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Old 09-24-2010, 07:00 AM   #1
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Tire pressure increase

Most people once they pressure up don't look again till probly tomorrow or later. I have pressure pro and I start at 110 lbs in all tires. After about an hour of driving, I'm up to 130 in most. The tires say 120 lbs max cold, should I be concerned? Aluminum rims say 120 lbs max also? I have 22.5 tires.
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Old 09-24-2010, 07:22 AM   #2
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Marty,

Why do you start out with 110 LBS when your tires state 120? Is that because of your weight measurements?

I know this will go against the grain of a lot of people, but I set my pressure at what the sidewall max cold pressure says, and sometimes 5 lbs above and leave it at that.

I don't adjust after any increase in pressure after driving.

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Old 09-24-2010, 08:10 AM   #3
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The recomended max cold pressure allows for the increase when the tire heats up. The rim rating allows for the same. No adjustment is necessary. Under inflation will cause the sidewall to flex excessivly with the end result of uneven tire wear and poor handling,
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Old 09-24-2010, 08:18 AM   #4
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I know this will go against the grain of a lot of people, but I set my pressure at what the sidewall max cold pressure says, and sometimes 5 lbs above and leave it at that
Yep thats against the grain. You are most likely way overinflated which means that your tire footprint will be mostly to the middle of the tire which gives poor handling, rougher ride, uneven wear, and increased chance of puncture from foreign objects.
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Old 09-24-2010, 08:59 AM   #5
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Originally Posted by howie-2005 View Post
Most people once they pressure up don't look again till probly tomorrow or later. I have pressure pro and I start at 110 lbs in all tires. After about an hour of driving, I'm up to 130 in most. The tires say 120 lbs max cold, should I be concerned? Aluminum rims say 120 lbs max also? I have 22.5 tires.
Thanks,
Marty
You should ALWAYS go by the Spec. Sheet inside the cubboard door.
Whatever pressure is printed on the sheet for each tire, that should be the max. pressure. Not the sidewall.

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Old 09-24-2010, 09:02 AM   #6
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My tires are stamped 95 lbs all the way around, dual and single.

The door sticker says 90 lbs for the front and 80 for the rear

I'm a way over inflated


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Old 09-24-2010, 10:34 AM   #7
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Yep thats against the grain. You are most likely way overinflated which means that your tire footprint will be mostly to the middle of the tire which gives poor handling, rougher ride, uneven wear, and increased chance of puncture from foreign objects.
Ditto what he said.

As you probably know already, getting at least axel weights (if not 4 corner) and then going to the tire mfg inflation charts is the only way to really get the correct pressure for your rig.

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Old 09-24-2010, 10:49 AM   #8
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I think the OP is asking if the increase in pressure after the tire heats up is a concern and the answer is no. Once the cold inflation is set there is no need to adjust after the tire heats up. Under inflating does more damage than over inflating as it will cause excessive heat buildup which can cause tire failure.

I have always wondered about those stickers placed in the coach by the manufacturer. How do they know what weight I have in the coach and how much of the load each tire is carrying.
The last set of Michelins were on my old coach for ten years and down to the wearabars when I replaced them. I always ran them at max cold pressure, and will continue to do so. Dont see how I can ask for better performance than that.
I might also add that I use 303 on the tires regularly.
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Old 09-24-2010, 11:58 AM   #9
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Under inflating does more damage than over inflating as it will cause excessive heat buildup which can cause tire failure.
When I start out on a long trip I always check the tires temp after the first few stops for gas and rest by hand to see if one is running hot. Most of the time they are only warm to the touch and I don't worry from then on.

A temp gun would probably be a good device to have for that purpose.

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Old 09-24-2010, 12:17 PM   #10
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Set the tires to the correct cold inflation pressure (I use the load charts + 5 PSI on the truck tires, sidewall maximum load cold inflation pressure on the 5th wheel tires - YMMV) and don't worry about pressure increases due to temperature. The tire manufacturers take that pressure rise into account when they establish the cold inflation pressures.

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Old 09-24-2010, 12:50 PM   #11
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I cannot believe there are so many uninformed people on the forum!! You do NOT go by the MAX on the side of the tire... you do NOT go by the tag by the drivers seat... These are only to help you NOT go to high as in MAX and Suggested as a starting point on the drivers side tag.
WEIGH it and set the pressure according to weight by the tire manufactures specifications chart available at your dealer or on the web.
Do it right and maybe there won't be so many blow outs!!

PS... NEVER add or remove air from a hot tire... CHECK and ADJUST only on a COLD tire
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Old 09-24-2010, 01:27 PM   #12
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I cannot believe there are so many uninformed people on the forum!! You do NOT go by the MAX on the side of the tire... you do NOT go by the tag by the drivers seat... These are only to help you NOT go to high as in MAX and Suggested as a starting point on the drivers side tag.
WEIGH it and set the pressure according to weight by the tire manufactures specifications chart available at your dealer or on the web.
Do it right and maybe there won't be so many blow outs!!

PS... NEVER add or remove air from a hot tire... CHECK and ADJUST only on a COLD tire
Right on!

The max pressure on the sidewall is just that - the max pressure the tire can safely hold.

The pressure on the sticker by the door or in the cupboard is the pressure for the max weight the axle is designed to carry.

The CORRECT pressure is, as Rick Long states, determined by weighing each corner of the coach and using the tire manufacturers pressure chart for the size and type of tire in question. Set the pressure on each axle according to the max corner weight on that axle.

Back to the question of the OP, I agree with what Rusty said. Cold inflation pressures take pressure increases due temperature rise under normal operating conditions into account. Excessive temperature rise is a sign of possible problems such as under inflation or overloading.
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Old 09-24-2010, 01:30 PM   #13
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We took the Beaver out to Redlands and did some things to it. Part of the deal was to weigh the rig and thereby set tire pressures. I personally do not mess with air pressures as a blow out can lead to a very bad day. I know this does not answer your question but I follow this philosophy on my motorcycle, car's and Motorhome. Too much air or too little makes for bad handling and unnecessary wear.
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Old 09-24-2010, 02:26 PM   #14
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Now just for fun let’s define “cold”! Just last week I was underinflated up in Asheville, NC @ 5:30 AM because it got down to 52 degrees F. But, by noon I was right back on the my desired 95 to 100 range with a OAT of near 70 degrees F. When the manufacture determines the ideal pressure they certainly must use the universal standard temperature don’t you think, (20 degrees C/68 degrees F)
Or maybe take your choice of:
NTP - Normal Temperature and Pressure

NTP is commonly used as a standard condition for testing and documentation of fan capacities:
  • NTP - Normal Temperature and Pressure - is defined as air at 20oC (293.15 K, 68oF) and 1 atm ( 101.325 kN/m2, 101.325 kPa, 14.7 psia, 0 psig, 29.92 in Hg, 760 torr). Density 1.204 kg/m3 (0.075 pounds per cubic foot)
SATP - Standard Ambient Temperature and Pressure

SATP - Standard Ambient Temperature and Pressure is also used in chemistry as a reference:
  • SATP - Standard Ambient Temperature and Pressure is a reference with temperature of 25 degC (298.15 K) and pressure of 101 kPa.
ISA - International Standard Atmosphere

ISA - International Standard Atmosphere is used as a reference to aircraft performance:
  • ISA - International Standard Atmosphere is defined to 101.325 kPa, 15 degC and 0% humidity.
ICAO Standard Atmosphere

Standard model of the atmosphere adopted by the International Civil Aviation Organization (ICAO):
  • Atmospheric pressure: 760 mmHg = 14.7 lbs-force/sq inch
  • Temperature: 15oC = 288.15 K = 59oF
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