Asked and Answered but need simplification

[kboucher]

I want to make sure and run the right tire pressure to balance safety and a comfortable ride but the Sticky post and all the reading is so convoluted my head is spinning.

Is there a Cliff note version of how much pressure? Do I have to go down and weigh it with all the factors being adhered to? I will do what it takes but man this is confusing.

So my question what tire pressure should I run on my (new to me) 2019 Open Road 36UA - tires being Michelin 255/80R22.5 radial - Sticker on the door reads -

GVW - 26000
Front - 9000 - Cold inflation 100psi
Rear - 17500 - Cold inflation 100psi

Thoughts?

[Podivin]

Until you take it to get weighed, do what it says on the sticker.

[Old-Biscuit]

Originally Posted by Podivin

Until you take it to get weighed, do what it says on the sticker.

YEP^^^^^

Sticker is based on Full Weight

Get CAT Scale weights then you can adjust air pressures for load being carried

[groswald]

Originally Posted by Podivin

Until you take it to get weighed, do what it says on the sticker.

What Podvin said. Until you know exactly what your rig weighs, the only safe course is to inflate to the stickered values.

After you weigh it, in travel trim, you can adjust per the tire manufacturers table.

I weigh our rig at least once early on every trip to ensure we’re still where I think we are.

Regards,

Randy

[Shadow5501]

The 100PSI recommendation is fine, but it’s higher than they really need to be. As everyone notes, a four corner weigh is the best option. But these can be difficult to find.

Let’s look at the Michelin book that specifies the required inflation pressure based on the weight. You can find it here: https://www.michelintruck.com/assets...k_Sept2011.pdf. Page 14 has the RV specification for your 255/80/22.5 tire.

RVs can have uneven weight right versus left by several hundred pounds, so we will take that into account as well.

The front axle is rated for 9,000lbs, so 4,500 each tire. Looking at the top line (single - lbs) in the guide for your tire, an inflation pressure of 90PSI Is sufficient for 4,620lbs. We should perhaps accommodate a 250lbs side-to-side weight difference, so let’s say 92PSI. That is your minimum for the front.

The rear axle is rated for 17,500lbs, so 8,750 for each dual tire. Looking at the 2nd line for your tire, 95PSI is good for 8,820lbs. Probably want to bump that to 97 to accommodate side to side differences.

These are your minimum PSI. Since tires bleed down over time, inflate them a couple PSI above these targets to accommodate bleed down, temperature changes, etc.

If you weigh the rig you might be able to tweak these a little bit lower, which will definitely improve ride comfort while maintaining safety.

[kboucher]

Originally Posted by Shadow5501

The 100PSI recommendation is fine, but it’s higher than they really need to be. As everyone notes, a four corner weigh is the best option. But these can be difficult to find.

Let’s look at the Michelin book that specifies the required inflation pressure based on the weight. You can find it here: https://www.michelintruck.com/assets...k_Sept2011.pdf. Page 14 has the RV specification for your 255/80/22.5 tire.

RVs can have uneven weight right versus left by several hundred pounds, so we will take that into account as well.

The front axle is rated for 9,000lbs, so 4,500 each tire. Looking at the top line (single - lbs) in the guide for your tire, an inflation pressure of 90PSI Is sufficient for 4,620lbs. We should perhaps accommodate a 250lbs side-to-side weight difference, so let’s say 92PSI. That is your minimum for the front.

The rear axle is rated for 17,500lbs, so 8,750 for each dual tire. Looking at the 2nd line for your tire, 95PSI is good for 8,820lbs. Probably want to bump that to 97 to accommodate side to side differences.

These are your minimum PSI. Since tires bleed down over time, inflate them a couple PSI above these targets to accommodate bleed down, temperature changes, etc.

If you weigh the rig you might be able to tweak these a little bit lower, which will definitely improve ride comfort while maintaining safety.

Thanks for the great and simple answer.

