You need to delete the old tire meshes around lines 1076-1086.
Example:
flexbodies
67,73,154, 0.5, 0, 0, 0, 180, 0, GYJDTireL.mesh
forset 67, 73, 131-154
42,48,182, 0.5, 0, 0, 0, 180, 0, GYJDTireL.mesh
forset 42, 48, 179-202
62,72,159, 0.5, 0, 0, 0, 0, 0, GYJDTireL.mesh
forset 62, 72, 155-178
37,47,205, 0.5, 0, 0, 0, 0, 0, GYJDTireL.mesh
forset 37, 47, 203-226
Then go into the config and clear and regen the cache. That should get rid of the white shell.