matching fwa tire sizes

joe 1 · Feb 11, 2009

I have a Case IH 885XL with 18.4-34 rears and 12.4-24 front tires. Is this the correct combination or not? I have seen others with 13.6-24 on the front and wondered which is the proper size.

JMS/.MN · Feb 11, 2009

Proper matches are in the operator manual of the tractor. Important to run the right ones.

RodinNS · Feb 11, 2009

Depends on the axle and transfer box ratios. 13.6 and 14.9 are the more 'normal' matches I've seen with 18.4 rears, but that does vary.
The best suggestion I can make is that you figure out the transmission output speed, rear axle FINAL/TOTAL reduction ratio, transfer box ratio and front axle TOTAL ratio. Then get the tire 'rolling circumference' for your tires (or the proposed replacements) from the tire manufacturers website. With that information you can calculate the theoretical ground speed for both the front and rear axles. With that in hand, you want to get the front 'leading' (turning faster) by 1-5% (I'd aim for closer to 5%). Find a tire combo that will do that.
At just a guess, I'd say that if you presently have trouble with the tractor 'plowing' or scuffing the fronts then the front tires are too small... Beyond that you'll need to compute the ratios out to know what tire you need.

Rod

GA Dave · Feb 11, 2009

To add to the confusion. David.............

http://www.external_link/farm-tractors/001/1/5/1156-caseih-885-dimensions.html

matching fwa tire sizes

joe 1

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JMS/.MN

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RodinNS

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GA Dave

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