Tire Tread and Gear Ratios

[RobertN]

Not sure about your application, but when I switched my old Kubota B8200 from R3 turf to R4, the rim size was different was different for turf vs R4. I looked at R1 and the rim size for the factory spec tire was a different size rim too(R1 was narrower tire and rim front and rear).

And, all of those setups varied in height, so matching tires and rims had to be right or else the overall gear ratio would be wrong and cause front end wear.

 

[IH3444]

Alliance 550 Multiuse R-4 Tires | Farm Tire Warehouse

Alliance 550 Multiuse R-4 Tires. Agricultural R-4 Industrial Tractor/Construction Radial tire Developed for Specific Applications on Industrial Tractors, Backhoe Loaders, Municipality and Industrial Tractors dealing mostly with Transport on Hard Surfaces and Compact Construction Machinery.

www.farmtirewarehouse.com

 

[oakhilltop]

It sounds like replacing all four tires of any tread pattern with four new tires of the same size of a different tread pattern may not always work. And maybe even the same tread pattern could be a problem. This seems really f'd up to me. Kinda like bicycle tires where a 26 x 1.75" tire and a 26 x 1 3/4" tire are different sizes.

But it's very possible that I'm still not getting it.

 

[dadohead]

You can figure the ratio by knowing rolling circumference of both front and rear tires then applying the axle ratio the manufacturer uses.
The equation: rc of front x ar, divided by rc of rears.
This will fall anywhere between 1-5% depending on manufacturer.

When I designed tractors at Deere... we'd use SLR: static loaded radius. In later years it got more difficult to get precise numbers from the manufacturers on their tires. Suppliers moving out of the segment? Production moving to low cost countries?

 

[LouNY]

When I designed tractors at Deere... we'd use SLR: static loaded radius. In later years it got more difficult to get precise numbers from the manufacturers on their tires. Suppliers moving out of the segment? Production moving to low cost countries?

The SLR is what I still look for when looking at tires, I have always been surprised that the SLR and the rolling circumference (RC) almost never agrees with the (2πr) with the loaded rolling circumference always being a bit over the loaded radius x 2 x pi., but always a long way from the diameter x pi.

which is what I can change with tire pressure.

 

[SPYDERLK]

The SLR is what I still look for when looking at tires, I have always been surprised that the SLR and the rolling circumference (RC) almost never agrees with the (2πr) with the loaded rolling circumference always being a bit over the loaded radius x 2 x pi., but always a long way from the diameter x pi.

which is what I can change with tire pressure.

Growth of squirm losses within the contact patch.

 

[dadohead]

With the center of the rear axle being the origin (0,0,0) of the tractor model, the SLR determines the "ground plane".... all the lift systems relate to ground. Pretty big deal getting a good SLR number.

"Grown tire" is another number the tire manufacturers used to provide... not so much in recent years. Tires, of course, grow with age. Need to know how much to keep fenders, belly mowers, etc out of their path!

 

[rScotty]

Knowing the brand and series of tires the manufacture tables should get you the Overall diameter and hopefully the loaded radius or circumference. With those numbers the alternative tires can be located by those numbers, or with a bit more math the ratio of the front to rear tires can be calculated and all the other tires sizes compared looking for the same ratio. Yes the tires and possibly the rims can be swapped around at the dealers, one issue that could rear it's ugly head would be warranty work if something in the drivetrain fails during the warranty period.https://www.tractorbynet.com/forums/threads/tire-tread-and-gear-ratios.592608/reply?quote=7212057

That's right, except that the only number you really want to compare is the "Loaded Rolling Circumference" - sometmes known as just "LRC". Because a loaded tire is no longer a round shape with the axle in the middle, the average person can't get there by doing a simple calculation from radius or diameter. LRC is easy to measure; hard to calculate. Let the manufacturer measure it.

The good news is that some tire manufactures are now have an app on their website which allows you to choose any of their tire F/R pairs and it will report the LRC Lead/Lag ratio between those tires. Your tractor tire salesman ought to know that....but it's a newish app so he may not.

Then all you need to do is to look up your tractor's front to rear internal transmission ratio in the specs in the shop manual and choose tires to match. If the ratio is not in the specs any tractor mechanic can measure it.

Sometimes the tractor manufacturer will change that internal transmission ratio depending on what tires a buyer orders on a new tractor. It's a job best done when the tractor is being built.

I've done this several times now. Tire swaps can be a lot of work for what you get and often involves at least one set of new front or rear rims. I would recommend going with the manufacturer recomendation.
rScotty

 

[rScotty]

With the center of the rear axle being the origin (0,0,0) of the tractor model, the SLR determines the "ground plane".... all the lift systems relate to ground. Pretty big deal getting a good SLR number.

"Grown tire" is another number the tire manufacturers used to provide... not so much in recent years. Tires, of course, grow with age. Need to know how much to keep fenders, belly mowers, etc out of their path!

The reason why SLR doesn't work with simple 2 pi calculations is beause when a tire is loaded the axle is no longer in the center of a circle. The SLR is shorter between the axle and ground than it is between the axle and top of the tire.
So trying to get from Loaded Radius to Calculate Loaded Circumference is difficult because the shape is not round. Measuring either one directly on the grond is easy.