Tire pressures...again!

[wolfe10]

Originally Posted by Tireman9

I have also talked with Eric at TecnoRV about ambient not being any specific temperature. He seemed to understand the issue. Don't know if/when he will update his video.


Pressure is really simple.
Pressure shown in the tables is the minimum the tire needs to support the stated load when the tires are "cold". "Cold" means the tires are not warmed up from being driven on or in direct Sunlight for the preceding 2 - 3 hours. With the exception of people who are checking pressure indoors with either heat or A/C, this "COLD" means at the Ambient temperature, which is the prevailing air temperature. So the only correct time to check air pressure is when the tire is at the outdoor air temperature, before you start driving and before it gets warmed up by the Sun..


Don't know how to make this clearer.

100% CORRECT!


And once set, use a TPMS to monitor PSI so you will know if that board with a nail you just drove over talked the tire into letting its air out BEFORE it damages the tire.

[vlamgat]

Originally Posted by Tireman9

Ambient IS NOT 70°F. I have contacted the author and publisher of that incorrect information.

Ambient is actually 20 deg C as set out by ISA and there is also an ambient air pressure of 1015 mb if I recall correctly. Tires are not an exact science, very far from it so Michelin (in particular) because of its aerospace and racing product as well as the LT law suit, has been more particular in referencing ambient as it does have a considerable effect with respect to relative load. The company says but hardly expects its customers to conform, that the load rating is at 20 deg C which because so many of us have not been able (nor should we) to detect any difference between 20 deg C or 30 deg C; or for that matter 70 deg F or 90 deg F we have been able to "get away" with inflating to the level we desire at any temperature ambient before departing. Chasing 3 or 4 psi for the sake of a temperature change with gauges of dubious accuracy, is something that would be very difficult for a tire manufacturer to require even though they do so for aerospace and racing.

So as has been pointed out so many time: make sure the tire is not underinflated for the load at whatever temperature exists at the coolest ambient you are likely to encounter that day. If that pressure for that load produces a harsh ride, take a few pounds out as in 3-5, no more especially if you are over inflating by10% or some other factor. You should probably not inflate to less than 75% of the max stated pressure for the max load, whatever the load or ambient in order to maintain bead integrity but when I asked the Michelin technicians where they got this from, their answers were all over the place. Essentially a combination of detected pressure to observed test blow outs on a dynamometer that showed a tire being considerably more stable when failing at pressures over 75% of the maximum load as compared to pressure below this level. But its not backed by any science and the French guys said they see much more tire stability in failures of larger tires than smaller ones irrespective of pressure.

I have a Michelin, Goodyear and Bridgestone tire distributor and Wheel & Brake Shop so get to talk to these people regularly as to why & how and the differences between my race, passenger, truck, trailer, RV small; 18 wheel and aircraft tires. I am amazed at how little testing goes into things non aerospace and race. Largely done they way they were done before; tested on a dyno; tested on the road - and if no problems - go into production. Not a lot of record keeping or destruction testing as is done with aerospace where destruction testing is performed in ambients from -40 to 140 F at density altitudes from -1000 feet to over 15,000.

[757driver]

Originally Posted by vlamgat

Ambient is actually 20 deg C as set out by ISA and there is also an ambient air pressure of 1015 mb if I recall correctly. Tires are not an exact science, very far from it so Michelin (in particular) because of its aerospace and racing product as well as the LT law suit, has been more particular in referencing ambient as it does have a considerable effect with respect to relative load. The company says but hardly expects its customers to conform, that the load rating is at 20 deg C which because so many of us have not been able (nor should we) to detect any difference between 20 deg C or 30 deg C; or for that matter 70 deg F or 90 deg F we have been able to "get away" with inflating to the level we desire at any temperature ambient before departing. Chasing 3 or 4 psi for the sake of a temperature change with gauges of dubious accuracy, is something that would be very difficult for a tire manufacturer to require even though they do so for aerospace and racing.

