When ET and MPH Are Not a Match?

dibbons said
There is a formula to determine what ET one should be running based on MPH in the quarter mile. ET = 1353/MPH or MPH = 1353/ET

my mph was 108 so it should run 12.52 but my best was 12.72
my mph was 104 so it should run 13.00 but my best was 13.29

When I punch my MPH into the formula, I find my ET is .2 or .3 slower than indicated by the math. I wonder where I am losing time? Thank you.

As has been pointed out most of the time formulas dont match up real good,but the most comon missmatch of numbers is the one in your example and that is due to having the power to get alot of MPH but not the chassi to make full use of it to get a low ET,most of it can probably be found in the 60foot.