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  1. #1
    Silver Member
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    Dec 2008
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    218

    Default Tires sizes

    OK. I don't know how tires sizes work. I need help.
    My JD 1050 manual recommends
    Front:
    7-16 lug
    or 27/8.50-15 turf
    I actually have a 27/8.50-15 lug

    Then they recommend 13.6-28 rears or
    21.5L-16.1 turf
    I have 44X18 20 turfs on it. That is how I bought the tractor.

    I am considering going with a stock size, narrower rear tire for better winter traction. Are the two fronts that the recommend the same diameter? If so, I could go with a 13.6-28 lug rear (and different rim). I'm not even sure that my current tires are the right diameter for the tractor to not bind in 4wd, although I never had a problem with all turfs. Not enough traction I think.

    Help please!

  2. #2
    Veteran Member irwin's Avatar
    Join Date
    Feb 2007
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    1,279
    Location
    SE Conn
    Tractor
    2004 Kubota L35TLB, '89' Cub Cadet 1541

    Default Re: Tires sizes

    I spent a lot of time researching tires and rolling circumferece when I switched my turf tires with R4's... There are several tire sites that have the info if you search the sites. This is a link to Titan tires..put your tire sizes and see what they offer and you can check for rolling circumference's front and rear....Titan Wheel and the firestone ag tire site Firestone Agricultural Tire Division : Products


    Below is the formula for front wheel lead (you do need to find out what your MFWD ratio is)..I copied this to my PC and not sure where the site is anymore....

    Can I use a different size tire on my 4wd tractor?Proper tire sizing/matching on front wheel assist tractors is a function of insuring that the front axle 'lead" specification is kept within acceptable design and operational limits. Front axle lead (or slippage) is necessary on front wheel assist tractors in order to realize the benefits of front axle tractive assistance. Desired front axle lead is expressed as a positve increase in front axle speed over that of the rear axle, usually in terms of percentage (ideally +1%-+5% for most front wheel assist tractors). Lead percentages outside of this range will lead to problems such as accelerated tire wear, difficult steering, loss of tractive assistance from the front axle as well as increased drive train wear with premature failures. Negative lead (or slippage) will, from the outset, totally negate any potential advantages offered by front wheel assist. Determination of the front axle lead (slippage) for a given tractor is easily determined if one has access to the following information;
    Front tire rolling circumference
    Rear tire rolling circumference
    Front/Rear drive train ratio of the subject tractor
    Rolling circumference specifications are available from the tire manufacturer. This is the only tire "specification" that matters for this calculation. Rim size is of no importance at this point.
    Drive train ratio is available from the tractor manufacturer.
    Calculation for determining front axle lead is as follows; Front Tire rolling circumference x Front/Rear drive train ration %Slippage= Rear Tire rolling circumference Example; Front tire size- 11.2x24 with rolling circumference of 129.6" Rear tire size- 18.4-28 with rolling circumference of 175.9" Tractor Front/Rear ratio= 1.4 129.6 x 1.4 181.44 175.9 = 175.9 = 1.031 (1.031-1) x100 = percentage 1.031-1 = .031 .031 x 100 = +3.1% front lead (Good!) Now, what will occur if we substitute a rear tire size of 18.4x30 having a rolling circumference of 183.5"? 129.6 x 1.4 181.44 183.5 = 183.5 = 0.989 (0.989-1) x100 = percentage .0989-1 = -.011 -.011 x 100 = -1.1% front lead (Notice that this is negative lead meaning the rear axle is over- running the front axle. This is obviously a bad choice of rear tire size for the given front size. In order to use the 18.4x30 tires on this tractor, it would be required as well to install 12.4x24 front tires having a rolling circumference of 137.0". This will result in a lead of +4.52% which is within the desired range of +1.0%-+5.0%. If you have owned a 4wd tractor for any length of time, you have probably noticed that the front tires have a tendency to wear at a higher rate than the rear tires. This is normal. Keep in mind that, because of the design slippage of the front axle, when 4wd is engaged the front axle is, in effect, trying to "outrun" the rear axle. Since the rear axle is supporting 60% of the total tractor weight, the front axle cannot drag the rear axle along with it at its slightly increased speed; therefore the front wheels must be content to slip (or spin). Did you ever watch a teenager "peel out" at a red light? This is exactly what is occurring in the front axle, only at much lower speeds with the associated tire wear being nearly imperceptible. Interesting to note is the fact that the rate of front tire wear decreases as the tread wears. As the tread wears down, rolling circumference is reduced, bringing the front axle lead (slippage) percentage closer to 0%. This serves to illustrate why it is important to be judicial in the use of 4wd, avoiding usage on hard surfaces as much as possible. A related subject is the use of front loaders on front wheel assist tractors. Ideally you want to maintain a load bearing ratio between the front and rear axles of 40%front/60%rear. Asking the front axle to carry more than this share is setting yourself up for expensive repairs down the road. It is important to use appropriate counter-balance on the rear of the tractor to offset the loads that are carried in the loader bucket. Take note that front axle components are generally smaller and of lighter construction than the rear axle. These front axle components were not designed to support 60%, 70% or in some extreme cases up to 90% of the total "load".
    If your rear axle is scooting along, just barely contacting the ground now and then, this means the front axle is supporting near 100% of the total weight of the tractor, loader and bucket payload! This is an almost iron-clad guarantee of front axle failure! Be cautious when changing tire sizes. Even the same size from different manufacturers can have a significant impact on front axle leads.
    .....Tim

