How to fix bump steer?
 

I just finished a GTM tt kit and they had me raise the steering rack with spacers. My question is would this cause bump steer, and how would I fix it?

I can't see how it would cause bump steer since you are just changing the angle of the tie rod.

Raise the tie rod end by the same amount ... but before contemplating it, measure the bump steer first.

How do u measure bump steer?

Bump steer is the car bouncing off of the bump stops. Easiest fix is to cut the bump stops, how much is the question right? You can cut some off and put a zip tie on the strut to see if the bump stop is indeed hitting the vehicle. The ziptie will stay at the highest compression of the strut. I don't think that you should get bump steer just by them raising your steering rack its usally associated with being lowered on springs as coilover systems are already tuned to prevent it.

Bump steer is the amount of toe change as the frot suspension moves from full bump to full droop.

The only way to measure it is with the springs removed from the front suspension and the vehicle is lifted thru its full suspension movement (bump to droop) with a toe gauge fitted.

All race prep shops will have this capability - most alignent shops don;t like doing it because the car is on the alignment hoist for an hour or more (unless the shop is happy for you to be last customer on Saturday before closing and you supply a slab of beer to the tech(s) so they will stick around and help-out.

It also requires and alignment check afterwards lust in case somethogn was changed in removing and re-fitting the springs.

The ideal is zero change in toe as the suspension sweeps thru its movement from bump to droop but that is not easy to acheive. If anything, slight tow-out in bump is better, but that can cause the car to turn in strangely as the outside wheel can toe-out in roll as well - and that can feel just plain wrong !!!

Read Carroll Smith's "Tune to Win" series of articles for more details

Lower the car... Problem solved.

If the tie rods are level when the car is rolled out your about as good as you can get.

Not quite correct ... the inner tie-rod ends and outer tie rod ends need to make a parallelogram with the inner lower susension arm pivot points and the lower ball-joint and shifting the rack by spacing it will affect this relationship.

Best you consult a suspension guide to see this correctly as I dont have the time to type it all out ...

SPL suspension will have bumpsteer correctable tie rod ends coming out soon

Wrong.

Rusty. Should I upgrade to SPL outer tie rods to reduce bump steer or will it be over kill to use those?

I got spl tie Rod ends which come with bump steer spacers because I was changing nearly every arm anyways and was doing it all at once


If u are getting spl FUCAs u might as well do the tie rod ends at the same time while the car is up and presumably at an alignment shop

And u should be getting spl FUCAS because they're awesome

Yes. I've gotten almost all the SPL parts already. FUCAs, endlinks and rear arms but I didn't get the outer tie rods. Any noticiable difference from OEM?

i changed everything at once (literally . . . coils and the whole SPL catalog)

last time i did it was on my 240. Changed to a quicker S13 HICAS steering rack and pillow-ball tie rod ends. Removed from slop from the steering and made the car feel much more connected to the road

Thats pretty much what changing rubber for metal bearings will do anywhere, really, but since these are steering components it should give feedback more directly to your steering wheel. On a sports car, feel is good. On my lexus, feel is bad.

if u haven't installed that stuff yet, i'd get the SPL ends and do it all at once. its just more convenient and cost effective. IIRC they aren't that expensive (if ur already in the weeds with SPL, they're one of the least $$$ items)