Found an easy to use tire calc that does pretty much everything for you. Just thought I'd share the link

http://www.1010tires.com/TireSizeCalculator.asp

Does revs per mile and everything

 

Yes its a pretty decent little tool to use, especially if you don't really know your stuff like me

 

technically its not hard, there are tire websites that tell you the info needed to know.

if not, that would be a good tool to use.

 

yeah, I can do the math too but it's quick and easy and displays it all on one page so it's easy to look at. I like it. thought others might find it useful for a quick reference.

 

i agree. as easy as it may be, i have an app on my phone i refer to often to save time. not downing it at all. just had to be said.

they also sometimes show mph diffs and groung clearance chances which help as well.

 

Another good way is to mark your tire, and on a paved surface rotate it once by moving forward until it turns once, measure the inches, then get on the computer and find a inches to milimeters calculator and insert the inches, then you receive your new mm circumference.