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Old 02-07-2011, 12:13 PM   #1
GAT
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Ball Ground , Georgia
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Tire pressure

I can't seem to get an answer about proper tire pressure from the people that installed my 225/75/15 D range pressure. They put 40psi when I picked them up. Three months latter when I got ready to tow I went back to see the recommendation and they told me to go up to the rating on the side wall which is 65 psi. Who knows what is correct. I plan to tow over 1000 miles for my first real trip next week. Thanks for suggestions.
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Old 02-07-2011, 12:26 PM   #2
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I believe that with the D load range tires and the trailer that you are talking about, you need to be at 65 psi. 40 psi is underinflated for the weight that you are carrying, and may cause tire overheating at highway speeds.

Brian
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Old 02-07-2011, 12:33 PM   #3
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Quote:
Originally Posted by GAT View Post
I can't seem to get an answer about proper tire pressure from the people that installed my 225/75/15 D range pressure. They put 40psi when I picked them up. Three months latter when I got ready to tow I went back to see the recommendation and they told me to go up to the rating on the side wall which is 65 psi. Who knows what is correct. I plan to tow over 1000 miles for my first real trip next week. Thanks for suggestions.
The correct tire pressure also depends on the load.

"D" tires are maxed out at 65 psi, for the load of 2500 pounds plus, per tire.

But, when they are inflated with "air" that pressure increase with temperature. That in itself, can cause a tire to fail, should it get hot enough.

A better inflation media is to use "nitrogen".

If the trailer will be at a moderate load, then 55 to 60 psi is plenty.

Also, to keep the tires from getting a hot spot due to scuffing, the running gear should be properly balanced and kept that way. Some owners add balancers such as Centramatics, which keeps the running gear balanced from 25 mph and up.

If the Airstream has 3 or 2 piece hub and drum assemblies, it's also wise to check them to make sure one is not way out of balance as they are, all too many times. Centramatics would not help that situation, and a rebalance would be often required.

The old 3 or 2 piece hub and drums, are sometimes found to be as much as 3 pounds out of balance.

Andy
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Old 02-07-2011, 12:41 PM   #4
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On the side of the tire there are numbers that give you the tire pressure at max load for the tire. The max load will be different for load range "D" tires as compared to load range "E". As will the air pressure.
Here is the way I do it. This is only an example. If the max load of the tire is 2000# and the max air pressure for that load is 65#.
4 tires on the trailer can carry 4 x 2000 = 8000 pounds.
My trailer weighs 6000# loaded and ready to go. With the trailer weight being 3/4 of the max weight of the tires. 6000/8000=3/4.
I take 3/4's of the max pressure of 65#. 65 x .75 = 48.75 round it off to 50#.
Now keep in mind that the 6000# weight of the trailer is not all on the tires. If it were there would be 1500# on each tire. When the trailer is on the tongue jack or hitched to the TV there is some tongue weight. A properly hitched trailer will have at least 10% of the total weight on the tongue.
Since the TV is carrying some part of the total 6000# there really isn't 1500# on each tire on the trailer.
I would not run the tires at their max pressure if they are not carrying close to the max rated weight.
Airstream trailers are sensitive to hard rides. They can't stand the beating. Popped rivets etc. So why make the trailer ride on rock hard tires if it isn't necessary.
I don't tow my trailer any faster than 65 mph. Part of my routine is to check the wheel bearing hubs and tires for excessive heat each time I fuel up. This method has been succesful for me over the years.
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Old 02-07-2011, 02:32 PM   #5
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This makes it pretty easy.

Just saw this on eHow. Sounds like a pretty good rule of thumb. Divide the weight of the vehicle by 100. That's the tire pressure.
So if I used this formula on a 6000# GVW trailer and the tongue weight of the trailer is 600#. Trailer weight on the tires is 5400#. That means 54# (plus or minus 2 pounds) of air in the tires. Pretty close to what Andy recommended. Pretty easy to remember too.
Tires can be scuffed by bad shocks as well.
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Old 02-07-2011, 03:36 PM   #6
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That might work well for you, but I would follow the recommendation of the tire maker and the load on the tires. The same trailer could have D or E rated tires and the tire pressure would not be the same for both.
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