reading tire sizes

[thatguy]

OK, someone help me out here...

What does the tire size 26X12-12 or 26x12.00-12 mean? which is width? diameter? radius?

thanks

brian

 

[73jeep]

26 x 12.00 - 12

The 26 = overall tire height in inches.
The 1st 12.00 = overall tire width in inches.
The 2nd 12 = The wheel-rim diameter in inches.

 

[thatguy]

thank you

b

 

[rk246]

Okay so on the 3830 14.9 X 24?

 

[ZJ_HR]

14.9-24 equal to old way of marking 14.9/13-24

14.9" is width of tire, 13" is height of tire, and 24" is rim diameter.
So, total height of tire will be 50", and according to new designation, your tire will "sound" 50x14.9-24.
Here in Europe every day are more common metric size tires, with similar designation as car tires.

 

[daTeacha]

So is there a move toward a uniform sizing system for tires on these things? I remember when car tires had letters for width and the rim size. Then there was a letter and a number for aspect ratio and the rim size. Now there is a width, aspect ratio, rim size, speed rating and load rating at speed plus the load range.

 

[ZJ_HR]

Personally, I like milimeter measured tires more, maybe because we use metric system here.
All metric sized tractor tires are radials, when inch sized can be ether radials or cross ply (bias).
Seems that all is in history and habbits. Here tractors use wide, low profile radials when there are more common normal bias tires mounted as duals.

On my smaller tractor there are 8.3/8-20 and 12.4-28, when on bigger one are 360/70-20 and 420/70-30.
Problem is that there are no that small metric sized tires for older tractor.

 

[rk246]

Thanks, can you tell me what the formula is to figure out the tire size? My truck used to have 35 x 12.50's x 16.5's that was easy, 35 inches high 12.5 inches wide, now it has 315 x 75's x 20's, now I know that 20 is the rim size but I don't get the rest of it, and the tractor size thing really threw me off, How do you know that it is 14.9 x 13? I can understand the 24" thing for the rim, but the rest doesn't make sense to me?

Thanks

 

[ZJ_HR]

Read some manufacturers tire size charts. And we have lot older tractors here; some of them have 14.9/13-28 and some just 14.9-28. Both tires are equal in height. Tire dimensions are not changed just a designation. Just few sizes, for example, which have similar diameter/circumference:

old des. ....... new des. ... similar metric ... low profile metric
11.2/10-24 ... 11.2-24 ... 280/85-24 ... 320/70-24
12.4/11-24 ... 12.4-24 ... 320/85-24 ... 360/70-24
14.9/13-28 ... 14.9-28 ... 380/85-28 ... 420/70-28
16.9/14-28 ... 16.9-28 ... 420/85-28 ... 480/70-28

Just for example, rims are 24 and 28", can be 20, or 30" or ...

You mentioned 35x12.50x16.5, or other (tractor like) designation will be 12.5/9.25-16.5.
Metric ones 315/75-20 are 12.4" wide, 9.3" high, but 20" rim seems too big, as this wheel will have 38.6" diameter, which is higher then old 35", except if you notice bigger tires and higher vehicle.

 

[daTeacha]

This should be simple, but it's pretty confusing. Kubota offers an Ag tire as standard on the L3400. The size is 11.2 -- 24. They also offer an industrial tire for the same tractor in size 15 -- 19.5. Now I understand that the last number is the rim size. The turf tire size is 13.6 -- 16. For the industrial and turf option, they give an overall height for the front tires, but not the rears. R4 front is 27X8.5 -- 15 and for turf the fronts are 25X8.5 --14. In the size system for the rears, is the first number the width or the height of the tire? If it's the width, how do I figure out the overall height for the optional tires?

Regarding small metric tractor tires, it would seem that the Japanese tractors should have metric size tires in their home market. Maybe you could find a source there in Europe that can get them direct from the factory??

 

[JustGary]

<font color="blue"> "now it has 315 x 75's x 20" </font>

Or maybe written 315/75-20. This means that the tire is 315mm (12.4") wide, the tread is 75% as tall as the width is wide (or 9.3"), and use a 20" rim. So for your case, the mounted tire should stand roughly 9.3" * 2 + 20" = 38.6" tall. Measure your tires to see how close that comes.

