Info on matching front to rear tires on FWA tracto

Posted by DAN9-Midwest on September 17, 2006 at 06:24:09 from (67.142.130.26):

I recently learned way too much about replacing tires on FWA tractors and front-to-rear tire size relationships and thought I would pass it along for others. Take it or leave it I'm just trying to be helpful. I found little on this site about it. It is very important.
Every FWA tractor has a "front-to-rear gear ratio" and the manufacturer states this in it's manuals or website info. For one tractor, it was .741
The inverse of this is 135 (1.00 divided by .741 = 135) Some state the ratio this way and most are in the 125 to 150 category.
Multiply this number by the rolling circumference "RC" (get from published tire data) of the front tire size.
Mine was 137--- so 135 times 137 (front RC) equals a given number (1849). Divide this number by the RC (rolling circumference) of the REAR tire (179) and that's the number we're looking for expressed in percent.
It is 135x137=1849 divided by 179= 103.3%. It's gear ratio times front RC divided by rear RC.
The example above gives 103.3 % and means the front tire is turning "pulling" 3.3% faster (positive) than the rear and this is OK. A number below 100 would be a "negative" number and indicate the front was pushing against the rear and is very bad. Positive good, negative very bad.
Suggested is positive 2% to 5% and negative never suggested. Negative will "load" and probably damage a transmission, front gear case and grind up the tires, especially on harder ground.
If one gets a negative number they need to change rolling circumference (tire sizes) until the right poitive relationship (+2% to +5%) is found and then change tires. For the correct RC of a particular tire, you have to check THAT tire's website because an 18.4-34 from one source may not be the same RC as the 18.4-34 from another. This especially matters with smaller compact tractors I was told.
The above exercise answered a question I have wondered about for years and is a combination of advice you can get at the Firestone and Titan websites. I also spoke with a tire engineer on this and THAT sounds like a fun job unless you did the Explorer tire. Hope this helps.

Replies:

• Re: Info on matching front to rear tires on FWA tr RodInNS 17:17:48 09/17/06 (0)
• Re: Info on matching front to rear tires on FWA tr Hugh MacKay 11:09:26 09/17/06 (0)
• Re: Info on matching front to rear tires on FWA tr Wardner 10:56:04 09/17/06 (0)

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