Real world difference between 16" and 18" rims with 31 tires

[Martinjmpr]

I think the cost difference comes from the tires for larger wheels being more expensive to produce (more bead area, etc.). 16s and 17s are similar in cost for the most part, 18s and larger are where it really starts to get expensive.

Ah, I hadn't thought about the longer bead, that does make a bit of sense. I suppose that could count for some additional cost but wouldn't you think that after the tire had been in production for a few years any additional cost would be fully amortized?