Tire psi over chart values

[Milford 47]

Originally Posted by RVPioneer

What, exactly, is picky about correcting a false statement?

Would you like to clarify the false statement with your facts? Please proceed

[Milford 47]

Originally Posted by stewgrady

What would the consequences be of running tires over the psi chart values but not over the max pressure on the tire? Is there a problem with running tires at the max tire pressure and the coach being at a lesser weight than Max?

This thread started out pretty simply with a straight forward and good question from a person wanting to do the right thing and be safe in doing so

There is absolutely nothing wrong with running name plate sidewall PSIG on a Coach/Truck/Car if the tires and wheels installed are per the OEM and were selected to cover the possible loading of such vehicle

Sure you can optimize and lower psig and many do so, is there a danger in not doing that, HECK NO!

[RVPioneer]

Originally Posted by Milford 47

The vast majority of tires fail due to under inflation

Here’s the false statement.

Under inflation is one of the common causes of tire failures. It is not the cause of a majority of failures. You actually agreed with that correction.

[Sonic]

A few posts have touched on this, but isn't it all relative?
Tire Rack says a tire is overinflated at more than 20% of the recommended (aka minimum) PSI.
My coach has been weighed at each wheel position and the rears and Tag come out to 75 PSI. I am surely not going to run at them at 120 PSI (60% higher than the manufacturer recommends) without negative effects.
I could get away with it on the steer tires recommended at 95 PSI but even that would exceed 20% over.
I see this issue as being relative to how the tires are matched to the actual weight of the coach vs. a standard yes/no answer.

[RVPioneer]

Originally Posted by Sonic

A few posts have touched on this, but isn't it all relative?
Tire Rack says a tire is overinflated at more than 20% of the recommended (aka minimum) PSI.
My coach has been weighed at each wheel position and the rears and Tag come out to 75 PSI. I am surely not going to run at them at 120 PSI (60% higher than the manufacturer recommends) without negative effects.
I could get away with it on the steer tires recommended at 95 PSI but even that would exceed 20% over.
I see this issue as being relative to how the tires are matched to the actual weight of the coach vs. a standard yes/no answer.

Exactly. Thank you.

What may seem like a simple question that deserves a simple answer is not always the case. Particularly in this situation where we have absolutely no information on the coach.

It’s like asking “How long does it take a plane to fly from point A to point B? We don’t know the plane or the locations of either point.

Our situation is similar to yours. If we blindly ran at max psi, we’d be 26-33% above the recommended pressure for our weight. Suggesting that someone will be better off, or safer or won’t create a dangerous situation by just inflating to max and hitting the road is providing advise based on a complete lack of information.

Weigh the coach and check the chart. Whatever pressure you decide to run, it will at least be an informed decision.

[Domo]

Originally Posted by RVPioneer

The Michelin document says that an RV owner needs to know the “fully loaded” weight of their coach in order to determine the correct tire pressure from the chart.

A fully loaded coach is not necessarily a coach at its GVWR. We operate our fully loaded coach at ~3,000lbs below GVWR. There are, what surely must be internet rumors, that indicate some folks operate their fully loaded coaches above the GVWR.

The tire pressures in the chart are the MINIMUM recommended cold pressure for a given load.

I think we're trying to agree - despite our wording.

When I've talked to Michelin (which I have done a few times when reading the lore on these forums) they indicated the recommended chart pressure was where you start the day. It is not minimum, it is where they want the tire to be inflated for the given load before the vehicle has move one mile (in the pdf I've posted earlier).

Their chart instructions and personnel do not refer to the charts as the minimum. They refer to it as the absolute target pressure given the load and tire when setting pressure for the day. Granted, as soon as you drive that pressure goes up - all within their design profile when started at the correct chart pressure.

Am I missing something? Perhaps you have access to documentation I've not seen and this would not be the last time!!!!

As always - the goal is to help provide the best advice and interpretation given our sources of information. And thanks for helping nail this down so that others can remain safe.

[Sonic]

^^ Recommended and minimum are synonymous in this case.
It's the recommended minimum PSI required to support the specified load. Kind of confusing.
In the PDF you posted, minimum is referenced or alluded to in at least a couple of places.
"Checking the load/inflation table below shows that a cold tire pressure of 95 psi will support 5,510 lbs. on a single front tire."
The "will support" is the key, indicating in this example that you should go no lower than 95 PSI.

[Milford 47]

Originally Posted by RVPioneer

Here’s the false statement.

