Classing calculation question

[Nissan Racer]

When calculating pips, do you start at the Starting class % eg. my Sentra at 56.5% T1, or do you start at the base % for Starting class +1 eg. Starting class +1 - GT4 = 60% and calculate from there?

[gatherer]

start from 56.5... your car's base.

[Nissan Racer]

thanks!!!!