WheelCollider: veering/drifting bug?

I know there have been a bunch of questions related to this but I’ve not yet found a satisfactory answer. Apologies if you’re sick of hearing about this!

I’ve created a super simple ‘car’. With four gameobjects with wheelcolliders positioned precisely symmetrically around the body (which has a rigid body attached). The car is placed on a simple plane. If i make the car ‘go’ by adding motortorque to the back wheels, the car will veer to one side quite dramatically as it travels.

Is this somehow expected behaviour or a bug? If it’s expected, why is it happening?

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The reason for the drifting seems to be some kind of bug related to fixed timestep. The drifting can be removed by reducing the timestep, see animated gif below for a before and after.

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Try adjusting the angular drag. With a bit of messing about you can get rid of the drift. Also, make sure all your wheels have the same mass and make sure wheels and car body masses are realistic amounts.