Tire size definition

[Cliff_Johns]

What do the fields in a tire size mean? For instance,
if the tire was shown as

26x12.00-12

What would that translate into?

OK, so I'm new to this.

Cliff

 

[Cliff_Johns]

Oh, yes, and what does it mean when the last number
is left off as in 12X16.5

Cliff

 

[Inspector507]

Cliff,
You might want to download the Goodyear Handook from here Goodyear

That has a lot of good info to help you understand tractor tires

Jerry

 

[Cliff_Johns]

OK. I downloaded the 2Mb file and it had a lot
of information. Very interesting. Now I know what
R1-4 really means etc. Good close up pictures of
tire tread configurations and all that.

That document said that the number before the dash
is the "Nominal cross section" which I take to mean
the width of the rubber at it's widest point. The number
after the dash is the rim diameter which is obvious. The dash means it's bias ply rather than R for radial.

I could not find where it said what the number before the
X is, for instance in 29X12-15 nor what it means when the
rim size is left off as in 12X16.5

I'm looking at a NH brochure and there are some confusing
numbers there. For instance, for a TC29 lists R4 tires as
Front 25X8.5-14 and rears as 15X9.5

What is the number before the X? Why is it larger in the
front tires than the back tires (which I would think would
be bigger in every way.)

I do apologize for the silly questions, but I can't find
anywhere where this is written down. Maybe I missed
it in the Goodyear documents, but I don't think so.

Any other pointers? (or could someone in the know
just tell me)
Thanks,
Cliff

 

[JD4610]

If the brochure says 15X9.5 it's a misprint. It's supposed to be 15X19.5 I believe.

Although it is most common to write out tire size as (section width) - (rim diameter) as in 7-16" some people will write it out as 7X16". It really means the same thing, but not technically correct.

If you get all three numbers you get (outside diameter) X (section width) - (rim diameter), like 31X10.5-15" truck tires.

So, those 15X9.5 tires really are 15 inches wide, on a 19.5" rim (typo corrected.) No outside diameter is specified.

 

[Cliff_Johns]

I see, so where it says for a TC18 that the front is
23X8.5-12 this means the front tire is 23 inches in
diameter, 8.5 inches wide and a rim of 12 inches.
Where is says right next to it that the matching rear
tires are 12X16.5 This does not mean the tires are
12 inches in diameter and 16.5 inches wide (which I'm
glad to hear), but rather that it's 12-16.5 as in 12
inches wide on a 16.5 inch rim and some unspecified
actual tire diameter.

Strange way to do it, I think, but I very much appreciate
the answer. Thank you.

Cliff

 

[RobertN]

It is odd how they figure this stuff, especially when you have metric stuff, the older "inch" stuff.

Some tire do have the full spec for, ie your 23x8.5-12. As you have found out, it is 23"diameter, 8.5" wide, and uses a 12" rim.

For those 12.4-16's, that is an older way to spec it. It is a 12.4" effective tread, with a 16" rim. They do not show the diameter in this spec. In the old days a lot of car/pickup tires were specced that way. I remember my Dad's Jeep in the early 70's running a 10.50-15 tire.

The most informative way to find tire info is the books, or manufacture web pages. It is most important for these 4x4 CUTs which require front to rear ratio matching, since the front tire are shorter than the rear.