I have a 98 Durango 5.9L and it currently has 31x10.5x15's on there. I am gonna be upping the wheel size to 18's. How do I figure the tire size to put on there. I will going to the triple digit size. I believe the equivalent of what I have now is 235/75/R15. Any help would be awesome! Thanks.

 

I believe it would be 225/45/R18? I am probably wrong, but taking a shot at it. Lol.

 

Here are the Specs:

235/75/R15:
Rolling Radius: 230.44 cm
Total Diameter: 73.35 cm
Sidewall Height: 17.63 cm

I tried to find the closest match to Rolling Radius and Total Diameter as possible, seeing as a 31-10.50 is about the largest size you can put on a D without rubbing.

Best Match I could find is:

215/65/R18:
Rolling Radius: 231.44 cm
Total Diameter:73.67 cm
Sidewall Height: 13.98 cm

 

Also, changing your tire size to this size from the 31-10.50's will only make your speedometer off by 0.4%. Meaning you will only be going 0.4% faster than your speedometer reads.

 

235/75/r15 is a 29.5" tire on a 15" rim (what I have at the moment)

this tool should help you convert between the metric and english tire sizes
http://www.miata.net/garage/tirecalc.html

 

http://www.kouki.co.uk/utilities/vis...ize-calculator

thats what I am using lol, yours is the same thing guy

but that one actually gives an outline. I like that guy. Of course my calculations are correct 215/65R18 will fit exactly the same as his current tire with 15s.

 

These tires have a 10.7 sec width and a 30.6 diameter for 31/10.5/15 http://www.tirerack.com/tires/tires....=yes&tab=Specs, and These have a 10.7 sec width and a 30.5 dameter for 265/60/18 http://www.tirerack.com/tires/tires....=yes&tab=Specs

 

I can do the metric size conversion. That's why I know the equivalent size. You think its 215/65/R18? I wasn't quite there huh? Lol! Appreciate all the help guys. That calculator will be handy for getting the right size on my Ranger too. It's all jacked up. It's lowered like 3 inches and the tires are the wrong size. We just bought like this, its a mess. Lol. Has the speedometer thrown off by 15-25mph. Terrible.

 

once you get the tire size sorted out you can have the computer programmed to show the correct speed

 

Yep, cause I'm sure it'll be off a tad. I just want some bigger wheels, I believe it'll look better. I've got lots planned for this beast.