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Murray
Join Date: Sep 2003
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2004-02-28          78175

Could anyone comment on why my 2210 is such a joy to steer in two wheel drive and so difficult in four wheel drive. On any surface hard or soft,wet or dry,crawl speed or less a maximum turn is almost impossible without major wheel slippage.
Various tire pressures make little difference. The MMM weight should produce a balanced weight distribution on each wheel I would think. If this was a homebuilt tractor I would say the front axel gear ratios were wrong. Any opinions.


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psimonson
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2004-02-28          78195

I think you're describing the "normal" binding action that occurs when most any vehicle, (car, truck or tractor) is locked in 4WD. Gear ratios in the front and rear axles should provide an identical ground speed when traveling straight ahead but when turning you create two different paths for the inner and outer wheel on both the front and rear axle.

For example, if we assume the outer front wheel turns in a 72” radius and the front axle is 30” wide, the radius the inner front wheel turns is only 42”. When you are going straight the front and rear track. When you turn, the rear end follows the front end in much the same way as a trailer and moves in a tighter radius than the front end. Let’s say the outside rear wheel in our example follows a 64” radius so with the same 30” tread width, the inner rear tire would follow a 34” radius.

When you’re turning in two wheel drive the spider gears in the rear end allow the rear tires to turn at a different rate compensating for the difference in the size of the circle they are making. When you shift to 4WD you ask the front spider gears to do the same thing but, because the front and rear are solidly coupled, there is a bind created because all 4 tires are turning different radii. Some all wheel drive vehicles have a viscous coupling between the front and rear axles, rather than a gear box, to provide some slippage between the axles in addition to the speed differential allowed left to right by the spider gears.

Tire pressures should be in line with mfr. recommendations to get the theoretically correct ratios for traveling straight ahead. There have been threads that talked about checking footprint as well as pressure but, because of my racing background, I check all new vehicles with a pressure gauge then I jack up the front and rear separately and measure each tire’s circumference with a narrow ruler to be sure they are within 1/8", or so, on the same axle. Radials are pretty consistent but some supposedly identical bias ply tires vary by inches at the same pressure. This could be due to manufacturing differences but in some cases it is simply the result of different pressures needed to seat the bead on the rim when the tire was first mounted that stretched the casing. ....

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DRankin
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2004-02-28          78212

Every 4wd I have ever owned (car, truck or tractor) has done the same as you describe to some degree. Just the nature of the beast I think.

I would guess that the super-short wheelbase and tight turning radius on your tractor make it more noticeable. ....

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Murray
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2004-03-01          78370

Thanks to all who responded to my wheel slippage situation. My mowing pattern was to use my paved driveway for turn arounds to reduce wear on the grass. This worked well with my previous mower(Honda 4 wheel drive and 4 wheel steer)(Eight seasons same tires)
The 2210 will dictate staying on the grass and slow wide turns. Problem is slopes on my property demand mowing in four wheel drive. The other problem is I really like the rest of this tractor.
Thanks again ....

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Art White
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2004-03-01          78447

The problem you have is common on many four wheel drive tractors for farm use as well as on mowers! Air pressure often can reduce it but you can balance your air pressure easiest on the driveway just by driving and engaging and disengaging the four wheel drive lever with ease and no grinding or restriction. Kubota introduced Bi-speed turn years ago and it cures the problem and actually allows you to turn as tight as two wheel drive! ....

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kwschumm
Join Date: Feb 2003
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2004-03-01          78450

Art, I did a search on Kubota's web site for bi speed and the only hits were for discontinued products. Why did they drop it? ....

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Art White
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2004-03-01          78452

I thought the B-2410 still offered it but I might be mistaken as there was a lot discussed at the meetings. The unit was not the most popular option as most people don't need it and 400 dollars is 400 dollars! ....

