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Old 05-24-2011, 10:43 AM   #1
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Increasing Tire Pressure

I recently took the first trip for the year in my 2003 Pace Arow and had installed a tire pressure monitoring system. I adjusted the tire pressure to the Michlien specs 80 psi front and 90 psi rear naturally based on my weight.

The pressure was set at an ambient temperature of 65 degrees. The trip was about 35 miles and ambient temperature was approx 70 degrees.

Now my question, the tire pressure on the rear tires increased 11 pounds per each dual tire and also about the same in the steer tires. The tire tmperature was 84 to 86 degrees. I realize that some increase in tire pressure happens, but I thought that 11 pounds seemed like alot for the short distance. Is this normal? When it gets hot do I have to check the tires again? Also what are a good set of high and low pressure readings to set in my monitoring system? I am currently 15 increase and 5 decrease. I would appreciate any advise as this has got me confused.
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Old 05-24-2011, 10:48 AM   #2
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What you're seeing is about in line with my experience too. Mine are infalted to 90 and after a while on the road they'll read around 105. The inside duals might get a little higher but not much.

I went with factory settings on my TPMS for low pressure alert. I don't recall right now just what those are but I think it sounds an alert at around 4% loss and another more urgent alarm at 12%.

Good luck...

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Old 05-24-2011, 10:50 AM   #3
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I am going to say the internal air pressure was higher temp .
however you never adjust pressure on a hot tire. the manf. sets the pressures for loads on a cold tire and its calculated the increase in temps and pressure from driving.
that being said....
just for arguments sake...makes sure your brakes aren't dragging causing friction heat and wheel bearings.


road surface temps, and conditions also play a big part in heat and expansion


you could calculate the air volume in the tire at the pressures you set and then do the math to see what temps would drive each subsequent air pressure change
but there are many variables to contend with.
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Old 05-24-2011, 11:56 AM   #4
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On my TPMS I can see up to a 20 psi increase in the summer heat on my drive tires. I see a little less on the steer tires.
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Old 05-24-2011, 05:47 PM   #5
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Set the TP in the morning prior to leaving, then leave it alone. It will increase with temperature, but that's the way it should work.
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Old 05-24-2011, 09:36 PM   #6
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80 in front? That seems awful low... 22k chassis, 14k in back, 8k in front... back tires are carrying 3500 pounds each, front tires holding 4000 pounds need more rpessure than rears?
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Old 06-17-2011, 03:37 PM   #7
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I spent a fair amount of time of telephone with RV manufacturer and tire manufacturer. Eventually, I got transferred to an engineer at the tire company. He was pretty surprised, as most "end-users" never make it to him. He told me that he was not supposed to answer questions regarding tire use from the general public, but he was reluctantly willing to hear me out on what I'd learned so far, and let me know whether I was barking up the wrong tree.

Basically, what you need to do is to weigh each side of each axle (2 axles for standard RV, 3 axles for tag-equipped, so you'll end up with either 4 or 6 measurements). Then, for each axle, take the higher of the two measurements, and double that to get the "axle-load", which you can find on your tire manufacturer's chart to calculate your optimal tire pressure. Make sure to select the dual-tire pressure for the dual-axle tires!

After all that math, you'll be tired, so go to sleep! :-)

In the morning, before the tires warm up, and before driving on them, inflate (or deflate!) each tire to the calculated optimal pressure for the axle. Update your TPMS alert settings if you use one, and hit the road.

Anyway, that's what works for us! YMMV!

Safe travels!
littlec
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Old 06-19-2011, 01:16 AM   #8
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Quote:
Originally Posted by littlec
I spent a fair amount of time of telephone with RV manufacturer and tire manufacturer. Eventually, I got transferred to an engineer at the tire company. He was pretty surprised, as most "end-users" never make it to him. He told me that he was not supposed to answer questions regarding tire use from the general public, but he was reluctantly willing to hear me out on what I'd learned so far, and let me know whether I was barking up the wrong tree.

Basically, what you need to do is to weigh each side of each axle (2 axles for standard RV, 3 axles for tag-equipped, so you'll end up with either 4 or 6 measurements). Then, for each axle, take the higher of the two measurements, and double that to get the "axle-load", which you can find on your tire manufacturer's chart to calculate your optimal tire pressure. Make sure to select the dual-tire pressure for the dual-axle tires!

After all that math, you'll be tired, so go to sleep! :-)

In the morning, before the tires warm up, and before driving on them, inflate (or deflate!) each tire to the calculated optimal pressure for the axle. Update your TPMS alert settings if you use one, and hit the road.

Anyway, that's what works for us! YMMV!

Safe travels!
littlec


Forgot one thing!

Before consulting the manufacturer's chart, you may want to add some weight in anticipation on your next fuel stop or water fill, if either tank is mostly empty..
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Old 09-04-2011, 05:28 PM   #9
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so in end if u got a 1993 33' fleetwood pace arrow min weight 14K max weight 18K what like 90 lbs in front 90 lbs in back even though rated for 110?
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Old 09-04-2011, 09:00 PM   #10
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Please do a Google search on the words, "goodyear tire inflation guide" without the quotes, and "michelin tire inflation guide" without the quotes. Read what the manufacturer states. Read especially the percentage of change regarding temperature change, and the psi change for altitude change. Also factor in the change in tire temperature based on running down the road at legal speeds. They all play a part.

As stated, and as the manufacturer states, only check tires when they are at cold ambient temperature. So best time would be before the sun has hit them for a long period of time, or the outside temperature has increased. And as the mfg's state, never let air out of a hot tire.

Read their information, you will get much more out of it than being told by us "tire experts."
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Old 09-05-2011, 08:41 AM   #11
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Quote:
what like 90 lbs in front 90 lbs in back even though rated for 110?
Not sure where you got the "rated for 110", but if you mean the max pressure shown on the sidewall, that is just what it says - a max load pressure.

Get the tire inflation table for your brand of tire and look up the size and actual weight carried by each axle. Your 90 psi may be about right, but without further information nobody can give you an answer.
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Old 09-10-2011, 09:48 PM   #12
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Quote:
Originally Posted by Gary RVRoamer View Post
Not sure where you got the "rated for 110", but if you mean the max pressure shown on the sidewall, that is just what it says - a max load pressure.

Get the tire inflation table for your brand of tire and look up the size and actual weight carried by each axle. Your 90 psi may be about right, but without further information nobody can give you an answer.
Not true!
On a truck tire it is the MINIMUM cold pressure to support the maximum load. With the tire charts it is again the MINIMUM cold pressure to support the load given.
Quote:
From page 2 of the 06/07 Michelin RV Tire Guide: "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."
Quote:
From page 2 of the 04/09 Michelin RV Tire Guide:
AIR PRESSURE REQUIREMENT
The amount of air pressure required in each tire depends on the weight of the fully loaded vehicle. So the RV owners cannot determine the tire’s correct air pressure unless they know their vehicle’s actual weights. 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. The lower the air pressure, the lower the load that the tire can carry. A complete load and inflation table is available at www.michelinrvtires.com; MICHELIN® RV Tires: Guide
For Proper Use and Maintenance and RV Tire Information – MWL43146; and the MICHELIN® Truck Tire Data Book – MWL40731.
Quote:
From page 6 of the GoodYear RV Tire Care Guide
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.
On car tires IT IS the maximum cold pressure the tire should ever have.
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