Tires true to size?

Hello! I just purchased a 2017 Tundra TRD 4x4. It currently has some lower end all terrain tires. They are 275/65/18---supposedly this tire should be 32.1" in diameter. However, it measures to 31" on my stock rims. I'm looking to go to a 275/70/18 BFG mud terrain. Said tire should be around 33.2" per one of those online tire calculators. Am I correct to assume it will actually be around 32" as the 275/65 were about an inch shorter than the calculator said?

I don't want any issue rubbing nor do I want to raise/level.

thanks!

 

Sounds like the truck you purchased has some wear on the tires. I up-sized to the tire you're suggesting and it is 33 2" tall but you'll get the actual sizing correct depending on the new tire manufacturer... I'm rocking Cooper ST MAXX and they're true to your calculator sizing...

 

If you look on the tire manufacturers sites, it states that the tires are measured unmounted and not inflated.

 

Sizes can vary a little by manufacturer. For example, Cooper XLTs in 275/70-18 are visually smaller than Wildpeaks of the same size. Not a hugh amount, but Wildpeaks are visible bigger, few tenths of an inch taller, wider. Tire manufacturers will often list the height and width so you can compare vs other brands and sizes. Both Discount tire and Tire rack will show you height as well.