Tire Pressure

Topic: Tire Pressure (Read 1107 times) previous topic - next topic

Tire Pressure

November 24, 2014, 05:40:14 pm

This year I purchased new tires and while at FOT for my annual service, last week, I had the coach aligned. Wayne Musser,
Chassis Center Coordinator for Foretravel did a great job. He told me I had too much air pressure in my tires. I have had my coach weighted, each wheel and knew the axle weights. Following the pressure chart from Michelin, I set the pressure while the tires were COLD, the added a little extra. Some say 5 lbs. extra, some say 10% extra. According to Wayne the tire pressure should be set while the tires are HOT. According to Wayne, it is possible to exceed the wheel rating and face a wheel blow-out by setting them cold.. Setting the pressure while hot will increase, slightly, your mileage and provides a smoother ride.

I adjusted the tire pressure while the tires were hot on my way home. Sure enough I got a smoother ride and maybe a little better mileage. I found this interesting and since FOT has been doing this for years and recommending, It must work or there would be many more blow-outs. Food for thought.

Roy

Re: Tire Pressure

Reply #1 – November 24, 2014, 05:47:17 pm

The tire manufacturer's inflation tables are based on COLD inflation. I respectfully disagree with anyone who suggests other than the tire manufacturer.

Re: Tire Pressure

Reply #2 – November 24, 2014, 05:51:17 pm

Quote from: Roy Dameron – November 24, 2014, 05:40:14 pm

According to Wayne the tire pressure should be set while the tires are HOT.

I'm not saying he is wrong....but that is completely opposite every bit of tire advice that I have heard/read/been taught for the 50+ years I've been driving.

What is "HOT"? After sitting a couple hours in the sun, after a drive around town, after 100 miles on the Interstate? Too many variables...

I'll set mine cold (I air them up 5 PSIG high the day before, then check and adjust early the next morning before the sun hits them - when all tires are at exactly the same temp)

Re: Tire Pressure

Reply #3 – November 24, 2014, 06:17:44 pm

Many expert opinions, many wrong, like me, I found all the wrong things like 110psi front, 105 psi drive COLD and don't care what the self appointed EXPERTS think.
Cheers & relax

Re: Tire Pressure

Reply #4 – November 24, 2014, 06:18:27 pm

Seems like crazy advice to me, 180 degrees from industry recommendation. The Alcoa aluminum wheels are forged and won't fail. I have run 110 psi cold all around ever since we picked ours up. Everyone has their ideas so it's almost like politics or religion.

Pierce

Re: Tire Pressure

Reply #5 – November 24, 2014, 06:23:14 pm

Wayne is absolutely INCORRECT.

But suggest you go to Michelin's website and "get it from the horse's mouth":

Tire Guide, Warranties & Bulletins | Michelin RV Tires

Click on "RV Tire Guide".

Irrespective of tire brand, ALL tire pressure recommendations are COLD (i.e. at ambient temperature before driving).

BTW, I am in the "go by the chart (which gives the MINIMUM PSI for a given weight) and add 5 PSI". This is assuming you have weighed your coach at its heaviest-- i.e. with full fuel, potable water, gray and black if you travel with them full (we do not) AND that really big Wallymart trip.

Re: Tire Pressure

Reply #6 – November 24, 2014, 08:15:19 pm

I need to note that although I did lower my tire pressure, I did not go below the charted cold pressure setting.

Checking out the Michelin RV Tire guide, on page 18, it sounds like they are saying the the inflation charts are for one axle two tires, except for the RV Charts and they are for an axle and one tire so you need to double the weight of the heaviest axle end.

"In the load and inflation tables, SINGLE means an axle with one tire mounted on each end, while DUAL means an axle with two tires mounted on each end. In an RV application, the loads indicated represent the total weight of an axle end. When one axle end weighs more than the other, use the heaviest of the two end weights to determine the unique tire pressure for all tires on the axle. The maximum cold pressure for each axle may vary, depending on their weights. These tables are applicable for all RV axles, whether or not they are power-driven."

How do you read this?

