rollout is just another way on how u calculate the gear ratio....
people who use rollout are those oval racers who run on foam ( pan cars )
the use rollout as a ratio cause the foams wear down and the ratio would be different cause the Diametar of the tire would be smaller when it wears off.......
so asuming ur 6.81 FDR ur roll out would be 33.49mm per rev which means that ur tires move 33.49mm if ur motor makes 1 full 360 turn
and from there u could calculate the speed of ur car if u know ur motor speed under load say its a stock motor and under load its 16000 RPM ur speed would be 29.27KPH
and if ur tires is smaller the top sped would be less
well for ur question ... i would say it depends ... cause if u gear the stocker right to the roll out a mod motor is going teorically u will be of the same speed but it depends on the track ... and the motor itself
heres a plain example ... i wont calculate i m LAZY figures are all made up
say a 14 turn is geared at 9.6 FDR and a 27 turn is geared at 4.8 FDR and asuming that the 27 turn the rollout is 32mm and the 14 turn the rollout is 16mm with the same tire diameter of 60 mm and the motor speed under load of the both motor is say 18000 for the stock and 36000 for the mod
teorically it will be of the same speed but then it depends on the track. say all tires driver etc etc being equal except the track well the mod might have the edge over the stocker cause it WILL have better acceleration.....