[cas3]

get the wheels off the ground, wrap around the tire once with masking tape, have your helper spin the wheel while you make a nice line with pencil or fine point marker. works good to hold the marker on the edge of a piece of wood to be steady. make a nice line. if it sucks, do it over. tape is cheap. actually, in school they taught us to spin the wheel and spray paint around the tire, then scribe a line with a pick. i have found that the marker or pick is less likely to try and follow the tread pattern if running on smooth tape. you cant just measure from the tire tread, its not accurate. now have your helper hold the dumb end, you read the smart end. should be 1/16 to 1/8 i believe