Tire Replacement intervals???

[Crasher]

Originally Posted by fottip

And for "Crasher": No, I'm not one of those who "inflates the tires to what is stated on the sidewall regardless of the weight it is carrying".

I own the same "43 QGP" bus as you, and, having been in communication with the Tiffin Chassis Plant Mgr Gary Harris, I use the tire pressures he recommended, and they're different for each of our 3 axles, not "what's stated on the sidewalls".

Glad to hear you don't use the sidewall pressure. Some do without regard to load. Does Gary know what each of your axles weigh? I had a number of conversations with him when he replaced my proportioning valves with manual regulators. After I relayed my findings to him, Tiffin changed how they deal with the drive axle to tag axle weights. There was no mention of tire pressures at that time. It was left to me to inflate according to the weights I sent him. Does he now have a pressure recommendation different than the load inflation chart from Michelin?

[Tireman9]

Originally Posted by slemnah

RU499, as an ASE Master Technician I would strongly recommend that you lower the tire pressures to the recommended pressure or to the pressure weight table recommendations. The tire pressure will increase quite a bit when the tire gets hot and you will be severely overinflated. Please google Motorhome tire inflation. You are putting yourself and others at risk. You have been very lucky If you have a 10y/o tire with max pressure and haven’t had a problem.

Sorry. As an ASE Master Tech you may understand brakes and generators but whoever taught your class on tires did you a diservice.
As a Tire Design Engineer with 40 years experience I would advise that if people are not overloading their tires or running faster than 65 for ST tires or 75 for any other tire in RV application you do not have to worry about the hot tire pressure if the cold pressure is set at a level high enough to support the measured (truck scale) load. You might want to check my profile for info on my RV Tire Safety blog and brush up on your tire knowledge.

[Tireman9]

Originally Posted by Philswrench

If you are going to run max pressure , you should make sure to set your max pressure with the tires hot and carrying the weight you normally carry

As a Tire Design Engineer with 40 years experience I can say that is absolutly the WRONG advice to give out.

Pressure is always the "Cold Inflation Pressure" when discussing load capacity or level to set to.

CIP is measured when the tires are at Ambient temperature. i.e. have not been driven on for at least 2 to 3 hours and have not been in direct sunlight for prior 2 - 3 hours. Best time is in Morning before in sunlight.

[Tireman9]

Lots of opinions but as a Tire design Engineer I would offer the following.

Since rubber "ages" at different rates due to temperature changes it is impossible to provide an exact answer any more than you cannot prediceexactly when the jug of milk will go bad.

However the general advise is.
1. Replace tires when they are 10 years old
2. If you bought the tires new and they were 2 years old or younger at the time of purchase and you NEVER ran them at thlower than the minimum pressure needed to support the measured load on that tire or drove faster than 75 you might stretch to 10 years of use.
3. Starting at 5 years and each year after that you need to have a "complete" tire inspection. This cannot be done by simply walking around the RV and measuring tread depth. I suggest a "Free Spin" tire inspection with bright work lights.
4. If you ever drove on the tire when it had less inflation than the minimum needed to support the measured load on that tire it should be dismounted to include interior inspection.
5. When inspections are done you should get something in writing from the tire company store indicating the tires were judged to be in good condition.

[Breezy2006]

I think it depends on various things, as previous posts have indicated. How many months of outside exposure do you have? Are the tires covered when outside? How many trips and miles do you drive? Inspection is key. 10 years of summer inside storage, 1-2 months per year of outside exposure with covers in long term stays and 8k miles or more per year should get you to 10 years.

[fottip]

Originally Posted by Crasher

Does Gary know what each of your axles weigh? I had a number of conversations with him when he replaced my proportioning valves with manual regulators. After I relayed my findings to him, Tiffin changed how they deal with the drive axle to tag axle weights. There was no mention of tire pressures at that time. It was left to me to inflate according to the weights I sent him. Does he now have a pressure recommendation different than the load inflation chart from Michelin?

I think he does. I tried to make sense of the generic Michelin inflation chart when we bought to coach, and couldn't, which lead me to get in contact with Gary, who was very helpful and forthcoming.

I asked for his recommendations on tire pressures. He asked if I had weighed the coach, and I hadn't. I went to the local scales and weighed it, and provided that info to him. He recommended 110 steer/90 drive/80 tag. At the same time, he recommended that if we needed to come to the Tiffin Service Center in the future, he recommended we have the adjustable tag axle valves installed, but that if we didn't, we'd still be within spec limits.

As it happened, we had occasion to go to the Tiffin Service Center in Dec 2016 for other reasons, and had the tag axle proportioning valve modification done then. The service center job involved weighing the coach to get individual wheel-weights before and after the job, so I had that info available.

Afterwards, I contacted Gary again and asked if I needed to make any changes to his previously-recommended total axle tire presures. Since the work had included weighing each axle at both sides on the Tiffin plant scales, I had that the 6-point info, and provided it to Gary. He said no, keep them at the same pressures I recommended before - 110/90/80.

Note to lurkers: The above data pertains to a 2012 Tiffin Allegro Bus 43QGP. Extrapolate it to any other vehicle at your own risk.

