Hi Richard, I made one of these years ago (and still have it) from two discarded Bunsen burner stands! First adjust the height of the two pointers to the centre of the front wheels. Then position the long bar across the car so and adjust the pointers to just touch the rim at the rear of the front wheels of the car (inside or outside of the wheel depending on the length of the bar and the perceived difficulty of manoeuvring the whole assembly without loosening anything). Mark the rim at this point. Tighten the stands onto the long bar. Roll the car forward (or backward half a turn of the marked wheel, so that the mark is now at the front, reposition the gauge at the front of the front wheels. Check the gap - if the gap is negative (ie you cannot position the pointer where it needs to go) you need to think about toe in vs toe out (my SP25 spec is for slight toe out) and whether you are on the inside of the rim or the outside of the rim. To make this work, you need to set the gauge for the smaller dimension and then assess / measure / correct the gap for the larger dimension. Don't forget as you adjust the steering rack (or arm length) that the correction will effect both measurements, so you need to repeat the whole procedure after each adjustment. Rolling the car, reduces any error due to the wheel having any run out error - you can check for this before you start using just one of the pointers of the gauge against the rim (after jacking the wheel clear of the ground), rotate the wheel and see how whether it stays just off the pointer around 360 degrees. A small run out (say 1/16 inch) will potentially introduce an error between 0 and 1/8 inch into a toe in measurement that has to be accurate to within about 1/8 inch! Note the laser and mirror based tools used in today's commercial garages are also subject to wheel run out errors (possible on all 4 wheels!), but I have never seen the run out of the wheels being checked first. The left hand pointer in your photo appears to be straight so will only work if you measure inside the wheels. Having used this method for a few years, I have now given up and adopted the "parallel strings" method - there are videos on youTube. Hope this helps Dave Posted by DaveT 19/06/2017 12:53:46
