Love the way this list server only puts occasional posts of mine up. Grr!
Here's link to a simple picture showing bump steer.
http://i44.photobucket.com/albums/f48/fox-trapper/Spitfire/bumpsteer.jpg?t=1187259934
Simply put, bump steer happens when things don't move the same. The
suspension arms go around one arc, and the steering rod goes around a
different arc. So the tires turn from side to side as the wheels go over a
bump.
Fact, you cannot eliminate bump steer. Before you jump up and down
screaming "oh yes you can", read on.
All the focus in this thread on bump steer has been for straight ahead
driving. You can eliminate it for that condition...sometimes. But cars
turn. As soon as you turn the steering wheel you move the tie rod ends out
of position, and bump steer comes right back. The tighter you turn, the
more bump steer you get. That's just basic geometry when it comes to cars
front suspensions and steering.
How bad bump steer is depends on the design of the suspension and the
steering components. Something like a Spitfire with a double wishbone
suspension and rack type steering gear isn't that bad when it comes to bump
steer. A McPherson strut suspension is much worse. Steering box and relay
rod types of steering can be remarkably bad, just watch a 4x4 truck twisting
around offroad some time to see this one.
Bump steer is directly related to suspension motion. The less a suspension
moves, the less bump steer there is, no matter how bad the geometry.
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