Under inflation is one of the common causes of tire failures. It is not the cause of a majority of failures. You actually agreed with that correction.

Must have been sleepy

Low inflation or low tire pressure is certainly the cause of most tires failing due to the heat build up with either the side wall or tread separating

[Milford 47]

Originally Posted by RVPioneer

Here’s the false statement.

Under inflation is one of the common causes of tire failures. It is not the cause of a majority of failures. You actually agreed with that correction.

So you think over inflation is?

What are the weights on your rig, noticed you don't have a tag and usually they push the limits if loaded fairly heavy

[Milford 47]

Originally Posted by RVPioneer

Here’s the false statement.

Under inflation is one of the common causes of tire failures. It is not the cause of a majority of failures. You actually agreed with that correction.

https://www.tires-easy.com/blog/top-...-tire-failure/

Now if we switch gears and talk about the leading cause of failures due to impact then it becomes sidewall punctures

By far many people fail to properly maintain air in their cars, trucks, motor homes, and so on at the required pressure

Again the tire isn't going to blow up because it is inflated to sidewall psig

Remember the Ford debacle a few years back with the roll overs of the SUV's

Over inflation, I think not

[RVPioneer]

Originally Posted by Milford 47

So you think over inflation is?

What are the weights on your rig, noticed you don't have a tag and usually they push the limits if loaded fairly heavy

No. Did I ever say that over inflation causes most, or a majority, of tire failures?

Let me check. Nope.

Maybe this will help. Most, or a majority, means more then half, or 50%.
Most common is a completely different animal.

Let’s try an example. If there are 12 things that cause obesity, the most common cause may only make up 10-15% of the cases. It could even make up 49% of the cases. The other 11 things would all be a lower percentage than the most common cause. In all likelihood, a number of factors would contribute to a person being obese. In this example we can identify a cause that is the most common factor, however, we cannot identify a single cause that is responsible for most, or a majority of obesity cases.

See the difference?

Our coach has a GVWR of 33K. Fully loaded with 115 gallons of fuel, 107 gallons of water and 42 gallons of propane, it is ~30K and very close to being 1500lbs under on the each axle. It has a 400hp Cummins ISL, a 10K towing capacity and we flat tow a ~5K Jeep.

Any other questions?

[richard5933]

Commercial truck companies do NOT blindly run the max pressure in their tires. They run the appropriate pressure for the max weight they'll be carrying and the tires they use.

For the company I drive for some trucks have inflation stickers marked at 105 and other trucks have different pressures marked.

Why not overinflate?

Poor handling, poor ride quality, refined braking power, and tire wear issues to name a few things.

Your rig, your choice. But, why not follow the advice the manufacturer provides?

[Gordon Dewald]

Originally Posted by Milford 47

Majority of trucks run the sidewall psig to get the maximum life from the tire

I would agree with you but we would both be wrong.

Most trucks run the max because they are carrying the max. Trucks that carry high volume low weight product run at reduced tire pressure in accordance with the charts.

If you run low weight high tire pressure the center of the tire will wear faster than the edges. Once the center is to the wear bars it should be replaced even if the edges still have lots of tread.

Your tires your game. Coaches tires will run out of time long before the tread is worn out even if always inflated to the max.

[yeloduster]

There is quite the talk comparing our MH tire loading vs over the road trucks. While there is no standard that I am aware of for 40' or less motorhomes there is for trucks.

See the attached drawing. Federal law limits GVW to 80000 lbs. There is also a minimum length limit for that weight. See attached drawing for typical 5 axle semi or in other words an eighteen wheeler. Note that front axle is 12000 lbs and all other axles are 17000 lbs for a total of 80000 lbs.

That means that the front tires are loaded to 12000/2=6000 lbs each. The tractor drivers and trailer tires are loaded at 17000/4=4250 lbs each. According to the internet (the internet is always correct!) the most common size on over the road trucks is 295/75R22.5.

Consult the attached chart. Note that the 295/75R2.5 tire requires an inflation of 110 PSI for 6175 lbs. It also shows inflation of about 70 PSI for a 4300 lb load.

The internet seems to agree that most truckers run 110 PSI on 12000 lbs front axles. It also suggests that even though the charts say they should run 70 PSI in the driver and trailer tires they settle on something between 85 and 95 PSI. Seems like truckers may get into the same arguments about tire pressure as we MH drivers do!

So the statement that a max loaded truck ie. 80000 lbs has tires that are at max load is incorrect. As a matter of fact they are well under max load. My MH is closer to max load on my drivers than an 18 wheeler!