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Old 08-31-2012, 11:15 AM   #15
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A few comments/opinions:

* Heat buildup in tires comes mostly from sidewall flex, which is increased by under inflation. While heat buildup may be better tolerated in milder climates, it is a serious concern in areas where highway temperatures exceed 110 degrees.

* Due to tire construction and belts, radial tire footprints are less affected by variances in tire pressure. For example, my personal observation (with no supporting measurements) is that there is very little difference in the footprint of our LR-E tires between inflation pressures 65 and 80 psi. In fact, on our 19-foot Bambi, I do not observe any difference in the sidewalls, either.

* Tire manufacturers recognize that pressure builds as tires heat up; that's why they specify to measure pressure when tires are cold. Normal pressure buildup is OK when underway; so don't worry if tires exceed the maximum pressure printed on the sidewalls, especially if the initial/cold pressure started at the maximum rated psi.

* Tow vehicle weight varies widely with the number of passengers and cargo. Therefore, the OEM tires usually have a wider variance between empty and full weight; and tire charts or previous experience will determine the best pressure to use, based on actual tire loading at the time. Image how much the weight varies between driving with only the driver when commuting, and when you add four people, the tongue weight of your Airstream, and a pickup bed of camping equipment, including extra water and fuel.

* Trailer tires are usually rated close to the maximum weight of the trailer (probably so that manufacturers can put on the minimum/cheapest tires that will carry the load, to save money); and travel trailers, more often than not, are fully loaded, unlike tow vehicles. Therefore, unless the trailer is consistently run "empty", maximum pressure should be used.

Based on the above, our Bambi tires are E rated and always inflated to 80 psi; and our tow vehicle tire pressure is adjusted according to whether we are towing or not.
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Old 08-31-2012, 11:41 AM   #16
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Originally Posted by Phoenix View Post
Based on the above, our Bambi tires are E rated and always inflated to 80 psi; and our tow vehicle tire pressure is adjusted according to whether we are towing or not.
Did your tires come stock or are they replacements? Do you know the weight rating of your Tires? E seems pretty Stiff for a Bambi, and at 80psi I would think it would bounce down the road.?

When I ran my Carlisle's at 65 psi (MAX) they ran hotter than at 60 psi. They also gain more psi up to 4 psi and when ran at 60 psi only gained 2 psi.

I will play with my New E rated Michelins LT tires, but am guessing I will run them around 60 - 65 psi as they are E tires and my Carlisle's were D rated.
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Old 08-31-2012, 12:33 PM   #17
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Originally Posted by purman View Post
Did your tires come stock or are they replacements? Do you know the weight rating of your Tires? E seems pretty Stiff for a Bambi, and at 80psi I would think it would bounce down the road.?

When I ran my Carlisle's at 65 psi (MAX) they ran hotter than at 60 psi. They also gain more psi up to 4 psi and when ran at 60 psi only gained 2 psi.

I will play with my New E rated Michelins LT tires, but am guessing I will run them around 60 - 65 psi as they are E tires and my Carlisle's were D rated.
Jason,
I am not trying to pick at your data. Well maybe I am. A couple years ago on some tire pressure thread I published a table of change of tire pressure with altitude. It was greater that one would think. My point is that the differences you are quoting are less than differences that normal environmental factors can cause. here is a short list.
Air temperature
Altitude
Temperature of road surface
Composition of road surface
Sun shining or not, and if there are clouds, how thick and how moist are they.
Wind velocity and direction
Humidity
Precipitation type and rate.
Is the road straight or winding.
Etc.

This is not even mentioning differences in how you are driving.

Ken
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Old 08-31-2012, 12:53 PM   #18
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Jason,
I am not trying to pick at your data. Well maybe I am. A couple years ago on some tire pressure thread I published a table of change of tire pressure with altitude. It was greater that one would think. My point is that the differences you are quoting are less than differences that normal environmental factors can cause. here is a short list.
Air temperature
Altitude
Temperature of road surface
Composition of road surface
Sun shining or not, and if there are clouds, how thick and how moist are they.
Wind velocity and direction
Humidity
Precipitation type and rate.
Is the road straight or winding.
Etc.

This is not even mentioning differences in how you are driving.

Ken

So in fact it could be worse?? My point is MAX tire psi is not always required and I think we have been told to run at the max because it is better. Now I believe this is not true... I don't think running 80psi on my new tires is going to be good for AS. I think it will be to hard of a ride... Plus the chart on tire pressure from Michelin (I got the same tires as yours) says up to 7000# tires can be run at 50 psi. Now that is for a truck. I will start at 60-65 psi and see how they look and what temps they run at, and go from there.
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Old 08-31-2012, 12:55 PM   #19
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load/pressure

Here is a chart for ST tires. It is the same for all manufacturers for a given tire size. This information is taken from the Tire and Rim Association which is the standard keepers for tire manufacturers.
Attached Files
File Type: pdf TireLoadPressure.pdf (53.3 KB, 52 views)
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Old 08-31-2012, 01:04 PM   #20
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Here is a chart for ST tires. It is the same for all manufacturers for a given tire size. This information is taken from the Tire and Rim Association which is the standard keepers for tire manufacturers.
That just gives you the max PSI, What people need to know is what PSI for what weight. Just because you can put 65 psi in your tires doesn't mean you should..

People don't run the max PSI on their car or truck? So why run the max on a AS. Run what your weight is plus some for extra cargo. When towing I up my PSI on my SUV by 10 psi to 55 psi. front and back. I can go up to 80 psi but don't need to. MY trailer (originally) was 4800# dry. Now i'm betting its over 5000# plus everything else I'm up around 6000+. I don't need to run my Trailer up to 80 psi, It will just bounce down the road...
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Old 08-31-2012, 01:11 PM   #21
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Originally Posted by purman View Post
That just gives you the max PSI, What people need to know is what PSI for what weight. Just because you can put 65 psi in your tires doesn't mean you should..

