Just throwing this out there because I did it this way and it worked really well.
You can use AddTorqueInRadians to apply a torque force to the wheels instead. This works more similarly to how throttles in vehicles work, and also gets around needing to detect collisions. Because the wheels are having a torque force applied to them and it is the friction between the wheels and the ground pulling the tank forward.
When the tank leaves the ground you can still apply the torque and spin the wheels, but the tank won’t be pushed around because the wheels aren’t making contact with the ground.
You may need to mess around a bit with it and the friction but it worked pretty well for me!