Re: Tire Pressure

Reply #7 – November 24, 2014, 08:19:33 pm

Yes, Michelin lists pressure recommendations based on axle weights, so you have to combine individual wheel weights.

Re: Tire Pressure

Reply #8 – November 24, 2014, 08:21:06 pm

Side to side weights vary, set pressures based on heavier wheel or wheel set. Duals are still duals RV or not

Re: Tire Pressure

Reply #9 – November 24, 2014, 08:38:38 pm

Quote from: wolfe10 – November 24, 2014, 06:23:14 pm

Wayne is absolutely INCORRECT.

(+1).......!!!!
Not only wrong but potentially dangerous advice, if taken seriously!
Neal

Re: Tire Pressure

Reply #10 – November 24, 2014, 08:40:59 pm

I agree with all of the recommendations in this thread except for the recommendation from Wayne. He gave me a chart that showed recommended pressures about 10 psi less than the recommendations from the Michelin manual on the Michelin web site.

Wayne has aligned the front end of our coach twice, and replaced the steering gear one time. Each of his repairs/adjustments resulted in an improvement in the condition of the coach. However -- after he replaced the steering gear and later adjusted the centering of the steering wheel, we experienced a catastrophic blowout of the top seal of the steering gear. The customer service representative at R. H. Sheppard told me the cause of such a sudden and severe failure is failure to properly adjust the pressure relief plungers on the steering gear. We had the seal replaced in Billings, MT. Marilyn and I adjusted the pressure relief valves in our driveway. Indeed, one of the pressure relief plungers was not properly adjusted.

I recently took the coach to Big Truck Alignment in Nacogdoches, TX, for steering adjustment. They trued the tires, checked all joints in the steering system, and adjusted the toe of the front end alignment. They centered the steering wheel to my satisfaction. They allowed me to watch the entire process and explained what they were doing. They also showed me wear patterns that indicated I should run higher pressures in the tires. I had been running cold pressures according to the Michelin charts (10 psi higher than Wayne's recommendation). Since the adjustments at Big Truck Truck Alignment I have been running pressures about 10 psi (cold) above Michelin recommendations on steer tires and about 15 psi (cold) above Michelin recommendations on rear tires. The coach has handled better than any previous time in the 4 1/2 years we've owned the coach.

Wayne has a lot of experience working on Foretravels. He has done some good service for us. However, I vigorously disagree with the recommendation that Roy reported that he received from Wayne regarding tire pressure. I also disagree with the recommendations Wayne provided to me regarding tire pressures.

I plan to replace tires in 2015. I plan to go immediately to Big Truck Alignment and have them true the steer tires and check the alignment. I also plan to inflate the tires to a pressure above recommendations in the Michelin chart (cold) and below the maximum pressure labeled for the tires.

We do use the coach in a wide range of temperatures. I've found that a change of more than about 40F will likely warrant an adjustment to bring the cold pressure to a suitable value for the conditions. I check and adjust pressures first thing in the morning, before the sun shines on the tires. Usually, the lowest ambient temperatures (and lowest pressures) occur at that time.

Re: Tire Pressure

Reply #11 – November 24, 2014, 10:21:13 pm

Don't ever let your tire air pressure exceed the maximum printed on the sidewall or you're very likely to have a belt separation when you hit a pothole at highway speed, and a few minutes later you'll have a blowout if you don't feel the tire failing and stop first. This happened to me multiple times with my car when I believed the nonsense I read about adjusting tire air pressure right up to the maximum printed on the sidewall. Since I lowered my tire air pressure I've never had a belt separation. If you adjust your tire air pressure in a cold environment and then drive to a warmer environment you should adjust the air pressure a little lower than the maximum so you won't go over pressure when you get to the warmer environment. It's not worth the risk. At highway speeds your fuel efficiency is mostly determined by aerodynamics, which of course is very poor for a motor coach. I always check my tire air pressure in the morning before I drive the coach. I would let some air out if I ever discovered the pressure was higher than the maximum printed on the sidewall... On an almost completely unrelated subject, don't ever run tube type motorcycle tires at low pressure off road, like all the magazines say, because you'll pinch the tube and have to ride a hundred miles back to camp on a flat tire... multiple times if you're as easily swayed by stupid stuff you read as I was, just saying. Common sense goes a long way. Don't mess around with tire air pressures. Stay away from the maximum and the minimum pressures. Always stay between what Foretravel suggests on the coach's data plate and what the tire manufacturer shows on the sidewall regardless of the temperature.

