Spec. tire height Vs. Actual tire height

[DeanM2]

In my experience, tires are NEVER as tall, when mounted, as the specs. say they are. Currently, my 275/55R20 tires (20x9 wheels) are supposed to be 32" tall. They are actually 30.5" tall.

What factors affect the actual tire height when mounted? And if I want to go to an 18" wheel with a tire that is 2 inches bigger in diameter (when mounted) than the current ones, how do I have any confidence in achieving that 2 inch increase?

 

[HSKR R/T]

In my experience, tires are NEVER as tall, when mounted, as the specs. say they are. Currently, my 275/55R20 tires (20x9 wheels) are supposed to be 32" tall. They are actually 30.5" tall.

What factors affect the actual tire height when mounted? And if I want to go to an 18" wheel with a tire that is 2 inches bigger in diameter (when mounted) than the current ones, how do I have any confidence in achieving that 2 inch increase?

Weight of vehicle and air pressure effect installed height. But sizes also vary some from manufacturer to manufacturer, and even between different tires from same manufacturer. Overall construction differences as in sidewall stiffness, tread design, whether is has rim protector or not. I wouldn't worry so much about finding a tire exactly 2" taller. Just get a size you want in the tire you want.