Hey there @RaymondGuo_007! It could be that the normals are revered on the tires themselves. You could either reverse the normals in a third party modeling program like blender, or in the material, check the two sided boolean. If that doesn’t correct the issue, could we see the material setup?
Are you sure its not bad skin weight in your 3d program?
Turn the wheels to the left or right there and see if they follow the bone or bend. Are the wheel meshes a 100% weighted to their corresponding wheel bone.
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