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TomG
Join Date: Feb 2002
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2004-03-02          78473

The front drives in most 4wd tractors lead the rear drives by 5% travel or more. In tight turns even this lead isn't sufficient but more lead would place greater stress on the front drive when not in a turn. There's really no good solution except for a differential in the front drive shaft. Not only does the tire slip in turns but the 4wd in effect also quits. Carrying weight on the 3ph may lessen lawn damage but it also would make back-flips more likely when going up hills.

Sounds like you're doing the work without going off the grass. It's good to keep in mind that using 4wd on high traction surfaces adds to wear and tear--especially with heavy weight in a loader. Front tires have to do a fair bit of slipping whether in tight turns on the straight. Greater traction places greater stress on the drive train. ....

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bigpete
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2004-03-03          78689

Hi, Tom. Not to nitpick, but I believe the front wheel "lead" in a properly set up 4WD is typically 1% to 5%. Any more than that and the front drive would be noticably trying to pull/drag the rear drive (faster spinning and tearing front wheels) even in sraight forward operation. You can accidently create an over-lead by increasing front wheel size, or decreasing rear wheel size. You can create and "under-lead" push condition by doing the opposite.

You are right about the front differential as a solution. I've never heard Kubota owners talking about bi-speed turn in comparisons over the years. Not that it didn't exist, but perhaps it wasn't a total solution, or was not worth the extra cost as an option. Pete ....

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Art White
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2004-03-03          78696

Pete, at one time it was offered on all of the B-series. Now they only use it on the B-2410 and the larger M-series. Yes it does sell for more but the market has not been strong or the marketing is weak! ....

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TomG
Join Date: Feb 2002
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2004-03-04          78739

Pete: Nit picking is good in my book since most of the mistakes we make are to be found in the detail. Probably need a better term than not picking though. I believe you're right in the up to 5%.

I have heard stories of people who had tractors that used obsolete tires who couldn't find factory matched sets and ran more extreme leads OK. Excessive lead is a better choice than lag. They probably were on soft surfaces and didn't carry much front-end load. They also probably went through front tires pretty fast and took service life off the front drive train. Probably could pull through tight turns pretty well though. ....

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Art White
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2004-03-04          78744

Tom, Deere tried 7% led on the 55 series as well as laying the tires down on the side so to miss the frame on the tractors and be able to turn a axle at near 55 degree's like the cometition. Here with the stone they had a lot of trouble with sidewall cuts and also wore out tires on the front in about 1000 hours vs the 1500 to 2000 on the competitions tractors that only use 5% for the max lead with many fatoring in less. Don't get me wrong as that was a managable fault on the best of the tractors they have ever built. It does drive up the cost of ownership but that is the just one of the choices everyone makes when they pick their brand. ....

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bigpete
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2004-03-04          78761

Tom, the only reason I am able to "nitpick" is because I just recently learned about some of the math behind the lead issue. Of course it was from a link recently posted on another web board, so I cannot claim any credit or expertise here. I will post a link below to the original resource. The two factors I found insteresting were, first, the magnitude of impact on lead/lag from what seem like minor changes in tires sizes and "rolling circumference." And second, the effect front tire wear has on reducing lead percentage over the life of the tire. That is, a properly set up lead on a 4WD tractor will diminish over time (become clsoer to a 0 % lead) as the front tires wear.

And finally, after reading a lot recently about 4WD tractors becoming more difficult to steer after increasing rear tire size, this resource also mentions steering difficulty from improper lead, but without much discussion on that symptom. Pete ....


Link:   Can I use a different size tire on my 4WD tractor?

 
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Murf
Join Date: Dec 1999
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2004-03-04          78770

The lead/lag ratio is very important to the life of a 4wd CUT.

A large municiplaity near here had a fleet of B-series 'Botas that were used for maintenace of public housing complexes as grass cutters (with MMM's) in the summer and front-mounted blowers for the sidewalks, etc., in the winter.

The problem was they had to cover some distances using roads and sidewalks in the course of the daily routine, this quickly reduced the front tires to bald carcasses. The high cost of replacement turfs over passenger car radials made some bright spark buy the cheaper ones instead. The following year they were ALL in the surplus equipment auction, not one of them had a transmission left intact. The change in lead/lag ratio combined with running on paved surfaces which didn't allow much if any tire slip tore the TX's apart VERY quickly.