[Crasher]

If you want a four position weight check with your State Patrol Vehicle Inspection office. They carry individual scales for spot checking. They came to my WI home and did it for me at no charge. They we glad to help me get the correct pressures.

[jadatis]

Filled your GAWR's , together with loadindex 138/135 L found on google, in my made extra safe calculator
Gave:
front single load, 9000+10% reserve/ 105 psi
Rear dual load , 17500lbs+10% / 111psi ( unrounded 110,16 psi) .

Recomended 100psi is for GAWR with no reserve, and here front kept the same as rear, for easy to remember reason. And read back from american list wich is made with a formula that leads to lower pressure, or higher loadcapacity's then the european calculation, and my calc even higher pressure, and to my conclusions closest to ever to be constructed ideal formula.

Most RV of these Weights are seldom overloaded on the axles, so as long as you did not weigh, this is safe, and if real axleweights, comfort and gripp still good.
Max speed of this tire is 75mph ( L speedrated) , so for comfort and max reserve, you can even go higher, but not allowed on your G load tires ( max-and reference-cold pressure 110 psi)

Disclaimer: if weights and tirespecifications are as I determined, so check it.

[kboucher]

Originally Posted by Crasher

If you want a four-position weight check with your State Patrol Vehicle Inspection office. They carry individual scales for spot-checking. They came to my WI home and did it for me at no charge. They are glad to help me get the correct pressures.

What does a four position weight check mean and do I have to ask for that when I go in?

[wolfe10]

Originally Posted by kboucher

What does a four position weight check mean and do I have to ask for that when I go in?

It means each wheel position weighed individually.


You will need to determine before you go that they do that-- very unlikely that scales designed for OTR trucks can do that.


The reason this is preferable to just weighing each axle is that it would be very unusual in an RV for there to be perfect left/right weight distribution. Units with a galley slide are almost guaranteed to be heavy on that side.


With individual wheel position weights, you take the heavier wheel position on each axle to go to your tire manufacturer's inflation table to determine the MINIMUM PSI for that weight. All tires on that axle get the same PSI based on the heavier wheel position. Add 5-10 PSI to the minimum as a safety reserve.


If all you have is axle weights, ASSUME one side is 15% heavier than the other.

[Camp CA]

Inflate tires to the maximum "cold" pressure stated on the tire sidewall before your trip for best wear and fuel mileage.

[wolfe10]

Originally Posted by Camp CA

Inflate tires to the maximum cold pressure stated on the tire sidewall for best wear and fuel mileage.

While you can do that, if the tires were properly speced such that there was a healthy safety reserve/they are not being asked to carry the max they are rated for, the result will be a HARSH RIDE and perhaps a little more "darty" handling.


As an example, the tires on our coach have a "sidewall PSI" of 120. Weighing and even with a 10 PSI safety reserve from the tire manufacturer's recommended minimum PSI, they are set at 90 PSI. An extra 30 PSI-- no thank you.


Sure, if your chassis/coach builder speced minimum tires, the side wall PSI and needed PSI may be the same. Only the scales will tell you.

[Podivin]

Originally Posted by Camp CA

Inflate tires to the maximum cold pressure stated on the tire sidewall for best wear and fuel mileage.

Which, depending on the rig, is also a great way to get a rough ride and/or poor handling.

When I bought my first RV the tires were inflated to the sidewall pressure. The darned thing wandered all over the road and got 'stuck' in every long-ways crack in the road. When I lowered the inflation to be what the manufacturer suggests in the sticker by the driver's seat the handling was SO much better, and the ride noticeably smooth.

[arcaguy]

Originally Posted by Camp CA

Inflate tires to the maximum "cold" pressure stated on the tire sidewall before your trip for best wear and fuel mileage.

You will not get better wear, the tire will wear in the middle and not on the edges. While it's true you will get better fuel mileage you will also increase your braking distance as you won't have as much traction. The proper air pressure is the proper air pressure, anything more or less is improper air pressure. This is why manufacturers publish inflation tables.