calculating bump steer on alignment machine
 

I was thinking about measuring bump steer on an alignment machine, and I had a few questions. Please correct me or give me some pointers
1) measure ride height
2) remove springs, use jacks to hold up the chasis of the car
3) place a jack under each tire measure toe and camber at +3,+2,+1,0,-1,-2,-3"

Now if I add or remove spacing on my tie rod, I would have to realign my car and then measure bump steer again, or would I be able to be lazy and just add the tie rod spacers and check my toe change as the suspension is raised and lowered, and just look for minimal toe change. This is real tedious work!

Easier way to do it guys?
Best to have the chasis level right? I wouldn't get a proper measurement by only jacking up the front?

thats pretty much how we do it, i'd suggest starting at the bottom and going up, as the bottom is easy to find. since you're on a machine, also look at what camber does, or rather doesn't do

So I can just change tie rod to spindle distance and not look at the actual toe spec, but mainly just how much change there is right?
I'm curious because the fc might be easy, but some other catsi work on ate a total pain to do suspension work

I wouldn't worry about aligning it again after you add spacers, at least until you rough in the bump steer, then align it and then do all your small changes to get it where you want. bump steer doesn't change a whole lot with arm length, the angle is much more important. and small amounts of down or up spacing shouldn't change the static toe a whole lot, the tie rod pin is like 10-15* or something?

i'd put the car as low as it can go, and set toe to zero (and maybe camber to a round number), and then raise it up, and see what it does.

The shop where I keep my race car - SantaFeGarage.com - has a fixture that allows them to measure bump steer on the alignment rack. They pull the car down for bump using the fixture and raise it with cross jacks for droop.


They bumped my FB race car and my 85 Fox Mustang. Both of these cars use heims instead of tie rod ends and the spacers needed to fix bump were not what you might expect. On the racecar the spacer stacks are slightly different side to side.


All of the alignment settings were made first, then bump was corrected and alignment settings were rechecked. Santa Fe also ballasted both cars to simulate my weight.

I know of another way. Pm me if your interested.
Make sure you lock wheels both ways while compressing and decompressing suspension.
You can fix bump with wheels straight but to get it perfect with the wheels moved in various positions is harder.
I went through all this with my subframe i built for my 20b car