I think your problem here would be you using ROR 0.38.67, which no truck on the site is meant for- thats why the tires are not showing up.
Also, on the 2nd matter, I think you would be using the OpenGL rendering system, which makes the game a bit laggier, and turns the trucks psychedelic. (from experience)
Try using the DirectX rendering system. and using this version of ROR- .http://sim-monsters.com/index.php?/files/file/294-rigs-of-rods-037117/
Its much better for the trucks on this site.
150th post yes