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Old 01-15-2016, 02:35 PM   #1
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Tire Inflation Yet Again

I know the best advice is to base inflation on four corner weights and second best is front weight and back weight. But what about the MH owner that has neither one? I know I could go get it weighed. But what is the best advice in the mean time for how much air to put in?

Thor recommends 90 pounds all around. I have had two different tire people tell me 100 is better on the front (not sure of their reasons). I saw someone on the forum that just adds 5 pounds to the MH manufacturer's numbers (that would be 95 all around for me).

Your advice, and why please?
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Old 01-15-2016, 02:47 PM   #2
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I picked up one of the IR thermometers for around $20 and use that to keep an eye on the tires while traveling. I'd set to the mfg recommendation, drive it and check the temps. If they're all running about the same, call it good. I run from about 105 to 120 depending on outdoor temps. Side in the sun generally run 5-10 deg above the shade side.

I'm running about 10,700 on the front and right on 20K on the rear. Tires are at 100 front and 110 rear.

Higher pressures mean a more harsh ride.
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Old 01-15-2016, 03:01 PM   #3
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A lot of people make this way over complicated. The manufacturer placed a sticker in you unit specifying the tire inflation numbers. These numbers are based on the gross axle weight ratings and the tire manufacturers weight tables. Yours says 90 all around. I suspect in the majority of cases, this number is all you need to know.
If you are like Lucy and haul around a bunch of rocks then by all means go get your coach weighed to make sure you are not overloaded.
If you think the ride is too harsh and you could benefit by reducing the PSI, then go get it weighed and adjust based on the tire tables.
Otherwise try to spread your load evenly between front/back and side to side, keep it at 90, get in, and drive.


Just my opinion, others will vary.
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Old 01-15-2016, 03:03 PM   #4
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If you don't have actual weights then running the pressures on the sticker is the best thing since that's the maximum your rig should ever weigh. Even then it could be low as some come from the factory weighing just below or even over before you load anything.
You still need four "corner" weights though.
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Old 01-15-2016, 04:23 PM   #5
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Originally Posted by Mr_D View Post
If you don't have actual weights then running the pressures on the sticker is the best thing since that's the maximum your rig should ever weigh. Even then it could be low as some come from the factory weighing just below or even over before you load anything.
You still need four "corner" weights though.

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Old 01-15-2016, 07:02 PM   #6
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PSI carries the weight. Low tire pressure makes heat. Heat kills tires.
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Old 01-16-2016, 08:27 AM   #7
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Use the 90 psi number until you get to a scale - but get to a scale fast. Your local truck stop most likely has a CAT scale (or you can Google locations) and in 10 minutes and $10 you will have all the numbers you need to inflate your tires correctly.

Four corner eights are the gold standard but places that can do them properly are few and far between. You can easily estimate and correct for the individual weights by using your axle weight, your calculator, and your tire tables for your size tires. Here's how:

Front axle weight + 5% /2 = front wheel load. Look this number up in your tire table for single axles. Add 5 psi to the table pressure. That's your front axle tire inflation number.

Rear axle weight + 5%/2 = rear wheels load. Look this number up in your tire table under dual wheel axles and add 5 psi to that number. This is your rear axle tire inflation pressure.

Front pressures usually will be higher than rear pressures, but not always.

The 5% is to compensate for any side to side differences you may have on that axle. If you ever do individual wheel weights you will see some side to side differences. You will still inflate all tires on that axle to the same level as required by the heaviest side.

So, in twenty minutes you will have everything figured out and tires inflated properly.

As timetogo said - underinflated tires generate heat, and heat kills tires. On the other hand, overinflated tires give you a poor ride, reduce braking efficiency, and cause wear issues.
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Old 01-16-2016, 09:27 AM   #8
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I do it a little different even though I do weigh the coach. I don't have the factory tires on the MH anymore and I went from load range 'F' to 'G'. I got the weight/PSI chart from the tire manufacture and set the air pressure to the max axle rating of my coach. I am actually a little over but the ride is much better, my rears are at 80psi and fronts are at 70 psi.
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Old 01-16-2016, 09:28 AM   #9
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Originally Posted by sbleiweiss View Post
I know the best advice is to base inflation on four corner weights and second best is front weight and back weight. But what about the MH owner that has neither one? I know I could go get it weighed. But what is the best advice in the mean time for how much air to put in?

Thor recommends 90 pounds all around. I have had two different tire people tell me 100 is better on the front (not sure of their reasons). I saw someone on the forum that just adds 5 pounds to the MH manufacturer's numbers (that would be 95 all around for me).

Your advice, and why please?
When all else fails, air them up according to the chart for the GVWR rating, then add 10 - 15psi for a cushion. Logic here is that you could very well be loaded to max and the cushion will take care of all the variables. Changes in ambient, side to side differences, slow leaks that aren't immediately discovered, extra people that weren't figured in...etc...etc....
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Old 01-16-2016, 09:43 AM   #10
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One thing I always found funny that is hardly ever mentioned when the "Tire" subject comes up is no one ever mentions tire wear......... for me, weighing,manufactures pressure suggestions, did not work in the handling and tire wear. After some time, of adjusting for the tire wear(When I pull it into the garage, with a dusty floor, I can see the tire surface contact with the floor on the tire) and handling problems, it drove a lot better and my tire's are wearing even across the tire surface. I have seen on here members post about bad tire wear and from the photos, they were either under inflated or over inflated, and they post as to having their Coach weighed and adjusting to the proper inflation pressures provided by the tire manufacture..............Just something to ponder,,,,,,,,,,..........
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Old 01-16-2016, 03:18 PM   #11
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When all else fails, air them up according to the chart for the GVWR rating, then add 10 - 15psi for a cushion. Logic here is that you could very well be loaded to max and the cushion will take care of all the variables. Changes in ambient, side to side differences, slow leaks that aren't immediately discovered, extra people that weren't figured in...etc...etc....
Just be Carefull that when you add 10 to 15 psi for a cushion ? ( I would never inflate above the manufactures recommendation ), that you are not going over the MAX inflation pressure printed on the side of tire.
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Old 01-16-2016, 03:27 PM   #12
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Just be Carefull that when you add 10 to 15 psi for a cushion ? ( I would never inflate above the manufactures recommendation ), that you are not going over the MAX inflation pressure printed on the side of tire.
Pressure "printed" on the side of the tire is not the maximum when on RV/truck tires. It is the minimum to support the maximum rating of the tire.

From the Michelin RV Tire Guide:
Quote:
"If you look at the tire's sidewall, you'll see the maximum load capacity allowed for the size tire and load rating, and the minimum cold air inflation needed to carry the maximum load."
From page 6 of the GoodYear RV Tire and Care Guide:
Quote:
"How much air is enough?
The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load."
From TOYO:
Quote:
Q: What are the consequences of inflating the tires to accommodate the actual loads?
A: If the inflation pressure corresponds to the actual tire load according to the tire manufacturer’s load and pressure table, the tire will be running at 100% of its rated load at that pressure. This practice may not provide sufficient safety margin. Any air pressure loss below the minimum required to carry the load can result in eventual tire failure.
But then they go ahead and publish a weight/pressure chart allowing lower pressure for RV's!!

From the August 2010 Motorhome Magazine "Tread Carefully" tire article:
Quote:
The maximum load capacity allowed for the size tire and load rating and the minimum cold air inflation needed to carry that maximum load are located on the tire’s sidewall.
From our owners manual:
Quote:
Federal law requires that the tire’s maximum load rating be molded into the sidewall of the tire.
If you look there, you will see the maximum load allowed and the cold air inflation pressure required to carry that stated maximum load. Less air pressure restricts the tire to carry a lighter load.
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Old 01-16-2016, 04:09 PM   #13
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Federal law requires that the tire’s maximum load rating be molded into the sidewall of the tire.

If you look there, you will see the maximum load allowed AND the cold air inflation pressure required to carry THAT stated MAXIMUN load.

LESS air pressure restricts the tire to carry a lighter load.

This says that the MAX air for the MAX load.

You want to go 10 to 15 psi over that !!

What am I missing ?
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Old 01-16-2016, 04:38 PM   #14
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Go get the thing weighed on a truck scale and quit guessing. No one should be driving around not knowing if they have an axle overloaded or guessing what pressure they should be running at.
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