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Old 06-18-2016, 10:47 AM   #15
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Originally Posted by Texbeachbum View Post
I just had 6 new tires installed. They are 120 PSI max. I had MH weighted They only did steer axle (6600 lb) and drive axle (12540 lb) Total weight 19140 lbs. This was weighted with full tanks and full of gas. MH fully loaded for road. Tire place told me not to go under 105 PSI. Also 16 ply tires. What pressure should I use. I have 110 in them now.
You should use the tire pressures shown on the tire manufactures inflation chart for the particular brand and size of tire.... using the weight carried by the tire.

Get one from the dealer.... or try Googling "inflation chart for XXX tires", (replaceing the Xs with the tire name & size).

'96 Safari

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Old 06-18-2016, 12:36 PM   #16
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Originally Posted by Texbeachbum View Post
I just had 6 new tires installed. They are 120 PSI max. I had MH weighted They only did steer axle (6600 lb) and drive axle (12540 lb) Total weight 19140 lbs. This was weighted with full tanks and full of gas. MH fully loaded for road. Tire place told me not to go under 105 PSI. Also 16 ply tires. What pressure should I use. I have 110 in them now.
We can go in a thousand different directions here, so let me simplify this for you. I am not a tire expert but I have done a lot of studying on this topic over the past two years. I'll try to condense it here for you to simplify your question and the answer.

Weighing you coach is always a good way to start the process of choosing tires. We need tires that will carry the coach load, within coach build limits, and give a margin of safety overhead. Example: The original Michelin's on my coach were at max load rating right out of the factory door. We have only been in this coach for about two years. Early into our ownership we drove to Freightliner in Gaffney, SC to have the chassis evaluated and serviced. Upon doing the 4 corner weigh we discovered that one of the wheels was a bit over the tire/chassis weight spec. We, over time, did a load adjust to compensate. I just was not happy with the old tires because they were being loaded to the max.

In my studies, this is what I learned: Choose tires that are not at the max loading for your rig. This seems only like common sense.

Set the air pressure per axle. The heavy wheel is the pressure to set the axle for. Your tire manufacturer has a chart to give you the best psi value.

Always check your tires cold and out of the sun.

The tire pressure marked on the side of the tire is the minimum psi needed to meet the maximum load rating of that tire. If you put more air pressure in the tire it does not mean that the tire can safely carry more load than designed for.

Running more psi than your load requires only hardens the ride comfort.

Wet air, air not passed through a dryer/filter, will expand more than dry air. It is a rule of thumb that your tires will gain rolling pressure caused by road friction and ambient temperature. Not all tires heat the same when under way.

As stated earlier, I have removed the original Michelin's and replaced the steers with Continentals and the drives with Toyos. The mix is not ideal. I can't say that I used wisdom here but the mix is working well. Both sets are "green" tires. Both have low roll resistance characteristics. The Toyos are the better $$ value and are as good a tire as the Continentals. Both sets are H rated and can be charged to 120psi. I run 110psi all around.

I am using a TPMS. This is a good tool to use for a warning of a pending failure alert. If one tire start to show a psi far out of the range of the others, it is a good time to pull over and give a good look see. From personal experience I testify that a blowout is a good thing to avoid! $$$

With the new tires, the temperature gain, when underway, is not as great as with the old tires. It was not unusual for the old set to get to around 130+ psi when traveling. The new tires, on the first time out, got up to about 124psi and not much more. The trip was 430 miles long and all in one day from OR to WA. It was a good, comfortable drive.

I hope all of this helps. There is a lot more that can be added to this. I think this should answer most of your questions.

Happy trails and many of them.

Rick Y

Rick & Melissa Young, 2011 Itasca Meridian 40U, Frtliner XCL, Cummins ISL 380HP/DEF, Allison 3000 MH, 2014 Honda CR-V, SMI AF1, Blue Ox, EEZ TPMS, TruCenter steering control
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Old 06-19-2016, 04:01 PM   #17
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Based on the info Texas posted here is my suggestion.

New tires at 7 years is reasonable. If your weights were when loaded as you would normally travel i.e. heavy you are is good shape.

I figure the minimum cold inflation you should run is figured this way:

Lacking individual side to side weights I suggest assuming a 45/55 side to side split. So heavy front would be 3,630#. Load tables say 70 psi minimum. I suggest you run +10% to avoid day to day pressure changed due to temperature changes or 77psi and then round up to an easy number to remember or 80 Psi Front

Rear 3,449 per tire dual which would be 75 min. Add 10% and round up and we get 85 psi rear.

Since your tires are LR-H you have lots of reserve if you need to increase inflation to support more load. Remember you do not want to exceed the axle max and all tires on an axle should have the same inflation.

Hope this helps. If you want to learn more about tires you can check out my blog.

Retired Design & Quality Tire Eng. Read my tire blog RVTireSafety.NET to learn more about RV tires, valves & wheels. Read THIS post on why Tires Fail
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