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Old 05-18-2014, 05:30 PM   #1
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Tire Pressure

The manufacturer of our tires, (Kelly Armour Steel), recommends 110 psi in the front tires, and 100 psi in the rear tires. On our 2001 HR Imperial, with 295/75/22.5 tires, I don't seem to be able to get but 100 psi in any of the tires. I've tried using my Porter Cable pancake compressor and the on-board compressor to no avail. I even bought Auto Zone's best tire inflator trying to inject more air, with no success. Whats up?
Grady Ray
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Old 05-18-2014, 05:44 PM   #2
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Quote:
Originally Posted by Grady Ray View Post
The manufacturer of our tires, (Kelly Armour Steel), recommends 110 psi in the front tires, and 100 psi in the rear tires. On our 2001 HR Imperial, with 295/75/22.5 tires, I don't seem to be able to get but 100 psi in any of the tires. I've tried using my Porter Cable pancake compressor and the on-board compressor to no avail. I even bought Auto Zone's best tire inflator trying to inject more air, with no success. Whats up?
Grady Ray
What's the PSI rating on your compressor? If it is less than 125 PSI you will have problems Rufus
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Old 05-18-2014, 05:48 PM   #3
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I would not go with the tire mfg psi recommendation and use the HR Imperial manufacturers recommendation until you get the coach weighed. The only accurate way to determine proper tire pressure is to get all four corners of your MH weighed separately. If there are no scales available in your area, go to a truck weighing scale that provides a separate front and rear axle weight. With that information see if Kelly has an inflation table and use the amount for your tire size and carrying weight. If Kelly does not have a table available, you could use Michelin or Goodyear.
We purchased an older class a as a downsize and the former owner told me he had a lot of trouble with tire blowouts and always inflated the tires to 95 psi which is the max pressure for the tires. I had the rig weighed, added an amount for carrying weight of gear, clothes, water etc and referred to the tire mfg. table. Turns out the recommended pressure was 85 for both front and rear. The former owner undoubtedly had problems due to over inflation. Used above process on our former 38' Class A and always had excellent tire life without problems.
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Old 05-18-2014, 06:05 PM   #4
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Thanks Rufus, but it's 135 psi.
GR
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Old 05-18-2014, 07:14 PM   #5
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If you will get the compressor running and then put your inflator onto the tire and continue to hold it on there until you stop hearing air flow or minute or so after compressor stops you will get more air in. I have a sears craftsman that pumps up to 125 psi. Using the above method I can get about 107 to 108 psi in my fronts. It's a slower process but it works. I got tired of waiting so I bought a new compressor for my shop that pumps up to 200 psi. Now I have no problem at all. If yours pumps to 135 psi you should be able to get around 110 to 115 with no problem. Also check to make sure your air outlet is putting out the full 135. There is a knob that limits pressure for lower rated tools where you can adjust outlet pressure down. Should be turned full clockwise for max pressure.

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Old 05-18-2014, 08:18 PM   #6
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Originally Posted by figallegro View Post
I would not go with the tire mfg psi recommendation and use the HR Imperial manufacturers recommendation until you get the coach weighed. The only accurate way to determine proper tire pressure is to get all four corners of your MH weighed separately. If there are no scales available in your area, go to a truck weighing scale that provides a separate front and rear axle weight. With that information see if Kelly has an inflation table and use the amount for your tire size and carrying weight. If Kelly does not have a table available, you could use Michelin or Goodyear.
We purchased an older class a as a downsize and the former owner told me he had a lot of trouble with tire blowouts and always inflated the tires to 95 psi which is the max pressure for the tires. I had the rig weighed, added an amount for carrying weight of gear, clothes, water etc and referred to the tire mfg. table. Turns out the recommended pressure was 85 for both front and rear. The former owner undoubtedly had problems due to over inflation. Used above process on our former 38' Class A and always had excellent tire life without problems.
Would like to get my 35' HR weighted, do most truck stops have these scales? How much does it cost to weigh them?
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Old 05-18-2014, 08:24 PM   #7
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To inflate 22.5 size RV tires you need a minimum of 155 psi compressor.

