"If you measure ½" difference, actual toe is only ¼"
By measuring the exact same tread block you are taking out any variation due to bent rims or tire irregularities."
Broncobowsher this may explain something I have been doing wrong on my Bronco for years. If I understand correctly you are saying the measurement of the toe for the spec is 1/4" (for example) that is total toe from the center of the wheels to the rim edge? This forms a small triangle which ends up being a small angle pointing inward of the tire when viewed from the top. I have been setting toe by measure the front and rear distance (as you suggested with tape) and setting the toe as the total difference. I set the distance at the back to be 1/4" (for example) greater the rear than at the front toeing in the tires. If I understand correctly I have been over toeing it because my distance is twice as large.
Does my question make sense?
Actually under-towing.
Toe is based on something like a 29" tire. It is the front of the tire being that much narrower then the track width (centerline) of the tires. Getting the centerline at home is very difficult at home, but measuring front and rear off the same reference point is rather easy. So instead of measuring the toe in based on the
radius of a 29" tire, you are measuring toe based on the
diameter. Now for that 29" tire baseline, nothing to worry about. Since you are slightly below the centerline of the tire you are measuring pretty close to that 29". And with as little toe as there is, the error due to oversized tires doesn't add up to much of anything. Someone who is good with math can tell us how many thousandths of an inch change there is between measuring a 29 and a 33" tire.
Another thing I add to the toe measurement is how worn the parts are. New ball joints and steering linkage, on the lower side. Used parts, add a touch more toe so the drag will pull the on the play of the used parts and the wheels will pull into the normal toe.