Yep, tire size(front and rear for different reasons) and gear ratio all affect reaction time. On the driver side alcohol, caffeine, and some drugs(prescription and shall we say nonprescription) can have an effect on reaction times.

Many years ago a friend was consistantly loosing in the first or second round. I told him to knock off the pot the day before and after weeks of denial he finally tried my suggestion and hello, all of a sudden we're going home after midnight.

How many older racers do you know who can't hit the tree anymore? Heart meds are notorious for this.