Go Bottom6200 vs 7200 tires AGAIN
 | John Fundy
Join Date: Posts: 1 
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2003-04-09 52859
Gentlemen,
Thanks for all the expertise. What I don't understand is this. The B6200 manual list the correct turf tires as front 20.5X8-10 and rear as 29x12-15. However, the same manual lists two sizes of turf tires for the 7200 as either (1) front 20.5X8-10/rear 29X12-15 OR (2) front 20.5X8-10/rear31X13.5-15. Note in both cases the fronts are the same, but the 7200 supposedly can handle two different rear sizes. My question: Why is it okay for the factory to list two different rear tire sizes for the B7200, but not the B6200? Apparently I'm missing something, hence, your help. One more point: As an ag tire wears, it is very likely to lose 2" on the diameter (one inch per side-this would be a bald tire) Why is this okay?
PS: Hey murf,good to hear from ya! Hows the "L"?
John Fundy
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 | WillieH
Join Date: Feb 2003 Posts: 543 New England 
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2003-04-09 52861
John -
This is why I was able to bump up from a 20.5 to a 23 on the front...and up on the rears abit. Staying in the ratio window allows you to do just that. I have said for many years already, exactly what you just questioned...the tire wears down hence losing circumference size...what happens to the ratio? Some will argue that the rears and fronts will wear at the same rate. Not necessarily. Hence the ability to have different sized tires, still matching within a design window of size acceptability.
I believe that the 31's in the rear, and the 20.5's in the front, will be noticeable on the engagement in and out of 4wd. This will, I believe create a difficulty on the fly for engagement as well as disengagement. Your gonna be operating at the far end of the front size spectrum, matched with the 31 rears.
Willie H. ....
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 | DRankin
Join Date: Jan 2000 Posts: 5116 Northern Nevada 
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2003-04-09 52874
Man, you guys are really making me do my homework.
Here is the answer.
By roughly doing some of the math on this web site, it is theoretically possible to match up the same 20.5 inch tire to a "big" 29 inch rear or a "small" 31 inch tire and not get out of the ratio window.
My 4100, with it present tires, gets 1.45 front tire rotations to 1 rear wheel rotation in two wheel drive.
In 4wd, with the diff/lock engaged the ratio goes up to 1.495 to 1, or about a three percent "overdrive" for my front tires. Firestone says anywhere between 0 and 5 percent is acceptable, so I am right within range.
I think I have a lock on this concept, so holler if you have questions. ....
Link:
Click Here
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| WillieH
Join Date: Feb 2003 Posts: 543 New England
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2003-04-09 52886
This is starting to sound a lot like the B vs. BX dilemma a few weeks back...
Mark, I agree with what you have posted from Firestone, however, I would think that the real critical element would not be from what appears to be a tire wear standpoint as much as a mechanical standpoint that Kubota designed into the gear ratios for proper operations. Maybe I am looking at something totally different than everyone else is, but how can any tire maker stand firm and tell a consumer how to set up a tractor, or any other vehicle, for proper mechanical function?
We have already established, and proven that the revolution ratio between front and rear, must fall into a particular window...that's a given, or damage will be had to the drive line. The confusing element, in which I think we all will agree, is the ambiguity that, in this case, orange applies from one unit's text to another. If, as John has pointed out, all of these tractors in question utilize the same tire sizes, front and rear, with or without a wear off factor, they "should" all work on any or all of the tractors in doubt, relative to what orange writes.
In the past, I have sat down with the calculations, and sized out tires/wheel sets for fronts and rears to work properly on 4wd's. Still doing it the same today as I did many years ago - The problem...potentially a slanted eye on the other side of the pond, that fell asleep while documenting text to cause confusion.
Willie H.
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| Morgan
Join Date: Jul 2003 Posts: 126 Albany, NY
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2003-04-09 52889
Hey if your front/rear diameter ratio is not exactly to specs and you're going to be working in loose soil or mud or gravel it won't matter, the tires will slip in the dirt and make up the slack. Just don't go on asphalt. No interstate travel. Off road only.
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| DRankin
Join Date: Jan 2000 Posts: 5116 Northern Nevada
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2003-04-10 52910
Willie, I have documentation from Deere and Kubota that they set the gear/tire ratios to run fast on the front axle.
The only difference between them and Firestone is Firestone says how fast the front axle should run and they describe how to calculate it.
My 4100 came with Firestone/Bridgestone tires, and the numbers I am crunching are right in line with what Deere posts. I feel much more comfortable now matching tires front and back and having a way to see if I am doing it correctly.
BTW, I do believe the front tires would wear down faster and change the ratio, but I have also noticed that the front tires are set up toward the high end,(+5 percent)when new. As they wear down that percentage drifts down, toward zero. ....
