L5030HST Tires and Lead/Lag

[46Willys]

This is a continuation and clean-up of my previous post from a few days ago. I have learned a lot from you guys and I have one last confusion.

My L5030 apparently has an axle ratio of 1.56 (ratio between front and rear axles)

Original tire specs:
Front: 9.5-16 R1 with rolling circumference 98"
Rear: 14.9-26 R1 with rolling circumference 156"

Or optional R4 tires:
Front: 10-16.5 R4 with rolling circumference 90"
Rear: 17.5L-24 R4 with rolling circumference 145"

rolling circumference = RC
I am just using manufacturer RC's. I have not personally measured the tires.
Attached is one of the documents where I found the calculation below.

Using the calculation:

(RC of front tire x Axle Ratio) - RC of rear tire
_________________________________________________ x 100 = Lead/Lag
RC of rear tire

Or, I found this on-line calculator:
Lead Lag Calculator (titan-intl.com)

Okay, so my question - Every combination I use comes up with a negative number. If I understand this right, it should be a positive number. Am I understanding this right? It appears that my rear tires will be pushing the front tires. Did Kubota design this tractor with a -2% lead/lag? Does this mean the front tires should be larger than original design?

 

[GrizBota]

Interesting. Here’s a link to the table and tread from which the 1.56 “gear ratio” appears to have originated for this conversation.

L Series Wheel and Gear Ratio Data

It’s clear you indeed realize that the “gear ratio” in the referenced table is most likely actually the difference in overall gear ratios between the front (turning faster) and the rear (turning slow) axels. There’s a post from December of ‘23 by @rbargeron which provides what I believe to be the true terminology, which is "Transference Ratio".

I agree with your math and conclusion that, although the math suggests the front tires are lagging the rear, that’s probably not what is actually occurring or Kubota’s design intent. I’m curious as to wether the data in the table might have a typo.

 

[46Willys]

Interesting. Here’s a link to the table and tread from which the 1.56 “gear ratio” appears to have originated for this conversation.

L Series Wheel and Gear Ratio Data

It’s clear you indeed realize that the “gear ratio” in the referenced table is most likely actually the difference in overall gear ratios between the front (turning faster) and the rear (turning slow) axels. There’s a post from December of ‘23 by @rbargeron which provides what I believe to be the true terminology, which is "Transference Ratio".

I agree with your math and conclusion that, although the math suggests the front tires are lagging the rear, that’s probably not what is actually occurring or Kubota’s design intent. I’m curious as to wether the data in the table might have a typo.

That is the chart where I found the axle ratios. I have looked quite a few placed and I have not found any other references.

 

[GrizBota]

That is the chart where I found the axle ratios. I have looked quite a few placed and I have not found any other references.

Not really any more enlightening on this exact quandary, but in the post below (and in post 20) of that link @rbargeron explains how one could calculate the transference ratio “if” they knew all the tooth counts on the various front and rear axel gears. Wish we could find that.

Transference Ratio

FWIW, for the lead ratio to be positive 2.0% with the R1 tires (using your data above) the transference ratio would need to be about 1.62.

“If” the table has a transposition of a couple digits and the ratio was 1.65 vs 1.56, then the lead would be about 3.7%, certainly a reasonable value/expectation. But that’s a straight out WAG.

 

[GrizBota]

Are we using the right formula?

Check out the formula at this site.

Lead-Lag Ratio

For the R1s that formula yields (98*1.56)/156 = 0.98, which is a 2% lag…hum about the same place we ended up previously.

 

[46Willys]

Are we using the right formula?

Check out the formula at this site.

Lead-Lag Ratio

For the R1s that formula yields (98*1.56)/156 = 0.98, which is a 2% lag…hum about the same place we ended up previously.

Yes, I visited that site also. I think the math is right. The thing I cannot verify is the transference ratio for the L5030. I still find it hard to believe that Kubota designed the ratio this way and that no one has ever discovered the issue. It feels like I am missing something.

 

[46Willys]

Yes, I visited that site also. I think the math is right. The thing I cannot verify is the transference ratio for the L5030. I still find it hard to believe that Kubota designed the ratio this way and that no one has ever discovered the issue. It feels like I am missing something.

I looked through other 50 HP tractors in that database. They all have the same thing.

 

[rbargeron]

Not really any more enlightening on this exact quandary, but in the post below (and in post 20) of that link @rbargeron explains how one could calculate the transference ratio “if” they knew all the tooth counts on the various front and rear axel gears. Wish we could find that.

I didn't find a list, but I found "tooth counts" for my Kubota's by looking at the tractor cutaway drawings in the WSM for the model, and the online factory parts list for that model, which usually includes the tooth count for each gear.

Following the power flow from the engine to the wheels gets you to the overall ratios for front and rear wheels. For the circumference of the tires, I used the common ag tire aspect ratio of .85 height-to-width times two, plus the rim diameter , all times 3.14 which gives the theoretical travel distance per revolution. Comparing those two distances gives the DIFFERENCE to be made up by distortion and slippage at the tire/ground contact patch.

Tire/ground contact is a pretty involved field of study. Our tractors move fairly slowly - imagine what's involved in auto racing. Dick B.

 

[46Willys]

Are we using the right formula?

Check out the formula at this site.

Lead-Lag Ratio

For the R1s that formula yields (98*1.56)/156 = 0.98, which is a 2% lag…hum about the same place we ended up previously.

I contacted my local Kubota dealer and they confirmed that the Axle Ratio for my L5030 is 1.564. So, it looks like Kubota builds tractors with almost 3% (2.92% to be exact) lag. Or, from the calculator: -2.92 lead/lag.

I plan to replace all the tires and go with one size larger on the front.

I appreciate the comments from you guys.

 

[GrizBota]

I contacted my local Kubota dealer and they confirmed that the Axle Ratio for my L5030 is 1.564. So, it looks like Kubota builds tractors with almost 3% (2.92% to be exact) lag. Or, from the calculator: -2.92 lead/lag.

I plan to replace all the tires and go with one size larger on the front.

I appreciate the comments from you guys.

Thanks for the follow up.

Seems odd Kubota would built these tractors with a 3% lag. My SWAG is that there’s something we’re not appreciating about either what to do with Kubota’s numbers, or what else is going on mechanically in the gear sets. Would be interesting if some of the other folks that have tread this ground before us came up with a similar conclusion.

 

[46Willys]

Thanks for the follow up.

Seems odd Kubota would built these tractors with a 3% lag. My SWAG is that there’s something we’re not appreciating about either what to do with Kubota’s numbers, or what else is going on mechanically in the gear sets. Would be interesting if some of the other folks that have tread this ground before us came up with a similar conclusion.

I agree completely. While I have been a gearhead all my life and played with jacked up pickup trucks, I cannot believe I am the first one to discover this issue (if it really is an issue) on my first Kubota tractor. But I can't see what I am missing. I will appreciate the person who educates me before I buy tires.