Trying to understand tire size and ratios

woolyAcres · Oct 2, 2015

clemsonfor said:
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.

I'm not looking to buy tires. I was just curious about this because those Orange tires showed up in a Craigslist 'Yanmar' alert I haven't deleted since I bought my tractor. My rears aren't great, but they are servicable. I'd like wider tires to improve stability and reduce ground pressure. I don't have a ton of mud but I do/will use the tractor quite a bit in the yard so something with a larger contact patch might reduce wear and tear on a still fragile yard. My first choice would be industrial style tires, but I'm not about to swap rims and tires. Not to mention the Ags on the front of mine are in good shape. The rears may well be original however but they hold air just fine.

For what it's worth, I looked at the link Daryl Green provided in his thread about tires and, at least with the Firestone Super-Trac 23, I found:

Tire Size Rolling circumference (inches)
9.5-24 123
11.2-24 128
12.4-24 135

Based on this, I'd say tires that fit 24" rims don't all have the same outside circumference. Not only are the tires wider they must be 'taller' as well. Maybe I'm mis-reading this?

California · Oct 2, 2015

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

Driving straight, yes. But look at the tire tracks you make on a curve, in snow. The front tires' path has a longer radius than the backs; the front tires go a greater distance to get around the curve. So a + bias is preferable to neutral or negative just from the perspective of distance traveled.

Also - seems to me you want the front to pull the nose to the side when you turn the wheel, so faster helps. The alternative, front slower, would push the front wide on a turn.

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

Bottom line of the chart in post #1: "Velocity ratio of front and rear wheels".

woolyAcres · Oct 3, 2015

California said:
Bottom line of the chart in post #1: "Velocity ratio of front and rear wheels".

Got it. VF/VR = 1.03 -> 3% faster for front.

Are we in agreement that as long as the Front:Rear rolling circumference ratio remains consistent with factory specs, the 4WD system should be okay with it? Not to be silly, but just to illustrate the point, one could put tiny little wheels on the tractor, or Monster-Truck wheels, as long as the ratio is preserved?

California · Oct 3, 2015

Assuming that's a reply to me - Your understanding matches what I think that means. But I don't have any practical experience applying this theoretical stuff. I hope somebody can answer this knowledgeably.

winston1 · Oct 3, 2015

Looked in a 276 repair manual. It states 0% front wheel pre run percent. 6% wear limit.

Looked in a 220/226 repair manual. It states 1 to 4% pre run percent. 0 and 6% wear limit.

So I expect somewhere from 0% to 6% might keep from tearing something up??

woolyAcres · Oct 3, 2015

California said:
Assuming that's a reply to me

At the real risk of being pesky, yes it was but also an open invitation to others. Thanks for your thoughtful responses.

woolyAcres · Oct 3, 2015

winston1 said:
Looked in a 276 repair manual. It states 0% front wheel pre run percent. 6% wear limit.

Looked in a 220/226 repair manual. It states 1 to 4% pre run percent. 0 and 6% wear limit.

So I expect somewhere from 0% to 6% might keep from tearing something up??

Maybe there's a bit more slop in all this after all. There isn't any pavement within a mile of me. My tractor will only ever see gravel, dirt, and mud so possibly getting to within a couple percent of spec would be good enough?

It's mostly academic anyway. I've got other tractor issues to solve before worrying about tires. Thanks to everyone for their input.

clemsonfor · Oct 3, 2015

Your probably right thinking about it I am sure thats true. Like truck tires generally the wider the tire the taller as well (ignoring those tall low profile gangster tires).

Your assumption I would assume correct. Not sure why I did not think of it that way?.

woolyAcres · Oct 4, 2015

woolyAcres said:
Strangely, most other specs I have for this machine, and what are actually mounted on my tractor are 9.5-24 rear Ags.

I was wrong about what was on my tractor. I've got 11.2-24 on the rear of my tractor. I guess I got the 9.5 from the brochures and other material I'd been reading but never actually looked. Mine are Bridgstones, made in Japan. It would surprise me to have 30+ year old tires on this but that's certainly possible. They even have Japanese characters on them (along with english).