One of the studs in your above pic has a shine on it close to the wheel. It almost looks as if the nuts are skipping threads rather than backing off. Are the threads feeling like they a fitting properly or is there a fair amount of play in them?
On another note a torque wrench is a really good idea. Don't skimp on the model.
On another note a torque wrench is a really good idea. Don't skimp on the model.