No tires

#1 On the server, one typically calls setWheelTire with a datablock name to set up the wheel.
See Car.cs WheeledVehicleData::onAdd

Presumably, the DefaultCarTire datablock does not exist (or is not a tire).

It is hard to say what would cause this. I would think that usually a script syntax error in the datablock (usually above the onAdd method in the file) would cause the rest of the script file to not be processed so the onAdd function wouldn't be able to be called.

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I tried intentionally making a bad shapeFile field in my
datablock WheeledVehicleTire(DefaultCarTire)
and it resulted in your error message. Most likely, the file can't be found, or perhaps the wheel dts file is bad. Try and change the shapeFile value to another wheel file that still works to confirm this.

Alternately, load your wheel up in the ShowToolPro to verify that it will load and display. If it has all the correct features in the ShowToolPro, then it most likely will work in game.