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Old 10-25-2018, 07:53 PM   #1
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What is correct tire pressure on a Class A - 34 ft

We put our motor home in the shop before our summer trip after staying the winter in our AZ home. Had points to cover and one was to check all tire pressure.

About 500 miles to our destination while on I-10 we had a blowout on an inside back passenger tire. Thank goodness we had ERS. The gentleman arriving with a tire as our RV doesn't carry one he proceeded to get to work. It was bad and we were lucky to have minimal damage. He told us that we should have 90 lbs pressure and the one next to it had 65. He checked the rest and they were at 65. $750 lighter we were back on the road. We had him put all tires at 90 and had no further problems to our destination, or on the 1000 mile trip home.
We went into the RV Shop and asked why the bill listed all tires put at 65 lbs pressure and said we had a flat. The Manager of the shop asked us to please check the label on the manufacturer tag and see what it says. Tag read 65 lbs of pressure.
Any thoughts? Anyone have same problems. ERS tech said they were low and rubbing against each other and we were lucky no other tires had blown.

Thanks in advance
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Old 10-25-2018, 08:21 PM   #2
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Most tires have a 'minimum' and maximum pressure. Read the tire again.

There isn't a 'normal' pressure for MH tires. It all depends on your weight so have it weighed and check the manufacturers web site for correct tire pressures. The best way is to do a 4 corner but if not, weigh the front axle then the whole rig. You can subtract the front from the total and find out how much weight is on the rear axle.
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Old 10-25-2018, 08:26 PM   #3
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Wink Weigh it...

You need to get your coach weighed, loaded as you normally travel. Then go to the load inflation table from the manufacturer of your tires and inflate according to the actual load they will be under.

Do not blindly inflate to the maximum on the sidewall of the tire... that could be correct but probably is nowhere, near the proper psi. Also, ignore any sticker from the RV manufacturer as they had no clue what your actual weights {real world} would be. Get thee to the CAT Scale.

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Old 10-25-2018, 08:32 PM   #4
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The pressure on the sidewall of heavy duty tires (any vehicle with a GVWR of 10,000#'s or more) in NOT the maximum the tire should ever have. It is the minimum cold pressure to support the maximum rating of the tire. This allows for the pressure gain due to heat from driving.
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Old 10-25-2018, 09:02 PM   #5
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The ERS guy was wrong. If it shows 65 on the sticker that is based on your gvwr so without weighing your coach 65 was correct but 90 is over inflated and will cause problems.
How old are your tires?
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Old 10-25-2018, 10:08 PM   #6
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My opinion the RV shop that said read the tag did you a BIG disservice! Most RVís have on the drivers door or some where in the front a list for tire pressure & your tire sidewall should also have pressure limits! 65 is way to low! The higher the pressure the more load the RV can manage. Weighing the RV can show you how much your carting around. I always pushed my tire pressure just under max. Tire age is also important. 7/8 year old tires are at their limit. Look to replace regardless of tread appearance
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Old 10-25-2018, 11:58 PM   #7
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Quote:
Originally Posted by Monacoach View Post
The ERS guy was wrong. If it shows 65 on the sticker that is based on your gvwr so without weighing your coach 65 was correct but 90 is over inflated and will cause problems.
How old are your tires?
Hubby can't remember but we have slowed down - full timed from 1992 to 5 years ago with many different rigs and never a blowout like this. Have had this unit about 10 years. and didn't put them on for awhile after we bought it. Know it means years not mileage for tires. Have now sold it to friends from Tasmania to travel the US and resell or store if they like it. It is 21 yrs old, good upkeep and they have seen it. Won't take delivery until 202 so will have last rv trip next summer before hubby turns 87. I will be looking for a smaller rv for me to drive after they pick it up.
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Old 10-26-2018, 12:13 AM   #8
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Proper pressure determined by weight and tire manufacturers charts.

The sticker doesn't know how your coach is loaded.

Until weighed and proper inflation is known, inflate to the max cold pressure listed on the tire sidewall.
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Old 10-26-2018, 12:17 AM   #9
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1) I AM NO EXPERT, but (**) 65 sounds too, too low for most 19/ 22-inch tires on a Class-A, that can be as much as 110-120-PSI? 2) What is tire sidewall label MAX COLD XX PSI? 3) What is tire brand/ size/ label? (NOTE: **E.g. On class-c, MAX 80 PSI LT225/75r16E tires, many rear duals pressure is 80, and dropping rear to 70 PSI REDUCES AXLE capacity by 1,000 lbs. Many front axles at ~5000# on class-c inflate to 65-PSI, with rear DUALS at 80-PSI);
P.S. HAVE READ OF SOME RECALLS ON INCORRECT TIRE PRESSURE LABELS, might try a recall search for your RV vehicle
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Old 10-26-2018, 06:15 AM   #10
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The 65 psi is determined for GAWR's , and you are not allowed to go over them. So this should be enaugh .

But pressure should be enaugh to laws of nature, so no overheating of any part of tire, when driving max speed you use( and wont go over for even a minute).

So if this " pigheaded Dutch selfdeclared tirepressure-specialist" wants to calculate a safe pressure for you, he needs specifications of motorhome and tires.

Configuration ,I make of your story, is front 2 tires on the axle( single load) and 1 rear axle with 4 tires( duall- load) , but correct me if wrong.

Then you would expect front higher advice pressure then rear.

But colllect the data, and I will put it in my made motorhome- tirepressure- calculator, in wich I use a formula that leads to higher pressure then the official european, snd add 10% to axle weights.

Best ofcource would be weighing as already mentioned, but to check the advice of 65 psi, those are calculated for gawr with no reserve, and calculated with the american formula ,wich leads to lower pressures then the european formula.
There is always weightdifference R/L on the axles, and advice goes from gawr/2 so always to low pressure for most loaded tire on the axle, when driving with gawr and speed for wich pressure is determined. Luckily in practice speed is lower and loads often also lower, wich still gives it some reserve.

But the measured 65 psi can be inacurate, in real can be 5 to 10% lower, so 60 to 55 psi, and there goes your reserve.

If only once the tire gets overheated, the damage is ireversible, and the beginning cracks, crack further with every next deflection , about 10 times a second , when driving 50mh. Untill after mayby only 3 years the tire is that much damaged that it blows.

Highening the pressure to an already damaged tire by to much deflection for the speed used, only speeds up the damage, so if your other tires also where overheated once, they will soon blow too, and then the 90 psi will be blamed.
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Old 10-26-2018, 09:10 AM   #11
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I can't imagine a 34 footer needing only 65 psi. What size tires are these we're talking about here?

On our 19.5 inch Bridgestone tires, the tire pressure chart starts at 70 psi when used with a dual set up. For singles, the chart starts at 80 psi. I'm taking it that those would be the minimum pressures i'd ever dare to run in these tires, no matter what the motorhome weighed.
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Old 10-26-2018, 10:03 AM   #12
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First question that comes to mind is, "What 'manufacturers tag' are you looking at?". If that refers to the one on the side by the driver seat, it should be fine unless your coach is severely overloaded. If something else, it is probably irrelevant.


Agree strongly with those who said 65 psi sounds low for most any 19.5" or 22.5" tire, but probably ok for a 16".


So please tell us more, i.e. what "tag", what size tires, and what coach GVWR and axle GAWR's? Without that info, we are all just guessing.


Note1: His profile shows an Itasca Suncruiser 34 ft, but no model year.
Note#2: 65 psi is the minimum inflation for the smallest 19.5" tires, e.g.a 225/70R19.5. Even the 245/70R19.5 is 75 psi minimum. No 22.5" is less than 70 psi. (Data from Michelin RV Tire Gide)
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