Proper tire inflation

[Poke a Long]

In reading various threads, questions come up about correct tire pressure. Good year has a chart for all tires, if you'd like it here goes; Goodyear RV Tires and then find inflation, these are spec's for all tires.

[Ray,IN]

Keep in mind the figures for load/inflation are the minimum acceptable pressure, not necessarily the optimum. (it's in the fine print)

[Mr_D]

Yep, here's some of the info:

Quote:

From page 2 of the 06/07 Michelin RV Tire Guide: "If you look at the tire's sidewall, you'll see the maximum load capacity allowed for the size tire and load rating, and the minimum cold air inflation needed to carry the maximum load." From page 6 of the GoodYear RV Tire and Care Guide "How much air is enough? The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load."

[FastEagle]

Vehicle manufacturers set recommended (correct) tire pressures. They are found on the vehicle’s tire placard and in it’s owner’s manual. If there are deviations for unusual load requirements your owner’s manual will have the recommendations for those conditions.

Tire manufacturers provide load inflation charts to provide vehicle manufacturers a quick reference for OE tire selection. They are also used by after market tire dealers (mechanics) in their selection of tires that differ in size from a vehicle’s OE tires.

There must always be a recommended (cold) tire pressure to work from. Otherwise, tires with less than 20% of that pressure would always be in danger of being “run flat”. (Tires with a 20% loss of tire pressure from the recommended (cold) pressure requirement are considered to be in a “run flat” condition and will be quickly destroyed).

http://www.safercar.gov/Vehicle+Shop...nd+Load+Limits


FastEagle

[Mr_D]

Your info is for car/light truck tires, I assume we're talking about RV/truck tires on this forum so that's what my info is predicated on.

Quote:

Originally Posted by FastEagle Vehicle manufacturers set recommended (correct) tire pressures. They are found on the vehicle’s tire placard and in it’s owner’s manual. If there are deviations for unusual load requirements your owner’s manual will have the recommendations for those conditions. Tire manufacturers provide load inflation charts to provide vehicle manufacturers a quick reference for OE tire selection. They are also used by after market tire dealers (mechanics) in their selection of tires that differ in size from a vehicle’s OE tires. There must always be a recommended (cold) tire pressure to work from. Otherwise, tires with less than 20% of that pressure would always be in danger of being “run flat”. (Tires with a 20% loss of tire pressure from the recommended (cold) pressure requirement are considered to be in a “run flat” condition and will be quickly destroyed). FastEagle

On an RV the ONLY time that provided pressure info is correct is if you are loaded to the max OR you haven't weighed the rig. Weighing the rig on all "corners" is the ONLY way to come up with the correct pressure.

Quote:

From Michelin, their quick summation of two pages of their Recreational Vehicle Tire Guide: "The amount of air pressure you need to use depends on the weight of your full-loaded vehicle. So, you cannot determine your correct air pressure unless you know your vehicle's actual weights" "A tire that is overinflated for the load that it is carrying will also contribute to a harsh ride, uneven tire wear, and will be more susceptable to impact damage." From Toyo's Recreational Tire Vehicle Guide "The amount of air pressure in a tire determines the load that can be carried safely. Every Toyo Tire will have the maximum load and inflation molded in the sidewall of the tire. THIS LOAD AND INFLATION RATIO SHOULD NEVER BE EXCEEDED SINCE THIS CAN CAUSE HANDLING PROBLEMS, IRREGULAR WEAR, AND COMPONENT FAILURE. The proper amount if air pressure is always determined by the weight of your RV fully loaded. This weight takes into account all liquids, supplies, and passengers. Tires on RV applications are subject to a variety of more severs conditions when compared to automobiles or trucks. Because of many chassis and optional equipment differences, it is possible for an RV to be within its Gross Vehicle Weight Rating (GVWR), but overloaded when taking into consideration the weight if each wheel position. The only way by which you can know the safe load and inflation pressure for your RV is to know the actual weight of each wheel position under actual loaded conditions. Underinflation of a tire can cause poor handling, irregular wear, and decreased fuel economy. It also causes extreme heat build-up within the components of the tire, which can lead to failure. Overinflation of the tire causes deformation of the contact patch resulting in crowning of the center tread. This causes handling problems such as reduced traction, irregular wear, and an increased chance for impact damage." Firestone says: "Find the RECOMMENDED Inflation Pressure Always determine correct tire inflation pressure based on actual loads on the tires. Use the tiremakers’ recommendations (which you will find in load and inflation tables). Never use inflation pressures lower than those printed on the vehicle placard. All tires on both ends of an axle must have the same inflation pressure. If the load on each axle end is so different that different inflation pressures are recommended, use the higher pressure on both ends – or – redistribute load so that the same inflation pressure is recommended for both axle ends."

[FastEagle]

No. My statement about who sets tire pressures is correct across all lines.


Vehicle manufacturers set recommended tire pressures.　
　
If you will research deeply you will find that when retailers use load inflation charts to manipulate tire pressures for RV trailers or motorhomes those pressures cannot be less than the vehicle manufacturer's recommendations (Your Firestone reference points that out). Unless, Replacement tires of another size have been used and a new recommended tire pressure has been set for those tires. The easiest reference to use to understand the resetting of recommended tire pressures is Bridgestone's. It's easy to read and points out all the pitfalls most inexperienced installers will fall into.

FastEagle

[randco]

I run TOYO's, here's what TOYO says,

"What Air Pressure Should Be Used?

