More specifically the problem is that friction is applied to wheel and then propagates through chain of your constraints to the main body. For this to work correctly you need to scale the mass of connected objects in such a way that it’s as close to 1:1 ratio as possible. One way is to fiddle not with mass but with ‘mass scale’ property. Unfortunately this leads to a setup where 30 ton truck has a 3 ton suspension axles connected to 3 ton wheels.