Dr4Film ----- Richard
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Old 05-18-2014, 08:34 PM   #8
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There are a couple more threads that may be of interest.

Replace tires by age or Miles?
Tire inflation ideas

Tires and tire pressures seem to be an interesting and opinion prone topic.
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Old 05-18-2014, 08:43 PM   #9
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Originally Posted by Fred from Ga View Post
Would like to get my 35' HR weighted, do most truck stops have these scales? How much does it cost to weigh them?
Do a search for "CAT Scales" Most major truck stops have them - Usually about $8 to $10 and they are split scales so if you watch when you pull up on them and be sure to get the front axle on one section, the rears on another, and the trailer or toad on a third one you will get all three weights separately on the ticket for the same price. Most won't do a side to side weight. That is usually done on portable scales at RV conventions etc.
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Old 05-18-2014, 11:26 PM   #10
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Do a search for "CAT Scales" Most major truck stops have them - Usually about $8 to $10 and they are split scales so if you watch when you pull up on them and be sure to get the front axle on one section, the rears on another, and the trailer or toad on a third one you will get all three weights separately on the ticket for the same price. Most won't do a side to side weight. That is usually done on portable scales at RV conventions etc.
I also use CAT scales when needed, but my preference is to keep an eye out for state highway weigh stations that are closed for the day. In a lot of states, even though the weigh station is closed, the scales are still on and the display will show your weight. The big advantage here is that unless you have a trucker on your ass, you can weigh by axle, then pull around again and this time weigh only one side so you can calculate your individual wheel weights.
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Old 05-19-2014, 02:56 AM   #11
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Let me calculate for you what pressure you need.
Mayby its lower then what is adviced , and that pressure can be filled with your compressor or whatever.

Need at best those weighed seperate wheel(Pair) loads , second best axle weighing, but in lack of that we will have to do with the GAWR's and GVWR ( gross axle/vehicle weight rating), wich is the maximum that is allowed by law.
Then ofcource the build of vehicle like number of axles and tires per axle.

The tires I can surch back with google but best is if you give what is on sidewall
The maximum load and pressure needed for that , wich is called the maxloadpressure or reference-pressure, and is not the maximum pressure of tire.
Also speedcode ( N = up to 140km/87m/h , J=up to 100km/62m/h).
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Old 05-19-2014, 09:54 AM   #12
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I have been looking at and debating tire life and pressures on several threads. As well I have searched the internet at various times to try to clarify questions that come to mind.

Here is what I think happens.

Tire manufacturers develop a tire and give it a maximum weight and pressure rating. At that weight and tire pressure the tire is designed to flex a given amount, develop a designed amount of heat and deliver a planned life cycle including age and miles. I would think that the tire life would end with the tire worn out within the age life of the tire or maybe a bit before the tire aged from UV, ozone, temp, etc. At max weight and pressure the tire should be giving the best stability and traction for the design plus as good a ride as possible. A lot of factors and variables but some very knowledgeable people balance those through years of testing and field information.

Then they take the information and prepare a tire loading chart. I assume (me bad for assuming) that under the loads and tire pressures in the chart the flex, temperatures, handling, ride and life cycle remain very similar to maximum loading and pressure. Therefore the tire should last as long as if used under maximum load and pressure.

By weighing and knowing the actual weight of the loaded axles one could apply the tire pressure from the tire loading charts for optimal performance??? I think 4 corner weighing is good because to the extent possible we should have the side to side loading as close as possible. The rule is the tires on an axle are loaded to the max weight on either side of the axle.

As long as we maintain the tire pressure from the loading chart as the minimum on the axle the tires should give the closest performance to the tire design. Inflating tires above the recommended in the tire chart may make them wear longer but will not make them age any better. Most complaints are the tire will age long before the tread is worn out.

I think over inflating tires must have some detrimental side effects. I have read information (some anecdotal) about reduced traction, uneven wearing and reduced stability. Certainly it gives a harsher ride and with the investment in a MH do we need to have the rolling 3.5 earthquake increased.

I have determined I will balance the coach side to side as best I can, inflate the tires based on corner loading, and have the tag pressure determined and adjusted based on the actual loading we will have on the coach (including trailer).

Long winded - sorry. My investment is too high to not use common sense and the knowledge and inflation charts provided by tire design engineers.
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Old 05-21-2014, 10:55 AM   #13
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Quote:
Originally Posted by Grady Ray View Post
The manufacturer of our tires, (Kelly Armour Steel), recommends 110 psi in the front tires, and 100 psi in the rear tires. On our 2001 HR Imperial, with 295/75/22.5 tires, I don't seem to be able to get but 100 psi in any of the tires. I've tried using my Porter Cable pancake compressor and the on-board compressor to no avail. I even bought Auto Zone's best tire inflator trying to inject more air, with no success. Whats up?
Grady Ray

Have you tried this method?
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Old 05-21-2014, 05:00 PM   #14
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I watch the gauge until it stops dropping, remove the chuck from the tire, then use the valve to release air until the on-board compressor kicks on. I wait until it get back up about 125 PSI before continuing to air the tire.
To expound on what MSHappyCampers is saying (as well as onechaddude) the issue is that there are really two pressure ratings for a compressor. The big numbers you see on the side of the compressor are the maximum pressure - the pressure at which the pressure switch stops the compressor motor. This is also known as the cut-out pressure.

The other pressure rating is the cut-in pressure. This pressure will always be lower than the cut-out pressure, often by at least 30 PSI. When the pressure in the compressor's tank gets below this pressure, the motor will start up to build pressure once again.

So the normal cycle is you start the compressor, and it will run until the tank reaches the cut-out pressure, then it will stop. As you use air, the pressure in the tank goes down until you get to the cut-in pressure at which point the motor will start again. When the pressure builds to the cut-out pressure, it will stop once again.

Take your typical 125 PSI portable compressor. The cut-out pressure is 125 PSI, but the cut-in pressure is probably only 95 PSI. There is no way you're going to fill a tire to 110 PSI by just connecting the chuck and waiting for the tire to fill. Once the tank pressure gets down near the tire pressure, air will stop flowing, and the tank pressure will stop going down. If this happens above the cut-in pressure, you're never going to pump more air to get things going again.

So, if this happens, the key is to bleed enough air out of the compressor tank to get the pressure below the cut-in pressure. Once the compressor starts building pressure again, quickly put the chuck back on the tire so you can pump some air into the tire. This will work until the pressure builds to where the compressor cuts off, then the pressure drops again. Then you will have to bleed off pressure again and repeat.

The other issue is that as the tank pressure approaches the tire pressure, the volume of air going through the hose will decrease, until you get practically nothing once you're within about 10 PSI. So you need extra pressure in the tank over and above what you want in the tire. A 125 PSI compressor is just about maxed out trying to put 110 PSI in a tire, it's going to take a long time.

The final consideration is the power of the compressor, which generally relates to the air flow it can generate. A small compressor, like a pancake compressor, won't compress the air very fast. I used to have a small 15 gallon portable 125 PSI compressor (rather larger than a pancake compressor) and it would take me a long time and many bleed/pump cycles to fill one tire - it was a combination of the low pressure and low flow rate from the compressor. It could take me 15 or 20 minutes to add 10 PSI to a tire.

I finally replaced that compressor, and now I have no issues: no bleeding down of the air needed to get the compressor running again, and only a minute or two to top off a tire. The new compressor has an 80 gallon tank, 175 PSI output, and a 5 horsepower two stage compressor that needs a dedicated 240 volt connection. It's as big as a small upright freezer, and not at all portable, but man can that thing pump air!
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