wheels without a slip

Though the question is not clear, You are trying to move your vehicle and it slips when you apply rotation to the wheel? It does not grip and slips (Traction)? If it is correct.

• I m assuming you have already tried adding a Physics material. If not create a Physics material (3D or 2D - not sure again) increase the friction to watever levels you want till it stops slipping and grips correctly.

If you are referring to auto rolling under the effect of gravity- then add a Hinge Joint between the wheels & the vehicle and make Motor Speed 0 - this would arrest the movement of the wheel completely and make ur vehicle stand still!