Tire Size--How important on 4WD?

[npalen]

The B9200 Kubota owner's manual calls for front tires 23x8.50-12 turf for 2WD and 24x8.5-12 for 4WD. Have a couple questions: First, is there enough difference in the rolling radius/circumference of the 23" and 24" tires to cause binding problems with 4WD? Second, is there any way to find out the gear ratio spec between the front and rear wheels on the 4WD?
I remember reading a thread sometime back regarding counting revolutions in a given distance but would rather avoid doing that.
I'm wondering also if the amount of air pressue in the front and rear tires is going to change the ratio enough to stress the 4WD.
Thanks

EDIT: Just noticed this thread so I better do some reading: http://www.tractorbynet.com/forums/showthread.php?t=252361&p=2937378#post2937378

 

[oldnslo]

It is only important IF you use the the Front wheel Assist.

 

[LD1]

On a 4wd, yes it is very important.

I think the rule is about 2% lead for the fronts. Meaning the fronts turn 2% faster. You can get a close idea of the ratio by taking the circumfrence of the fronts and the rears and assume a 2% lead and do the math.

When you have the fronts lagging (going to a smaller tire up front) is when you run into binding issues.

Why do you want to go to a smaller tire anyway???

 

[npalen]

The previous owner had replaced the front turf tires and it has 23x8.50-12's on it now. I suspect that is because the 24x8.50-12's are no longer available? Or, perhaps it had the 23" on it when new? I see that Firestone shows the 24" as discontinued and I don't think Titan/Carlisle show them in their catalog. Could be wrong.
Incidentally, I noticed that Firestone shows the rolling radius of both the 23" and the 24" tires as 10.4". So maybe doesn't make any difference which tire is used. That could certainly vary between brands and tire types. I see, upon further investigation, that Firestone also shows the 23" as discontinued.

23x8.50-12: Firestone Agricultural Tire

 

[art]

The 23 to 24 is not that much difference! We do balance lead lag ratios wih air pressure to get them so they are acceptable. A normal way is to drive on hard surface in fwd and see if it shifts out easily with our having to use the loader to lift the front so to release load on the drive train.

 

[npalen]

On a 4wd, yes it is very important.

I think the rule is about 2% lead for the fronts. Meaning the fronts turn 2% faster. You can get a close idea of the ratio by taking the circumfrence of the fronts and the rears and assume a 2% lead and do the math.

If kubota speced a 24" tire, that was probabally assuming a 2% lead. Going to a 23" tire is about 4% smaller. So that will give you in the ballpark of a 6% lead. IOW, your fronts are trying to spin 6% faster than the rears. While that isnt optimal for tire wear or traction, I doubt it is going to break anything. When you have the fronts lagging (going to a bigger tire up front) is when you run into binding issues.

Why do you want to go to a smaller tire anyway???

I would think that the opposite would be true, that the smaller front tires would increase the lag. Larger tires on the front would increase the lead, or am I missing something

 

[Just Bill]

Read Lead Lag 4wd Tires
This posting explains it very well.

 

[LD1]

You are correct. I had it backwards. Larger tires cover more ground per revolution thus increasing lag.

To the OP, If the rolling radius is listed as being the same, I think you have nothing to worry about. Maybe they just re-classified the tires?????? Cause the sizes listed arent always true numbers. Case in point, both the 23 and 24" tires you mention list a rolling radius of 10.4". Which would effectivally make them both a 21" tire right?

I went back and edited my first post too. That way incase someone reads only the first few posts, they wont leave here mis-informed.

Thanks for looking out and correcting me.:thumbsup: I must have had a blonde moment:laughing:

 

[SPYDERLK]

You are correct. I had it backwards. Larger tires cover more ground per revolution thus increasing lag. ... :confused2:

To the OP, If the rolling radius is listed as being the same, I think you have nothing to worry about. Maybe they just re-classified the tires?????? Cause the sizes listed arent always true numbers. Case in point, both the 23 and 24" tires you mention list a rolling radius of 10.4". Which would effectivally make them both a 21" tire right?

I went back and edited my first post too. That way incase someone reads only the first few posts, they wont leave here mis-informed.

Thanks for looking out and correcting me.:thumbsup: I must have had a blonde moment:laughing:

:confused3:
larry

 

[LD1]

:confused3:
larry

One of them days:confused2: This is a perfect example of one of them times where you should listen to what I mean and NOT what I say (type):laughing:

With everyone's help, I'll get it right sooner or later right:thumbsup: