Bump steer has nothing to do with tire size or tracking on the highway grooves. Wider tires do have a tendency to follow the grooves more than narrow tires. Bump steer is the phenomenon where the vehicle hits a bump in the road and wants to "steer" on it's own in one direction or the other, hence the name "bump steer". This action is caused by the tie rod arc not following the same arc as the lower control arm. The change in traveled arc's causes toe-in or out to change throughout suspension travel. The correction involves measuring toe while moving the suspension through its range of motion as already expressed above. Toe in/out should never change as the vehicle goes into bump/rebound. Bump steer geometry is set at the time the vehicle is built and is usually with a .010" tolerance until someone changes a component in steering geometry such as a spindle or moves steering gear location. This a kind of a mute point as I don't think anybody who just spent near 40K on a new car is going to change steering geometry yet. If your real curious I’ll post some text and pics while I do the front-end on my own car with fully adjustable rod end steering linkage and center link. I suppose I could even video the whole bump steer adjustment and alignment.

I would not suggest anybody going into the near by tire store to get an alignment with their new wheels. The alignment is set at the factory and is deadly accurate (I don’t know how they do it) and we are having caster/camber issues with LX platform as it is. Don’t need the aftermarket guys messing it up yet.

 

Here's what the front end of my opentracking Mustang looks like, adjustable bumpsteer kit, tubular suspension, and all:

 

Since so many of you know what I'm talking about, answer this question for me.
Would I get bumpsteer if I get 245 or 255 wide tires (while keeping the same overall diameter)?
Thanks!

 

You can't get it if you don't have it now, unless you're changing the suspension geometry, which you won't with the setup you're proposing.

 

So why would my dead stock brand new Magnum bump steer? Poor suspension setup from the factory? It hasn't even had a chance to wear, it's done this since day one also. It has done it with 3 different sets of tires in varying sizes. Should I take ti back to the dealer and tell em fix this POS?

 

One more TSB, I guess.

 

Some cars just inherently have some bump steer. Are you sure you are experiencing bump steer? I wouldn’t go into the dealer and ask them to fix it. If you truly have a bump steer issue and you haven’t done anything to induce it the dealer isn’t going to know how to fix it. I’ve worked with hundreds of techs over the years and can count on one hand the number who know what bump steer is, less know how to fix it.