I've been having big trouble winning races in GTA3
-untill I decided to try and use Tank!
Start the race with common car, and check out the course of the race.
-try to find a good ambush spot along the course, tunnel or a narrow street or somesuch.
Now, restart the race with a tank. Quicklly, drive the tank to the ambush spot and wait for the competition to arrive there.
-when they do, just drive over them! Kaboom!
Now that the other cars are gone bust, you can slowly drive through the checkpoints and onto the finish line! Result!!!