Quick question that I should know, but do not - I have tried looking it up and cannot find what I am looking for.

I understand regular tire sizes such as P235/75/R15 what I don't understand is what for example are 31's - I would expect they are bigger than 235/75/15, but how would I quantify it?

A 31 would measure?

A 33 would measure?

Just trying to better understand some of what I am reading.

Keith

 

I was the exact opposite up until a month ago. A 33/12.50/R15 means the tire is 33 inches from top to bottom, AKA diameter. The 12.50 is the horizontal width between the sidewalls in inches. The R15 is the rim height in inches. I hope that helps.

 

that does help, thanks!

 

How to Convert Metric into Standard

For those of you who are confused on what metric tires labels mean I hope this helps. I still think the metric way is confusing.... Look for definitions at the bottom.*

Example of metric tire label: 265/75/R16

What they mean:
Section Width(mm)/Aspect Ratio/Rim Diameter(in)

To convert Section Width from mm to inches:
265/25.4=10.43" Section Width*

Figuring out Section Height from the Aspect Ratio:
10.43x.75=7.82" Section Height

To figure out Diameter from the Section Height:
Section Height x 2 + Rim Diameter*
7.82"x 2+16=31.64" Total Diameter

Put it all together and the closest standard tire size is:
31/10.50/R16

How they figure out what the Aspect Ratio is
7.82"/10.43"=.75 Aspect Ratio
Section Height/Section Width=Aspect Ratio

Aspect ratio: The relationship between section height and section width. The higher the aspect ratio number, the skinnier the tire, relative to its height. An aspect ratio of 75 means that section height is 75 percent of section width. A tire with a lower aspect ratio of 60 will have a "lower profile" than a 75, and a fatter look. This is normally the second number listed on a metric-sized tire.

Section width: The horizontal distance between the tire’s sidewalls. Expressed in millimeters, this number is usually the first number in a metric designation.

Section height: The vertical distance between the edge of the wheel rim and the top of the tire tread. Expressed in millimeters, this number is not usually marked on the tire.

Diameter: The actual height of the tire measured through the center, in inches. Not always marked on the tire.

 

There you go getting all mathy on us! Tryin to learn us sumpton Mister Smartypants?

 

I usually t'ain't no good at dem numbers eeder, I rectum twas jus cause it int'rested me that I figgured it out.

 

Here's a metric to standard tire conversion calculator:
http://www.rocky-road.com/calculator.html

 

HUH? haha

 

That just takes all the fun out of it though.

 

I understand tire size but what are the largest I can put on my 98 xj 4door with no lift yet?

 

A lot depends on how much your suspension is sagging. I bet you could run a 30" tire but I would bet you'll rub. Stick with some 29"s or 235/75/R15.

 

Thanks gave up two wheels and got my first xj this week

 

Actually what nobody is saying is that the second number of the metric size is not a dimension, but a percentage. The second number is the % of the first number that is the tire width in millimeters. This % is the height of the tire shoulder: 235/75 r15 is: the tire is 235mm wide, the shoulder (from the rim edge to the top) is 75% of 235, that is:176,25 mm. the R stands for radial, to distinguish from non/radial, although i doubt that non radial tires still exist. The 15 is the diameter in inches of the rim.
31x10.50 x15
31 inches high, 10.50 wide, on a 15in rim.
anybody knows what a 9.00x16 tire is?

 

Congrats on the new Jeep!

 

Thanks for clarifying that. The definition I used for the aspect ration didn't really say that it is a percentage specifically. I dont understand why metric tires have to be so confusing in the first place... Doesn't it make more sense to give just the diameter, width and rim diameter instead of the some percentage that you have to use to figure out the rest of the tire dimensions? And i have no idea what a 9.00x16 tire is.