badram

Hey all , I did search and found the formula for fig. the rpm but nowhere did I see if you go by the man. spec. for specific tire or actual meas. of tire and if you go by actual measurement is it the mounted meas. , unmounted , on truck , and if on truck front or rear , maybe too much thinking as I know it will also change with wear so when you come up with a fig. do you alter for assumtion of wear ? by the way new tire is Pro Comp Xtreme all terrain 305/65/17's and they look sweet on Pro Comp 1059's. Thanks..

Argo

you go by the actual measurement.

LonestarCTD

I did some checking and those are the same as 33x12.50R17's. Rev's per mile come to 625, regardless of manufacturer or type, if the sizing is the same. Hope this helps.

badram

Thanks guys , So being that this is a 33/12.50/17 we are just using a general 33 inch measurement by those calculations ? but all 33's arent truly 33 inches ? so then are we just looking for a middle ground.

smokin05

look here is a easy way measure from the ground to the center of the rim

we will say that number = 15'' for grins then it goes like this

15x2= 30 x 3.1416= 94.25"
this is the inches the truck moves in one rev.

now convert to feet by dividing by 12
94.25"/12= 7.85 feet

divide that number into 5280 (thats the feet in 1 mile)
5280/7.85= 672 revs per mile

just use your measurment and this formula and your set...

also it more accurate if you do this on your factory tires and then divide your new big tire revs into your factory tire revs this will give you the % your speedo will be off

peace

LonestarCTD

If you want a pretty good way of checking, go to http://www.4lo.com and click on the speedometer link on the left of the page. It will take you to a page where you plug in your original tire size, new tire size, and the speed you want converted. It will give you a pretty accurate speed based on the new tire size.

PurNLoud

discount tires website also has a link to figure this out