QUESTION: any problem adding larger front tires?

[TSO]

Since you have both tractor there now, why not measure the rolling distance on both fronts and verify that they are the same or nearly same. They may be wider but no difference in OD. If they are the same, you could even swap them out between the tractors

The fronts are definitely a different height ... not sure if you viewed the pic yet, but it's pretty apparent. The rears might be close.

 

[GManBart]

The distance covered in one complete revolution of front and rear tires on a Four Wheel Dive vehicle needs to remain as specified when the front drive gears were engineered. Go smaller and the drive line will be in a bind trying to skid the front rubber forward. Go larger and the front rubber will be trying to outpace the rear rubber and result in a bind with opposite forces.

For Example:
3.1416 x Diameter = Circumference
Circumference (rolling distance of one revolution) on a 24" tire is: 75.4"
Circumference on a 26" tire is: 81.7"

Adding 2" to the diameter would result in the tire traveling 6.3" further for each revolution too much for a drive line that requires a fixed ratio of circumference between rears and fronts. Tire width doesn't matter....within reason.

They offer different size rear tires on that machine with the same fronts...17.5Lx24 are an option, which are slightly shorter than the stock 14.9x24. That would change the ratio just as much as keeping the rears stock, and going up in size on the fronts.

Further, what about normal wear on tires? It wouldn't be uncommon for the fronts to wear much quicker for someone doing a lot of FEL work, but there isn't a spec in any manual I've seen stating that you have to replace the front tires when they are worn down beyond a particular size. If this was truly an area of concern, there would be a ratio listed in the owner's manual advising you that driveline damage could occur if you stray outside a certain ratio from front to back. Sure, putting tires that are vastly different on the fronts could be an issue, but something like TSO is talking about isn't drastic.

 

[RDrancher]

As someone stated, switching to larger tires only on the front can bind and damage the drivetrain, even in the dirt. I would switch to 10 ply R4 skid steer tires in the same size. You can even get them wider with a close enough diameter. I replaced my 6 ply Titans with 10 ply and the difference is substantial. Less sidewall flex and less chance of popping a bead. SS tires also have nice thick rim guards.

 

[GManBart]

Rather than theories based off what some guy said, somewhere, on an Internet forum, here's a way to calculate acceptable tire sizes:

Hint, there is a range of sizes that will work, and not cause damage (again, if that wasn't true, normal wear would cause damage).

The concept of front-wheel drive assist

 

[RDrancher]

Rather than theories based off what some guy said, somewhere, on an Internet forum, here's a way to calculate acceptable tire sizes:

Hint, there is a range of sizes that will work, and not cause damage (again, if that wasn't true, normal wear would cause damage).

The concept of front-wheel drive assist

Nice, but a 2" dia. difference will lead to excessive drivetrain wear at the least. My background is in 4wd offroad vehicles, mainly rockcrawling. Matching ring and pinion ratios with the same height tires is important, even in sand. Only in snow can you get away with more because of the slippage. Even sand and mud dragsters using larger tires on the rear change the r&p's to match the difference in tire height and they're basically spinning the entire run. Drive a 4wd truck out in the dirt with 31's on the front and 33's on the rear and you can feel the bind through the steering wheel. It's not internet lore, it's the real deal.

 

[TSO]

So are you suggesting that if I want larger front tires, I need larger rear tires as well?

I believe 16.9x24 us the next industrial size up, but dang those r pricey!

 

[rwork]

At one time, I'd thought about going to larger tires on my R3039H. Dealer said that I could do it, (all four tires / wheels) but at the tune of about $3000, I decided I liked mine just fine, as is !

 

[TSO]

At one time, I'd thought about going to larger tires on my R3039H. Dealer said that I could do it, (all four tires / wheels) but at the tune of about $3000, I decided I liked mine just fine, as is !

yeah I'm fine with the rear tire height; though I would like them to be wider like my LS tires. It's just the fronts is want taller/wider.

 

[GManBart]

Nice, but a 2" dia. difference will lead to excessive drivetrain wear at the least. My background is in 4wd offroad vehicles, mainly rockcrawling. Matching ring and pinion ratios with the same height tires is important, even in sand. Only in snow can you get away with more because of the slippage. Even sand and mud dragsters using larger tires on the rear change the r&p's to match the difference in tire height and they're basically spinning the entire run. Drive a 4wd truck out in the dirt with 31's on the front and 33's on the rear and you can feel the bind through the steering wheel. It's not internet lore, it's the real deal.

Auto, and tractor systems aren't the same...evidence vastly different size tires on tractors to start with.

Did you run the numbers through the formula on the site I linked?

Why would the manufacturer offer two different size (circumference) rear tires with the same fronts if it was outside of the acceptable range?

 

[Recoveryhill]

Auto, and tractor systems aren't the same...evidence vastly different size tires on tractors to start with.

The different size tires, front to rear are accommodated by gearing which compensates to equal the same rolling circumference, i.e. the smaller fronts are geared to rotate faster than the taller rears, a set ratio with no elastic in the works. All four wheel drive systems, even between auto manufacturers differ in the bits and where they are located. No four wheel drive system is different in that the bits need to make sure the distance rolled by both front and rear tires is within a fairly tight specification.

Your link provided information on "lead" relative to rolling circumference for tractor operation in various media, sand, rice paddy, etc. Interesting and new information for me, thanks.

Your assertion that normal wear is OK so why not bigger tires on one end or the other. Normal wear can be understood by the manufacturer and the system is capable of coping with this change when the original ratio of diameters is utilized. Once you inject a new variable, larger tires on one end or the other, into the system, the envelop is subject to changes outside the original design. Example, the rears have two inches of wear to the bar tread which assuming stock fronts, new or not is OK. Add two inches to the front and subtract two inches from the rear and now you are out not two inches but four.

My fronts have a nominal OD of 27", the rears 42". The difference in rolling circumference is 47.1 inches per revolution, a difference taken into account by Kubota engineers when they set the gear ratios. Say I go to new 29" OD fronts and the rears have worn 1" per side and are now 40" OD. The difference in rolling circumference is now 34.5 inches, a 30% change in the numbers the OEM designed into the driveline as opposed to a 15% change if I put new fronts (27") on a tractor with worn rears (40"). That translates into a 100% change in expected rolling differential.

I just hate to see a guy damage his drive line on the assumption that "diameter doesn't really matter", "that much". I would want specific information from the OEM....that's all.

Cheers