JoeL4330
Platinum Member
I put my two cents worth in the own-op forum where this is also posted.
Tire PSI question...
- Thread starter Podunkadunk
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Egon
Epic Contributor
On my toy tractor I'm not sure what the maximum or minimum is for tire inflation. I just experimented and found 30 psi on the front and 15 psi on the back worked well.
I also noted higher inflation pressures led to less flats.
On the truck the tires run at 80 psi.
I also noted higher inflation pressures led to less flats.
On the truck the tires run at 80 psi.
Billy_S
Gold Member
>>What pressure should I maintain in the front tires?<<
That depends on the amount of weight each tire is expected to carry, subject to the maximum air pressure recommended by the tire manufacturer, as stamped on the sidewall of the tire.
For example, your 420/70-24 will carry a maximum load of 3960 pounds at 20 psi. That same tire will only carry 3640 pounds at 18 psi. If a rear tire is expected to carry more than 3960 pounds, you will need to replace your tires with tires of a higher load carrying capacity, for example, 8 ply tires.
The 10x16.5 will carry a maximum of 3500 pounds at 45 psi. That same tire will only carry 2760 pounds at 30 psi.
What all this boils down to is that to correctly answer your question you would need to weigh each half of the tractor. Generally, I recommend the least amount of air pressure that can handle the load. If you want to weigh the front/rear of your tractor, I would be happy to tell you what air pressure you should run in your tire. Short of that, it is anyone's guess what the proper pressure should be.
That depends on the amount of weight each tire is expected to carry, subject to the maximum air pressure recommended by the tire manufacturer, as stamped on the sidewall of the tire.
For example, your 420/70-24 will carry a maximum load of 3960 pounds at 20 psi. That same tire will only carry 3640 pounds at 18 psi. If a rear tire is expected to carry more than 3960 pounds, you will need to replace your tires with tires of a higher load carrying capacity, for example, 8 ply tires.
The 10x16.5 will carry a maximum of 3500 pounds at 45 psi. That same tire will only carry 2760 pounds at 30 psi.
What all this boils down to is that to correctly answer your question you would need to weigh each half of the tractor. Generally, I recommend the least amount of air pressure that can handle the load. If you want to weigh the front/rear of your tractor, I would be happy to tell you what air pressure you should run in your tire. Short of that, it is anyone's guess what the proper pressure should be.
bigjohnkub
Bronze Member
On a flat surface, the tire treads should be flat against the ground. Maximum traction. On a tubeless front I/C tire used on a loader, go up to prevent popoff during turning with a load . On ag. type we inflate 14 in rear and 28 in front.
JoeL4330
Platinum Member
As I mentioned in the other thread, where you asked the same question:
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As long as the tire is still "pneumatic"--that is, sidewalls flex and rim isn't on the ground, then the number of sq. in. of tire patch on the ground times the psi is the weight on that tire.
Or, conversely, (don't do this) air down the tire until the rims touch, then add some air and check the psi. That's the minimum needed to support the load. If it's less than 20psi, air up to 20 psi in order to make sure the tire won't come off the rim (i.e., break the bead) when turning. If, on the other hand, in order to get the rim off the ground you would need more psi than the max inflation pressure listed on the sidewall, then get bigger tires, or a tire load rating that can support a higher max inflation pressure, or a smaller load. This is all for static load and if you were zipping along uneven ground, you would have to account for dynamic loads (jounce and rebound) which, in fact, flex the sidewalls and the friction of the cords raises the temp and/or the pressure (sometimes dramatically which is one reason a tire "blows out").
So, I suspect what Kubota is tellin' you is that they size the tires and spec the load rating of those tires so that with 20 psi they can carry the max rated load for their loader fully laden, account for dynamic forces, keep the bead intact, and provide some cushion (in the sense of shock absorption) for that boulevard ride.
This is the same logic that your auto manufacturer uses to tell you to put, say, 28 psi in the rear ...unless you are fully loaded (with passengers and golf clubs) and/or drive at sustained high speed, in which case increase it, say, to 32 psi, but stay below the max inflation of, say, 36 psi...
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As long as the tire is still "pneumatic"--that is, sidewalls flex and rim isn't on the ground, then the number of sq. in. of tire patch on the ground times the psi is the weight on that tire.
