Define Binding if Tires Mismatched

[phaser]

My rear tires are pretty good, but the fronts are clearly worn, and I still haven't decided on what tires to buy, and I need to be educated on what binding is.

If tires are mismatched, could someone describe how one would know if there is "binding" taking place on a 4x4?

Does binding occur on soft surfaces such as soil, or only on hard surfaces such as pavement?

Dose binding only occur if the 4x4 is engaged?

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[skeets]

The axle ratio of front and rear are matched to turn at the same rate with a certain size tire one each end,, SO if you run different size tires than what is called for, in theory one set be it front or rear will be turning faster than the other and in so doing will cause a bind on the gears in the transfer case because one set if trying to turn faster that the other ,, wear on the tires is taken in to account in the build, but going to a different size tire/wheel with out changing the other end to the same ratio will cause you problems. Im sorry if that's confusing but I cant think of a simpler way to put it

 

[phaser]

The axle ratio of front and rear are matched to turn at the same rate with a certain size tire one each end,, SO if you run different size tires than what is called for, in theory one set be it front or rear will be turning faster than the other and in so doing will cause a bind on the gears in the transfer case because one set if trying to turn faster that the other ,, wear on the tires is taken in to account in the build, but going to a different size tire/wheel with out changing the other end to the same ratio will cause you problems. Im sorry if that's confusing but I cant think of a simpler way to put it

Thanks, I understand. Does this also applies to HST? (edit: from further reading I gather it applies to both geared and hst transmissions)

If binding is occuring, can you hear it, feel it, or what?

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[Bulldog]

Yes, it will / can do it on HST models.

The more experience you have the easier it will be to notice if it's binding but regaurdless of your experience level you can feel it when / if it happens.

You can feel it in the steering because it's going to drive funny. Since you are replacing the front tires when you are in 4wd the frontend will feel like it's trying to walk side to side as you're driving. 2wd you'll feel nothing out of the ordinary. In 4wd on the dirt you may notice the front lugs act like they are just barely trying to spin and roll up a little dirt. The bigger the difference in tire size the worse it will be. You'll also notice it will be harder to shift out of 4wd because the drive train is in a bind.

Hope this helps.

 

[gpreuss]

Normally the front tires are running 2-5% faster then the rear tires. It is a function of the gears; regardless if it is straight gears or HST. If you put your transmission in neutral (either HST or gears) you should be able to push the tractor by hand on concrete. Put it in 4WD and it will be really difficult.

A simple way to check is to put your tractor on a long stretch of packed dirt/gravel. Put it in 2WD. Mark the starting point on a rear wheel. Move ahead exactly 1 turn of the rear wheel and stop. Mark on the front tire where it is touching the ground. Back up to the starting point. Put it in 4WD and again go ahead exactly one revolution of the rear tire. The mark on the front tire should be about 10-30 deg farther up, indicating the front wheel turned more.

The ratio of the front to rear wheel speeds is the Drag Ratio. Your dealer should be able to get the information for you, or you can take a parts manual and work through the gear ratios - Kubota supplies the tooth count for every gear. It is typically around 1.5; the front wheel turns 1.5 revolutions for each turn of the rear. You can find the ratio of the tires by looking up their Rolling Circumference (RC) or diameter. RC should be the better number, although I have had no issues with just diameters. The tire ratio should be a bit smaller than the drag ratio, i.e., if the drag ratio is about 1.56, you would want around 1.50 for the tire ratio.

You shouldn't notice a lot of difference in dirt. 5% would be about .05" per bar of an AG tire. On concrete it may leave a trace of rubber smudge. You might notice a bit of noise from the engine. If the ratios are way wrong, the tractor will lug down, and the smudge will be pronounced.

On a car or pickup truck, the drag ratio is usually 1. On the tractor you want the front end to pull the rear end.

 

[phaser]

Thanks for that information Bulldog, and gpreuss. that,s very helpful.

One of the tire brands my B7100 factory manual specifies is Good Year, 6-12 (RC-68) on the front, and 8.3-16 (RC-94) on the rear (based on the Power Torque R-1 currently on my tractor).

So the factory tire ratio is .72 (68/94 = .72), correct? and 1.5 is the max tire ratio?

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[gpreuss]

94/68 = 1.38; mjac ran a thread in 2011 that said the drag ratio for the B7100 is 1.4664. That would calculate to about 6% fast - OK (1,4664/1.38=1.06)