People don't run the max PSI on their car or truck? So why run the max on a AS. Run what your weight is plus some for extra cargo. When towing I up my PSI on my SUV by 10 psi to 55 psi. front and back. I can go up to 80 psi but don't need to. MY trailer (originally) was 4800# dry. Now i'm betting its over 5000# plus everything else I'm up around 6000+. I don't need to run my Trailer up to 80 psi, It will just bounce down the road...
Read it more closely. It give maximum load for a given PSI. So if you read it the other way, It give the minimum PSI for a given load.

Ken
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Old 08-31-2012, 01:14 PM   #22
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Well how about everyone start measuring tire temperature profiles at different pressures and see what you get, myself included. I expect I am running my tow vehicle tires at too high of a pressure and the wear patterns on the tires I just took off support that. Another way to determine proper pressure is using the chalk test. Put a chalk mark on the tire and drive a few feet. If the mark is more faded in the center then too much air if on the sides then too little. The temperature test is better.

Perry
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Old 08-31-2012, 01:23 PM   #23
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I guess it directly relates to your situation and set up. I run my AS tires at 50 each and my TV (E rated) tires are 50 up front and 60 in the back. For me the ride is super smooth. I have to remember to knock the rears to 50 when I done or my truck rides like a tank!
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Old 09-01-2012, 09:26 AM   #24
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Trailer tires at maximum sidewall pressure. No exceptions.

Tow vehicle:

1] Within vehicle manufacturer placarded limits
2] Also respecting any FF/RR bias

Load versus pressure for the TV. After 1.5 hours of steady state driving, should not see more than a 3-5 psi pressure rise (from cold). The "lowest" air pressure (respecting the above) with this low pressure rise is the number to try to achieve for best handling, braking and tire life. A few more pounds (respective of percentage change) for slightly better mpg, perhaps. On the rollover prone pickups/SUV's this is even more important.

You all might read around on BARRY's TIRE TECH website, by a tire engineer who has recently taken an interest in RV tires (especially the problematic ST). The above is just a condensation of that, and from the RV.net thread "Revised" from a little earlier this year.

A quality tire pressure gauge, a trip or two to the scales (not just for hitch rigging), and some record keeping to know the TV tire pressure range from solo/unladen to solo/laden and to the highest wheel position weights when towing.

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Old 09-01-2012, 03:18 PM   #25
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Our 26' Argosy has a GVWR of 6200#. I have run 3 years and almost 20K miles with the pressure at 55#. Haven't had a single tire problem. No rivets popping etc..
Have left items on the counters by accident. They are still there upon arrival. Towing speed is about 62 mph.
Never run the E rated tires on the TV over 65#.
I check the pressure in the morning before departing and about once every 600 miles or so.
When I stop for fuel or at a rest area, I check for hot spindles and wheels (for brakes running hot) and give the tires a kick.
Been doing this for the last 51 years of driving, pulling every kind of trailer one can imagine with every kind of load as well.
Although I haven't kept track. I'll bet I haven't had to change more than 1 tire every 5 years. I would bet that 80% of those flats were caused by junk on the road.
Maybe I'm one of the lucky ones. Don't know.
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Old 09-01-2012, 05:45 PM   #26
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So, If I currently have D rated tires--@ 65 psi and now I am thinking of changeing to an E rated tire, can I still run at 65 psi or do I have to increase to the 80 psi--I ran my tires (last falls trip) at 60 and had a blow-out. All other trips I took, I was running at 50 psi. It would seem to me that when I added the extra 10 lbs of pressure, my AS bounced more that it did at the 50. I have a 30 Classic rated @ 8700 lbs.
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Old 09-01-2012, 06:21 PM   #27
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So, If I currently have D rated tires--@ 65 psi and now I am thinking of changeing to an E rated tire, can I still run at 65 psi or do I have to increase to the 80 psi--I ran my tires (last falls trip) at 60 and had a blow-out. All other trips I took, I was running at 50 psi. It would seem to me that when I added the extra 10 lbs of pressure, my AS bounced more that it did at the 50. I have a 30 Classic rated @ 8700 lbs.
D rated tires have a load of 2540# I believe. If your running tandem the total load for all four is a little less say around 9000#. I need to find the chart to be sure.

My tires have a load capacity of 2680# but on a dually trailer they have a load of 4470# They are E rated Michelins... 225 75 R16

So you should be running pretty much max psi of 65 or 60 psi on your tires because you are pretty close to you max rating on your tires.

I ran 60 psi on my D rated Carlisle tires and my trailer is under 7500 lbs loaded..
Goggle your tires chart on line to find the exact load range for 4 tires.

So to answer your question "YES" you can run lower than 80 psi. But the Michelin chart for my tires says 65 psi would be less than what they want for your trailer weight. 70 psi would be recommended. But you need to consider what you have in the trailer. Dry weight is different the loaded weight..

Whatever tire you switch to, look at the weight ratings for that tire and what minimum psi you can run at that weight..

Good luck, this is a hot topic...
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Old 09-01-2012, 08:58 PM   #28
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The pressure/load range tables are not for trailers.

There is a reason ST tires are marketed as having "stiffer sidewalls", and the reason is the forces trailer tires undergo which passenger vehicles do not. The trailer is levered -- jacked -- into positions, and not just in backing. Turns, again, leveraged by the tow vehicle exert pressures against the trailer which passenger vehicles do not undergo.

The "best" tire has much to do with matching the load of the trailer, yes, but the sidewall printed maximum pressure is a requirement for trailers.

Go read your owners manuals.

Or tell us why more than one tire engineer is wrong on this subject.

.
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