Donald brown 40 yard dash time?

On a track and having another person use stop watch to time you.

I remember reading somewhere it was 4.5 seconds, but in the days when Jim brown played the 40 yard dash wasn't really a standard measurement of a players speed like it is today, and players times...

It was 4.45 seconds coming into the NFL.

The worlds fastest 40mm dash time 3.8sec _______________________________________________________________________ That is unofficial and unproven The official and proven fastest is 4.09 seconds.

divide by 2.5? well its not as accurate because they can slow down get a slow start etc but its kinda accurate