Basically on the street, whoever is in front when the leader lets off basically. Its really hard to determine because you always have the idiots who have a book of excuses. If you want to see whos faster, take it to the track.

 

when the car in front is pulling away through at least one full gear, its over.

when the car in front is getting reel'd in, the head car must continue floored and allow the other guy to overtake him for an official kill..
if the head car backs off and claims the vicotry as the other car catches up, its a punk out, but still a win.

if the race hasnt even started yet OR if it was over and both slowed down only to have the other guy take off without notice (from behind) its a ricer fly by.

my favorite though is seeing somebody start a full-on fly by from a ways behind you and let em get up to your bumper, floor it, and STILL blow them away

i feel really sorry for the guys that feel a fly by is a legitimate racing tactic.