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Old 02-21-2013, 10:26 AM   #1
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Tire Pressure

We are relatively new to our 2011 Four Winds Chateau 21C. It seems to wander all over the road more that it should. I got it weighed - 3520 lb. steer axle, 7580 lb. dual axle and the loaded tow dolly 3060 lb. for a total 14160. Full gas tank, some water and all of our stuff. The tires are Michelin LT225/75/R16E. Currently I use the air pressure from the door sticker as 75 psi front and 65 psi rear. According to the Michelin RV tire pressure chart:
PSI----- 45---- 50--- 55----- 60--- 65----70
single 1790 1940 2060 2190 2335 2440
dual ---3260 3530 3750 3990 4300 4440
I believe these weights are for each tire on the single axle 3520/2=1760 lb. The chart says 45 psi is the pressure. That is 30 lb lower than the sticker pressure.
The dual axle is a little closer 7580/2 = 3790 or 60 psi.
Am I doing anything wrong? Any help would be appreciated
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Old 02-21-2013, 03:41 PM   #2
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Make sure you are using the correct pressure chart. Here is the latest: Michelin-Truck - Truck Tire Data Book New Your tires pressure chart is on page 22.

I called Michelin about this just a few days ago and I was told to only use corner weights to determine the pressure to use. I was told axle weight alone is not accurate enough to use. I was told to use max tire pressure until I can get accurate corner weights. The problem with just using axle weights is in our RVs it's not uncommon for one side of the axle to be significantly higher than another. On my RV my fridge, bathroom, black tank, generator and slide are all on one side. Using the axle weight to determine pressure would be using way too low a pressure on one side resulting in a possible blow out.

I encourage you to call Michelin at 1-888-622-2306 and speak to them directly. They can explain it far better than I can. I was impressed when I called. They pick up first ring without having to jump through hoops. The person that picks up the phone is the person that will answer your question. Hands down the best customer support ever. After that phone call I was sure I will always buy Michelin tires.

My problem is there is no where around me that can do corner weights. So until I can get the proper corner weights I am using the upper end of the pressure charts.
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Old 02-21-2013, 04:50 PM   #3
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I use the amounts on the tires. I usually put about 5 to 10 lbs less than max on fronts and max on the duals.
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Old 02-21-2013, 06:01 PM   #4
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Very important: use the tire pressure on the door placard and not on the tire.

Reason: the door placard should have been placed by the rv manufacturer and is specific to the vehicle. That tire could be used on a bunch of different vehicles all with completely different air pressure requirements.

This applies to your rv, cars, any vehicles.
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Old 02-22-2013, 07:40 AM   #5
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Tire pressures are important but do not discount the front-end alignment, which is usually done by the chassis manufacturer before the house is built on it.
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Old 02-22-2013, 07:50 AM   #6
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I don't think the OP is doing anything wrong -- tire pressure is suppose to be based on the weight of the vehicle (ignore what's on the tire). What I don't understand is why the wide disparity between what is on the door sticker and the tire chart - if it were me I could call the RV mfg and ask them to explain.

My rig came with D rated tires (60 lbs) - when I traded tires I moved up to E rated tires (80 lbs) but kept the tire pressure at level recommended on door sticker (60 lbs). When I finally got rig weighed I adjusted levels down to what was recommended by tire tables - don't recall specifics but the rear tires were close to sticker but the fronts were lower (but not as big as the OP is talking about).

As far as driveability I found that new shocks and a good front end alignment made a World of difference. Many/most RV's come with lousy OEM shocks - I waited until CW ran a special on Belstein's which they installed for free - wish I had done sooner.
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Old 02-22-2013, 07:58 AM   #7
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Quote:
Originally Posted by paulmlac View Post
Very important: use the tire pressure on the door placard and not on the tire.

Reason: the door placard should have been placed by the rv manufacturer and is specific to the vehicle. That tire could be used on a bunch of different vehicles all with completely different air pressure requirements.

This applies to your rv, cars, any vehicles.
The problem with using the door placard air pressure is they assume you are at the GAWR for both axles. This isn't always true. Especially for those of us with smaller class C's. I am well below my GAWR for both axles. The manufacturer just assumes you are going to load the vehicle to max. For some this is probably true. For me this is not true. For the best tire wear and comfort you should get corner weights and use the charts accurately. Again this comes directly from Michelin and not me. Nothing wrong with using the pressures listed on the placard and it gives you a large safety zone in case you do load the RV up to max. But if your like me and no where near GAWR you end up with a harsher ride and possibly uneven tire wear.

In the end I am doing like you and running the pressure listed on the placard. One day I will figure out how to get corner weighs.
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Old 02-22-2013, 08:19 AM   #8
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Quote:
Originally Posted by rcase13 View Post
The problem with using the door placard air pressure is they assume you are at the GAWR for both axles. This isn't always true. Especially for those of us with smaller class C's. I am well below my GAWR for both axles. manufacturer just assumes you are going to load the vehicle to max.
That makes sense to me. Most of the larger Class C's are maxed out on weight when the leave the dealer but that might not apply to smaller rigs - could explain the disparity the OP has encountered.
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