Re: Tire Pressure

Reply #12 – November 24, 2014, 10:56:01 pm

All else being equal, it's much safer to run a higher pressure than lower pressure. Do you think trucks adjust their tire pressure when they are loaded vs unloaded?

Under inflating tires = heat --> death of tire.

Somewhere, some place, I heard that a truck tire that was run greatly underinflated should be removed from service and could explode when air is added to it. Maybe this is true, maybe it isn't....I just heard it on the interwebs.

Re: Tire Pressure

Reply #13 – November 24, 2014, 10:58:56 pm

Quote from: Pierce & Gaylie Stewart – November 24, 2014, 06:18:27 pm

Seems like crazy advice to me, 180 degrees from industry recommendation. The Alcoa aluminum wheels are forged and won't fail. I have run 110 psi cold all around ever since we picked ours up. Everyone has their ideas so it's almost like politics or religion.

Pierce

p

Take this as a comment from endless testing with hundreds of Foretravel owners/ customer. every single customer reported better ride and handling by adjusting the tire pressure to match the actual lode.

Owners, red faced, yelling at me. Came back later and thanked me.

Why would I waste my time if, for sure, there was no benefit?

Dangerous in wet road conditions to run on the center rib IMO and experience.

Coach wanders.

Re: Tire Pressure

Reply #14 – November 24, 2014, 11:35:15 pm

Bob,

Could you clarify your statement. I think the majority of us believe in and practice: "adjusting the tire pressure to match the actual load."

The question is, knowing the actual load, what are you suggesting in terms of PSI as compared with the tire manufacturers Inflation Tables for the actual loads?

Re: Tire Pressure

Reply #15 – November 25, 2014, 07:23:40 am

Quote from: wolfe10 – November 24, 2014, 11:35:15 pm

Bob,

Could you clarify your statement. I think the majority of us believe in and practice: "adjusting the tire pressure to match the actual load."

The question is, knowing the actual load, what are you suggesting in terms of PSI as compared with the tire manufacturers Inflation Tables for the actual loads?

Brett I assume the charts are the same things as the tires sidewalls load vs pressure rating?

Just precalculated?

Weighed countless coaches then calculated the percentage of the max loading from the sidewall rating and reduced the tire pressure the same percentage

Re: Tire Pressure

Reply #16 – November 25, 2014, 08:34:31 am

"Powers Tire" in Nacogdoches installed my tires and told me they do a lot of Foretravels and Gregg recommends 100 in front and 90 each on the duals. I find this works well with all loads. I try to keep 95 in the rear and 103 in the front. Besure to adjust for colder weather. Everyone is an expert but everyone may be in the general area.

Re: Tire Pressure

Reply #17 – November 25, 2014, 09:32:10 am

Quote from: Caflashbob – November 25, 2014, 07:23:40 am

Brett I assume the charts are the same things as the tires sidewalls load vs pressure rating?

Just precalculated?

Weighed countless coaches then calculated the percentage of the max loading from the sidewall rating and reduced the tire pressure the same percentage

Bob,

I have never had reason to calculate the percent of max load vs PSI. It COULD BE (no idea) if the equation is linear or not. I do know there there is a minimum PSI for each tire, irrespective of load. This often comes into play on tag axles.

To me it has always been easier to use the expertise of the tire manufacturer's engineers who have taken the time and effort to generate the Inflation Charts.

And, as has been properly posted already, per the tire manufacturers: "Use the heavier wheel position on each axle to go to the Inflation Chart. The chart will tell you the MINIMUM PSI for a given weight. Many add a 5-10 PSI cushion to account for changes in loading, and moderate temperature changes. Do not exceed the PSI on the sidewall of the tire.

