please help w/ tire size formula

[kps36]

I know I have seen it here before, but after searching for about 2 hrs. I need to ask for assistance.
My son is going from 225/70/14 (stock) to BFG AT kos that are 27/8.5/14 (non metric)on his 95 Ranger. I would like to know what the conversion looks like and, as a percentage, what is the speedo diff ? i.e. at 'real' 60mph, speedo says 64 mph. If need be, I will go side/by/side with the Volvo (the only vehicle with stock size tires) and do it that way.
If I had the formula though I could get a new speedo gear and fix altogether.
Please advise.
thnx.

 

[tbomb]

you mean the tire size conversion? you can go to www.explorerunderground.com and use the wheel wizard (theres a link kinda in the middle of the main page.) sorry i cant help with the speedo calibration.

 

[jimbo74]

www.4lo.com has a calulator table... it will help you out with both of your situations

 

[Jim F]

Here's a few calc's that might me useful:

http://www.miata.net/garage/tirecalc.html

Dead Link Removed

http://www.thegrid.net/thedrivetrainpage/rpmcalc.htm

 

[kps36]

Thanx guys.
Jimabena, that site is GREAT. I have bookmarked it for future use. Except for telling me what speedo gear I would need. Turns out there is 1/2 mph diff in the 2 sizes after converting the metric to inch to match the AT sizing. Not that much diff at all.
Again, GREAT site, use those Calculators he has.
.
Lata.