Alright, I fixed all of the issues mounting the wheel. Only two problems I cant fix:
1:Its loving impossible to drive. Can I have invisible wheels along with the one I have, or can one vehicle have only one type of wheel?
2: My wheel moves; I want it to work like you did the segway.
I had the same problem on the segway but eventually what I did is I made 4 wheel mount points, but made the front 2 invisible. So the ones that you don't see are the ones that steer it and you just see the back ones.
You could try and do that for yours, although I'm not sure what you can do to only have 1 visible wheel. Maybe you could have hub0-3 around the vehicle to keep balance and to steer, and set their wheel to be empty.dts and then just put hub4 in the middle where you need it.
How did you paint it?
Also, I'm having some problems with the model in-game. I'm sure the gun is small enough in Blender, but it comes up like this in-game:
I have no idea what the hell is up with the shine on it.
It's cause you assigned the textures improperly. Don't use the materials buttons, just use UV editor, and your textures have to be a square of 8x8,16x16,32x32,64x64 etc.