Tire Inflation Tables Work

[Crasher]

I just replaced the tires on my motorhome. They were still good with 60% of the original tread depth. They were six years old with 50,000 miles. The drive axle required only 80 psi to carry their load. I should have run 85-90, but felt that was too low and ran 95-100 psi cold. When I measured the depth of those tires, the centers were 9-10/32" and the outer depth was 11-12/32 or 20% more rubber on the outside. A classic case of over inflation when the center wears more than the outer edge. The Michelins were 16/32" when new. In the end, the tires would age out before the tread is below a safe depth, but this proves that with proper weighing and using the load inflation tables tires will perform as designed and wear evenly. The steer tires needed 110 psi for the load and I carried 115. They had even wear across the tread.

[Gary RVRoamer]

Thanks for the real world data. The tire manufacturers and their engineers provide detailed inflation specs, yet many RV owners think they know better for some reason and use more (or less) than the infatuation tables call for..

[Unicorn Driver]

Thanka for posting.

The previous owner of my coach had all tires at 100psi. After a weigh and checking the tables it recommended 90 in the rear and 85 up front. I have not got around to deflating them yet. I am waiting for a cooler day.

[Ivylog]

I run 5psi over the load tables because I’ll keep going in a heavy cross wind (shifts a lot of weight) to the down wind side.

Big MHs tend to be heavy on the front axle requiring larger tires on the front than what’s needed on the rear...especially the tag. I put 315s on the front of my 42’ Dynasty at 7 years instead of the 295s it came with. At 10 years I put 11R22.5s on the rear as I ran 80 psi in the drive and 70 in the tag. Had to increase the drive to all of 90 in the drive and the tag to 75 because of the lower load rating of the 11Rs

Just bought 315s to replace the 4 year old cracking Michelin 295s for the front of my new ride ( NO not Michelin)...will probably keep with 295s on the rear as this rig is heavier. Will put one of the Michelin on the roof as a spare...about all it’s good for.

[Tireman9]

Nothing wrong with running +10% over the inflation needed to support the MEASURED load on your tires.


So what if you got a little extra center wear. You are going to replace RV tires on age anyway.


The key is you want to avoid tire failure by running a bit more inflation than the minimum PLUS running a TPMS Plus doinan annual detailed inspection as I cover in my blog. Tread depth inspection is OK for cars but IMO this would be like going to a Cardiologist and being satisfied with the nurse just taking your temperature.

[DryCreek]

Originally Posted by Tireman9

So what if you got a little extra center wear.

Contact patch is larger when the tire properly aired. Larger contact patch (surface area) gives better traction in all conditions.

[Tireman9]

Originally Posted by DryCreek

Contact patch is larger when the tire properly aired. Larger contact patch (surface area) gives better traction in all conditions.

Except increased inflation will give better steering responsand better fuel economy and possible better durability.

[Crasher]

I think the key is to never let a tire get below the recommended pressure for the load it is carrying. 5% more is where I try to run. It allows for different morning temperatures and altitude changes without having to "chase" the pressure.

[beenthere]

so whats said by some is you may have a failure if you run what the "engineer" says is enough PSI for the load?? For others its the tire placard is ineffective? so what are the engineers paid for?? My thoughts are that if they don't think of or put situations like when turning fast corner and the assumed load doubles from load transfer then what, do I worry cause nobody can agree?? ...no wonder people have to ask so they can blame someone or think I'm gonna blow.
So I'm just gonna fill to max inflation so I get better fuel mileage , and of course better handling, then theres piece of mind cause I filled em good.. oh I forgot the right temp to fill them at.. where I live in june it can be 35 degrees in morning, and that's when everybody says to fill em, morning . then in afternoon its 100 degrees, so what is psi now without moving yet.. or how about when its 80 degrees in morning then cold front goes thru and its only 65 degrees when you leave??.. so what to do, who to listen to??. I could go on but jeez it'll just be responded to with this or that and in the end its still this is what id and this is who knows better and then those who just do...…… now for tire flames

[Tireman9]

