I figured pavement.
1/8th isn't too bad.
Bump steer, for short track cars, should be zero on the left front (or as close as you can get) and .040 -.0625 outward per inch of spindle travel on the right front.
The piliminary design factor to help prevent bump steer is to have the tie rods parallel to the lower control arms, and same length as the lower arms. This allows the lower control arm and tie rod to swing together in the same arc.
(Straight out of dang near any chassis book)
I've got a few pages on how to set bump steer.
Steve