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Old 08-31-2012, 08:27 AM   #1
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Max PSI

Hey guys! I was wondering how close to the max psi you run in your tires? Iv got E rated tires on my TV (80 psi max). I figure Id run 70 psi in the rears and 60 in the front. As for the trailer, Im unsure on the max psi but I figure I will put 5-10 psi under the max. Is this a good idea? I know the more air you put in, the less sidewall flex, thus less heat generation. But at the same time, more pressure means when it does heat up, the pressure will increase even more which could lead to bad things... What do you guys think?
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Old 08-31-2012, 08:34 AM   #2
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If I were towing I would keep it close to the max on the rear and maybe 10lbs less on the front. Look on the plack on the drivers side door. It will tell you what the factory recommends. My Excursion says 45 in the rear and 35 in the front and it came with D rated tires. I have E rated tires on it and I could probably get away with the factory numbers but I usually boost it up a bit. When towing I think I run 70 psi in the rear and 60psi up front and it is probably overkill. The best way is to measure time temps on the sides and in the center. When the center is running hot you have too much air if the sides are running hot then too little air. When all three temps are the same you are close. When you get over 200F slow it down.

If you are towing with a truck and you have 2000lbs of stuff in the bed then I would run the max pressure. You maybe able to find a pressure versus load chart from the tire manufacturer.

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Old 08-31-2012, 08:40 AM   #3
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Why run the max? I did 3000 miles a few weeks ago. I ran my E rated tires on my TV at 45psi. I ran my D rated trailer tires at 60 psi. I noticed when a ran them higher the pressure went up faster and they ran hotter. Max psi is not always the best. If I was putting 4000 lbs of gravel in the. Ack of my truck I would run the psi up close to max. But other than that high pressure is just to keep your tires cooler. But I found that higher pressure doesn't always mean cooler tires.


Also higher pressure makes for a rougher ride. Which AS don't like and neither do I.

And also why would you run different pressures in front and back? Keep them the same.
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Old 08-31-2012, 08:44 AM   #4
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You are right Jason if you have your tires way overinflated they will run hot in the center because that is where all the friction is. The center part of the tires is carrying more that it's share of the load. They will also wear in the center.

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Old 08-31-2012, 08:50 AM   #5
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Quote:
Originally Posted by perryg114
You are right Jason if you have your tires way overinflated they will run hot in the center because that is where all the friction is. The center part of the tires is carrying more that it's share of the load. They will also wear in the center.

Perry
I'm not talking over inflating. I run under max psi all the time. Never to the max. Reason. Tire pressure goes up as he tire warms up. So if you start at the max it will go over the max, and then you will be running an overinflated tire. I watched my tires gain nearly 4 psi in temps over 100 degrees. I also noticed if the tires started out over 60 psi they ran hotter and gained more psi also. Not sure why. Will be interesting to see what the new michelins do on our trip to Zion NP in a month.
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Old 08-31-2012, 08:57 AM   #6
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On my Chevrolet 3500 tow vehicle, I run 80 psi on the rears and 70 psi on the fronts. I am hauling a 3,000# truck camper in the bed all the time. On the 7,400# Airstream, I have Michelin 16" LT's that I run at 72 psi.

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Old 08-31-2012, 09:14 AM   #7
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The label on the tire usually says 80psi cold inflation pressure. I would assume the manufacture has already accounted for the rise in pressure with use.

I maybe running too much pressure in my tires.

Perry

Quote:
Originally Posted by purman View Post
I'm not talking over inflating. I run under max psi all the time. Never to the max. Reason. Tire pressure goes up as he tire warms up. So if you start at the max it will go over the max, and then you will be running an overinflated tire. I watched my tires gain nearly 4 psi in temps over 100 degrees. I also noticed if the tires started out over 60 psi they ran hotter and gained more psi also. Not sure why. Will be interesting to see what the new michelins do on our trip to Zion NP in a month.
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Old 08-31-2012, 09:33 AM   #8
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One man's opinion.... As inferred by some of the posts, tire pressure is load related. The real question is what the tire contact patch looks like. Running max pressure on a lightly loaded tire can cause it to dome a bit and reduce the contact patch. Tire pressure is a function of tire design and load. That's why the max pressure is expressed as being rated at max load. As the load is reduced, the tire pressure can be reduced to maintain a good contact patch. What the function of load reduction is to pressure reduction is dependent on tire design. However, the function is usually not directly related. That is, 50% max load does not call for 50% max pressure.
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Old 08-31-2012, 09:34 AM   #9
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Manufacturers publish load tables so if you need to use less then max pressure just pick the right pressure for the load. For instance the E rated tire at 80 lbs goes to D rated at 65 lbs.
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Old 08-31-2012, 09:55 AM   #10
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Im not "overinflating" them. 70 psi is under the max of 80. And I prolly didnt mention what I was haulin lol. My AS of course! 31 footer. 4680 dry weight, 580 tongue weight.

I did some calculation thing on the internet to see how much my truck would sag. According to them... less than 3/4 of an inch (.70")... hardly believeable. If thats the truth then there is hardly any weight on the back of my truck and I wouldnt NEED to run higher psi
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Old 08-31-2012, 09:55 AM   #11
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So if you are at max psi you are at max load on your tires. This would then seem you may want to get different tires as you are maxed out. I think I will find the tire chart for my Michelins and figure out my best psi as I know it's. It 80 psi.
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Old 08-31-2012, 10:02 AM   #12
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http://www.michelinrvtires.com/miche...ion-tables.jsp
For other tires the tables are nearly the same
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Old 08-31-2012, 10:07 AM   #13
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My tire size isnt on there
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Old 08-31-2012, 10:14 AM   #14
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Look here:
Michelin-Truck - Truck Tire Data Book New

According to this I can run my E tires at 45-50 psi.. To run at 80psi I would have to have a trailer that weighs 9800 #

Very interesting.. I'm betting most people are running their psi to high...
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Old 08-31-2012, 10:15 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, 10:41 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, 11:33 AM   #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, 11:53 AM   #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, 11:55 AM   #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.
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File Type: pdf TireLoadPressure.pdf (53.3 KB, 71 views)
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Old 08-31-2012, 12:04 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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