For speedo re calibration though, they must be measured when mounted.

 

yes they do

 

Also if your thinking about regearing you should use mounted diameter.

 

just do what most guys do...say it's bigger than it really is.

 

The metric sizes tend to run small. The domestic sized tires 35 X 12.5 tend to be noticeably larger. Especially width wise.

A guy I wheel with bought some 315 / 70 / 17 thinking they were 35's. Once mounted, they did look closer to a 33 than a 35. He dumped them after a couple weeks and ordered 35 X 12.5.

It also depends on tire manufacturer -- BFG tends to run the smallest. GY tends to run closer to stated size.

 

I have good year Kevlar's and they are 315/70-17 and they measure very close to 35 mounted but I do keep them aired rather high at 35 psi. Most people on here I notice run around 28 psi.

 

X2!! here here,