Tire pressure (max PSI not shown on sidewall?!)

[AndyD]

3901 with Galaxy Marathoner R4 tires. I cannot find a max PSI listed on the sidewall. The only mention of PSI is to not exceed 35 when mounting. I found a catalog with specs online which I believe shows the max PSI for my fronts (27x8.50-15) as 45. I've been keeping them at 30 based on the sidewall, but what planet am I on where the max PSI is not listed on a tire's sidewall, and you have to go to an online catalog to find it? I'm new to industrial/agricultural tires so is there some universal system for calculating PSI from the data on the sidewall?

Also, what pressures are people using for dirt-only machines where traction is important? Our tractor never leaves our property, which is sloped and frequently muddy, snowy, or icy. Used mainly for moving material in the loader, smoothing areas with the box scraper, and plowing snow with a front blade, with chains for rear tires.

 

[jaxs]

I've never seen a tire that didn't have recommended inflation listed on side wall. Is it possible your tire is designed to preform various tasks by changing inflation and that precludes a standard psi? It's common to see tires on say a backhoe with far greater psi than a similar size on an ag tractor. I encourage you to press mfgr for recommended inflation and if they don't come through, inflate to same psi as ag tires of same size and plies. Yes, plies matter, 4 ply can run at much lower psi than 6-8-10 due to sidewall flex.

 

[jimh406]

Fwiw, there isn't any reason to put maximum pressure in a tractor tire. Many people run too much pressure.

 

[jaxs]

Fwiw, there isn't any reason to put maximum pressure in a tractor tire. Many people run too much pressure.

Very often on light duty trucks where max psi on door jam is for when truck is carrying max load which is seldom if ever for many.

 

[Sammy3700]

I may get corrected for my thoughts but, I have two 3800s one with R4 one R1 same tractor as yours just older R4 tires I run 15 in rear year round so far no problem with slipping in the rim, front 20 when mowing without loader on, loader on I bump the front up to 35 loading dirt and gravel with a 60” bucket.

 

[GreensvilleJay]

I'd love to see pictures of BOTH sides of that tire ! Can't believe the PSI isn't on one or the other.

You should run max PSI in fronts when carrying heavy loads,or you risk blowouts.
There's a minimum,which varies, depending on how the tires were put on.

Several posts about tires coming off the bead, as wheel provides traction, tire stuck in heavy soil and bead is 'broken'.

Wonder if the tractor owner's manual has a chart of PSI / duty listed ??

 

[AndyD]

I posted an update shortly after my first post but it doesn't seem like it is here. I did locate the max Bar on all four tires, inside a small logo of a tire cross-section. Unfortunately, the writing is so small on the fronts that I can't read it. And the max bar on the rears is different than what the online catalogs shows (by 4 PSI).

And to clarify, I'm not looking to put max PSI in any of my tires, but the max PSI rating for any tire is crucial to know.

Talked to the tire shop who does the tires for the Kubota dealer; they recommended 40 in the front, 20 in the rear.

 

[InTheWoods]

...Also, what pressures are people using for dirt-only machines where traction is important?

You might take a look at your tractor Operator's Manual...

 

[chim]

27X8.50-15 6PR C Galaxy Marathoner SS TL | OTRUSA.COM

The Marathoner features Galaxy's Mud Breakers, designed to eject mud from the tread. They deliver the best high traction skid steer characteristics of ...

www.otrusa.com

 

[PaulL]

Good that they have it, annoying that it's unreadable.

I think the logic is that for dirt work, you run the lowest PSI you can without the bead breaking/tire spinning on the rim. That is reasonably low, around 15psi.

For loader work, you need enough in the fronts to not squash them under load. Typically quite a bit more than 15. I'd say 30-ish.

But I'm not sure it's true you need max psi for loader work.

For road work, that's a bit different.

 

[mikester]

 

[GreensvilleJay]

It just HAD to be the INNER tire, of course !!!!

 

[Hydro]

Rear tire air pressure will change with the amount of load on the 3pt hitch -- find the range for your empty and loaded situation.
Drive onto concrete with no load on the rear of the tractor -- stop with a tire lug down -- adjust the air pressure so there is a gap at the outside of the tire lug (between the lug and concrete) , that you can slide your pocket knife into about 1/2" -- This is your unloaded tire pressure.
Now hook the tiller or scraper blade , which ever is heavier . Do the same measurement -- This is your loaded tire pressure .
Write these numbers in your operators book or note book.

Usually people are lazy and will seek a compromise in air pressure to keep from adjusting when they change implements .

You can do the fronts using same procedure

 

[NCL4701]

Also, what pressures are people using for dirt-only machines where traction is important?

R4’s. 40 psi front. 15 psi in loaded rears.

Dealer delivered with 40 in front; good got loader work. They had 35 in loaded rears. Wouldn’t shed red clay mud worth anything, traction was disappointing to say the least, rode like it was on four overinflated basketballs. Reduced rears to 20 psi: noticeable improvement. Reduced to 15 psi, which is where we ran our old 2WD tractors with R1’s: much better. Haven’t run one off a rim. Haven’t spun a rim in one. If 20 psi isn’t giving you the performance you’re looking for, consider trying 15 or something in between.

From a tire perspective, traction on dirt depends on how many, and how much of, the tread bars are in the dirt/tire contact patch. For mud, it also depends on ability to shed mud. Tire flexion is important to both. Too little pressure: rim can spin in tire, bead can break and tire deflate or get pushed off rim sideways. Too much pressure; depending on the specific tire can have as little as one bar on the ground causing poor traction, if inflated tire has a rounded profile it can have less than full width of the bar(s) on the ground, too little impact from bumps and holes absorbed by tire flexion is hard on both machine and operator.