Maybe you could try making the dirtbike massless (by checking the massless property) and adding a invisible part that covers the bike that acts as the mass so its not front heavy or back heavy you can also make the player massless to but im not sure how to do that really. also not sure if this works as im not experienced with vehicles either lol
You need more mass in the front of the bike to prevent the bike from flipping over when going over hills. It’s the same reason bikers lean forwards when they’re going up a hill, you’re trying to push away from the force of gravity. The same is happening here with your bike. You should implement some type of force to counteract the force of gravity, thus preventing the bike from flipping backwards.
Edit: Adding a traction force would also work. What I mean by traction force is a force that keeps the bike oriented correctly based on the normal of the surface the bike is standing over.
I’d suggest looking into the tuning of the A-chassis.
From what I’ve seen it’s pretty well made and informs you where to make changes to fine tune your vehicle.
Unless anyone has experience with using the A-chassis script for motorcycles then I doubt you’ll get much help here.