For another example, a 315/60-20 is only 60% as tall as the width, so it should stand 7.4" * 2 + 20" = 34.8" tall, which is very similar to your old 35 X 12.5 tires, except for the rim size.

- Just Gary

 

[daTeacha]

So metric designations use aspect ratio, just like car tires. Now what about the English designation with the slash and without the slash? With no slash and 3rd number, is there a way to determine the height of the tire?

 

[rk246]

Wow they have to make it all very confusing, I am pretty sure my tires on my truck are not 38 inches tall, they actually look a little smaller than my old 35 x 12.50's? I can understand that designation, since it is straightforward, but the whole aspect ration thing throws me off, So is this the same for the tractor tires then...

 

[Shawk]

Here's a shameless plug if you're looking for a new set of tires.... /forums/images/graemlins/wink.gif I have a new set of 4 that were just listed in the classifieds. Any interest... just let me know. 26/12/12 18/850/10 Thanks

 

[daTeacha]

Aspect ratios are simply a comparison of the height of the tire above the rim to the width of the tire.

Picture a tire on a rim sitting in front of you so it could roll directly away. Now cut in half top to bottom so you are looking into two more or less round holes, one at the top and one at the bottom.

Focus on the top one. Measure how high the top of the tire is above the steel rim. Measure how wide it is. Compare the two, height/width That's the aspect ratio. Sporty car tires have aspect ratios between 35 and 60. Let's use 50 as an example. A tire that is marked 235/45 x 17 is 235mm wide at it's widest point. It is half that tall above the rim, or 105.75 mm. Since that 105.75 mm is both above the rim at the top and below the rim at the bottom, you can find the height of the mounted tire by adding 211.5 (105.75 x 2) mm to your rim of 17 inches.

There are 25.4mm in one inch, so a 235/45 tire on a 17 inch rim will result in a standing diameter of 211.5/2.54 or 8.33 inches plus the 17 making for a tire/wheel that is 25.33 inches tall with no load on it. If you mount a tire with a higher aspect ratio, the combination will be taller. One with a lower aspect ratio will be lower.

 

[CT_Tree_Guy]

Let me have a crack at it: aspect ratio is the height of the tire from the ground to the bead expressed as a percentage of the width (as measured at the outmost edge of the sidewalls). A 60 series tire would be 60% as high as it is wide. Higher series (eg. 70, 80) are taller relative to width, lower series (35, 40) are shorter relative to width. (Hmm, I guess you just said all that - oh well).

I think aspect ratios go as low as 25 and as high as 85. Twenty five series would look like rubber bands stretched around a coffee can, handle like the car was on rails, and destroy your rims the first decent pothole you hit. Eighty-five series would have a crazy amount of sidewall flex - definitely not a performance tire. /forums/images/graemlins/tongue.gif

There's a great book that the tire shops use - I got a year-old one that was about to be chucked (car & truck tires only - no tractors). Full of great info - OEM tire sizes, optional tire sizes, lug patterns, wheel nut torques, rims sizes and offsets (5.5J. 5.5JJ, 6J etc.), speed ratings, rotation patterns, approved rim widths for different width tires, who makes what "house" brand of tire, load and inflation tables, how to decode all the little abbreviations stamped on sidewalls, all the good stuff. It's just called (Year) Tire Guide, Bennett Garfield Publication, Boca Raton, FL. 561-997-9229. $10.95/copy (maybe a little more now), or as I say, see if you can mooch an older copy from your tire guy.

Enjoy, it's a real page-turner, I couldn't put it down!

***Spoiler warning - the nail did it.) /forums/images/graemlins/laugh.gif /forums/images/graemlins/shocked.gif

 

[daTeacha]

There's quite a bit on tires that I extracted from a Ford engineer who specs out tires for the different cars they offer posted on the VWenthusiast.com site. Go to the main forum and look in the stickies at the top. This is all car related stuff, but a lot of you guys seem to be car junkies, too. I guess if it has an engine, I'm interested in it.