Swapping Tire Sizes But Keeping 4WD Happy

[Norcal M5]

Hi Folks,
I have been looking for tires and wheels to convert my NH TC34DA to ag tires and found that I can get a great deal on a new pair of rears from a Mahindra 4035 (14.9 x 24, diameter 48.5") on wheels that fit my tractor hole and lugs. Now, I need to make sure I get the right ratio of sizes when I buy my fronts (I'll be happy to pay to get custom wheels if necessary) to keep the 4WD working correctly.

Here is the set of tires NH recommends: Front 7x14, Rear 11.2x24

Has anyone figured this one out previously? Is there some kind of chart?

 

[Ford tractor]

It's pretty easy to figure out.

Measure the actual circumference of the tires that are on the machine. Divide the rear number by the front number. (I would also determine the ACTUAL ratio of the mfg's AG option)


Then use that ratio and the new rear tire circumference to see what front tire circumference you can get. If you have to choose either slightly larger front tires or slightly smaller --- go larger. The front tires should be about 5% faster than the rear tires when in 4wd. Going 10-12% faster is better than 2% slower.

 

[Norcal M5]

Thanks! I suppose It's OK to go with measuring the diameter only, since circumference is diameter times pi, a constant, it seems the relationship would be the same. I'll be up at the farm tomorrow and will do this on the R4s that are on it.

I think the only place where I'm stuck at this point would be specifying the fronts so that the diameter (and circumference) come out right. It would be great to get the diameter on tires when ordering. Any dealer that I buy from is likely far from here and I'm not used to seeing that on the sizing in the ads. Maybe the dealer knows?

 

[Creamer]

Here is a tractor tire diameter calculator.
tractor tire sizes? - Pirate4x4.Com

You should be able to find what you need here!

 

[Zebrafive]

Check the website of the brand you are interested in, they should have all the specs listed.

 

[Ford tractor]

Thanks! I suppose It's OK to go with measuring the diameter only, since circumference is diameter times pi, a constant, it seems the relationship would be the same. I'll be up at the farm tomorrow and will do this on the R4s that are on it.

I think the only place where I'm stuck at this point would be specifying the fronts so that the diameter (and circumference) come out right. It would be great to get the diameter on tires when ordering. Any dealer that I buy from is likely far from here and I'm not used to seeing that on the sizing in the ads. Maybe the dealer knows?

Just measuring the diameter is a lot less precise than the circumference. You're call, but it's not that much more difficult to wrap a string around it and measure the string.

Also, tires with the "same" size are often off by a significant amount. Especially if you are crossing manufacturers.