OK I'm a admitted suspension dummie..please define BUMP STEER

It refers to a situation where the wheel is steered by raising & lowering the car in relation to the wheel... This is caused by the length of the tie rod... It should match the length relative to it's position in the trapezoid created by the upper & lower control arm....Raising & lowering inner or outer end of the tierod changes it's position in the trapezoid & therefore it's relative length..

Toe in [ or toe out ] is set at ride height when the front end is aligned. If the amount or degree of toe in changes as the wheels move up and down in response to bumps in the road or to hard acceleration or braking forces then you have bumpsteer. Bumpsteer results in unplanned, unexpected changes in direction even though you haven't tried to move the steering wheel. Most old Mopars have some bumpsteer, but it can and should be minimized. Excess scrub radius can result in some similar feeling, but that's a subject for another day.

IMHO, in most street cars if you adjusted the bump steer from like 1/2" at the 3" extreme length to 0, most owners would not feel it.

99.9% the time someone complains their stock geometry car has too much "bump steer" they have a worn or incorrect suspension part on their car.

It's an extremely mis-used term.

I was looking at a 53 Dodge today that certainly qualified as having bump steer.. It was new enough to have unequal length A arms but old enough to have a drag link connecting the spindles....

In simple terms, bumpsteer is the amount of change (normally toe) the front suspension encounters during the full range of travel. On my race car, I check the change in toe from suspension unloaded (jacking the car from a central point) and then loading the suspension fully as if you encountered a bump. Making adjustments to minimize the overall change.

Most any car will have some level of bumpsteer. In racing you can feel a unacceptable level when hitting bumps or dips at a fairly high speed. Believe me, at a buck-fifty you don't want your car wandering.

As a rule of thumb to get started, by making your tie rod parallel with your lower control arm when the car is sitting at rest, the change in geometry will be minimized during dip or bump (splits the difference).

Hope this helps!

OK Thanks everyone for that bit of info..now I know what everyone is talking about ...