So as has been pointed out so many time: make sure the tire is not underinflated for the load at whatever temperature exists at the coolest ambient you are likely to encounter that day. If that pressure for that load produces a harsh ride, take a few pounds out as in 3-5, no more especially if you are over inflating by10% or some other factor. You should probably not inflate to less than 75% of the max stated pressure for the max load, whatever the load or ambient in order to maintain bead integrity but when I asked the Michelin technicians where they got this from, their answers were all over the place. Essentially a combination of detected pressure to observed test blow outs on a dynamometer that showed a tire being considerably more stable when failing at pressures over 75% of the maximum load as compared to pressure below this level. But its not backed by any science and the French guys said they see much more tire stability in failures of larger tires than smaller ones irrespective of pressure.

I have a Michelin, Goodyear and Bridgestone tire distributor and Wheel & Brake Shop so get to talk to these people regularly as to why & how and the differences between my race, passenger, truck, trailer, RV small; 18 wheel and aircraft tires. I am amazed at how little testing goes into things non aerospace and race. Largely done they way they were done before; tested on a dyno; tested on the road - and if no problems - go into production. Not a lot of record keeping or destruction testing as is done with aerospace where destruction testing is performed in ambients from -40 to 140 F at density altitudes from -1000 feet to over 15,000.

OMG this is getting ridiculous!! Ambient temperature is the air temperature surrounding an object such as a tire, it has nothing to do with a supposed standard.

Also, if you are going to quote ICAO ISA please get it right. Standard temperature at sea level is 15C (59F) and standard pressure is 1013.2 millibar or 29.92” Hg.

[RM Art]

From decades of heavy load carrying on flatbed trailers, in box trucks, in dump trucks, in 1 ton and 1.5 ton pickups, towing boat trailers... IMO - and, as I've done for 5 decades:

For heavy loads, RV's included, I recommend tire inflation to be at 100% of manufacturers sidewall embossed pressure limit. Time to check pressure is early in morning after tires are completely cool. The 100% pressure limit should be set at whatever the ambient temperature is wherever you are at.

If during one [1] day you are to travel from one extreme temperature area to another extreme temperature area [say 10f to 110f - or 110f to 10f] then the pressure in tires may need "sensible" adjustment during that day. Once you spend the night in the either greatly increased or decreased temperature condition... the next morning, when tires are heated or cooled to that locations ambient temp, I would then set my tires' to the 100% inflation pressure recommended by the manufacturer - and, usually imposed on the side wall.

common sence usually rules!!

Your experiences may differ and you may experience different results than me. But - That is the way I've been doing it for 50 years!

[drwaynesmith]

Fill the 6 rear tires of an Entegra to max load pressure and it would be bouncing down the highway like a basketball. Am smiling just thinking about what the passengers would be thinking.

Originally Posted by RM Art

From decades of heavy load carrying on flatbed trailers, in box trucks, in dump trucks, in 1 ton and 1.5 ton pickups, towing boat trailers... IMO - and, as I've done for 5 decades:

For heavy loads, RV's included, I recommend tire inflation to be at 100% of manufacturers sidewall embossed pressure limit. Time to check pressure is early in morning after tires are completely cool. The 100% pressure limit should be set at whatever the ambient temperature is wherever you are at.

If during one [1] day you are to travel from one extreme temperature area to another extreme temperature area [say 10f to 110f - or 110f to 10f] then the pressure in tires may need "sensible" adjustment during that day. Once you spend the night in the either greatly increased or decreased temperature condition... the next morning, when tires are heated or cooled to that locations ambient temp, I would then set my tires' to the 100% inflation pressure recommended by the manufacturer - and, usually imposed on the side wall.

common sence usually rules!!

Your experiences may differ and you may experience different results than me. But - That is the way I've been doing it for 50 years!

[RM Art]

Originally Posted by drwaynesmith

Fill the 6 rear tires of an Entegra to max load pressure and it would be bouncing down the highway like a basketball. Am smiling just thinking about what the passengers would be thinking.

So... what pressure do you run them at and what is max pressure on your tire's sidewall?

You ever tried max pressure? Or, are you simply conjecturing that your Entegra "... would be bouncing down the highway like a basketball."

[Gary.Jones]

I've stopped reading this thread.. Anything important to know and understand was written many pages of posts ago....

