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  1. #1

    Join Date
    Mar 2002
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    44
    Location
    S. Maryland
    Tractor
    FF205D

    Default tire size/ratio, replacement discussion, big repost

    Tire size: engineering
    "http://messenger.yahoo.com/messenger/mboards.html"?"http://me
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    ger_scotty"
    (M/Colorado) 4/25/01 9:14 pm


    "The math works out the same. The compared ratio of the circumference
    of the two tires in question will be equal to the ratio of the radii
    of the same two tires."
    Whoa...I'm not as sure about that. But I am sure that having an
    engineer's perspective would be useful. Suppose that the tire is on
    soft ground - As most ag tires are used. What radius do you use to
    calculate the circumference...The radius from center to outer end of
    the lug? Or the one to the ground surface? What if a tire is loaded
    or low on air? what happens to the measurement then? And if anything
    does happen which is more important: a full bucket in the front or a
    heavy implement in the rear?
    I've a feeling that these are pretty tricky questions, and it sure
    would help to know the answers.
    To get a Firestone engineer I just typed in a question where they
    said to ask technical questions (at the Firestone web site) and
    several of them answered me.... But I didn't ask the questions above.
    After all, why let them have all the fun?


    Re: Tire size: engineering
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    undguy34421"
    4/26/01 12:53 pm


    "The math works out the same. The compared ratio of the circumference
    of the two tires in question will be equal to the ratio of the radii
    of the same two tires."
    'Whoa...I'm not as sure about that. But I am sure that having an
    engineer's perspective would be useful.'
    Mathematically, it has to be, under set circumstances. For the
    following, lets assume that the tires in question are circles, and do
    not deform, or that they at least deform equally to a similar
    degree.Ok, you have two circles, one larger than the other. Measur
    ethe circumference of both circles. measur ethe diameter, and the
    radi of both circles. Using C=piXd ( for all those non-geometrically
    inclined, c= circumference, d= diameter, r=radious ( which is .5 d ),
    and pie can be represented as 3.14 ) At comparison ( ratio )of the
    circumferencs of both circles must equal a comparison ( ratoi ) of
    the radi of both circles. Assuming the following: equal load between
    front and rear,proper inflation of tires, zero, or similar rate of
    deformation of both tires being measured including load and inflation
    variables, and true measured depth of the tire from it's center, not
    just where the tire penetrates the ground's surface. It is also
    helpfull if the front and rear tires are of hte same design, both
    knobby ag, or flattend turf. For the ag tires, circumference from
    middle to the end of a knob can be used, if both front and rear are
    ag tires. Even though real circumference will differ due to soil, and
    other conditions.

    Suppose that the tire is on soft ground - As most ag tires are used.
    What radius do you use to calculate the circumference...The radius
    from center to outer end of the lug? Or the one to the ground
    surface? What if a tire is loaded or low on air? what happens to the
    measurement then? And if anything does happen which is more
    important: a full bucket in the front or a heavy implement in the
    rear?
    Equal load is assumed for the purpose of the above calculation, but
    unequal load, uneven ground and other variables including tire
    pressure and amount of tread wear will have some effect of the
    compaired ratios. This is a static comparison, but should yeild a
    ratio that is within an acceptable error range for choosing tire/rim
    sizes.


    Re: Tire size: engineering
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    ger_scotty"
    (M/Colorado) 4/26/01 7:13 pm


    Soundguy, I see where you are starting from when you say:
    "Mathematically, it has to be, under set circumstances. For the
    following, lets assume that the tires in question are circles, and do
    not deform, or that they at least deform equally to a similar degree".
    Well, that's the whole problem with selecting tires in a nutshell. I
    wish we could too, but we don't get to use those nifty assumptions
    and simple formulas. It turns out that the radius is not constant
    because the tires do deform. They also do so unequally front to rear.
    We gotta get more sophisticated with the math.


    Re: Tire size: engineering
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    c3647"
    (54/M/Mpls MN suburbs) 4/26/01 4:33 pm


    It seems to me it is easier and a **** of a lot less controversial to
    mark the tires, mark the floor, roll the tractor forward one
    revolution of the tires, mark the floor again and measure. I am an
    engineer too, but pragmatism has it's place.

