Trying to understand tire size and ratios

[woolyAcres]

I've been reading through some of the documents I have (or have been given) on my YM240D. This table about transmission, gears, and tires caught my attention. I'm trying to understand what it says/has to do with replacing my tires (when that time comes). I look at this and conclude that the front:rear wheel ratio for the YM240D with AG 6-14 tires (1947mm circumference) in front and AG 9-24 (3166.32 in the rear) is 1947:3166 =~1:1.62. Strangely, most other specs I have for this machine, and what are actually mounted on my tractor are 9.5-24 rear Ags.

Am I reading this correctly? I guess my question really is "how does one figure out what tire options exist for this tractor".

My fronts are pretty new but my rears are gonna need replacing at some point. I know California has larger wheels (rims and tires) on the rear of his YM240 but since it's only 2WD I don't know if this kind of change is a big deal. From what I've read (mostly here on TBN) with 4WD machines keeping the rolling circumference ratio consistent with manufactures specs is a good idea if you want to keep/use 4WD.

The reason it comes up now (and not when I actually start shopping for new rear tires) is because there's a set of Kubota wheels/rims for sale that piqued my interest. 7-16 front and 12.4-24 (liquid filled) rears. I don't have the money for this now, but I do want to understand it.

Can anyone shed some light on this? Thanks.

 

[George2615]

On 4WD tractors the F/R ratio is important to prevent binding of the gears within the transmission. If your YM240D is only 2WD you wouldn't have to worry about F/R ratio and could run whatever rear tires or tire rim combination will fit the bolt pattern you have. For 4WD you need to keep the ratio close to factory specs. There have been other threads about keeping the F/R ratio close to factory specs (I think I read within 5%) or damage could occur.

 

[woolyAcres]

On 4WD tractors the F/R ratio is important to prevent binding of the gears within the transmission. If your YM240D is only 2WD you don't have to worry about F/R ratio and can run whatever rear tires or tire rim combination will fit the bolt pattern you have.

I figured that was the case for 2WD models. I've got 4WD so it appears this is something to pay attention to.

 

[normde2001]

I've been reading through some of the documents I have (or have been given) on my YM240D. This table about transmission, gears, and tires caught my attention. I'm trying to understand what it says/has to do with replacing my tires (when that time comes). I look at this and conclude that the front:rear wheel ratio for the YM240D with AG 6-14 tires (1947mm circumference) in front and AG 9-24 (3166.32 in the rear) is 1947:3166 =~1:1.62. Strangely, most other specs I have for this machine, and what are actually mounted on my tractor are 9.5-24 rear Ags.

Am I reading this correctly? I guess my question really is "how does one figure out what tire options exist for this tractor".

My fronts are pretty new but my rears are gonna need replacing at some point. I know California has larger wheels (rims and tires) on the rear of his YM240 but since it's only 2WD I don't know if this kind of change is a big deal. From what I've read (mostly here on TBN) with 4WD machines keeping the rolling circumference ratio consistent with manufactures specs is a good idea if you want to keep/use 4WD.

The reason it comes up now (and not when I actually start shopping for new rear tires) is because there's a set of Kubota wheels/rims for sale that piqued my interest. 7-16 front and 12.4-24 (liquid filled) rears. I don't have the money for this now, but I do want to understand it.

Can anyone shed some light on this? Thanks.

See if anyone knows the difference in a 7-16 front and a 7.00-16 front:confused3:

 

[California]

I know California has larger wheels (rims and tires) on the rear of his YM240 but since it's only 2WD I don't know if this kind of change is a big deal.

They are 12.4-24 on Kubota (outer) rims that bolted perfectly to the Yanmar discs (centers), installed by a prior owner. On a 2x4 this is harmless.

I see in your Yanmar gear chart they specify 3% 'lead' in the transmission gearing, ie fronts go 3% farther than rears. I think some lead is needed because steering causes the front to take a wider radius turn than the rears.

But it seems to me that more than 3% lead could cause extreme wear on a high-traction surface; that lead is in effect trying to stretch the tractor to a longer wheelbase and the tires are forced to skid - until something breaks. That's just theory but I wouldn't exceed Yanmar's specs.

I don't think 3% in the transmission gearing is mathematically the same as the ratio of tire diameter, I think you have to consider that the little tires have to make more revolutions to cover the same distance. I'll leave it to some mathematician to figure that one out. I think the model is that the F/R ratio of distance travelled has to stay the same if you buy different tires.

And as Norm points out, 7.00 isn't the same as 7-. Maybe comparing the various manufacturer's tire spec charts will clarify this.

 

[clemsonfor]

My ym240 has 9.5x24s as well as anything i have heard of. you need to keep them the same difference as factory so the drive line does not bind up. that said the tires your looking at should just be wider is all and not taller.

Just curious why are you already looking to swap tires? your have the tube showing? Really deeply cracked? or will he swap that beast of a pto pump for them?

I think if i were you i would focus my cash on getting my loader sorted out. I doubt unless in very steep or very boggy (to float you more) terrain you will see any benefit to the wider tire.

 

[clemsonfor]

.

I don't think 3% in the transmission gearing is mathematically the same as the ratio of tire diameter, I think you have to consider that the little tires have to make more revolutions to cover the same distance. I'll leave it to some mathematician to figure that one out. I think the model is that the F/R ratio of distance travelled has to stay the same if you buy different tires.
.

this is a true statement i beleive

 

[woolyAcres]

I see in your Yanmar gear chart they specify 3% 'lead' in the transmission gearing, ie fronts go 3% farther than rears. I think some lead is needed because steering causes the front to take a wider radius turn than the rears.

In other words, the front are 'pulling' the back along (just a little ~3%)?

 

[woolyAcres]

I see in your Yanmar gear chart they specify 3% 'lead' in the transmission gearing, ie fronts go 3% farther than rears. I think some lead is needed because steering causes the front to take a wider radius turn than the rears.

How did you get 3% from the chart I posted? I'm still missing something....

 

[woolyAcres]

I think the model is that the F/R ratio of distance travelled has to stay the same if you buy different tires.

This is what I'd gathered from reading around (here mostly).

I find it interesting that this model (and other Yanmars as well I don't know) came with several different tire options. I wonder if:
1. they all have the correct ratio
2. they all fall within a 'range' of acceptable
3. internals on these models changed such that the differing tire schemes all met the requirements