Metric tire sizes explained.

I see a lot of people are having a hard time with metric tire sizes on this board. I keep reading about people saying I have 235s, or i have 245s or 285s etc... this means nothing. If you want to share the size of your tires you need to list the whole size. 235 or 245 or 285 or whatever is nothing but the tread WIDTH, not height of the tire. We don't say "I run a 12.50" or "10.50" tire when talking about tire heights, likewise, we shouldn't talk about just the tread width with metric sizes. 235/40/17 is a whole different tire than 235/75/17. At the same time, it could be 235/70/17, 235/65/17, 235/60/17 and so on and so forth.

I know, its much easier to talk about tires in inches when talking tire heights. Saying you run 33's or 35's is much easier than listing 3 sets of numbers just to explain the height of the tires, but you really need to if you want a correct definition.

Here's a little explanation:

The first number is the tread width. The second number is the aspect ratio (percentage of the tread width that makes up the sidewall) and the third number is the rim size. For instance, a 235/70/17 is 235mm wide, the height of the sidewall is 70% of 235mm and it fits on a 17 inch rim. For this particular tire size, 235mm equals about 9.25 inches wide. 70% of 235 mm is 164mm or 6.45 inches, so 6.45x2 is 12.9, which is the height of both bottom and top sidewalls, plus a 17 inch hole in the middle means this tire is 29.9 inches tall. Make sense?
For this reason a 235/75/16 is going to be a shorter tire than a 235/75/17.

Sometimes you'll see another set of numbers after the tire size, such as 98T, or 106S, or something different, which are the weight ratings and speed ratings. The numbers 98 or 106 for the weight ratings don't really correspond to anything weight related, they just let you know relatively how much weight your tire is rated for. Speed ratings do actually correspond to a specific speed. If you exceed the speed or weight that your tire is rated for, you could damage your tire, and/or create an unsafe situation. All cars come with a recommended weight rating and speed rating for tires from the factory. You can go above the weight and speed rating that came with your car/truck, but not below. By putting higher weight or speed rated tires on your car/truck, you'll just suffer from a rougher ride, but not much else.

Speed ratings:
M=81mph
N=87mph
P=93mph
Q=99mph
R=106mph
S=112mph
T=118mph
U=124mph
H=130mph
V=149mph
W=168mph
Y=186mph
Z=149+mph

Weight ratings: (Per tire, I skipped a few)
80=992lbs
82=1047lbs
85=1135lbs
87=1201lbs
90=1323lbs
92=1389lbs
95=1521lbs
97=1609lbs
100=1764lbs
102=1874lbs
105=2039lbs
107=2149lbs
110=2337lbs

I hope this clears a little bit of cloudiness with the metric confusion.

Great explanation, thanks.

Oh, and I never want to buy a metric tire.

Metric tires work better in Canada because they don't have miles anymore. What kind of a county is that anyway where they have kilometers per gallon (and it's a 5 quart gallon)????????

Man thats confusing! Nice post.

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

this converts metric to english

PIE= Is round

CAKE= Is square
So there..LOL.. I have 33's

I don't see the confusion, it's not like XJs came stock with 20" rims, 17" rims, 14" rims, 13" rims, or any other crazy stuff, they came with 15" rims.

P205X75X15 tire is a 26" tire.
P235X75X15 is a 29" tire.

Anything above that and people tend to buy "DiameterX treadwidth X rimsize" rated tires, like 31X10.5X15 .

What's the confusion? The web is full of metric tire conversion programs.

Zuki-Ron said:

I don't see the confusion, it's not like XJs came stock with 20" rims, 17" rims, 14" rims, 13" rims, or any other crazy stuff, they came with 15" rims.

P205X75X15 tire is a 26" tire.
P235X75X15 is a 29" tire.

Anything above that and people tend to buy "DiameterX treadwidth X rimsize" rated tires, like 31X10.5X15 .

What's the confusion? The web is full of metric tire conversion programs.

Click to expand...

Actually, they came with 15 and 16 inch rims, the latter of which is almost always metric. 15 inch rims have metric for smaller sizes and imperial measurements for larger sizes. The confusion is not in whether or not I can convert metric to imperial, but I'm trying to get information out to people who might not understand what metric sizing means. Did you read my post?

But who the hell started a tire sizing system with Width (metric) x Profile (ratio) x Wheel Diameter (inch). In the good old days it was Width (inch) x Wheel Diameter and you had a 60 series or 70 series which was the profile ratio. If you gonna go metric, go all metric, not this half and half shit!

igotanxj said:

Actually, they came with 15 and 16 inch rims, the latter of which is almost always metric. 15 inch rims have metric for smaller sizes and imperial measurements for larger sizes. The confusion is not in whether or not I can convert metric to imperial, but I'm trying to get information out to people who might not understand what metric sizing means. Did you read my post?

Click to expand...

Of course I read your post. What a question.

You created that post because you believe folks are confused as to what they are speaking about.

The standard wheel size on an XJ is 15". So, when I see someone post that they are running 235s, I automagicly understand that to mean that they are running 235X75X15s.

For everyone who may be confused about a tire measurment system which has been around for a good 40 years, go to the tire MFGs website, or even TireRack.com and look up your tire (or the one you are thinking of buying) and the MFG issues spec sheets for the tires they make.

For example, if you want to run a BFG AT/KO in a 235X75X15, and you want to compare it to a Cooper Discover AT in a 235X75X15, you will find the BFG is a taller tire by a fraction of an inch. The reason I bring this up, is when you go to the "english" tires sizes, the size difference becomes more significant.

A list of MFG links would go well with this post, but really, I just use TireRack.com , look up the tire I'm looking at, and click on "specs".

i think most people who dont understand the metric tire measuement system dont care enough to spend twenty minutes figuring it out...

the metric system is retarded, i dont care how many websites tire rack has explaining shit... it doesnt make sense... if you have to do math... you took the whole point of putting the size on the side of the tire....

thanks for trying... but most of us dont care to learn that system..... most of naxja will run 31's plus...

when people say they run 235's.... all i hear is STOCK... in which case, who cares about tire sizes? its a grocery getter
...

everyone ive met who wants to teach you the metric system is just doing so because theyre trying to recoupe their time wasted learning it for a tire jockey job.

Quick correction- 235 is the nominal width of the casing (normally measured from sidewall to sidewall), not the tread width. A 235/x/x tire is ~9.5" wide across the casing, but the tread is normally considerably smaller (my Dueler A/Ts have a treadwidth of around 7", although the casing is nearly 10", as an example).

Hallo. I love the way you Americans talk about tire sizes.
As an European I use now only 30",31",32". and the tireguys in Holland are looking or I am coming from Mars.
But you have to admit , that mm is very easy ,instead the inches. Especially the small sizes of things. LOL

'92 XJ with 31"x 10.5"x 15. BFG Muds. :dunce:

wim hoppenbrouwers said:

Hallo. I love the way you Americans talk about tire sizes.
As an European I use now only 30",31",32". and the tireguys in Holland are looking or I am coming from Mars.
But you have to admit , that mm is very easy ,instead the inches. Especially the small sizes of things. LOL

'92 XJ with 31"x 10.5"x 15. BFG Muds. :dunce:

Click to expand...

our women use your tire system... for their little girl cars....

AND NO, its not VERY EASY... 31x12.5x15 would be an example of easy... see how the numbers are real numbers that actually mean something...? you guys should try that..., instead of letting a german design your tire size system....

its not impossible, if i cared, i'd use a converter online... just cut the BS about it being an 'easy system'....
i wouldnt mind the MM stuff, but the aspect ratio? come on... its a tire with three dimensions...

typical americans... doing it right, with a minimal ammount of work... yeah... TYPICAL...

wim hoppenbrouwers said:

Hallo. I love the way you Americans talk about tire sizes.
As an European I use now only 30",31",32". and the tireguys in Holland are looking or I am coming from Mars.
But you have to admit , that mm is very easy ,instead the inches. Especially the small sizes of things. LOL

'92 XJ with 31"x 10.5"x 15. BFG Muds. :dunce:

Click to expand...

We use the small sizes as a special trick to keep our brains sharp. For woodwork we can add up 1/4" and 5/16" and 1/8" to get a 3/4" measurement. Measure twice, cut once.:idea:

Is this the one example of the US standard of measurement being easier to understand than the metric version?
Billy

xcm said:

i think most people who dont understand the metric tire measuement system dont care enough to spend twenty minutes figuring it out...

the metric system is retarded, i dont care how many websites tire rack has explaining shit... it doesnt make sense... if you have to do math... you took the whole point of putting the size on the side of the tire....

thanks for trying... but most of us dont care to learn that system..... most of naxja will run 31's plus...

when people say they run 235's.... all i hear is STOCK... in which case, who cares about tire sizes? its a grocery getter
...

everyone ive met who wants to teach you the metric system is just doing so because theyre trying to recoupe their time wasted learning it for a tire jockey job.

Click to expand...

You are right Google can help you find everything you need to know!


Also my rig has 235/75r15's on it and it is really close to stock height but its not a grocery getter its a green trail warrior!

Google tells you that the metric system was invented by a british dude that nobody in britain listened to but the frenchies took it on to be different than everybody else (which they are). In a bizarre chain of events, the germans adapted the frenchie system. We are lucky that we got out of that bizarre chain of events before 1776.