You can reduce lag by adding a feature which people can increase the speed of the game. However, you can't really reduce the physics engine, because that would make things inaccurate. Here are some possible options:
1. Rather than right-clicking the game and selecting quality, low, the game has that feature in options.
2. Only show vertices on the chassis and wheels.
3. Change color to metronome.
4. Only show vertices on the track.
5. Only show the track that is vertically parallel to the car.
6. Reduce visible frames to 1 second, 2 seconds, etc.
7. Make everything invisible except the car and track.
However, for those who want to see their cars as a super-cool one, same for the track, there can always be features that do such.
Here are some possible options:
2. Background and foreground.
3. Smooth coloring of parts and seamless points of the car.
4. Speed effect.
5. Cooler chart & font.
6. Sound Effects.
Think of some more ideas!