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| WillieH
Join Date: Feb 2003 Posts: 543 New England
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2003-04-10 52912
John Fundy -
This has gotten way off track...the fact is, as "great" as documentation is, and as much of it as there is, the bottom line is that the 31's in the rear would really be making the fronts spin at the higher end of the "designed" operating window. Realize the ease of engagement / disengagement now, then put the 31's on and realize the e / d then. You'll see the difference first hand. Point being as I have said earlier, as Morgan said earlier, and others will agree, if you have a situation where undue stress is applied from the slight mismatch of tire size ratio, so long as you are operating in slippery / greasy / loose surface, the stress will be absorbed in the slippage of traction. Just remember to disengage when back on the highway!
Willie H.
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| DRankin
Join Date: Jan 2000 Posts: 5116 Northern Nevada
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2003-04-10 52924
I don't want to start a urination olympics here, but I think Willie made a typo.
The taller rear tires would push the front tire rotation closer to a neutral balance and the smaller rear tires would tend to let the front tires run a little faster.
The disengage advice on hard surfaces is good advice for any 4wd tractor of any make and model with one exception: braking.
You may encounter a situation where keeping it in four wheel drive is the only way to achieve the braking power you need pulling a heavy load downhill or at transport speeds. That alone should give you the incentive to run the tests listed on the Firestone website to make sure everything is balanced.
It seems the overall gearing on your Kubota is very similar to my 4100. I have 20.5 inch tires on the front right now and 29.75 inch tires on the rear. Testing proves they are a +3 percent.
These are actual measurements, not numbers printed on the tire. In fact, my experience has been that tires are almost never the size printed on the sidewall.
I would bet that the 31 inch tires are shorter than advertised and may match up well with a "true" 20.5 inch front tire. The Firestone test and a tape measure applied to the proposed new tires will give you the info you need to make a quality decision. ....
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| WillieH
Join Date: Feb 2003 Posts: 543 New England
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2003-04-13 53089
Hey John Fundy...
Are you ready for ONE more reply concerning the tires?
As YOU asked from the gitgo, tire size compatibility from a B7200 set vs. a B6200 that you have, and manuals for.
The B5200,6200,7200 all accept the same sizing, period.
Your questioning about the tire size 31x13.5x15, will it work? YES!!!! It will work just fine. I put a pair on the rear of my B5200 just to make sure. No mismatch at all. In fact as, I believe Art pointed out, most of the B series units, with exceptions such as the B20,21,22,4200,8200,9200, all make use of the same size chassis, same gearing, same tire sizing. To go one step farther, even some of the mechanicals are totally interchangeable of the drive line.
Turf sizes (fronts/rears): 20.5 X 8 X 10 / 29 X 12 X 15,
20.5 X 8 X 10 / 31 X 13.5 X 15,
R4 sizes (fronts/rears): 20.5 X 8.5 X 10 / 10 X 16.5,
21.5 X 8.5 X 10 / 10 X 16.5,
23 X 8.5 X 10 / 12 X 16.5 These are the most common. The R4 sizes are not listed in the manuals as you may have deduced. However all work with thier respective tire size "mate" and all have the same bolt pattern for rear wheels, from 1976 to present...six lug with six in. ctr's. The fronts changed from four lug to the six lug with your B5200/6200/7200 series orange, and are still in use today on various models.
Willie H.
P.S. - Mark H.- Typo, not at all. If you apply a larger tire in the rear, without changing the tire size in the front, this change will force the front tire to engage in a higher number of revolutions than before to satisfy one revolution of the larger rear size tire. Hence spinning the front tire faster, (more revs), to achieve one full rev of the rear. This is a simple law of physics. In fact, the basis for achieving more power in low range gearing...one is essentially, changing the gear ratios by changing a mating gear size, whether it be larger or smaller than that of a given fixed gear size, to achieve either more power or less power.
'nuff said! Let's Move On!
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| DRankin
Join Date: Jan 2000 Posts: 5116 Northern Nevada
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2003-04-13 53091
I also think the tires as described will work.
I have a different physics book, apparently.
Maybe we are saying the same thing, Willie, in different words. Like you I have done a lot of research and experimentation.
I have just replaced the tires on my 4100 and the numbers I have used here are borne out in the real world.
But as you have pointed out, we have beat this to death.
See you on the next thread. ....
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 | Art White
Join Date: Jan 2000 Posts: 6898 Waterville New York
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2003-04-14 53102
Sorry I missed this but you have two different types of tires here as the 31's are a bar turf and have a different profile that the other size. ....
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| WillieH
Join Date: Feb 2003 Posts: 543 New England
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2003-04-14 53111
Art -
The 31 X13.5 X15's that I have and that I believe John was referring to, are infact full blown turf tires, not the bar turfs. These babies that I have, consist of approximately 1.5 inch "square-ish" trapezoid tread blocks, about 1 inch apart. No bars, and once loaded make excellent lawn rollers.
Willie H. ....
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| Art White
Join Date: Jan 2000 Posts: 6898 Waterville New York
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2003-04-14 53120
Well, this gets more indepth here boys, as when I get into the big book with the pictures of styles of there tires they go to the BAR-TURFS for that size on those tractors. They do also use the tire you described Willie but not on that ractor. The Bar turf is a lower profile than the standard turfs. ....
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