[fottip]

Originally Posted by Tireman9

the general advise is Replace tires when they are 10 years old

Ok, you're the "engineer". I lost a front tire on a 40' Class A at 70mph at about 7-8 years of age. How 'bout some real-world "rubber-on-the-road" experience?

The blowout resulted in repairs costing over $7K and several months downtime, and these were name brand, major market tires, not some Asian-knockoffs. I learned a hard lesson from that experience, one that taught me that trying to extend the life of RV tires to "10 years", or some such fantasy time period, is false economy at best, and any advice to try to keep them in service that long is inviting expensive trouble.

YOU run them 10 years. I run them 5 - not a day more. YMMV

And good luck with that.

[Crasher]

Originally Posted by fottip

110/90/80.

Those are the same pressures I arrived at using Michelin's load chart which is probably where Gary got his numbers. However, I added 5 psi to the steer tires which keeps them at or above the minimum 110 psi cold through altitude and temperature changes.

[fottip]

Originally Posted by Crasher

Those are the same pressures I arrived at using Michelin's load chart which is probably where Gary got his numbers. However, I added 5 psi to the steer tires which keeps them at or above the minimum 110 psi cold through altitude and temperature changes.

Fair enough - I hadn't gone back and tried to run the individual axle weights through the chart. But Gary's "been there, done that", and whatever he says, goes with me. The thing is, the "chart" doesn't account for different axles, and where weight proportioning comes into play, I think that's important. At any rate, that's what I'm doing, and it seems to get the job done.

[CampDaven]

I prefer Michelin XZA2 Energy. They last a long time. I set the air pressures as I like to. The ride comfort is custom selected according to my preference.
Life is good.

[ga traveler]

Originally Posted by fottip

Ok, you're the "engineer". I lost a front tire on a 40' Class A at 70mph at about 7-8 years of age. How 'bout some real-world "rubber-on-the-road" experience?

The blowout resulted in repairs costing over $7K and several months downtime, and these were name brand, major market tires, not some Asian-knockoffs. I learned a hard lesson from that experience, one that taught me that trying to extend the life of RV tires to "10 years", or some such fantasy time period, is false economy at best, and any advice to try to keep them in service that long is inviting expensive trouble.

YOU run them 10 years. I run them 5 - not a day more. YMMV

And good luck with that.

Why do you say 10 years is a fantasy time period? 10 years is what both the major manufacturers recommend. It seems to me the manufacturers would like to sell more tires and would recommend tire changes more often, thus selling more tires.

[Mr_D]

Originally Posted by Crasher

Not sure what to read into your above response. I'm not sure which "Dumb" advise you are referring to. Are you one of those that inflates the tires to what is stated on the sidewall regardless of the weight it is carrying or do you weigh each location and inflate per the load inflation tables supplied by the tire manufacturers? Just curious.

My '09 Country Coach owners manual says to inflate to the pressure on the Federal plackard and not reduce it due to lighter weight. So that's what I do.

[Mudfrog]

Originally Posted by fottip

Ok, you're the "engineer". I lost a front tire on a 40' Class A at 70mph at about 7-8 years of age. How 'bout some real-world "rubber-on-the-road" experience?

The blowout resulted in repairs costing over $7K and several months downtime, and these were name brand, major market tires, not some Asian-knockoffs. I learned a hard lesson from that experience, one that taught me that trying to extend the life of RV tires to "10 years", or some such fantasy time period, is false economy at best, and any advice to try to keep them in service that long is inviting expensive trouble.

YOU run them 10 years. I run them 5 - not a day more. YMMV

And good luck with that.

Did you determine the cause for the blowout? Could it have been debris the tire hit? Might you have run the tire with too low a pressure at any time in its life?

As was stated, there are just too many variables to make an absolute prediction. Most agree that the 10 years is pretty much maximum. Of course that time can be reduced immensely on tires that have not been taken care of.

[fottip]

Originally Posted by Mudfrog

Did you determine the cause for the blowout? Could it have been debris the tire hit? Might you have run the tire with too low a pressure at any time in its life?

As was stated, there are just too many variables to make an absolute prediction. Most agree that the 10 years is pretty much maximum. Of course that time can be reduced immensely on tires that have not been taken care of.

No "debris", and I have ALWAYS been religious about correct inflation pressures in ALL my vehicles, all my life. I check tire pressures in the coach before we get on the road EVERY TIME, NO EXCEPTIONS.

As I have posted earlier, most people don't go to the trouble of dessicating the air they put into their tires, and moisture DOES deteriorate from the inside. I do that now, with filters on my shop air system.

It was an extremely unnerving experience, one I intend to avoid in the future. I firmly believe it was simply because the tires were old and deteriorated. It invalidated my previous belief that keeping tires properly inflated and watching the exteriors for signs of cracking/deterioration were sufficient to stay safe. This proved TO ME that those beliefs are misleading and incorrect, and I now adhere to a strict 5-year replacement interval, regardless. Did I mention, "REGARDLESS"?

That's what the experience taught me. You? Do what you want-it's your coach. With a 36,000+ lb coach and 8 tires underneath, all under heavy loading, erring on the side of conservative is the only way I want to go.