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Old 05-11-2016, 09:33 PM   #15
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Originally Posted by Tireman9 View Post
Load & Inflation tables are available for the major tire companies.
No, they're not. They used to be, but not now. Nor for ordinary P-series and LT tires used on most tow vehicles.

Here is link to Michelin RV applications.
Michelin doesn't publish load/inflation charts for ordinary tires used on most cars, SUVs and pickups. The Michelin RV chart includes only the XPS that comes only in 16" sizes. That's an excellent tire if you happen to need one of the 16" sizes available. But if you want any other Michelin tire for 16" wheels, such as one of the LTX tread patterns, they don't list them because they don't qualify as an all position commercial truck tire. And they also do not include any of the sizes for modern SUVs and pickups with 15" or 17" or 18" inch wheels.

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Old 05-12-2016, 07:36 AM   #16
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Tire inflation pressures always seem to be very confusing to a lot of forum posters.

The Original Equipment (OE) tires set the standard for all subsequent replacements of like or dissimilar sizes. OE tires must fit into the minimum fitment parameters as described in various DOT safety regulations. Size, load capacity and inflation pressures are all selected by the vehicle manufacturer and are considered appropriate for each fitment. FMVSS regulations direct the vehicle manufacturer to set the recommended inflation pressures. Once set they are the minimum standard for that vehicle fitment - under normal circumstances. Any normal deviations will be found in the vehicle owner’s manual.

For this post FMVSS 571.120 is the safety regulation to read. It will have other FMVSS referenced document numbers to read that will tie all the necessary information together for you.

It is important to stress that vehicle manufacturers set recommended tire inflation pressures for all vehicles that are manufactured using FMVSS instructions.

Load inflation charts are a product of the tire industry. They are intended for use by vehicle manufacturers and installers of aftermarket tires. Their purpose is to insure the correct inflation pressures are established and maintained at a safe level in accordance with each applicable application (standard).

A properly inflated tire is one that is inflated to the value displayed on the vehicle’s certification label, tire placard or from information in the vehicle’s owner’s manual and done so under “cold conditions”. An over inflated tire is one that has a cold tire inflation pressure that exceeds the inflation pressure molded into the tire’s sidewall - under normal circumstances. There are provisions that allow ST and LT tires to be inflated 10 psi higher than sidewall pressure but it’s seldom, if ever used. When done the rims/wheels must be approved for the additional pressure.

Tire inflation pressures in between the pressures found on the labels and sidewall pressures are normally used for “plus sized” replacement tires.

I’m not going to go to the load carried scenario. In better than 95% of the time it’s not applicable for RV trailer tires and I personally would never recommend it. Look on the side of the road and see what it does for the truckers.

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Old 05-12-2016, 08:05 AM   #17
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Yes, for trailer application I strongly suggest the tires be set cold to the inflation on the tire sidewall. This will lower the Interply Shear in the tire structure which can lead to early failure (tread separation) if the shear force exceeds the aged strength of the belt package.
This strength decreases with time and decreases faster with time at higher temperature.

If you want to learn more about Interply Shear simply Google
Interply Shear Tires

Motorhomes and other motorized vehicles have different internal stresses. That is why they can use Load Inflation tables and measured loads to establish their minimum inflation levels.
Retired Design & Quality Tire Eng. Read my tire blog RVTireSafety.NET to learn more about RV tires, valves & wheels. Read THIS post on why Tires Fail
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Old 05-12-2016, 08:06 AM   #18
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I do find Goodyear, Bridgestone & Firestone tables for about a dozen LT tires. UNiroyal says they follow Michelin tables.

If you have a specific size you can't find let me know your measured load and I can look up the inflation.

RE Passenger sizes. I would not suggest towing anything much bigger than teardrop trailer with passenger car nor would I run less than the tire max if I were using P-Metric size on a trailer.

I have seen older TRA yearbooks on eBay occasionally for less than $10 and since the numbers do not change then as long as the sizes you are interested in are listed you would be good to go.

Retired Design & Quality Tire Eng. Read my tire blog RVTireSafety.NET to learn more about RV tires, valves & wheels. Read THIS post on why Tires Fail
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