    Bruce


    Re: Tire size: engineering
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    undguy34421"
    4/30/01 9:08 am


    Actually, in all honesty, I was just trying to come up with a 'quick
    estimate' way to calculate trie ratio's. Other variables aside, it is
    alot faster to measure the radii on the tires, than start up the
    machine, mark, roll and mark, then measure. ( albiet less acurate ).
    And as a spin, and proof, on pargmatism, 'the more you over tic the
    plumbing, the easier it is to stop up the drain'...


    Re: Tire size: engineering
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    ger_scotty"
    (M/Colorado) 4/26/01 7:40 pm


    Marking the tire and then rolling the tractor is the method I've been
    playing with for the past year (it is harder than it appears) - this
    after I finally ran into an impasse with mathematical methods. There
    are two big problems with the tire marking method. The first one is
    that it only works AFTER you have bought and mounted the tires...So
    it isn't much help in figuring out what tires to order. And secondly,
    it doesn't tell you anything about what the ratio is between the
    front and rear drive shafts - and after all, you are trying to buy
    tires to match the existing drive shaft ratio. Not vice-versa.
    Geeze! this is fun! Isn't it dandy problem! It makes me pity all
    those new tractor owners who simply go to their dealer and buy
    tires....I'll bet they don't even know what they're missing.


    Re: Tire size: engineering
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    undguy34421"
    4/30/01 9:49 am


    "Geeze! this is fun! Isn't it dandy problem! It makes me pity all
    those new tractor owners who simply go to their dealer and buy
    tires....I'll bet they don't even know what they're missing. "

    A friend of mine once said that reverse engineering was akin to
    forensic science.


    Re: Tire size: engineering
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    d_ym240d"
    4/27/01 1:02 am


    Jack up one side of the tractor so both left or both right tires are
    off the ground. Start up the tractor, put it in gear, 4WD and let it
    idle with the raised wheels turning. Count revolutions of the front
    and rear tires for a given time (say 2 minutes, doesnt matter as long
    as you count both front and rear for equal times). The Front-to-Rear
    driveline ratio is # of revolutions of front wheel divided by # of
    revolutions of rear wheel. Then buy tires such that the Front-to-Rear
    tire size ratio is the inverse of the Front-to-Rear driveline ratio.

    For example: Assume the front tire turns 60 times and the rear tire
    turns 20 times. The front-to-rear ratio is 60:20 or 3:1. Your tire
    size ratio would then be the inverse, i.e. a front-to-rear ratio of
    1:3.

    Use standard safety precautions while performing this dangerous
    experiment. :-)

    Rod


    Re: Tire size: engineering
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    actorlaird"
    4/26/01 10:39 pm


    After a person has determined the ratio is between the front and rear
    drive shafts........

    True or false?
    The circumference of the tire is nearly the same unloaded or loaded,
    even throught the radius to the ground can be much different.

    From Firestone: "The desired amount of lead is 2 percent, which means
    the front wheels are 2 percent faster than the rear wheels. Anywhere
    from 0 to 5 percent lead is considered acceptable. But no amount of
    lag is acceptable"

    Then after you have purchased your tires:
    Here is the link to that Firestone article about tire Lead/Lag.

    "http://www.firestoneag.com/tiredata/info/info%5Flead.asp"


    Re: Tire size: engineering
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    wap"
    (36/M/monroe, va) 4/26/01 7:52 pm


    So in the end it comes down to a guess...because there are
    differences in the deformation between the front and rear tires due
    to side wall high's tire loading and just plane old differences in
    tire construction so there is no constant so no mathematical equation
    to figure the correct tire sizing so you make your marks and make
    your guess....



    Re: Tire size: engineering
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    ger_scotty"
    (M/Colorado) 4/27/01 1:04 am


    Excellent questions! And I'll be the first to confess that I don't
    know the answers. As to the circumference question, I've heard good
    arguments both ways. In my own experiments I varied tire pressure
    instead of load and got results that I don't have much confidence in.
    I don't have any answers on the lead/lag argument...although
    Firestone's sounds confusing to me. They say that lag is more
    destructive to tires (and hard on transfer cases)than lead. But they
    don't explain why that would be so. Just off the top of my head they
    would seem to be slipping the tire or winding up the shaft the same
    amount but just in different directions. And why 2 to 5%? what is
    magic about those numbers?
    In cars I thought a front axle lead was so that the front wheels
    would maintain steering control....and the 5% was so that it would
    ALWAYS maintain steering control. I've personally built a 4wd vehicle
    with the front lagging and have to say that it was a bear to steer.
    Before you wonder, the axle ratio was labeled wrong and I had been
    too lazy to count the teeth in the pumpkin.



