I decided to break out my hudy setup station, and my 2mm hex, and do some measuring for our setup sheets. Lets start with bumpsteer and caster.

Bumpsteer - bumpsteer is what happens when you induce either more toe in, or more toe out, as the front suspension compresses. (bump-in, or bump-out). You can change how much or little bumpsteer you have by controlling the vertical angle of the steering turnbuckles. The more vertical the steering link goes as the suspension compresses, the more the turnbuckle will pull the steering block inwards, inducing bump out. So to reduce bump-out, you have to reduce the height of the ballstud on the turnblock. If you get bump-in, that means you need to raise the height of the ballstud.

What some people don't realize, is that changing caster, changes the relative height of the ballstud / turnblock, because more caster rotates the turnblock backwards, so it drops the ear/stud closer to the ground. So if you run 25 caster and set your bumpsteer to 0 (no bump in or bump out), and then decide to change your caster to 30, you actually dropped the height of the ballstud by 2mm. So I did a lot of testing and measuring just to make sure that the numbers are accurate. For ZERO bumpsteer:

• 25 caster = 0mm washer under turnblock ballstud
• 27 caster = 1mm washer under turnblock ballstud
• 30 caster = 2mm washer under turnblock ballstud

Ackerman - Ackerman affect is the difference between the turning radius of the inside wheel, and the outside wheel, in a corner. Because the inside of the car will natually track along a smaller circle, to maximize steering and minimize a slip angle, the angle of the tires need to match the steering radius. If you have too little ackerman, or too much, the slip angle means one tire is sliding instead of rolling, reducing steering.

I tested just two ackerman settings on the steering rack just for my own info, and got the following:

• 0mm under steering rack ballstud = 30deg and 23deg
• 1mm under steering rack ballstud = 30deg and 23deg

Zero change in ackerman. Might have something to do with the fact that the steering turnbuckkles are right about flat, straight across /perpendicular to the chassis. I think ill test again later with my plastic steering rack to make sure it's not my alu version.

Is your caster at the pivot or at the caster block? Im guessing 29 is a 1.5 or so?
At the front suspension hanger. For 26 or 29 degrees, you may actually have to actually unthread the ball stud a fraction of a turn in order to get 0.
My test was done with Lunsford ballstuds, which sit the tiniest bit lower... Using the khosbo ballstud, ar 25 caster, I couldn't actually get 0... I got a half degree if bump out. A lower ballstud is needed.

What does the .5 or 1 mm space do under front caster block?
Raises and lowes the front roll center. Lowering the suspension block should lower the roll center.