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Old Jan 30, 2008 | 01:12 PM
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sonoronos
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Joined: Dec 2007
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From: Fairfax, VA
Default Re: steering wheel question

Originally Posted by jackei
About the same force that we turn our steering wheel to make a turn, but in this case I'm keeping the wheel straight.
Jackei,

You bring up some really good questions.

I simplified a little bit earlier when explaining about the effect of wheel-knuckle force on the steering wheel. The simple explanation is that we get "complete isolation". The truth is that we get "near complete isolation". The long explanation is that the recirculating ballscrew racks have a holding/resisting force of F=2*pi*(Frictional Torque)*(Thread Pitch)+Force(steering damper). This means that the isolating force I spoke about is actually a linear function of frictional torque and thread pitch. Considering the relatively high steering gear reduction even taking into account the relatively low frictional torque of the ball bearings - the holding force (and therefore steering isolation) is designed to provide considerable isolation.

Now, I have not analyzed the Crossfire's suspension in any detail. It is possible that the Crossfire's suspension has some measure of bump steer - the fact that you mention this steering wheel wiggling occuring on uneven roads tells me this is a possibility. Bump Steer is a situation where a fixed tie rod length and pivot forces the wheel knuckle to turn when the suspension is compressed or extended.

I'm just guessing, but if you are noticing the steering wheel move and the front wheel suspension is at different heights on the left and right side, then you are experiencing bump steer.
 
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