    Re: Tire size: engineering
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    undguy34421"
    4/30/01 10:03 am


    "would be so. Just off the top of my head they would seem to be
    slipping the tire or winding up the shaft the same amount but just in
    different directions. And why"

    Leading to much, the tire spins,...lagging too much, the tire is
    pushed... And they had no answer as to why one was better than the
    other? Lets see... so all in all, one sige of the gear surface is
    wearing more than the other? The ring and pinion should be equally
    hard anyway? right? Kinda makes you wonder whay they didn't specify
    why leading was better than lagging.


    Re: Tire size: engineering
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    det32766"
    (51/M/Orlando, Florida) 4/30/01 5:18 pm


    To make it easy for you to understand the difference between leading
    and lagging and the resulting wear caused by same, try this simple
    experiment. Get a 20 foot length of 3/8 chain and pile it up in the
    middle of your garage floor. Now reach down and pick up one end. Now
    try and push the chain across the floor. If you haven't got it
    figgured out yet, It's a lot easier to pull something than it is to
    push it. Ergo front wheel drive. I just wish I had an engineering
    degree so that I could explain it to you better. Egads. Enjoy, Dola.



    Re: Tire size: engineering
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    undguy34421"
    5/1/01 7:24 am


    Thanks, I'm up on the difference of leading and lagging. I was trying
    to visualize what it was doing in the drive train, i.e. possibly
    wearing heavier one side of the tooth surface of the ring and pinion
    gear.... Seems like the windup would effect back through any
    differential present and load the drive shaft. Anyway.. moot point
    for me, as I only have a 2wd. Just a point to ponder.



    Re: Tire size: engineering
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    c3647"
    (54/M/Mpls MN suburbs) 4/26/01 11:55 pm


    I have replaced rice tires on the rear wheels of 2 different 4WD
    compact tractors. The first time I replaced the 8x22 rice tires with
    9.5x22 Firestone tires. I meassured the rolling circumference before
    and after. The two types of tires were within one inch of each other
    at 114 and 115 inches. The tractor works fine. On the second tractor
    I replaced 8x16 rices tires with 265R75/16 SUV tires. I measured the
    rice tire rolling circumference at 90 inches. The SUV tires were 90
    3/4 on the tire rack with no wheels. I put them on the tractor wheel,
    25 lb of air pressure, and measured them again - 91" this time. Again
    the 4WD worked just fine. I have a 4WD truck and a 4WD SUV, so I know
    all about driveline wind up and how it feels. Neither of the tractors
    feel like they have any.

    Bruce


    Re: Tire size: engineering
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    sejockey2002"
    (34/M/Auburn, Washington) 4/28/01 11:18 am


    I think I'll just go with the 265/75R16 tires and call 'er good. All
    this talk about math and engineering and static loaded windup ratio
    makes my head hurt.



    Re: Tire size: engineering
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    ger_scotty"
    (M/Colorado) 4/27/01 1:24 am


    Just for clarification, I believe that the aspect of the tire being
    measured for Rod's "tire size ratio" is what Firestone calls "rolling
    circumference". The method seems sound, though it didn't work for me
    when I last tried it about 5 years ago. When I tried it with any of
    the tires on the ground I got irratic results. I confess that it has
    been awhile and I haven't tried it again after doing it as follows,
    so it might be a matter of practice. I did it slightly differently: I
    jacked up all four wheels, did not start the engine, but put it in
    4wd and rotated one rear tire slowly by hand. You know you are doing
    this correctly when the opposite tire counter-rotates. You can feel
    through the tire when any of the spiders start to rotate, and have to
    start the count over. Doing it slowly by hand I didn't get confused
    by relative rotation of the spider gears in either differential and
    was easier able to count the slow movement of the tire.


    Re: Tire size: engineering
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    85302"
    (30/M/S/E Ohio) 4/27/01 6:05 am


    I've been lurking during this whole tire thing.........I'm getting
    dizzy and I think I'm gonna be sick......tooo much info at one time
    causes brain damage !!


