TIRES

[maddog2020]

I have a 2009 JD 4720. The rear tires are shot. They are R4 s. I replaced the front tires last year wit factory size 10x16.5. The rears are 17.5x24. I would like to replace them with 19.5x24s. I know they will fit they are only about 3 inches taller. My question is will this be a problem when tractor is in 4wd. I noticed same size tires tire vary a couple inches any from manufacture to manufacture

 

[dodge man]

I’d say three inches taller is to much.

 

[RayIN]

That larger rear diameter will ruin the front diff. if the fronts are the OEM size. The front tires will always be pushed when in 4WD

 

[maddog2020]

So id i decided to go with the larger rear dire what size would i need to put on front. Is there a chart a formula to figure that out?

 

[dieselscout80]

You want the fronts to turn slightly faster than the rear tires (called lead IIRC) and going larger on the rear will reverse that and not work.

That said look at the correct front to match the 19.5 tires. On the NH TC series the ones with 19.5 rear use a larger 12.5x16.5 front tire.

Maybe JD has an another tractor with them.

 

[scootr]

Curious why you want to change the tire size ...

 

[RayIN]

So id i decided to go with the larger rear dire what size would i need to put on front. Is there a chart a formula to figure that out?

Measure the OD of both front and rear tires(new) that came OEM, measure exactly,with tires off the ground; the more precise the better the outcome.
Then apply that differential ratio to prospective new tires.

 

[hayden]

Measure the OD of both front and rear tires(new) that came OEM, measure exactly,with tires off the ground; the more precise the better the outcome.
Then apply that differential ratio to prospective new tires.

Or look up the RC (rolling circumference) of the tire, which is effective circumference taking into account expected tire bulge.

 

[skipmarcy]

My Mahindra came with 10-16.5 on front and 17.4-24 on the rear (R4s) and I was snapping front axles quite a bit with the heavy loader work I did. After going back & forth with them and busting a front diff. I had to repair out of warranty, they told me the tractor should have had 16.9-24 on the rears from the factory. I had to purchase the tires myself and sold the originals to a guy with a backhoe. The axle breaking dropped to virtually none after the tire change. In later years I also went to 12-16.5 for my fronts and has been doing well for quite a few years. Lack about 3 hrs. of hitting 3300 hrs. on the clock.

 

[John0829]

If you put larger tires on the rear then you are changing the ratio between the front and rear... something is going to break and that something will be expense parts. If and I do mean IF you really want larger tires on the back then change to fronts to larger ones as well.

But what is it you expect to gain from the larger tires?

 

[maddog2020]

The John Deere 4066r which is the new equivalent to the 4720 is available with the larger 19.5x24. Just thought if I was going to replace the tires I would go with the larger ones. Probably wont gain anything other than to have bigger tires.

 

[RayIN]

Or look up the RC (rolling circumference) of the tire, which is effective circumference taking into account expected tire bulge.

Would that not be entirely dependent on inflation pressure?

 

[hayden]

Would that not be entirely dependent on inflation pressure?

Yes, and I expect it's based on the recommended pressure based on carrying weight. Measuring the diameter with a tape will depend on pressure as well.

 

[sandman2234]

Put a mark on the tire at the bottom of the circle and mark the ground at that point, then drive it forward till the mark is in the same spot and mark the ground again. Measure between those marks on the ground an you will have the rolling circumference.
David from jax

 

[CobyRupert]

Knowing the actual rolling circumference is the best way to know how you will be changing the tire speed (for a given gear, and the ratio with the front tires when in 4wd). If the tires are 3” taller the most the circumference can change is 3(pi) inches, or about 9.42 inches, or less.

…but why are the tires taller? Wear? Aren’t new just wider?

 

[dodge man]

Taller tires are usually considered better are’t they? Better traction? Otherwise big ag tractors would be running smaller tires. I went from a Kubota BX to a JD 2025r instead of a 1025r for the bigger tires. In the OP’s case it might not be worth the effort and expense to go bigger but I understand why he might want to.

 

[jigs_n_fixtures]

On industrial equipment with 4wd, they say not to have the diameter of the tires vary by more than 3%.

Going to a taller tire decreases the power at the tire adhesion point. Because the leverage from the center of the wheel to the adhesion patch is longer.

 

[Jaygyver]

What I did when Firestone stopped making my JD 770 R1 front tire size was to go to their website and miraculously found the rolling diameter in one of their white papers. My front tires were baby butt smooth and the rears were still around 60%.
I found some that were close but were still a couple of inches taller but made sure not to use 4x on the pavement or when not needed, then about 6 months later found some that were almost identical.
I didn't do a lot of bucket work but did definitely fill them to the max or more to save trips across the property.
It's funny, I never had a flat tire on the JD in the 27 years I've owned it even with the smooth tires and I basically used it in the pucker brush as a dozer, burned anything and everything in the fire pit, but within a year of buying the new LS I got a front tire flat. A nail in the tread part of the tire even.

 

[Highlandr]

That larger rear diameter will ruin the front diff. if the fronts are the OEM size. The front tires will always be pushed when in 4WD

Yep.

When I bought the NH TC33 (used) the front turf tires had been replaced with used R4s. Little did I know then that the front tires were smaller diameter than OEM/spec. When driving across the concrete pad in front of the garage the front tires left black marks and they pushed gravel. Until I replaced all the tires I used 4WD only when necessary.