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  1. #1
    Silver Member
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    Jul 2011
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    Camillus, NY, USA
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    JD 5425

    Default Understanding tire size

    HI Guys,
    We have a JD 2210 which is nice, but just way to low to the ground for our garden work. The rear tires are "26".
    We are looking at a JD 970 which has a "24" rear tire on the 4X4 model. The 970 stands much higher than the 2210 so how can it have smaller tires? Dosn't make sense to me! The rim size on the 2210 is only "13", while the 970 rims are much larger.
    What am I missing here?
    nckennedy

  2. #2
    Veteran Member KennyG's Avatar
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    SW Michigan
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    John Deere 2320

    Default Re: Understanding tire size

    Tractor tire size designations are a mess, but the main thing to understand is that there are two different systems. I quickly looked up the 2210 and it appears it has 26-12.00-12 tires. These are 12 inch rims, not 13 inch. Your model may be different, but the concept stays the same. These are low profile tires that have a total height of 26 inches, a width of 12 inches and a rim diameter of 12 inches. If these were old style tires where the width is about the same as the sidewall height, the width would only be about 7 inches ((26-12)/2). They are low profile to get a wider tire with the same height.

    The 4WD 970 appears to have 13.6-24 tires. This is a traditional tire sizing with a 24 inch rim and a tire width (and approximate height) or 13.6 inches. I would guess the overall height of these tires is about 51 inches. If it were converted to the three number sizing it would be 51-13.60-24 compared to your 26-12.00-12 tires.

  3. #3
    Gold Member Localmotion's Avatar
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    New Holland 50-86 / Siromer 204S / Case CK-28 / Cat 302.5 / Nissan L35.09 / Nissan Atleon 110

    Default Re: Understanding tire size

    If you think tyre sizes are confusing - what about trying to calculate the correct pressures??? I like to think I'm not daft, but have always struggled to work out exactly how to calculate the correct tyre pressures for tractors and machinery when it's not listed - I usually end up opting for the tried and tested method of kicking it!!!!
    Check out our website: http://localmotion-spain.co.uk

  4. #4
    Super Member
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    Default

    Quote Originally Posted by Localmotion View Post
    If you think tyre sizes are confusing - what about trying to calculate the correct pressures??? I like to think I'm not daft, but have always struggled to work out exactly how to calculate the correct tyre pressures for tractors and machinery when it's not listed - I usually end up opting for the tried and tested method of kicking it!!!!
    That's easy! Just inflate until they explode and back off 10psi...

  5. #5
    Silver Member
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    Jul 2011
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    Location
    Camillus, NY, USA
    Tractor
    JD 5425

    Default Re: Understanding tire size

    Oh, I see now. Dosn't make much sense to change the way they measure tire size, but now that I know that I get it. Thanks so much. Relieved to know that the JD 970 has much bigger tires. Sounds like just what the doctor ordered for our garden and light field work.
    Thank you gentilmen, appreciate it very much.
    nckennedy

  6. #6
    Veteran Member KennyG's Avatar
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    SW Michigan
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    John Deere 2320

    Default Re: Understanding tire size

    The change is really a reflection of how tires are made. Originally tires all had essentially a round configuration. As they became wider, a tread section was grafted on. It stayed this way until the 70's when radial tires became common and it was possible to make sidewalls strong enough to support a wide tire with a short sidewall. I'm sure a few others are old enough to remember when we all drove around on 6.70-15's and 7.50-14's. Then the R70, R60 and even R50 showed up make it really complex, but it was necessary to describe the higher performance tire dimensions.

  7. #7
    Platinum Member Edward. S's Avatar
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    John Deere

    Default Re: Understanding tire size

    Heres a info sheet that deere has.

    Understanding basic tire information

  8. #8
    Elite Member
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    Trivoli, IL
    Tractor
    SSTT (Sideways Snake Tain Tractor) and STB (sideways train box) tractor, dirt harvester

    Default Re: Understanding tire size

    Firestone Agricultural Tire has a descent explanations of tires and types.

    i filled out online brochure on there website, to get a tire catalog. and fairly good amount of pages and tire treads to choose from.

    =============
    remember with 4x4, 4WD, or MFWD tractors. if you get different tires, for rear or front, then you will need to get all 4 new tires most likely. so the rolling circumference stays the same. mis match front and rear tires, could possibly destroy the drive train on tractor.

    =============
    something to think about.

    tires are made out of rubber. and act like a balloon. the more PSI of air pressure, the more they expand, this can change the physical actual diameter of tire.

    the lower the PSI of air pressure in tire, the flatter the tire could become reducing the physical diameter of tire some.

    more weight that is placed on a tire at a given PSI of air pressure in tire. will physically change tire dimensions. were tire rests on the ground. have seen a few to many pickup truck rear tires look like a pancake, when someone wanted to fill rear with a bunch of wood, or something heavy.

    because tires dynamically change, based on air pressure in tire, temperature of air inside tire, and amount of weight being placed on tires. manufactures do not give a bunch of numbers. for all possibilities.

    instead they give, rim diameter, width of tire, and wall height, radius perhaps diameter of tire, some times dimensions are in inches, some times in metric, sometimes you need to do some math to figure out tire dimensions.

    lets not forget, same tire, might work on a couple different widths of rim sizes. one tire might fit a 11" width rim, or a 12" width rim. rim diameter being say 24" in diameter. width of rim can cause tire to physical change dimensions again...

    ======================
    then you have tractors marketed to specific markets. "gearing ratios" smaller diameter tires = slower speed but more torque, larger diameter tires = higher MPH but less torque.

    larger diameter tires might give more ground clearance under tractor, but can dramatically change COG (center of gravity) of a tractor, causing higher chance of roller tractor over.

    specific markets might be riding lawn mower on steroids, that does good mowing, but enough weight, and some extra traction for small gardening, snow pushing and like.

    specific market might be, less about mowing the lawn, and more about being a utilty tractor, to get everything else done besides mowing. perhaps given model number has option for a FEL (front end loader), or a better rear end hitch (3pt hitch)
    Ryan

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