B2150hst 4WD Tire Help - Lead/Lag Mechanical Ratio

[rScotty]

I've done lots of tire swaps over the decades and only two methods work for me. One is to use the factory tire size and it will always be correct. If you can't do that, you have to get the front axle ratio one way or another from a dependable source such as a manual or the manufacturer. If you can't find it in a shop manual, just keep calling the factory and try to talk with an engineer. It might take a while but eventually you'll get someone that knows something, if for no other reason than to stop you from calling. Short of an answer from an engineer, I want to see the ratio in print somewhere and not word of mouth from someone that says they know. Use the rolling circumference numbers from the tire maker's site when you get the ratio.

Little known fact here is that I have seen new Kubotas with the axle ratio on a sticker on the back of the seat. Go figure.

We ought to do a sticky on this site with the confirmed axle ratio of various models and the source for the number. It would make things easier.

I'd approach it differently: I believe that the only really reliable way to know the real ratio is to measure the 4wd axle ratio for yourself - as we've laid out.

A manual, a reference in print, or an engineer at the manufacturer can only tell you what they think it should be... That may or may not be what you have on your tractor, and it may vary by which optional tire and wheel set was on the tractor when it was originally built. In fact, that would be one reason for finding the axle ratio on a sticker on the back of the seat - and just hearing that makes me uneasy.

There is no way short of measuring your tractor's internal axle ratio to confirm what is in your own tractor.
By measuring it yourself you can tell what your internal ratio really is. Anything else is a guess.
rScotty

 

[sixdogs]

rScotty--yes, that is a good point for guys that know what they're doing but newbies can make mistakes. You can be mechanically capable and still get it wrong.


How about looking at the gears in a parts bin and then doing the math?

 

[LouNY]

Yes, if you could find the ring and pinion for both differentials,
then if your tractor uses bull gears or drop boxes or planetary gear sets for the final reduction in the rear axle,
then for the front after the differential will usually be spur and bevels gear reductions or a planetary reduction.
A lot of gears and math to work with especially with planetary gear sets.

As far as factory tires I have seen new tractors with considerable miss match, we had a New Holland that the dealers went thru several sets of tires (same sizes)
different brands to get a set with a good lead.

 

[B2150hsd]

Will try to find time tomorrow for the ratio test. However, Im thinking everything is close to acceptable or good enough. Here is the logic as to why:

- The spec sheet posted for the B8200 4wd is from Kubota
- B8200 uses same tires as the B2150
- Kubota ratio sheet states ratio of 1.691
- When comparing front and rear tire rotation in 2 wd on hard surface and the front tire completes one full rotation, the rear tire stops at ~2' oclock. In other words, it needs to rotate about 35% more. This matches closely to the 1.691 ratio.
- When disengaging 4wd its always smooth with no feel of binding


I may have wasted every ones time. I apologize if that is the case. My brain "was" wired for same size tires rotating equally on all hubs and not mixed tire sizes for different ratios on front and rear axles. :ashamed:

 

[rScotty]

Will try to find time tomorrow for the ratio test. However, Im thinking everything is close to acceptable or good enough. Here is the logic as to why:

- The spec sheet posted for the B8200 4wd is from Kubota
- B8200 uses same tires as the B2150
- Kubota ratio sheet states ratio of 1.691
- When comparing front and rear tire rotation in 2 wd on hard surface and the front tire completes one full rotation, the rear tire stops at ~2' oclock. In other words, it needs to rotate about 35% more. This matches closely to the 1.691 ratio.
- When disengaging 4wd its always smooth with no feel of binding

I may have wasted every ones time. I apologize if that is the case. My brain "was" wired for same size tires rotating equally on all hubs and not mixed tire sizes for different ratios on front and rear axles. :ashamed:

OK. I can buy those arguments. Since your tractor isn't hard to disengage from 4wd, that is pretty good evidence that the lead ratio is reasonable because you are not getting too much "windup" in the drive train.

I don't think of it as a waste of time. We had the fun of an interesting mechanical problem all by itself and worth it for that.
This gear ratio stuff and how it affects lead/lag geometry is not a simple basic mechanical problem.
It is one that takes some real mental work to even visualize what the problem is and what the solution would look like.
I've done it before, and it still took me some work (and a mistake or two!) to get it right.
So my feeling is we all owe ourselves congratulations for working through it.

And what we learned here is necessary knowledge for anyone who wants to go to different tires - especially when it involves different wheels or tire diameters - which is usually the case if changing between R1, R3, and R4 types of tires.
rScotty

 

[npalen]

Just to add more fun to the discussion: Does the rolling circumference of a tire change under load and do the fronts and rears change by a different factor?

 

[LouNY]

Just to add more fun to the discussion: Does the rolling circumference of a tire change under load and do the fronts and rears change by a different factor?

Yes :thumbsup:

 

[rScotty]

Just to add more fun to the discussion: Does the rolling circumference of a tire change under load and do the fronts and rears change by a different factor?

Yes. If the load didn't change things, then we could simply use arithmatic circumference of a circle instead of rolling circumference. Not only do front and rear tires change by a different factor due to their own constructiona & aspect ratio, but loads can be proportioned more to the front or rear as well. For that matter, the ground probably enters into it too,
It would be interesting to do the paint blob test with an empty FEL bucket and then the same test with a full load in the bucket.

You can drive yourself crazy trying to figure all the factors.... or just do paint blob test; it's more accurate than the math is anyway.

rScotty
- just noticing & wondering why I type 100 words & Lou types just one .... and we are saying the same thing .

 

[LouNY]

Because my bacon, fried eggs and toast were in front of me :licking:

 

[npalen]

Yes :thumbsup:

I probably should have been more specific when saying "load". I was thinking in terms of draft load.