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
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