Turfs on front, Insdustrials on rear?????

[Smokin Diesel]

Your mileage may vary.

I only had about 750 hours when the u-joint went. I'd agree with you, if I had lots more hours...

Mine did bind. You could feel it when moving from 4wd to 2wd. Everything I did was on dirt/field, and I used 4wd frequently. I did use it for some time before I was able to afford the front R4's.

Without a center differential, there will always be bind front-to-rear in a 4wd system. If you're doing any turning with 4wd engaged, you're putting more torque on that u-joint more quickly than you will with slightly dissimilar tire diameters. And since turning is pretty common, I don't see how you could single out a slight variation in tire size as the cause for failure.

If you we're using 4wd frequently because the rears were slipping, then that totally takes mismatched-tread-speed-induced-bind out of the equation. The driveline will only absorb as much torque as wheel slip allows. The u-joint doesn't know if the torque is from mismatched tires or from the rears slipping and giving up torque to the fronts. It's all the same.

My 2620 has three different tire types available from the factory; R1, R3, and R4s. If you divide the front and rear tire diameters of each flavor you'll get a percentage. What are the odds that you'll end up with the same percentage between the different types (keeping the same tread types - not mixing them up)? And what do you suppose that any of those percentages match the differences in the f/r drive ratios if you divide those out? The factory doesn't change the gearing with tire selection. Like I said before - my turfs bind in a straight line from the factory - my percentages don't match. If slight differences are a problem, then every B2620 w/turfs that rolls off the line is destined for premature driveline failure. Either Kubota hasn't figured this out, or they don't think it's a problem.

Some folks can get 200k miles on a water pump, some get 100k, and a few get 30k or less. It could very well be that you had a 750hr u-joint installed. How many hours do you have now?

 

[Duffster]

Without a center differential, there will always be bind front-to-rear in a 4wd system. If you're doing any turning with 4wd engaged, you're putting more torque on that u-joint more quickly than you will with slightly dissimilar tire diameters. And since turning is pretty common, I don't see how you could single out a slight variation in tire size as the cause for failure.

If you we're using 4wd frequently because the rears were slipping, then that totally takes mismatched-tread-speed-induced-bind out of the equation. The driveline will only absorb as much torque as wheel slip allows. The u-joint doesn't know if the torque is from mismatched tires or from the rears slipping and giving up torque to the fronts. It's all the same.

My 2620 has three different tire types available from the factory; R1, R3, and R4s. If you divide the front and rear tire diameters of each flavor you'll get a percentage. What are the odds that you'll end up with the same percentage between the different types (keeping the same tread types - not mixing them up)? And what do you suppose that any of those percentages match the differences in the f/r drive ratios if you divide those out? The factory doesn't change the gearing with tire selection. Like I said before - my turfs bind in a straight line from the factory - my percentages don't match. If slight differences are a problem, then every B2620 w/turfs that rolls off the line is destined for premature driveline failure. Either Kubota hasn't figured this out, or they don't think it's a problem.

Some folks can get 200k miles on a water pump, some get 100k, and a few get 30k or less. It could very well be that you had a 750hr u-joint installed. How many hours do you have now?

Well said

 

[RobertN]

I have only 1150 now. Not much for a 1985 manufacture. Yes, it could have been a week u-joint. However, when I finally got my R4 fronts, and compared them to the turf fronts, they were definitely taller, even though by the book they should have been less than 0.5" difference. It was also very noticeable the binding when shifting from 4wd to 2wd; always had to back up a tad to release tension in the drive train.

I understand the bind, and concepts you describe. Seen it in action on Jeeps and pickups. Was practically born in a '42 Ford GPW. Built them, run them on the rocks on Rubicon ect. I have seen the same brand, model and size 33x12.50's and 35x12.50's vary. Four of the exact same tire, obvious difference. Worked ok.

I don't discount what you are describing, it certainly has merit.

I did not have the two tires side by side originally; I went by published heights and radius. When they were side by side, it was obvious they were different.

I just will not mix and match tires again, unless I have seen them and can do a comparison. Like I mentioned, your mileage and experience may vary.

Without a center differential, there will always be bind front-to-rear in a 4wd system. If you're doing any turning with 4wd engaged, you're putting more torque on that u-joint more quickly than you will with slightly dissimilar tire diameters. And since turning is pretty common, I don't see how you could single out a slight variation in tire size as the cause for failure.

If you we're using 4wd frequently because the rears were slipping, then that totally takes mismatched-tread-speed-induced-bind out of the equation. The driveline will only absorb as much torque as wheel slip allows. The u-joint doesn't know if the torque is from mismatched tires or from the rears slipping and giving up torque to the fronts. It's all the same.