Best of luck. ....

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Art White
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2004-03-04          78779

I've seen much the same as Murf has. housing for the drives literally blown off the transmissions, drive shafts broken splines prematurely stripped as well as the tire wear. I hate to say it but in my years I've made a mistake or two on it but not to every destroy parts without correcting it! ....

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JDF415
Join Date: Feb 2004
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2004-03-04          78809

Over inflation increases the rolling circumference.
Under inflation decreases the circumference. ....

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JDF415
Join Date: Feb 2004
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2004-03-04          78811

On the JD 4000 series the overrun was as much as 6%. This would vary depending on what tires were on the tractor. The MFWD drive gears were changed toward the end of the 4000 series production run (Jan 2000). The new gears reduced the front axle overrun to around 2.5%. It makes a big difference in how much hp was required to drive the tractor with the MFWD engaged while driving on a hard surface. It is not recommended to drive with the MFWD engaged unless it is needed (muddy conditions, etc.) where the wheels will have slippage. Leaving the MFWD engaged when it is not need increases fuel consumption, powertrain wear, and tire wear. ....

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Art White
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2004-03-04          78845

Most all tractors built today can be operated in four wheel drive all the time as long as the tires are balanced between front and rear. If the tractor is bucking then there is a tire size or tire pressure problem which is still a size problem. They have been building them that way for many years there are some that will run at road speed without a problem and there are some that will not run at road speed do to the speed inbalance. ....

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bigpete
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2004-03-04          78846

Hey, Murray. I missed your question earlier. I'm not sure I would be the best person to ask, but I beleive the rear-to-front drive ratios are the result of a deliberate engineering objective and are not mechanically adjustable. Changing the rolling cirmumference of either fronts or rears will change the lead/lag effect, but the drive ratios are the comparative turning rates (revoluttions) of the front and rear drives. Therefore, they are what they are and the manufacturer can provide the ratios for any given tractor. I suppose somebody could drop in new gearsets or even a different axles. That would be more of a modification than a mechanical adjustment. Pete ....

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TomG
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2004-03-05          78873

I remember that discussion quite awhile ago now. What Pete says is right and some manufacturers publish front to back final drive ratios. Tires and pressure to an extent can change it but basically a tire set that is intended for the final drive ratio is what works best. Some tire manufacturers publish rolling circumferences or diameters. A tire set with the same ratio as the final drive ratio plus a lead allowance is how to calculated it I think.

In our discussion I think we figured out that the shape of a loaded tire doesn't really change the outside circumference, and one axle rotation is still puts about the same distance of rubber on the ground. What does happen is that weight sinks cleated tires into the ground, which does reduce lead. I believe that the circumference of front tires actually were measured with and without loads by a member who didn't find much difference. I always though there'd be some stretch to them but maybe nowhere near as much as I thought.

The problem with the flat spot is that the spot expends under load and increases traction due to both the weight and having more rubber on the ground. That (especially with turf tires) in combination with inadequate 3ph ballast and hard surfaces is what can really blow a drive train when doing heavy loader work and is a reason why pressures are important. ....

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DRankin
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2004-03-05          78880

It is a complicated issue. I measured the tire deflection under various load conditions and found, as I recall, about 1/8 of an inch difference on a tire with a 65 inch circumference.

As Tom has mentioned, just throw out the book when it come to deeply cleated tires. The rolling circumferences are calculated on the tire carcass size with the assumption that the cleats will be driven into the soil.

It gets really screwy when you figure the cleats on some small R-1 front tires are as deep as those on the rear. The net effect is that tires sized for proper lead under muddy conditions have drastic ratio changes the instant you drive onto a hard surface.

There is a method outlined on the Firestone website wherein you can compare front and rear tire rotation values over a measured distance with the front drive engaged and not engaged to determine the relative gears ratios and how much lead/lag you have.

Once you have that number, matching new tires is pretty easy. ....

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