Originally Posted by beenthere

so whats said by some is you may have a failure if you run what the "engineer" says is enough PSI for the load?? For others its the tire placard is ineffective? so what are the engineers paid for?? My thoughts are that if they don't think of or put situations like when turning fast corner and the assumed load doubles from load transfer then what, do I worry cause nobody can agree?? ...no wonder people have to ask so they can blame someone or think I'm gonna blow.
So I'm just gonna fill to max inflation so I get better fuel mileage , and of course better handling, then theres piece of mind cause I filled em good.. oh I forgot the right temp to fill them at.. where I live in june it can be 35 degrees in morning, and that's when everybody says to fill em, morning . then in afternoon its 100 degrees, so what is psi now without moving yet.. or how about when its 80 degrees in morning then cold front goes thru and its only 65 degrees when you leave??.. so what to do, who to listen to??. I could go on but jeez it'll just be responded to with this or that and in the end its still this is what id and this is who knows better and then those who just do...…… now for tire flames

There is no "right " temperature. "Cold" means not warmed from the sun and not driven ofthe last 2 to 3 hours. I would not listen to those that are confused about what Ambient temperature means.


You might read THIS post from an engineer with 40 years experience designing tires for Trucks, cars, pickups and Indy race tires.
You could listen to someone who has driven around a lot and thinks this qualifies him to contradict tire engineers and the US Tire & Rim Association.
You decide.

[Crasher]

Originally Posted by beenthere

so whats said by some is you may have a failure if you run what the "engineer" says is enough PSI for the load?? For others its the tire placard is ineffective? so what are the engineers paid for?? My thoughts are that if they don't think of or put situations like when turning fast corner and the assumed load doubles from load transfer then what, do I worry cause nobody can agree?? ...no wonder people have to ask so they can blame someone or think I'm gonna blow.
So I'm just gonna fill to max inflation so I get better fuel mileage , and of course better handling, then theres piece of mind cause I filled em good.. oh I forgot the right temp to fill them at.. where I live in june it can be 35 degrees in morning, and that's when everybody says to fill em, morning . then in afternoon its 100 degrees, so what is psi now without moving yet.. or how about when its 80 degrees in morning then cold front goes thru and its only 65 degrees when you leave??.. so what to do, who to listen to??. I could go on but jeez it'll just be responded to with this or that and in the end its still this is what id and this is who knows better and then those who just do...…… now for tire flames

No one says you have to listen to any of the suggested methods. It's your coach and your tires. Inflate them to whatever you feel comfortable with. I use the tables for all of my vehicles, but I might be a little Anal that way. They have worked for me for 60 years without a failure due to improper pressure. Each person needs to make their own choices.

[OverDo]

Crasher,
Thanks for the usable info. I try to set the cold (~70 deg. F) temps at 5-10 PSI below the pressure/load table recommendation. All the tires will pick up 10-15 PSI pretty quick and I like the ride and bigger contact patch that a correctly loaded tire gives. Most rubber failures are from high temperature generated from excessive flex (low pressure or overload). The TPMS temperature will always be lower than the actual tread temp. Modern tires are truly a scientific miracle. There will always be arguments but most people don't have a clue as to all of the hoops the tire manufacturers have to go thru to sell a tire in the USA. There is so much real world testing required that costs millions of dollars and most people never know anything or care about as long as the price is the lowest.

[Dav L]

Originally Posted by Ivylog

Will put one of the Michelin on the roof as a spare...about all it’s good for.

Hi, am thinking the same for my MountainAire....so, how do you get it on / off the roof? How do you mount it? Does the weight up there affect any handling (sway?)?

No other cosmetic place I can think of for mine. Can't fit in baggage (too big), and no place underneath.

[Crasher]

Originally Posted by OverDo

Crasher,
Thanks for the usable info. I try to set the cold (~70 deg. F) temps at 5-10 PSI below the pressure/load table recommendation. All the tires will pick up 10-15 PSI pretty quick and I like the ride and bigger contact patch that a correctly .

Sorry, but every tire engineer in the country will tell you to never start out with less than the load tables recommended cold inflation pressure. To do so is asking for serious tire failure. Underinflation is probably the greatest cause of tire failure due to the increased heat generated from excess sidewall flex and general breakdown of the casing. A Michelin tech once told me that if I inflate to the recommended cold pressure for the load, I should not be concerned about the rise in pressure from rolling resistance. The tires are designed to deal with the increased pressure.