Gary

[drwaynesmith]

The rears are Michelin 315/80r22. Max load pressure is 130psi. Have a Cornerstone, like most, run them at 85 psi. Based on load, should only be 80 psi, but Spartan recommends no lower than 85 psi to keep the tires firmly attached to the rims. No, have never tried running them at 130 psi!

Your good experience using max inflation pressure is probably based on vehicles where they maxed out the tires for the load they carry. That's the case for boat trailers, box trucks, etc. On an Entegra coach the rear tires are not the limiting factor, the axles are, the tires can carry way more weight than the axles ever could. On the lower end Entegra's of old the front tires were maxed out, but the rears have never been. On the Cornerstone's they're riding on the edge of minimum inflation. Max inflation would definitely have them bouncing down the road.

Originally Posted by RM Art

So... what pressure do you run them at and what is max pressure on your tire's sidewall?

You ever tried max pressure? Or, are you simply conjecturing that your Entegra "... would be bouncing down the highway like a basketball."

[drwaynesmith]

You've clearly not stopped reading this thread. Or editorializing.

Originally Posted by Gary.Jones

I've stopped reading this thread.. Anything important to know and understand was written many pages of posts ago....

Gary

[richard5933]

Originally Posted by RM Art

...For heavy loads, RV's included, I recommend tire inflation to be at 100% of manufacturers sidewall embossed pressure limit...

Your experiences may differ and you may experience different results than me. But - That is the way I've been doing it for 50 years!

Not all RVs are "heavy loads". The tires on my coach, which are the correct size and load rating, and yet they can carry 30% more weight than I currently have on the coach. Coach currently weighs 30,000 lbs and tires max out at over 41,000 lbs.

The semi I drove as a company driver also had tires capable of far more than our 80,000 max. We ran at 105 psi all around - plenty (including a safety buffer) for the load but still far below the 120 psi max on the sidewall.

Originally Posted by RM Art

So... what pressure do you run them at and what is max pressure on your tire's sidewall?

You ever tried max pressure? Or, are you simply conjecturing that your Entegra "... would be bouncing down the highway like a basketball."

I've tried the max on my coach. It road like a train on rails and did in fact bounce down the road like a basketball - a basketball with an angry player bouncing it. I can't speak for an Entegra but assume that the results in any air ride coach will be about the same - too much pressure will result in a harsh ride and poorer handling.

At the proper inflation my coach (with air ride all around) rides and handles great. With max pressure in the tires it was hard to control and was all over the road.

I have to ask - have you ever tried the proper inflation in your tires based on load & inflation tables? How did it ride/handle?

It's good that your method works for you, but it's not the industry standard and it's not the recommendation of the tire experts.

[drwaynesmith]

Now that is funny. You are a brave man.

Originally Posted by richard5933

I've tried the max on my coach. It road like a train on rails and did in fact bounce down the road like a basketball - a basketball with an angry player bouncing it. I can't speak for an Entegra but assume that the results in any air ride coach will be about the same - too much pressure will result in a harsh ride and poorer handling.

At the proper inflation my coach (with air ride all around) rides and handles great. With max pressure in the tires it was hard to control and was all over the road.

I have to ask - have you ever tried the proper inflation in your tires based on load & inflation tables? How did it ride/handle?

It's good that your method works for you, but it's not the industry standard and it's not the recommendation of the tire experts.

[RVPioneer]

It makes one wonder, why are there load and inflation charts? Maybe they’re on to something.

Information or ignorance, we are free to choose.

[richard5933]

Originally Posted by drwaynesmith

Now that is funny. You are a brave man.

It was a short ride - just long enough to warm up the engine a couple of years ago. We fill the tires to the sidewall max when we park for the winter, and I needed to get the engine warmed up to do some last minute maintenance. Would never want to make a habit of driving with the tires like that - way to harsh a ride and too difficult to handle.

[KanzKran]

I’m at 40 psi on the drive axle, and 48 psi on the steer, based on 110% of the measured axle weights and the inflation table values for these tires. Minimum pressure for maximum load per the sidewall numbers is 80 psi.

I don’t even know if my aluminium wheels can handle that much pressure. And don’t care, as they’ll never see it.