The pressure your tires require is determined by the vehicle manufacturer in conjunction
with the tire manufacturer and is based on the vehicle’s gross axle load.
Every vehicle is required by federal regulations to include a tire information placard. This
placard may also be referred to as the tire certification label or federal tire tag. Vehicle
manufacturers are required by federal motor vehicle safety standards (FMVSS) to apply
tires of a suitable size, load range and inflation pressure (as shown on the tire information
placard) that are capable of supporting no less than the gross axle weight rating (GAWR).
Consequently, the vehicle manufacturer’s specified tire inflation pressure is not arbitrary; it is established by federal safety regulations (ref: Code of Federal Regulations 49, 571.120, and Part 567).

Toyo Tire recommends that you maintain your vehicle’s cold tire pressure to the pressure specified on the vehicle tire information placard. Consult the owner’s manual for the placard position. In most cases it is placed on the bulkhead at the left of the driver’s seating position."

[Gary RVRoamer]

Say what you like, but the vehicle manufacturer has to base the tire pressure placard information on some ASSUMED weight of each axle. And we all know about assumptions. To cover their butts legally, RV manufacturers usually assume max axle loads on all axles. Once you KNOW the actual weight, you can use the tire inflation tables for a more finely tuned psi.

Toyo got involved in a nasty lawsuit when an RV manufacturer under-spec'ed the Toyo tire they were installing on their coaches, so Toyo wants to make sure they lay the legal responsibility squarely on the RV manufacturer.

[wa8yxm]

Regarding he pressure on the placard in the vehicle: This is usually the correct pressure for the tires as the vehicle left the factory.. Alas, Once we take delivery we start adding cloths, cosemetics, food, tools, pets, more food, bedding, and so on and so forth, often several thousand pounds of "Stuff" we bolt on Sat dishes, add electronics and more.. The correct pressure is thus changed.

So I can all but guarantee that the pressure on the tag is wrong.

Another pressure that many people mis-read

Maximum pressure xxx PSI

That is not what it says,,, Not even close,, What it says is:
Maximum LOAD of yyyyy pounds at maximum pressure of xxx PSI.

This is the highest pressure the tire is warranted to survive (NOTE: COLD pressure, hot pressure will be much higher) but is it the correct pressure.. Again the odds are nearly certain it's not.

In both cases there are exceptions.. Just very few and far between.

So, how do you find the CORRECT pressure? By use of scales.. You weight the rig. then you go to the Tire Maker's web page (linked to in one case in the original post) and look it up.

NOTE: They recommend "Wheel Weights" (A dual tire is one wheel) so for my 2 axle coach that is 4 weights, RF, LF RR and LR..

Some folks say that all tires on an axle should be same pressure.

I say both halfs of a dual wheel should be same, but the other end of the axle may or may not (Ideally the load is balanced so the pressures Are the same but .. Not always)

Can not find a scale... http://www.rvsafety.com

On the left is a link to a page that links to most major tire companies inflation charts

The "RV Weighing" link used to be on the left but now it is in the banner near the top.

[Clifftall]

Quote:

Originally Posted by wa8yxm Regarding he pressure on the placard in the vehicle: This is usually the correct pressure for the tires as the vehicle left the factory.. Alas, Once we take delivery we start adding cloths, cosemetics, food, tools, pets, more food, bedding, and so on and so forth, often several thousand pounds of "Stuff" we bolt on Sat dishes, add electronics and more.. The correct pressure is thus changed. So I can all but guarantee that the pressure on the tag is wrong.

On my Fleetwood, the tire pressure on the placard is the max cold air pressure for my MH if totally loaded to the 22,000 lb chassis rating. The proper pressure is almost always lower than that unless you are loaded to the max for each axle , but never higher if you are within the chassis weight rating. Therefore, you are correct in stating that the pressure on the "tag " is wrong, however the correct pressure goes down from there not up as you stated.

[wildtoad]

So help me out here... Placard on my Hurricane shows 80psi front, 90psi rear with 6k/10k GAWR ratings. According to the Michelin tire chart the 80psi is about right. Actually I could run 75psi. Where I have a question deals with the rear duals. The chart shows that at 5200 lbs (1/2 the gawr) I could run 65 psi, way less than the 90 psi on the placard. Do these charts assume you will never have a flat? Does anyone think 65 psi is enough air?

[Clifftall]

Quote:

Originally Posted by wildtoad So help me out here... Placard on my Hurricane shows 80psi front, 90psi rear with 6k/10k GAWR ratings. According to the Michelin tire chart the 80psi is about right. Actually I could run 75psi. Where I have a question deals with the rear duals. The chart shows that at 5200 lbs (1/2 the gawr) I could run 65 psi, way less than the 90 psi on the placard. Do these charts assume you will never have a flat? Does anyone think 65 psi is enough air?

Mine says 90 all around. The Michelin chart for my 235/80 22.5 tires for my weight( weighed all four corners ) calls for 75 front and 85 rear.

[USMCRET]

Kinda off topic, but not really...where do you guys get your mohos weighed? Does Flying J have the capability to do four corners? I stopped at a Loves on my last trip and the scales they had were raised and I saw no way to do the four corner weights.

[wa8yxm]

Not at all off topic and already answered in my earlier post for at least one place.
RV Safety, Merritt Island, Florida

Go to the "RV weighing program" link in the banner of links near the top of the page.

You can also go to any commercial FLAT scale.. the CAT scales you find at many truck stops and teh "J" scales at many flying J's are often "Bridge" scales (A bridge scale is raised above the ground) Though these do give good weight info, You can not do side to side.. Just axle.

Find a flat scale, a "segmented' one is best but not absolutly necessary.

Pull fully onto the scale so each axle is one it's own segment if possible, (If you have dual rear axle they can share a segment if they must)

Get the weights and then pull around again so just one side is on the scale and the other side is on the ground.. now you have axle weight, and wheel weight on one side.

Axle - 1 wheel = other wheel

Or .. as noted,, Click the link, Click the link, Click the link and make an appointment, They bring scales to you.