Strange physics bugs with a simple car model, PGS enabled

Hi. I was building a very very simple car model using default surface connection joints (e.g. stud → inlet) to try to go back to an older buildstyle, but I found a very strange physics issue with my car model. I have not edited the PhysicalProperties of any parts on my car.

Whenever I sit in the seat and hit W or S, the car drives forward with so much speed or force that it flips itself into the air.

I originally thought that it would be related to my R15 package since those have had recent issues with collision, but I found that this was not the case because my rig never hits any of the moving parts. I also tested this with an R6 rig and the issue was still present.

Here’s a place repro: Car.rbxl (16.3 KB)

If you lower the Torque of the VehicleSeat or raise the weight (change the Density) of the car, then the problem goes away.

With the default weight, a Torque of 1 works fine.

I don’t think this is a bug. I remember vehicles flipping out in the past if the torque was too high, too. You could say it’s a bug because you don’t expect it to happen, but I don’t think it’s new behavior.

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