My 2620 has three different tire types available from the factory; R1, R3, and R4s. If you divide the front and rear tire diameters of each flavor you'll get a percentage. What are the odds that you'll end up with the same percentage between the different types (keeping the same tread types - not mixing them up)? And what do you suppose that any of those percentages match the differences in the f/r drive ratios if you divide those out? The factory doesn't change the gearing with tire selection. Like I said before - my turfs bind in a straight line from the factory - my percentages don't match. If slight differences are a problem, then every B2620 w/turfs that rolls off the line is destined for premature driveline failure. Either Kubota hasn't figured this out, or they don't think it's a problem.

Some folks can get 200k miles on a water pump, some get 100k, and a few get 30k or less. It could very well be that you had a 750hr u-joint installed. How many hours do you have now?

 

[KennyV]

The rolling circumference is not the same as the static circumference...
If you want to check RC, you can either mark the tire on the tread so the mark will transfer to the ground. OR if you use the radius you have to measure the LOADED radius. Measure from the center of the axle to the surface of the ground.
The LR will vary from tire type due to tread design and thickness,
side wall ply thickness and flex,
front loaders will change this LR just by increasing the weight the tires carry,
and air pressure. Using air pressure alone you can greatly change the LR from right tire to left tire.
just because two tires standing without a load are different heights is not an indicator...
If LR (loaded radius) or the RC (rolling circumference) are the same you will have no problems. KennyV.
PS. Duffster and Smokin Diesel have it right...

 

[donn12]

Thanks. I was hoping I could do it and kind of forgot about it.

 

[RobertN]

I agree with Smokin Diesel, just he was not there to see the tires. I did all the book work. In real life the turf tires were bigger. Like over an inch taller installed. When I got my rear R4's, I did not have anything to compare the fronts to.

Still, my tractor broke. I have wrenched on 4x4's all my life. Understand lead/lag, et al. Wrenched on race cars. Saw stuff that worked, saw stuff that shoulda but didn't. Seen Jeps scatter u-joints on the rocks.

The books indicated it would work. Real life, it did not with the combo I had.

My whole point has been, check the books AND the tires.

The rolling circumference is not the same as the static circumference...
If you want to check RC, you can either mark the tire on the tread so the mark will transfer to the ground. OR if you use the radius you have to measure the LOADED radius. Measure from the center of the axle to the surface of the ground.
The LR will vary from tire type due to tread design and thickness,
side wall ply thickness and flex,
front loaders will change this LR just by increasing the weight the tires carry,
and air pressure. Using air pressure alone you can greatly change the LR from right tire to left tire.
just because two tires standing without a load are different heights is not an indicator...
If LR (loaded radius) or the RC (rolling circumference) are the same you will have no problems. KennyV.
PS. Duffster and Smokin Diesel have it right...

 

[savaytse66]

Just came across this thread in a search while trying to decide which tires to have my dealer put on a new BX25. I am considering R4s for the back and turfs for the front. My usage will be about 75% MMM and 25% FEL and BH work.

What I am not understanding is the discussion regarding 4x4 and tire size. Is everyone saying that the rolling circumference of the front and back tires need to be the same, or just the RC of a rear R4 vs a rear turf? Because the front and rear tires are different sizes anyway. So in my mind, I've got to believe that I can run R4s on the back and turfs on the front without having any problems, assuming the RC of the rear R4s are the same as what a rear turf would be.

Am I understanding correctly?

Thanks.

 

[TripleR]

Just came across this thread in a search while trying to decide which tires to have my dealer put on a new BX25. I am considering R4s for the back and turfs for the front. My usage will be about 75% MMM and 25% FEL and BH work.

What I am not understanding is the discussion regarding 4x4 and tire size. Is everyone saying that the rolling circumference of the front and back tires need to be the same, or just the RC of a rear R4 vs a rear turf? Because the front and rear tires are different sizes anyway. So in my mind, I've got to believe that I can run R4s on the back and turfs on the front without having any problems, assuming the RC of the rear R4s are the same as what a rear turf would be.

Am I understanding correctly?

Thanks.

I believe you have it right. We have run Ag tires on the front and orchard tires on the back of our MF375 since it was bought new in the late eighties and no problems have been encountered.

 

[CHDinCT]

Just came across this thread in a search while trying to decide which tires to have my dealer put on a new BX25. I am considering R4s for the back and turfs for the front. My usage will be about 75% MMM and 25% FEL and BH work.

What I am not understanding is the discussion regarding 4x4 and tire size. Is everyone saying that the rolling circumference of the front and back tires need to be the same, or just the RC of a rear R4 vs a rear turf? Because the front and rear tires are different sizes anyway. So in my mind, I've got to believe that I can run R4s on the back and turfs on the front without having any problems, assuming the RC of the rear R4s are the same as what a rear turf would be.

Am I understanding correctly?

Thanks.

You have the right conclusion but the real requirement is to maintain the same RC ratio of fronts to rears. The ratio is set by the 4X4 gearbox, so the tire ratios for turfs vs R4s would need to be the same. So, by deduction, if the rear R4's have the same RC as the rear turfs, your ratio would be the same and you would not be risking damage to your 4X4 gearbox.

I'm sure someone else could state this better, but I hope that helps.