"How is proper pressure related to tire size? For instance, if one changes from 165/80 to 185/65, how, if at all, would the proper pressure change?"
The short answer is, yes, proper tire pressure on the same car will vary slightly with different size tires. I refer you back to my post, above, on marking your tires with chalk to see if yours are at the proper inflation pressure for your car and driving habits. The chalk lets you see in a minute or two whether your selected tire pressure is right for your car. If you need a visual to go along with that, then here you go:
