LivingLikeEachDayIsMyLast

Who Is Credible Concerning Tire Pressures ?

17 posts in this topic

I've read scores of recommended tire pressures for motorhomes from numerous websites. Most all of them seemed to make sense when I was reading them. I own a 1995 Fleetwood Southwind 33' motorhome. Six months ago I had a new set of Goodyear tires model G670RV installed. The size being 225/70R 19.5, load range "F" with a sidewall maximum of 95 psi cold.

The tires were purchased at and installed by CamperWorld in Myrtle Beach, South Carolina. These people are a large full service operation & they sell & install hundreds of tires every year. They set the tire pressure at 95 psi on my tires. When I questioned the service manager, he told me to maintain 95 psi in each tire no matter what weight the motorhome was if I expected the warranty to be honored in case of failure. From what I have read & heard for years this gentleman is incorrect.

Regardless, I have maintained 95psi in the new tires. The tires appear to be wearing evenly & the rig handles exceptionly well. I'm perplexed somewhat that a dealer does not follow the pratices of the majority of the tire experts across the country.

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Hi LivingLikeEachDayIsMyLast,

Your coach weight may require the tires to be inflated to 95 PSI. If you know your coach's weight and check with the tire manufacturer's web site it may answer the question. In general, I find tire dealers inflate to maximum PSI just to be on the safe side. Tire dealers might be taking the position that the customer will not be diligent about tire PSI. Starting the customer out at maximum PSI and recommending they keep it there would allow the maximum amount of time between when the customer needs to check the tire PSI.

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Wouldn't it be nice if tire manufacturers would give a pressure required for a range of loads? That way, you could get your coach weighed by axle (and even tire position if you run lopsided) check the chart and you'd be dead on.

My advice has always been, if you err, err on the high side. Tires inflated to the max allowable pressure will run cooler. Lower pressures usually result in higher temperatures. If the tires appear to be wearing more near the center, drop the pressure 5# or so.

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If someone tells you categorically what tire pressure you should carry without knowing your wheel position/axle weights, in my opinion you have met either a clairvoyant (he can "divine" your coach's weights and weight distribution by looking at it) or an idiot (as he does not understand that PSI is WEIGHT DEPENDENT).

While you will hear and read a variety of answers/opinions, the best source of information on your tires is your tire manufacturer. They did not go to the trouble to develop and publish inflation tables (load/PSI tables) if the correct answer is "one PSI fits all".

Please go to this Inflation Table on Goodyear's website: http://www.goodyear.com/rv/pdf/rv_inflation.pdf

On page 2 you will find your tires. The table gives the MINIMUM tire pressure for a given weight.

Most recommend adding 5 PSI safety cushion to this minimum if you entered the table with the heavier wheel position weight on each axle.

Add 10 PSI to the minimum if all you have is axle weights to account for some left/right weight imbalance.

Do not exceed the pressure molded into the tire side wall or wheel maximum.

Brett Wolfe

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I've met tire people who were very informed and knew what they were doing. I've also met people who think they know what they are doing and aren't about to learn anything new.

My most recent event occurred two days ago. We had a flat tire on the outer rear, passenger side. We were in a construction area with cones set well over the center line so the right side of the coach was running on the shoulder. The Pressure Pro alarm sounded and indicated a pressure of 92 pounds, my normal is 105 on the duals. By the time I got to the shoulder it was 73 pounds. I stepped out of the coach and heard the hissing from the door. When I looked at the tire there was a cargo hook with some trailing webbing hanging from the outside rear tire.

Long story short, the tire was ruined and a temporary tire, not the correct size, was installed. I spent Monday calling around for 300 miles checking to find the newest tires I could. I eventually located some tires just over a year old. They were about 150 miles from where we were so we set out to get two new tires. When I arrived, I was pleased to find the tires were just three months old, dated 3010, the 30th week of 2010.

I specified the where and how I wanted them mounted. The worker who mounted the tires had his own ideas about how things would be done. We discussed several issues. He didn't know how to properly assess the roundness of the tire. I let him know that I knew he was fudging the results. He fussed that he was trying to get finished before they closed. Then he demonstrated his complete ignorance of the use of a torque wrench, putting the lugs on with an air wrench to the point where the torque wrench wouldn't move them at all. This from a shop that should have been more professional with their approach. Unfortunately, this experience is more the norm than the exception. In reality if you have taken a tire safety course from the RV Safety Institute you know more about tires than most salesmen or installers. The job pays poorly and there is little incentive to improve your knowledge. If the boss just wants tire out the door ASAP, you take short cuts.

We ended up returning to the shop shortly after they closed. There was a ticking sound as we drove and it was speed related. The installer was called back to work. When I explained, he said, "They're tires, tires don't tick." After some investigation it was determined that the weights installed on the inside of the front rims were impacting the wheel/brake housing as they rotated over the top of the wheel. The weights had to be moved and the wheels installed again. It turns out that tires do tick!

So who is credible when it comes to tires? You have to be your own expert. Read, study, learn as much as you can - it is a matter of self defense. Let the buyer beware!

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Regarding the torque wrench issue - Workhorse specs my lug nuts to be set at 475 ft pounds.

Over the years I have checked with several tire shops and RV shops along with three different road service guys and all but one had no way of checking for 475 ft pounds. One tire shop did have a 500 ft pound torque wrench - way up on a shelf with a lot of dust on the box - but they never used it.

I bought a 3 to 1 torque multiplier and a 250 ft pound torque wrench along with a 10 inch extension and 33 mm socket so I could do it myself if necessary. With the torque multiplier only 158 pounds of torque is required to yield 475 ft pounds on the output.

I have appointments next week to have new tires installed and the Workhorse brake recall performed. Neither shop has the necessary tools but both readily agreed to use mine. Hopefully I will have the torque set properly.

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Holy crap, 475 ft lbs. You are going to twist the nuts off. My Workhorse Chassis manual says 175 ft lbs. and that is pretty tight. Check your manual again.

I stand corrected. 475 is correct for your chassis. I know that 475 on mine would spoil my day.

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Brett Wolfe has given you excellent advice (as he always does - you can take his knowledgeable advice as gospel - he knows his subjects) about what is the correct pressure to carry in you tires.

The tire manufacturer's literature will always be the final word on proper inflation pressures.

In order to use the inflation charts, you MUST know how much weight is being carried by the tires.

1. To find that out, you MUST have your rig weighed - preferably at each corner to find the weight each tire or set of tires is carrying.

2. Then find your tire in the inflation chart where it crosses the weight the tires are carrying - listed there is the correct pressure for your application.

Running the maximum pressure will wear the center ribs of the tire prematurely and result in a harsh ride.

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Thanks Tom for serving our country in Viet Nam!

You are welcome! It was just one of those things. Unlike today's army, I could go home after a year and not have to return. One year was a long time to be away from family. I can't imagine the sacrifice that goes with repeated tours of duty overseas as our troops face today.

It did give me a new sense of the value of life and an appreciation of peace. For years I marveled at the peace of sitting outside in the evening and living in a land of peace with no real threat to your life. I don't think about it as often as I used to but it is still true. In most places in the US, there is no gunfire at night, no flares, no incoming rockets. Life is good here. Life is short - get it while you can!

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There is an easy way to arrive at an optimal pressure for each tire on your RV, truck, car, whatever. Get one of the laser thermometer guns. You can find them all over for less than $100. In THEORY, a tire that is perfectly inflated for the LOAD it is carrying, would show the same temperature across the face of the tread. (Inner tread ridge, middle tread ridge, outer tread ridge). In real life there is Camber, and a number of other factors that will affect the inner or outer temperatures. So in real life you are looking for an EVEN SPREAD of temperatures across the face of the tread.

You need to take the coach out on the highway and drive at normal speeds for say 10 miles. Get off at a ramp, and quickly pull over to a safe spot where you can take and record your temperatures. This must be done quickly as the temperatures will even out. For each tire you will record the temperature read on each of the 3 places on the tread.

A tire that has the correct pressure would have numbers of say 130 degrees Inner, 125 Middle, and 120 outer. The actual number values are not important, just the relationship between them. Notice in the above example, there is an even SPREAD across the face of the tread. A tire that is UNDER INFLATED would show say 145 degrees Inner, 130 Middle, and 140 Outer. In this case the Middle is too cool in relation to the Inner and Outer. A tire that is OVER INFLATED may show 130 degrees Inner, 130 Middle, and 120 Outer. Now the Middle is too warm in relation to the Inner and Outer.

In this way you can arrive at the optimal pressure for each tire. Just make sure you are not going outside the manufacturer's range.

In my case Goodyear says 95 lbs. This is the cold pressure for MAXIMUM load. Airstream says 70 lbs. (345 Motorhome) I have found that with our normal load, the fronts are 78 lbs., the duals are at 77 lbs., and the tags are at 72 lbs.

I hope this provides another idea that can help.

Rob

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I too have a 33' Fleetwood Southwind (1989), and I too was confused by what pressure I should set my tires to. The sticker on the inside of my coach says inflate to 70psi, but if I followed the inflation charts for my tires, they should be set to 65psi. The maximum PSI stamped on my tires also say 95 maximum psi. I took Bretts advise and err'd on the high side and inflate them to 70. No problems so far.

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I too have a 33' Fleetwood Southwind (1989), and I too was confused by what pressure I should set my tires to. The sticker on the inside of my coach says inflate to 70psi, but if I followed the inflation charts for my tires, they should be set to 65psi. The maximum PSI stamped on my tires also say 95 maximum psi. I took Brett's advise and err'd on the high side and inflate them to 70. No problems so far.

Chris,

Let's take a minute to see why there are three different recommended PSI's:

Sticker in the coach is the GVWR sticker and will give the correct PSI IF THE AXLES ARE LOADED TO THEIR FULL GAWR (Gross Axle Weight Rating).

The sidewall of the tire will give the PSI needed to carry the maximum load the tire was designed to carry.

And, as you did, using your actual weights to determine the minimum recommended PSI for your actual weights and adding a small safety cushion is the correct way to do it.

Brett

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Greetings everybody,

Let me add a comment to RobFike's note about using an thermometer to help check tires. I use an infrared thermometer to check the axle temperatures on our boat trailer, and often check the tire temperatures on the motorhome too.

Yes, its true that an under inflated tire will run hotter. So, a temperature differential between the tires can indicate something is amiss. However, please remember that the sun can also create a substantial difference. I have noticed temperature differences of 15-20 degrees between the sunny side and the shady side of our coach when traveling in the summer across the desert. However, the next morning when everything is cool, they all read the same as the start of the day.

Happy travels,

Tim Shields

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Few additional comments and hopefully clarifications.

Brett's post of 10/14 7:09 AM is spot on. My only clarification is that the inflation pressures in the charts are the inflation at ambient. This is called "cold" inflation but do not be mislead. "cold" is NOT any specific temperature.

What is meant by "cold" is when the tire has not been driven on more than a couple miles in the last couple of hours. This does not mean 10 miles down the road. The tire should not be in the sun for more than a couple of minutes. Best time to check is first thing in the morning before you start driving.

The Max pressure on the sidewall is the max "cold" pressure not the max you might measure when the tire is hot. You should not bleed down a hot tire to get to your "cold" inflation.

I also agree with the +5 or +10 psi over your minimum inflation.

====

BobFike is correct IN THEORY. The problem is that to get the real temperature you need to take a measurement within less than two or three minutes from running at speed. I do not mean two minutes after stopping.

You also need to be sure to get the same spot within the tread design as different parts of the pattern will give different readings.

I would not use this method for setting proper tire inflation. You could use this method for checking suspension or looking for a bent axle on a trailer.

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I was just thinking about this.

I went to check my tires first thing in the morning while camping.

The sun was out - but we were shaded. The tire show 92 psi. It showed 95 psi when I started the trip 2 days ago. The problem was the over night low was 28 deg. It's in the 50's at home, so I decided to get to warmer clime and then check again...

I ASSUME that a tire will run about the same psi/ temp once warm. (ie 100psi @ 60 mph @ 60 deg) regardless of where I started.

Is that right?

Few additional comments and hopefully clarifications.

Brett's post of 10/14 7:09 AM is spot on. My only clarification is that the inflation pressures in the charts are the inflation at ambient. This is called "cold" inflation but do not be mislead. "cold" is NOT any specific temperature.

What is meant by "cold" is when the tire has not been driven on more than a couple miles in the last couple of hours. This does not mean 10 miles down the road. The tire should not be in the sun for more than a couple of minutes. Best time to check is first thing in the morning before you start driving.

The Max pressure on the sidewall is the max "cold" pressure not the max you might measure when the tire is hot. You should not bleed down a hot tire to get to your "cold" inflation.

I also agree with the +5 or +10 psi over your minimum inflation.

====

BobFike is correct IN THEORY. The problem is that to get the real temperature you need to take a measurement within less than two or three minutes from running at speed. I do not mean two minutes after stopping.

You also need to be sure to get the same spot within the tread design as different parts of the pattern will give different readings.

I would not use this method for setting proper tire inflation. You could use this method for checking suspension or looking for a bent axle on a trailer.

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I was just thinking about this.

I went to check my tires first thing in the morning while camping.

The sun was out - but we were shaded. The tire show 92 psi. It showed 95 psi when I started the trip 2 days ago. The problem was the over night low was 28 deg. It's in the 50's at home, so I decided to get to warmer clime and then check again...

I ASSUME that a tire will run about the same psi/ temp once warm. (ie 100psi @ 60 mph @ 60 deg) regardless of where I started.

Is that right?

Well I don't have all the info needed to be sure, but if you are running 8% low and your normal heat gain is 40 degrees above ambient you might see enough pressure growth to get to your normal tire pressure but at the expense of running the tires hotter than they would normally run. As we all know heat is the killer of tires and the more hours you spend running your tires hotter than normal the more tire life you are using up.

Now if you know that 90psi is the minimum required to carry your load based on actual weights on each corner then it's no big deal. That's why you are inflating your tires to Minimum + 5 psi, to allow for day to day temperature variations.

If 95 cold is what is the MINIMUM required to carry your load you are in fact running your tires overloaded. Not a lot but overloaded none the less. Damage to tires is cumulative. Putting air back in a tire you operated while overloaded/underinflated does not "fix" the damage you have done any more than putting the burnt hot dog back in the fridge "fix" the burnt dog.

Now a couple of hundred miles at 3 psi low is not going to fail a tire BUT you are still doing damage and there is no clear answer as to how many miles you can run a tire X psi low before it fails.

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