Chassis dynamics, power, rear spinning out or not

tourist · Jan 28, 2014

Was discussing how DR-Z's handle over on Thumpertalk. A guy there had had a 50+ RWHP build iirc, sth. like 470cc. (The DRZ motor can be built to put out very nice power (and still be reliable)) Guy said it wasn't great in the dirt as the bike wanted to spin round and put the rear wheel out front under power.

Bergs don't do that - much - afaik. What gives?

Weight? Weight balance front/rear? Center of gravity / location of "pivot point" between front and rear? Front trail? Bergs are wayyy more stable handling than drz's to start with - does ot apply here also?

bushmechanic · Jan 28, 2014

could be anything really, but perhaps 50 hp isn't enough for dirt

nice big 140/80 rear tyre on the bergs ?

you would think he needs more traction under power so ... not enough HS compression damping in the DRZ shock (or too much) , not enough face shims on the main comp stack (or too many) , wrong spring with too little or too much preload and/or too stiff short stroke rebound

beyond that kind of stuff with my bike I found if the downward force under acceleration due to the swingarm angle and the chain pull moment isn't increased to match an increase in power the bike just doesn't work very well.

jcolleymx · Feb 1, 2014

First place I'd look is the shock spring setup - right one, right amount of sag, etc. Too soft will do that.

tourist · Feb 2, 2014

Thanks!

Yeah, I'm going to guess that the suspension is too soft. The general consensus is that the DR-Z is weakly valved - and easily fixable - and the springs are only good for the lightest of riders.

Interesting to think about - many thanks.

bushmechanic · Feb 2, 2014

yes something like that

if it worked fine with the stock engine and increasing the power altered the handling then the shock is the first place to look

everyone usually complains about the feel of the forks but it is always the shock that makes the bike work... or not.

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Chassis dynamics, power, rear spinning out or not

tourist

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tourist

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