Actually the time-to-0 increases linearly with speed, but the distance required increases quadratically with speed. If you're 75 feet back at 30mph (this seems

Actually the time-to-0 increases linearly with speed, but the distance required increases quadratically with speed. If you're 75 feet back at 30mph (this seems overly cautious?), you should be 300 feet back at 60mph. Basically to go from 60-55, 55-50, etc. takes the same amount of time, but you're traveling faster and therefore covering more distance throughout the course of the former intervals than the latter ones.