Tire size ratio

[CJN8]

I just picked up a new to me B7200 HSTD. The rear tires are goodyear 8.3-16 and the front are 6-12. One of the fronts is a fairly new bridgestone and the other is a nanchang 6-12 which is pretty worn. Should the previous owner have replaced both front tires at the same time to keep the size true? How do I make sure the ratio is correct? Any other considerations that I should be aware of.

Great site, great resource!!!
Nate

 

[Paulemar]

If it were me, I'd replace the worn tire with a matching Bridgestone when convenient for you. I'd do that just because I'd see the difference everytime I got on the tractor.
You can actually have a difference in tire diameter equal to the worn vs. newer tire with a un-noticed air pressure difference between the two.
If you are on a hard (concrete, asphalt) surface most of the time in 4X4 I doubt that there would be MORE tire wear or other damage with unmatched front tires than just the fact that you are using 4X4 on an hard surface. If you are on grass, soil, or other soft surface the tires will slip as necessary without causing stress. Save the old tire for a spare if you decide to replace it. Otherwise there's no real hurry in my opinion.

 

[CJN8]

Thanks for the reply. Is there an issue with sizing the tires from to rear? For example, do the front and rear tires have to be a certain diameter In order to maintain the proper ratios and prevent transmission wear? I have been reading up on it and it appears this may be the case.

 

[North Idaho Wolfman]

Mismatched, highly worn, improperly inflated and mismatched ratios on front or rear tires on a 4x4 tractor can cause serious wear and breakage issues!
Yes the previous owner should have replaced them in a pair!
You have a non stock set of tires on the rear, stock would have been 8-16 but your probably not too far off on the rears, fronts stock are 6-12's.

There is a ratio based on the RC (rolling circumference) of the tire that needs to be maintained for the tractor to run efficient and problem free.
The RC of a specific tire will vary between tire manufactures but will usually be in the ballpark of what is considered normal for the size of tire, one major exception is "rice tread tires" the vary greatly over normal tread.

 

[CJN8]

Thanks, great info, makes sense. The speed of the tires need to be the same so there is no binding. Looks like I need to do more research. Keep the info coming.

 

[CJN8]

Did some additional research, I am learning. The rolling circumference is 91" for the 8-16 and 94" for the 8.3-16. The 8.3-16 is .2 inches bigger in diameter. The 6-12 has a rolling circumference of 68". How do I calculate to see if the tire sizes are within the correct range and won't cause transmission problems?

Thanks
Nate

 

[North Idaho Wolfman]

Your about 3% off of stock, I think well within tolerance.
You should be fine with that setup!

 

[CJN8]

Is this the correct math?

68 x 1.464 = 99.552 / 94 = 1.059

Basically 5.9%

Stock would be:
68 x 1.464 = 99.552 / 91 = 1.093

9.3%????

What am I doing wrong?

 

[CJN8]

Thanks wolfman !!!!

 

[lsmurphy]

Is this the correct math?

68 x 1.464 = 99.552 / 94 = 1.059

Basically 5.9%

Stock would be:
68 x 1.464 = 99.552 / 91 = 1.093

9.3%????

What am I doing wrong?

What are your NEW front and CURRENT rear RC numbers?

 

[CJN8]

The rolling circumference is 94" for the 8.3-16. The 6-12 has a rolling circumference of 68".

 

[lsmurphy]

62 x 1.464 = 90.768 divided by 88 = 1.0314 minus 1 x 100 = 3.14 %

Above is an example of the math.


Yours-
68 x 1.464 = 99.552 divided by 94 = 1.0590 - 1 x 100 = 5.9063%

 

[lsmurphy]

If you have the R2s or rice patty tires on the rear........you need to move up to R1s and get your rear RC up around 97-98"

 

[tiredguy]

The rolling circumference is 94" for the 8.3-16. The 6-12 has a rolling circumference of 68".

Here's how to do the math:
Front tire RC divided by the Rear tire RC equals the Ratio.
68 divided by 94= .72 It's that simple no other formulas are needed no complications. That said several things need to be taken into consideration before you do anything. #1 make sure you know EXACTLY what combination of tires came OE ( original equipment on the tractor you're figuring it out for )
and get the tire manufacter's RC numbers for the tires. #2 do the math on them to determine what RC you have as a Ratio you need to stick with. #3
keep in mind that rim width is critical to keep track of with various sizes as the RC of a tire is figured when it's on the proper width wheel. #4 the variables CAN NOT exceed 2% between the sizes or your most likely CAUSE
DAMAGE to the driveline of the tractor when it "binds up" with the wrong ratio.
Al

 

[lsmurphy]

Here's how to do the math:
Front tire RC divided by the Rear tire RC equals the Ratio.
68 divided by 94= .72 It's that simple no other formulas are needed no complications. That said several things need to be taken into consideration before you do anything. #1 make sure you know EXACTLY what combination of tires came OE ( original equipment on the tractor you're figuring it out for )
and get the tire manufacter's RC numbers for the tires. #2 do the math on them to determine what RC you have as a Ratio you need to stick with. #3
keep in mind that rim width is critical to keep track of with various sizes as the RC of a tire is figured when it's on the proper width wheel. #4 the variables CAN NOT exceed 2% between the sizes or your most likely CAUSE
DAMAGE to the driveline of the tractor when it "binds up" with the wrong ratio.
Al

And what value is .72? in relation to what?

 

[tiredguy]

And what value is .72? in relation to what?

72 is the ratio front to rear based on the correct rolling circumference of the original equipment tires assuming they were correct to begin with. When I say assuming, I mean if the factory had the correct gears and tires to match it would certainly not bind up and break something especially if it lasts long enough to wear it out. As long as whatever tire changes are made so that the rolling circumference remains within the 2% allowable difference it will work correctly and not bind causing damage.
I learned this information through the Firestone Farm Tire Certified Dealer program which was put together many years ago by their tire engineers and as such it has always been 100% correct 100% of the time period. It's that simple and that good. The tire manufacterers ( the better one's ) are including the rolling circumference of their tires in their data along with the height width designed rim width etc so that you can use the RC to make sure that you're getting the coirrect sized tire or to do a changeover to other sizes styles ( R1 R4 Turf etc ) keeping in mind that many times wheel width and diameter may/must get changed to in order to keep the ratio correct.

IF you determine rolling circumference of the original tires and do the math by dividing the front tire RC by the larger rear tire RC you will get the ratio front to rear. It's a simple CORRECT formula that works 100% of the time whether it's a 14hp Kubota or a 300hp John Deere MFWD or 4WD tractor.

One of these days hopefully I will find the time and have the administrators post a "sticky" or whatever it's called and include illistrated drawings for determining the rolling circumference on the tractor itself when you don't have the tire mfg's rolling circumference. And hopefully links to the ag tire mfg's websites where tires can be looked up and tjhe pertinant data that goes along with them.
Al