math whiz's: need help finding a tire size the backwards way

[badkelly]

the hot wife's new grand cherokee has way oversized tires. i need to find a tire that's a little smaller diameter and height, but not so small it's stock. she has the 2" lift so stock would look really dumb.

stock would be: 235/65/17 on a 6.5"-8.5" width rim, 29.1" in diameter and 9.6" overall width.
currently equipped with 265/70/17 on a 7"-9" width rim, 31.7" in diamater and 10.8" overall width.

what i want is a tire that's about 30.5"-31" in diameter and about 9.5"-9.8" in width. in a nutshell, as narrow as stock, but taller than stock....but not as tall or wide as what we have now.

make sense? is there a formula that makes it easy to find sizes that way? i have found:
245/70/17 that's 30.5 diameter and 9.8 width and 235/80/17 that's 31.8 diameter and 9.3 width, but that is just doing an exhaustive search in one brand of snow tire. i'm needing to find a way to figure out a size tire from the dimensions i am wanting

[TanTahoe]

This site has always help me with tire conversions.
http://www.redrock4x4.com/tireconversioncalculator.html

[Wlfman]

Here's a good site:

rimsntires.com/specs.jsp

[canuckz71]

Take the section width and divide it by 25.4 to convert it into inches. I'll use a 285/75/16 as an example.

285mm/25.4 = ~11.22"

Next multiply that by the aspect ratio.

11.22" x 0.75 = ~8.415"

This gives you the height of one sidewall so double your last answer and add in the rim size to find the tire height.

~8.415" + ~8.415" + 16" = ~32.8"

I used rounded numbers but you will get the exact values if you use all of the digits.

Hope this helps out.


Edit - I should also add some tires run smaller or larger than advertised so keep that in mind

[Quyonmob]

Sounds like you have already figured out that a 245/70/17 is about as close as you are going to get to what you want.

[badkelly]

wow, you all are genius's. yeah, i found a tentative size but it's in a specific general snow tire(altimax arctic). it's easier if i can get a few sizes down and search across brands instead of searching for brands and trying to figure out the sizes of the tires they have available.

[ZZ4Blazer]

Tirerack.com has a ton of tire info. Including searching by 17" rim size for every sized 17" tire they carry. Should have an idea on the size you need, nut doesn't mean anyone makes it.

EDIT: 235/75-17 A bfg rugged terrain tire is listed as 9.3" section width and 30.9" OD.

[Quyonmob]

wow, you all are genius's. yeah, i found a tentative size but it's in a specific general snow tire(altimax arctic). it's easier if i can get a few sizes down and search across brands instead of searching for brands and trying to figure out the sizes of the tires they have available.

With how specific you are wanting, it's going to vary brand to brand and make to make, potentially as much as a 1/2" height and section width, within a 245/70/17.

Want exactly a 30.75"x9.75"x17? (used the middle of the road for your wanted specs)

= 247.65/70.5/17

Closest you might find is a 245/70/17. :D

[HD4Mud]

235 is your width measurement, so if you want a taller tire in the stock width, look for a 235/70 or 75. A 245/70 or 255/65 would be slightly wider and taller than stock but not as big as the 265/70. Personally, I wouldn't consider 265/70 way oversized. The more rubber you can put on the ground the better off you are unless you're driving on ice.

[badkelly]

ice is the key. and mileage, which is the other reason for the downsizing a little. less rolling resistance.

[Quyonmob]

EDIT: 235/75-17 A bfg rugged terrain tire is listed as 9.3" section width and 30.9" OD.

Horrible winter tire. Dangerous even. We pulled every set Rugged Trails off our fleet trucks in the winter after the first snowfall they ever saw.


ice is the key. and mileage, which is the other reason for the downsizing a little. less rolling resistance.

P245/70/17 Toyo G-02's. Incredible snow tire, specializing in ice traction.

[ZZ4Blazer]

I'm not a fan of them, just listed them as a reference tire.

[TennesseeWJ]

Looks like you're on the right track. I assume this a 99-04 with a 2" budget boost and factory wheels?

If so, 245/70/17 would be the size most commonly run without rubbing on that setup among Grand Cherokee owners (I used to own one myself).

[badkelly]

'05 with suspension lift (though it's just spacers under the rear springs). i haven't crawled under it yet to check out the front because i'm doing as little as possible right now to it so she won't gripe at me for throwing money at it and i would probably find stuff to do under there, like sway bars, shocks, panels. and it's about 10 degrees in the morning when it's sitting still :D

she drove it to denver the other day and was pulling in about 20mpg, so she's pleased with that. it gets about 14-15mpg in the city and only has a 20gallon tank. it just rubs when you crank the wheels

http://i112.photobucket.com/albums/n195/badkelly/2012-01-06091959.jpg

[TennesseeWJ]

10-4, good looking Jeep!

Curious to see what tires you end up with. My mom has an 08 Grand Cherokee Limited that runs a 245/60/18 from the factory (~a 245/65/17) and there isn't much of a selection in that size. Maybe you'll have better luck with the 17" rim and a little more room to play with given the lift.