A friend was driving for a team owner about 10 years ago and he was explaining to me how they were sitting up at night, looking at the weather for the next day (i.e., corresponding weather for run time) and calculating the gear ratios for 1-4th in the tranny, but also the rear gear ratio and tire size. It was like NASA engineering at its finest! They all factor into the equation in some form or fashion. VERY interesting seeing most all Chevy teams have the same HP.