And all PSI's are with the tires cold. Nothing to do with ambient temperature. It is at ambient temperature before they have been driven.

Re: Tire Pressure

Reply #18 – November 25, 2014, 09:55:46 am

Well ---- I run 100 lbs all the way around. Easy to remember and have never noticed any problems with UN-even tire wear. I suspect that a few pounds up or down is not detectable in any parameter relative to tire longevity. I would appreciate being set straight if I'm off track. Thanks and have a great day ---- Fritz

Re: Tire Pressure

Reply #19 – November 25, 2014, 10:16:30 am

Fritz,

Only way to KNOW is to weigh the individual wheel positions and look it up. You could be right on or off by 15 PSI.

You can get some indication by looking at your GVWR plaque (wall outboard of drivers position). The PSI on it are for each axle loaded to its GAWR FOR THE ORIGINAL TIRE SIZE (which will also be on the plaque) .

No idea if you are way under GAWR or over. Depends on coach, equipment and how it is loaded.

Re: Tire Pressure

Reply #20 – November 25, 2014, 11:21:27 am

My '96 with original sized tires and overall weight of 29,000 is as happy as I am with 85-90 psi in each tire. We rarely run over 57 mph as that seems to be the sweet spot for mileage. Replaced the last tires at 9 years. Don't yell, they'd sat on the shelf somewhere for four years before first installation just before we bought the coach in '05. those were Michelin and now with Continental.

Re: Tire Pressure

Reply #21 – November 25, 2014, 12:35:28 pm

In an ideal world where all parameters such as load, ambient temperature, speed and so on are constant you could set your pressures to their actual running pressure for the load carried IE hot. The flaw in this is everything changes all the time. That's why you should set your pressures COLD. Having the sun on one side vs the other will make quite a difference in actual pressure. If you inflate your tires when it's 100 deg out and drive up north where it's 40 deg you will see that your tires are now under inflated when cold.

In fleet service tires are run at their maximum reccomended loaded pressure. The trade off is more center wear and less traction. Reason? You can't constantly adjust pressures to loading. Tires are never run at their unloaded pressures as, if run loaded at them, tire failure will occur.

Low pressure is the enemy. It causes excessive sidewall flex and heat leading to ply separation and catastrophic tire failure.

Tire pressures are on the plate by the driver's seat. If in doubt use them. Better yet weigh each wheel at maximum loaded weight and look up the manufacturers pressure charts.

Tire manufactures have done extensive testing and have come up with the best compromise solution. Follow their recommendations.

Keith

Re: Tire Pressure

Reply #22 – November 25, 2014, 03:43:18 pm

Quote from: krush – November 24, 2014, 10:56:01 pm

Somewhere, some place, I heard that a truck tire that was run greatly underinflated should be removed from service and could explode when air is added to it. Maybe this is true, maybe it isn't....I just heard it on the interwebs.

I can vouch for that. Noted that one of my Michelins was flat after camping a few days in Missouri. Checked it as well as I could, it showed no damage of any sort, just looked like an almost new tire. Clipped the chuck on, started the engine, noted that the beads were still set and tire was inflating and walked to the other side of the coach. I heard two things, one the compressor pop off (120 psi on gauge) followed shortly thereafter by what sounded like magnum loads on a sawed off double barrel shotgun. Blew a hole right thru the sidewall and woke the rest of the campground up right smartly. Inspecting the tire when it was removed showed no damage whatsoever inside, other than a 2" hole thru sidewall.

Re: Tire Pressure

Reply #23 – November 25, 2014, 04:04:01 pm

I'm at the grand benching two years ago Michelin stated something to the effect that any tire that became deflated more than 20% below the inflation needed for the load that was on the tire should be dismounted and inspected prior to return to service.

It seems incredibly conservative to me but interesting what happened when you took a deflated tire to Max inflation

Re: Tire Pressure

Reply #24 – November 25, 2014, 04:29:00 pm

Throwing a boot on the inside and glueing the blow out rubber flap in place should make it like new

Had one blow underneath me and the double barrel shotgun sound was about right. It sure took off for the center divider for a second.

Pierce

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