Understanding tire sizes

[Anonymous Poster]

I need some info on understanding what tires sizes mean. Is there a good tire site that actually explains the numbers, or is it manufacturer specific?

In particular, my Ford 2120 manual specifies the following for turf tires:
front - 27-8.5-15
rear - 18.4-16.1

What does this mean?

Thanks.
GregM

 

[equipman]

gmccarty
In the case of your tires:
front - 27" is the overall height of tire
8.5" is the tread width
15" is the wheel diameter
rear - 18.4" is the tread width
16.1" is the wheel diameter
Are you 2WD or 4WD?
Lewis

 

[thcri]

Call me dumb, call me stupid, but why do they rate the front tire different from tha back. Why not just have the same ratings, each number meaning the same thing?


Murph

 

[RobertN]

Poke around these sites. In an upper menu, they have some good explanations of tire types, sizes, uses ect.

www.firestoneag.com/tiredata/ag_flotation/agflotation.asp
www.goodyearag.com/tirecatalog/SGLSize.html

 

[Anonymous Poster]

4WD.

GregM

 

[froggy]

Excellent sites for looking at various tire types and sizes.

 

[Anonymous Poster]

Lewis,

Since the rear wheel values don't have a height, and the front's do, does this mean all rear wheels are the same height?

And for the front tire, the height is measured from the center of the wheel, correct?

Thanks.
GregM

 

[Anonymous Poster]

Ok, the more I think and look into this, the more confused I get. Here are the recommended tire sizes from the owners manual.

Ag -
rear: 14.9-26
front: 9.5-16

Turf -
rear: 18.4-16.1
front: 27-8.5-15

So, if I understand this correctly, the rear wheel (rim) of the Ag's are 10" larger than the turfs, the front wheel of the Ag's are 1" larger than the turfs.

Am I reading this right?

GregM

 

[Anonymous Poster]

Not real important, but I just wanted to add...

The rubber part is called the tire... an usually the metal part is called the rim. And the assembly together is called a wheel.

Not just in tractors, buy autos too.

Ken H.

 

[RobertN]

The best thing, is to start with a base comparison of the tires you have. If you could provide the manufacture, then we can research the tire data in the web sites I noted before, or find the correct manufacturer.

Ok, now for the Ag tires you mention. That particular ag tire uses a much larger diameter rim than the turf's. It will have a fairly short sidewall, and has a somewhat narrow tread. You can probably get an Ag tire that runs on a 16" rim; It will have a big sidewall, will be a wider tread, and be more "balloony" for lack of a better word. The front Ag's are a bit wider than the turf, and do use a slightly larger diameter rim.

The turf tires now, they are more balloony. They are a floatation tire, and tend to be wider than Ag or R4 tires. They sperad the weight over a larger surface area, so there is less impact on grass. In the case of my Kubota, I use 16" rims for both turf and R4. But, the rim for the Turf is wider, because the tire is wider and needs the wider rim to properly support the bead and sidewall.

The important thing is that each tire is ratio matched to the gearing of your tractor. Unlike a 4x4 pickup, which uses the same size tire, and same gear ratio front and rear, the tractor uses a different size tire fron and rear. To adjust the geartrain, they have different differential gearing front and rear. The rolling diameter of the tire has to match with the gearing of the tractor, or else you will overload the axles and driveline and it will break.

So...

Your 14.9-26 rear ag tire uses a 26" rim, recomended width of 13". It has an overall tire width of 14.9". Overall diameter is 52". See http://www.firestoneag.com/tiredata/bias/rtr_tfr.asp

I tried to look up the front tire size at Firestone, but did not see a front ag.

I'll see if I can look the other tire sizes up later, or you can look. Between the Firestone and Goodyear sites you should be able to find the proper size tires and spec. I have to do a report for school... so I will look later....

 

[Anonymous Poster]

After reading the previous posts, in order to maintain my sanity, I have decided to purchase a new tractor in the event the tires on my old tractor wear out.

Rick

 

[RobertN]

It is not so bad. For the older tractors, like my B8200, only two tire types were offered, turf or ag. Both sets of tires required specific rims. If you had Ag's, and wanted turfs, you had to buy tires and rims, and vica versa. The tire sizes and rim diameters are different, but the rolling diameters were the same to keep the proper ratio. When I started the switch to R4, I had to research tire sizes to insure the R4 had the same rolling diameter and ratio as the specced Ag and turf.

Now, you can get R1/Ag, R3/turf, and R4's. All the tires differ in size, but the rolling diameter stay the same(or very close as to not make a difference) for a particular tractor(at least 4x4 tractor)

The Ag's and R4's tend to use the same back rim, and tend to be the same size specification. Ag's though, tend to use a narrower rim. Turfs use different, wider rims, although sometimes the same front rim works with the R4, which tends to be a wide tire.

So... For the most part, if you have turfs and want to switch to Ag's, you need rims too. If you want to switch to R4, you will need new rear rims, and maybe new front rims.

If you have R4's and want to switch to Ags, the back rim should work, but a narrower front rim is typically needed. If you want to switch to turfs, you need new tires and rims.

If you have Ag's , and want to switch to R4, you'll need a wider front rim. If you want turfs, you need tires and rims.

In the event that tires wear out, and you stay with the same tire type, then replacement should be simple.