That's true but in order to have the proper inflation for the weight it had to be that way. You not going to have 100psi in a 32 and 100psi in a 23 without be over inflated on the 32 for the amount of weight being carried. You can see that readily in the Michelin tire calculator. So to do a accurate test of contact width you have to have the proper PSI for the weight being carried.

I hope that made sense?!