Physics Simulation Forum

Hi everyone!
For few days/nights I'm working on a simple racing game. I'm programing in java with jBullet.
There are some things which I want to optimize and need help:
1. Grass ground should be more slippery than track, so when car drives of the track that is visible on breaking, handling. Ground and track are two separated collision objects(to make that easier).
I tried with:

Change is visible on other objects(tires laying around), but not on a vehicel.
2. How to implement handbrake?
3. Could Bullet help me detect when start-finish line is crossed?
Collision Filtering could probably be the answer. I'm missing further code of the spaceship game in Wiki, where power up is added to spaceship when picked.

Thanks