Or, one tire with equal sections covered with different dressings.
Although, using real dressings be messy (especially with the solvent-based ones) so maybe some type of coating to simulate the level of shine.
It would take some experimenting to get the simulated shine levelright, but it might work.
OR
You could just ask if the customer has a preference for low, mid, or high gloss. Chances are they will either have no preference or a strong preference (like "NO HIGH GLOSS CRAP!!").
Thoughts anyone?