Go BottomRolling Circumferece
 | Todd
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1999-11-16 10161
Is there any one out there who knows the formula to determine the rolling circumference of a tire? I'm looking to go to smaller turf tires on my 4wd tractor and need to make sure I'm keeping the front/rear ratios the same. Unfortunately it's not as easy as taking the diameter and multiplying by 3.1416.Any help?
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| Jack in IL
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1999-11-16 10163
You can look up the rolling circumference in tire data books such as those provided by Goodyear, Firestone, etc. ....
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| Todd
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1999-11-17 10178
Wish it were that easy. Unfortunately it's not listed for the smaller rear turfs as well as the fronts. Any one else know the formula? ....
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| scott
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1999-11-17 10193
on hard surface mark tire and surface roll tire 360 degrees or one full revolution. mark hard surface then measure distance beteen the lines. same for front or rear. ....
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| Todd
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1999-11-18 10198
Why is this so difficult? Let me try again...
1. I want to replace my exiting turf tires to reduce the height of the tractor. 2. I need to keep my front/rear tire rolling circumference the same ratio to maintain the positive slippage on the 4wd tractor.
3. Although most tire manufacturers list rolling circumference for "larger" tires, few smaller rear turfs, and no smaller sized front turfs have a rolling circumference listed in any literature I have seen, (Firestone farm tire data book).
4. As such, I am attempting to get the formula to determine the rolling circumference for tires.
5. Since I am looking for the "right" sized replacements and don't already have the "yet to be determined" tires that I will replacing the existing tires with I can not measure them the old fashioned way, (by marking the tire and driving one complete revolution and then measuring the distance).
Can anyone help with the formula or a literature source that will include the r/c for smaller turf type tires?
Thanks again ....
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| Roger L.
Join Date: Jun 1999 Posts: 0
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1999-11-18 10202
Why so difficult?? Well, at least you are ahead of the game by knowing that it is important to match revolutions of the front and rear driveshafts. Although sometimes this match is not one to one....it depends on how the shafts are driven of course. Yes, the information is hard to find on some tires. I've had the same problem. And yes, the circumference is not pi*diam. on a tire because it deforms as it compresses. Worse, the deflection will vary with load and with air pressure! Also, you are not going to be able to exactly match your existing ratio. So what are you willing to accept in percentage mismatch? I'll guarantee that if you compare the ratio of the tires you have on there now with
the drive ratios (drive shaft drive and differential gears) by counting the gear teeth that you will find that you already have some mismatch.
I can help you with this or at least provide a sounding board. First thing you need to do is measure the rolling circumference as Scott suggested and then count the gear teeth. What do you get for existing mismatch??
....
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| Jack in IL
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1999-11-18 10207
The "formula" for rolling circumference for Ag Tires (R1) can be found in the Engineering Handbook provided by the Tire and Rim Association. It is not "simple." The book has to be ordered from TRA and is most often used by vehicle engineers. The Firestone Farm Tire Book doesn't list RC data for the small turf tires you are seeking because as of now Firestone doesn't produce them. They are listed in the Goodyear Handbook which you can pick up at any Goodyear Farm Tire Dealer. (That one book includes agricultural tires plus terra-tires and turf-tires that Goodyear offers.) The turf sizes listed go down into the range of lawn and garden tractor sizes which are smaller than you would probably want on refitting a compact tractor. I think this is your best source for easily getting the data you want. When making the final selection of front and rear tires, you want the theoretical travel speed of the front to lead the rear by about 1-3%. ....
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| scott
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1999-11-18 10228
try titan tire.they have an 800 # on there web site.i called it when i changed from turf to r4.to get spec info. i am not sure of your reason to go smaller but i can tell you it will ride rougher ....
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| Todd
Join Date: Posts: 1
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1999-12-01 10556
Thanks for the information on obtaining rolling circumference figures for smaller sized turf tires. I have actually determined that I can use a 315/75-16 truck tire to obtain the diameter & r/c I need without having to downsize the rim to the 15 inch. My reason to go smaller is for a high density apple orchard. With the tight planting I don't have much room in the rows so both narrow and short is better.
Thanks again. ....
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