When we ran our Roundy Round car we checked the toe out weekly as part of our maintenance routine. We built a set up gauge that was nothing more that a piece of 1/2” square tubing with 4” legs. There were two of them and we held then against the sidewall of the tire and we compared the measurement difference from in front and rear of the tire. The only reason for the legs were to get above the bulge of the tire. If I was doing this for a street car today I would use a short 2x4 and a plum bob to mark spots on the floor and take the measurements. The other thing is that if you make changes roll the car back and forth and remeasure everything again.
