Kubota B6000 wheel/tyre size

flangefrog

Member

Equipment
Kubota B6000
Nov 29, 2021
36
4
8
29
Auckland, New Zealand
I have a Kubota B6000 4WD that has 4-10 front tyres and 7-14 rear tyres. I'm not sure if they're original.

Tractordata.com says the B6000 4WD has 6-12 and 7-16 tyres. it also says the B5000 has 4-10 and 7-14 tyres. I wonder if these rims and tyres could be from a B5000?

A lot of the B6000 tractors I've seen photos of have 5-12 front and 7-14 rear tyres.

Is my setup a standard one? Is the front to rear wheel speed ratio correct? Is there maybe a difference in gear ratio between the USA and Japanese/grey market models?

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Vigo

Member

Equipment
B6100, B8200
Jan 9, 2022
73
21
8
San Antonio Texas
I dont even think the various factory size 'sets' match each other all that well as far as that ratio. Plus tractor tires are notoriously inconsistent within a given size as far as their overall diameter (this brand runs taller, this brand runs wider etc etc). What I have noticed from driving a few of these things with various sizes is that if your 4wd lever feels like it's 'a little stuck' in 4wd when you try to shift it back to 2wd, the system is in a bit of a bind. If it never feels like that, you're fine.

All the nasty effects of a ratio mismatch come from traction. Traction comes from a bunch of things such as the surface you're on, the weight on the tires, and honestly last place behind those, the type of tire/tread.

You have a fair amount of control there in that if you're on a super grippy surface, don't use 4wd if not necessary. Also, if you plan to add a ton of weight to the tractor or use it heavily loaded (i.e. fel AND backhoe, weight on BOTH ends) then pay careful attention to how that 4wd shifter feels. The tractor in most cases will always slip a tire rather than break itself from a 4wd 'bind'. Unless you've got weight on BOTH ends (weight on one end just unloads the other end) and are on a grippy surface and NOTHING can slip.. then you might break something. But the tractor will feel like it doesn't want to move, just like it feels if you turn the steering wheel all the way in 4wd (trucks do this too). It won't sneak up on you if you're paying attention.

Id just mix and match any of the factory sizes that are in the same diameter ballpark front to back and run it. I've had 20.5-10, 22x8x10, 5.3-12 trailer tires and at least 3 different 6-12s on front(which varied substantially in diameter), and 7-16, 8-16, and 29x12.5x15 on rear. Only time i noticed anything nasty with the 4wd was with the 8-16s and 5.3-12s together on a tractor with FEL (enough weight on the front to make them do anything).
 

Tschutt

New member

Equipment
B5200 KUBOTA
Apr 9, 2022
3
0
1
Smoaks, SC
Hello,

I have a B5200 and I'm having the same issues. Did you come up with a path forward on this? If so please let me know what decision you made?
 

Vigo

Member

Equipment
B6100, B8200
Jan 9, 2022
73
21
8
San Antonio Texas
I operated two different b6100 4wds over the weekend, one with loader and box blade, one with loader and backhoe. One has 22x8x10 front and 29x12/5-15 rear, the other has 6-12 front and 8-16 rear. You can tell what's going on immediately when you touch that 4wd lever. It doesn't want to come out of 4wd when making any kind of hard turn, just like your diff lock doesn't want to disengage under the same circumstances. None of it has ever broken. I run these things hard. I avoid hard turns while in 4wd. Also avoid putting max power through only the front end (pull up on something as hard as you can with loader which unloads rear tires and then push/pull on it). But I use 4wd all the time because it's the safest way for me to operate on uneven terrain since it hooks the front wheels to the back brakes and gives you 4-wheel braking. I am reaching down and flipping the 4wd lever, the high/low range lever, and the steering brakes interlock thing all the time.

I highly recommend just learning to feel out the machine and learning to use 'mechanical empathy' rather than nitpicking the specs to death. Like I said, the tire diameter (technically 'loaded radius') is what matters, not the 'size' that's written on the tire. Thing about that is tractor tires all marked the same size AREN'T the same to begin with, and then depending on how much weight is on the tractor AND the surface it's currently sitting on, leaning etc, the tire diameter/radius CHANGES dynamically.. constantly..

The fudge factor here is huge because it has to be. Tire radii change in use, and vary from manufacturer to manufacturer, and even change with tire pressure. Even if the manufacturer gives you a 'loaded radius' spec, which some do, it depends on the weight on the tire and good luck finding out what weight number they used to measure or what that end of your tractor actually weighs sitting still, which barely matters because it moves.. and changes.. and you aren't going to run the pressure they used on the spec sheet which was probably max when what you actually need on a tiny Kubota is probably 10-15psi in fronts, maybe 20 with a loader, and honestly 5-10 in the back if you aren't carrying a bunch of weight.

So there's no way to think yourself into the perfect set of tires. You buy something in the right ballpark, run it, and nothing bad happens, and you move on.

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