Does the wheelie bar height change that much after the burnout? Why can't you just set it at the trailer beforehand...
I've always wondered, Don't these people have a level garage floor at home?
You are assuming nothing is changed or adjusted from the time the car is put into the trailer until it is on the starting line, or even from the last run - ride height, tires or pressure, suspension, weight, balance, how high the bars need to be for the desired pitch rotation, the offset in heights to make the car go straight, etc. Bars are used for tuning, not just to control wheelies. Especially in a car that is on and off the bars for much of the run.