    Re: Tire size: engineering
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    ger_scotty"
    (M/Colorado) 4/27/01 10:19 am


    JB, take a deep breath and for cripe's sake try not to puke all over
    the keyboard. It really makes them sticky and hard to work.
    Donsblack shows how to do it with a minimum of brain damage. Here is
    what I get from his message. First of all he is aware that windup
    exists and what it is. He knows its worth doing the extra work to
    match his tire sizes as close as he can - His method is crude, but
    better than nothing. And finally, he tests the limits of where he is
    getting windup and decides when he can and can't use 4wd. It sure
    makes sense to me, and all without cranial contusions or expense.
    Of course there are those of us who enjoy trying to solve the gear
    ratio problem in every picky detail. But then we have strong stomachs
    and minds and get our kicks punting some numbers and physics back and
    forth. Its a fairly diverse group.


    Re: Tire size: engineering (Lurkers)
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    nsblack"
    (57/M/Maryland) 4/27/01 8:49 am


    Also been lurking and also have changed from rice tires. Just went to
    the Firestone web site got diameters for tires on tractor. Bought
    same diameter and sized Diamond tread Bridgestones for rear, then
    went to a local tire store bought nearly same diameter USED truck
    tires. Got diameter on used tire from pamphlet at store. Bottom line,
    only time I notice ANY driveline difference in 4WD is when on
    pavement, so just don't use it there.


    Re: Tire size: engineering (Lurkers)
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    rmerjohn_2"
    (41/M/Cypress, TX) 4/27/01 10:22 am


    I am thoroughly enjoying the engineering discussion going on here,
    though it is making my 2WD 2200 look really sweet and simple.

    Seems like you should be able to buy tires with the same rolling
    circumference ratio, gear drive ratio and/or static load radius ratio
    (just to get you close) and then adjust air pressure to deal with
    excessive front wheel lead/lag which causes driveline windup. Isn't
    that really the bottom line?


    Re: Tire size: engineering (Lurkers)
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    undguy34421"
    4/30/01 10:13 am


    "I am thoroughly enjoying the engineering discussion going on here,
    though it is making my 2WD 2200 look really sweet and simple."

    Comr to think of it... my 2wd 1700 doesn't have any of these problems
    either.. <G>



    Re: Tire size: engineering
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    c3647"
    (54/M/Mpls MN suburbs) 4/27/01 8:40 am


    I used the same marks on the floor/tire method to determine front to
    rear axle ratio, I marked how far the tractor moved after the front
    tires made one rev and marked where the rear tires made one rev,
    measured both and divided one by the other. The only other math I had
    to do was convert 1/4 inches to .25 inches.


    Re: Tire size: engineering
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    undguy34421"
    4/30/01 9:38 am


    "Well, that's the whole problem with selecting tires in a nutshell. I
    wish we could too, but we don't get to use those nifty assumptions
    and simple formulas. It turns out that the radius is not constant
    because the tires do deform"

    I know they do.

    . They also do so unequally front to rear. We gotta get more
    sophisticated with the math.

    I know.. honestly, I wasn't trying to come up with a 2 page formula
    for calculating gearing. I was just playing with a quick hash.
    Besides.. if what one poster said was true, about a designed
    slippage, a simple rolling circumference won't be accurate either. I
    guess if we need complete accuracy, we need to see some design specs,
    or to measure a few gears.
























  2. #2

    Join Date
    Mar 2002
    Posts
    13
    Tractor
    Yanmar F16D

    Default Re: tire size/ratio, replacement discussion, big repost

    I have just bought a yanmar F16d and am looking for some turf tires. There doesn't seem to be much help at tire dealers on getting anything. I have built an excel spreadsheet to calculate tires sizes. It is all theoretical right now but I would appreciate it if someone would take a look at it and see if it makes sense. It takes into account slippage. What do you think. download the attachment and change the name to .xls I couldn't attach a file that ended in .xls. It is really an excel file. If that doesn't work email me and I will send it.
    Attached Images Attached Images

  3. #3

    Join Date
    Mar 2002
    Posts
    77
    Location
    southern ohio
    Tractor
    YM1802D

    Default Re: tire size/ratio, replacement discussion, big repost

    I just went threw all of this sme thing tring to find the right size turf tire for my 1802D what I ended up doing is getting turf tires for the back and leaveing the 4wd tires on the front .. I got 8.3-24 ANS firestones on back they have a really deep tread for a turf tire so I should get good traction still( not as good as ag tires but not a slick either.. what size are you looking for .. bridgestone/firestone seem to be only one with turf

  4. #4

    Join Date
    Mar 2002
    Posts
    885
    Location
    S Illinois
    Tractor
    Iseki TA 207

    Default Re: tire size/ratio, replacement discussion, big repost

    Check these out. I am really pleased with them.
    Attached Images Attached Images

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