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Old 09-17-2011, 11:22 AM   #15
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No argument about OTR manipulating tire pressure. Most of the time it is set at the maximum allowable on the tire. However, we are not talking about OTR truckers. The link is for RV tire care, and the example came off of the Goodyear tire inflation table. I will tell you that when I drove OTR for the private firm I was working for, I checked the tires every morning. I never had to worry about over the max as I was on the same route with basically the same temperature.

You will find a lot of OTR drivers that say they can tell by "thumping" the tire. Well, maybe they have a brain that can decipher those thumps, but I sure could not.

If it is 100 degrees outside I guess you could use the formula that there will be a 2% difference in pressure and adjust to that psi rating for 80 degrees. To complicated for me. I sure do see a lot of "road alligators," when I'm traveling an I'll wager they are 99% or more from OTR Trucks.

Yes, a good TPMS will facilitate having to get out the air gauge and check each tire manually. You just sit in the cab and look at the monitor. However, the pressure in the tire is still based on what I previously posted and is set accordingly. Once it is set you can then monitor it and it is a great tool if loosing pressure while going down the highway, and a TPMS may give you enough time to pull over. But, it does not tell you how much air to put in the tire for the weight you are carrying. That is still a manual calculation method. The TPMS is great for real time monitoring, but if you drop 30 degrees over night, look at the TPMS and it is 5 or 6 degrees below the recommended fudge factor setting you do not have to go out and put air in the tire. The manual tire gauge inspection will do the same thing.

The TPMS is a great tool, don't get me wrong here, please. But we still have to use our brain for the computations.

Happy trails.
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Old 09-17-2011, 12:43 PM   #16
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Air your tires to RV specks, and drive away. Most of you are trying to make this rocket
science. Might adjust if temp is 40 degrees one way or another on a long trip.
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Old 09-17-2011, 01:01 PM   #17
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Agree!! Some try to make this really hard... Fill to what the chart says for your weight, or, to what the coach OEM says if you havent weighed yet, and go...
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Old 09-17-2011, 01:50 PM   #18
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Wayne,

I know we aren't talking about OTR truckers but truck tires are truck tires. I am in the same camp as beach_fv and Midniteoyl. A lot of you want to make this way more difficult than it really is.
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Old 09-17-2011, 03:42 PM   #19
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Boy, the tire manufacturers could have saved a bunch of money on engineering and printing all those booklets on rv tire maintenance if they had only been reading these posts.

Air'er up, thump it with a stick and let'er rip.
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Old 09-17-2011, 08:30 PM   #20
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Yep! Agree.

I know you know, I posted what I did because of the misinformation that seems to be accumulating and spreading around. I just wanted the facts out there. Sure glad I don't believe in tire thumpin'. In the past several days I have seen reference to 10 degree, 1 psi change and that is NOT correct. Where it comes from, I don't know. As I stated, it is 10 degrees 2%(percent) change in pressure. Big difference as you go up in tire size and have 110psi or more.

At 30 degree change in temperature that is 6.6 psi difference and can mean overloading, or overinflated, depending on your "fudge" factor and which way the temperature swung. At an increase change, and if your tires max is 110psi, you are now 6.6 pounds overinflated. Personally, I just don't want to risk it. Two lives, and a pet, are depending on 6 tire footprints on the ground.

Ah! It will never be right, right?

Just the facts, Ma'am, just the facts.

And the others, what are, and where do you find the RV specs? Not quite so simple, but still not complicated. It is the tire manufacturer's specifications, not an RV specification in my opinion. That is one of the problems, people don't read the "booklets."
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Old 09-18-2011, 05:32 AM   #21
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The reference to 1 psi for every 10 degrees comes from the following:
Tire Tech Information - Air Pressure, Temperature Fluctuations

Longacre Racing Online -- Tech Article "Tire Pressure and Temperature"

Cool weather and tire pressure

Nitrogen in Tires : Information about Nitrogen Tire Inflation News, Benefits, Generator Dealers, Location Finder & More

Tire Pressure Vs. Temperature | eHow.com

I can't seem to find the 2% change for each 10 degrees anywhere. Do you have some reference for this?
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Old 09-18-2011, 07:27 AM   #22
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I think I'll just carry a stick for thumping and leave the calculator home.

Air'er up, give'er a thump and let'er rip.
Gotta be a major time saver too.
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Old 09-18-2011, 08:31 AM   #23
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Tire Pressure

I can just see it now! Huge traffic backups on Interstate highways while thousands of over the road truck drivers pull over to the breakdown lane to change the pressure in their "18" wheeled tractor/trailers. (As I drive right by them)
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Old 09-18-2011, 11:18 AM   #24
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Quote:
Originally Posted by randco View Post
...........I can't seem to find the 2% change for each 10 degrees anywhere. Do you have some reference for this?
Yes I do, it is in the Goodyear RV Tire Guide (and you can search for those terms) or take my word that this is what it states:

"The effects of temperature and atmospheric pressure.
Air temperature and atmospheric pressure effect tire inflation pressure. If the outside temperature increases 10oF,
tire inflation pressure increases approximately 2%. Conversely, when the outside temperature drops 10oF, the tire
inflation pressure lowers approximately 2%."

It is on page six to help everyone find it easier.

Now who am I to argue with the tire manufacturer.
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Old 09-18-2011, 11:27 AM   #25
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If memory serves me correctly Mile Cody at Camp Freightliner in August explained the tire pressure changes pretty much the same as the way WayneM does in posts 10 & 11.
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Old 09-18-2011, 05:27 PM   #26
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Quote:
Originally Posted by Wayne M View Post
Yes I do, it is in the Goodyear RV Tire Guide (and you can search for those terms) or take my word that this is what it states:

"The effects of temperature and atmospheric pressure.
Air temperature and atmospheric pressure effect tire inflation pressure. If the outside temperature increases 10oF,
tire inflation pressure increases approximately 2%. Conversely, when the outside temperature drops 10oF, the tire
inflation pressure lowers approximately 2%."

It is on page six to help everyone find it easier.

Now who am I to argue with the tire manufacturer.
You might be right, but on page 3 of the Toyo - RV, Motor home Tire Inflation, Safety & Maintenance - Techinal Bulletin (December 1, 2004) it says and I quote, "All tires lose air at the rate of 1 – 1.5 PSI per month due to natural permeation of the air through the tire’s rubber membrane. Always check the cold inflation pressure of any vehicle that has not been driven for several weeks and re-inflate the tires to the placard pressure before driving.

Tire pressure is affected by the ambient temperature to the extent of approximately 1 PSI per 10 degree (F) change in temperature. As an example, a 20 deg. (F) drop in temperature will result in a 2 PSI drop. A 20 deg. (F) increase in ambient temperature will result in a 2 PSI increase."

Now who am I to argue with the tire manufacturer?
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Old 09-18-2011, 05:38 PM   #27
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Quote:
Originally Posted by Wayne M View Post
You will find a lot of OTR drivers that say they can tell by "thumping" the tire. Well, maybe they have a brain that can decipher those thumps, but I sure could not.
On of the truckers magazines did a test of exactly this. They had 50 drivers "thump" tires. Of the 50 only two could detect a tire 20% (dangerously) low. So if a professional driver with years of experience can't tell...........
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Old 09-18-2011, 06:02 PM   #28
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Several years ago I put a TPS system on a motorhome and much later while traveling the low air alarm indicated a rear tire was low. I looked at the tires and not see a visable difference so got my handy dandy thumper and could not tell by thumping. The tire continued to lose air and I had it repaired (nail). I presume if the truckers thumped the a gazillion tires they might be able to tell a low tire but I sure couldn't even after thumping them a couple of years unless it was really low. So now its TPS backed up by a hand gauge.
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