  3. #3
    Silver Member
    Join Date
    Dec 2008
    Posts
    218

    Default Re: Tires sizes

    Thanks and great info. Looks like I need to stick with a tire that is about 45" in diameter to be good with the world. My current size should be ok too. I should have gone with the larger size diameter when I replaced the fronts. Live and learn. I lose about 2" of ground clearance. I will just tell myself that it makes the tractor less tippy when mowing hills. Clearance isn't usually an issue anyhow. Thanks again!

  4. #4
    Super Member
    Join Date
    Apr 2000
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    6,180
    Location
    central New York
    Tractor
    all makes and models

    Default Re: Tires sizes

    Twenty some years ago I had a customer that wanted a four wheel drive farm tractor with r-3 or rice and cane tires. Of coarse he all of a sudden in a big hurry for the tractor after he took six months to purchase so I had to try and find the right tires. The fronts were a problem, not to be available for 90 days!!!! The R-3's outer circumfence was the same as the next size larger tires with r-1 tread.

    I guess if he wanted to drive on the road in four wheel drive he would have been fine but not in a tilled field with the difference in the tread depth!! Would eat a u-joint in about an hour with greasing every twenty minutes!

  5. #5
    Member
    Join Date
    Oct 2008
    Posts
    27
    Tractor
    JD 950

    Default Re: Tires sizes

    Conservation,

    I have the same tires on my 950 front and back that you have. The 27 is the diameter of the tire (actual is 26.7 on mine), the 8.50 is the width of the tire (8.4 actual on mine) and the 15 should be the rim diameter. Mine are turf tires and found out the backs are liquid filled. I have no other ballast and it has handled superbly in the snow this winter (and I've been playing in 6 to 14 inches and going thru drifts up to 2 or 3 feet). I haven't slipped at all with the 4wd and locking the rear differential (when I got a little far into the ditch!). I've been happy I haven't needed chains in the least but I don't have hills. I seem to think the wider turf tires have been actually better in the snow. I am going to replace the 2 fronts because the sides are a bit split (and I considered R4s) but with the way that the turfs have handled, I'm going to replace them with turfs. They have worked well for me in the fields with brush hogging and we'll see how they work in the woods.

  6. #6
    Elite Member
    Join Date
    Nov 2005
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    2,929

    Default Re: Tires sizes

    Go to the Firestone Ag web site, check out hydroinflation.
    There is an unusual (nowadays) page turner to click on for next page,
    but EVENTUALLY you can get to tables that include rolling circumferences - which is what really matters.
    Keep them in the same ratio as whatever the factory recommendation says.
    If you know your front, rear and center diff ratios (unlikely, but you might be able to get them from a shop manual) use the formula posted earlier as a double check on the amount of LEAD, it isn't critical, but LAG is definitely BAD.

    Firestone - Choose Language should get you there.

  7. #7
    Elite Member
    Join Date
    Nov 2005
    Posts
    2,929

    Default Re: Tires sizes

    Ooops, either I had forgotten the layout or they changed it.
    Anyway, on the firestoneag site tire capacities and how to do it are under hydroinflation, but not much else.
    There IS a section specifically on lead/lag that shows how to measure the ratio of front/rear rolling circumferences of what you have (doing this with front drive disengaged).
    You can then compare that to the same excercise performed with front drive engaged to figure lead/lag.

    You SHOULD be able to get rolling circumference specs for just about any tire you consider buying, whether from Firestone or whatever other manufacturer's site.

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