

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