Or, conversely, (don't do this) air down the tire until the rims touch, then add some air and check the psi. That's the minimum needed to support the load. If it's less than 20psi, air up to 20 psi in order to make sure the tire won't come off the rim (i.e., break the bead) when turning. If, on the other hand, in order to get the rim off the ground you would need more psi than the max inflation pressure listed on the sidewall, then get bigger tires, or a tire load rating that can support a higher max inflation pressure, or a smaller load. This is all for static load and if you were zipping along uneven ground, you would have to account for dynamic loads (jounce and rebound) which, in fact, flex the sidewalls and the friction of the cords raises the temp and/or the pressure (sometimes dramatically which is one reason a tire "blows out").
So, I suspect what Kubota is tellin' you is that they size the tires and spec the load rating of those tires so that with 20 psi they can carry the max rated load for their loader fully laden, account for dynamic forces, keep the bead intact, and provide some cushion (in the sense of shock absorption) for that boulevard ride.
This is the same logic that your auto manufacturer uses to tell you to put, say, 28 psi in the rear ...unless you are fully loaded (with passengers and golf clubs) and/or drive at sustained high speed, in which case increase it, say, to 32 psi, but stay below the max inflation of, say, 36 psi...
texasjohn
Super Member
I had 20PSI in my front tires and all was OK for a while as I experimented with the FEL and moved light stuff. Then, one day, I grabbed hold of 2800 lbs with the FEL and happened to notice that the front tires were REALLY flattened. I immediately raised the pressure to the max on the tire itself... I don't recall right now... maybe 45 to 60 lbs... and have since been extremely glad that I did that.... seems to work fine in all circumstances and I'm ready for a heavy FEL load any time.
In your case, no FEL and just a few front weights, I think you would be fine to leave it at 20PSI.
In your case, no FEL and just a few front weights, I think you would be fine to leave it at 20PSI.
OP
Podunkadunk
Veteran Member
- Joined
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texasjohn said:
My thoughts exactly. I really didn't have a problem with the actual PSI issue...my problem was that Kubota is so vague in the manual. I think the technical writer was half asleep the day he was transcribing that page. You would think something as important as an operator manual would be precise and not ambiguous.
Billy_S
Gold Member
JoeL4330 said:
I can't imagine that is true. I have certainly never heard anything like that, in 29 years in the tire business. Logically it doesn't make sense to me. However, you got my curiousity up enough that I have put in a call to a Goodyear engineer. I will let you know what he has to say.
JoeL4330
Platinum Member
Billy_S: Well, let's see what your friend says ...you have noticed, as did one poster, that if you add a lot more weight the tire "flattens" ...that is, puts a bigger patch on the ground. And, as the poster found out, once the rims are about to touch the ground, the patch size can't get any bigger and it's time to increase the tire pressure (not exceeding the max spec on the sidewall).
You probably know, too, that if you "air down" some, you get more flotation ...because you have fewer psi inside the tire pushin' it out (or, pushin' on your gauge, when you check the tire pressure) ...and, in fact, it's that many psi pushin' on the ground at the contact patch.
You probably know, too, that to carry heavy loads, truck tires are a little bigger, sure, but mostly they run much higher tire pressures, say, 90-100 psi ...they are built stronger, usually more plies, and their load rating, say E, really just means that they can stand that higher psi. As some of us old timers remember, a crude, portable "weigh scale" was to measure the tire patches and multiply by the psi in each tire ...their total is the toal weight of the rig, more or less; the total for each axle is the weight that axle is carrying.
I'll be interested in what your friend says ...I could be wrong, of course
You probably know, too, that if you "air down" some, you get more flotation ...because you have fewer psi inside the tire pushin' it out (or, pushin' on your gauge, when you check the tire pressure) ...and, in fact, it's that many psi pushin' on the ground at the contact patch.
You probably know, too, that to carry heavy loads, truck tires are a little bigger, sure, but mostly they run much higher tire pressures, say, 90-100 psi ...they are built stronger, usually more plies, and their load rating, say E, really just means that they can stand that higher psi. As some of us old timers remember, a crude, portable "weigh scale" was to measure the tire patches and multiply by the psi in each tire ...their total is the toal weight of the rig, more or less; the total for each axle is the weight that axle is carrying.
I'll be interested in what your friend says ...I could be wrong, of course
