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RattVader · 04-05-2015, 02:30 PM

Ok,ok. I know...I got it.

But...the stated cold PSI on the sidewalls of my shiny new 1500 miles on them Michelins says they should be 110 psi! Now...is that another way of saying before I go anywhere,load anything,that should be the minimum pressure in these tires? But looking at a chart online from Michelin for these tires states..and this is based on axle weight and whether they are sinle or dual,it can vary anywhere from 70-110 psi. What am I not getting here?

Also I have looked everywhere..where is the placard in a 2015 Baystar for the tire pressure per axle? Thanks in advance for not getting annoyed!!

Mr_D · 04-05-2015, 02:35 PM

Well, first off the pressure on the sidewall of a motorhome size tire is NOT the maximum or even the recommended pressure.
The pressure on the sidewall of a Michelin RV tire and many others is not the "Maximum" the tire should ever have (unlike car tires) it is the minimum to support the maximum rated carrying capacity of the tire.

From page 2 of the 06/07 Michelin RV Tire Guide:

Quote:

"If you look at the tire's sidewall, you'll see the maximum load capacity allowed for the size tire and load rating, and the minimum cold air inflation needed to carry the maximum load."

From page 6 of the GoodYear RV Tire and Care Guide:

Quote:

"How much air is enough?
The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load."

From TOYO:

Quote:

Q: What are the consequences of inflating the tires to accommodate the actual loads?
A: If the inflation pressure corresponds to the actual tire load according to the tire manufacturer’s load and pressure table, the tire will be running at 100% of its rated load at that pressure. This practice may not provide sufficient safety margin. Any air pressure loss below the minimum required to carry the load can result in eventual tire failure.

But then they go ahead and publish a weight/pressure chart allowing lower pressure for RV's!!

From the August 2010 Motorhome Magazine "Tread Carefully" tire article:

Quote:

The maximum load capacity allowed for the size tire and load rating and the minimum cold air inflation needed to carry that maximum load are located on the tire’s sidewall.

Algoma · 04-05-2015, 02:59 PM

Mr D is correct, but I have a feeling that getting your coach fully loaded and having the corners weighed to establish the tire loads is a task you may not want to do. I would just use the pressures that Newmar post which is based on fully loaded axles. The chart with this info on my coach is posted on the wall next to the driver's seat. It may also be in one of the kitchen cabinets. Do not inflate to the pressures marked on the tires.
For example, the tires on my coach are marked as 120psi, which is the correct pressure for my front axle fully loaded. However, on the drive axle and tag axle the correct pressure for fully loaded axles is 85psi. If they were inflated to 120psi it would make for a very rough ride.

RattVader · 04-05-2015, 04:33 PM

Thanks guys. Ok I think I've got it..minimum pressure to support maximum load. And the placard was drivers side wall near floor. Newmar suggests 100psi for both axles..single front-dual rear. Fords sticker right underneath suggests 90 psi for same setup. Maybe I'll split the difference!! Last question(yeah right). Does the TOTAL weight of my toad count towards TOTAL overall wieght of combined cargo and motorhome or is it just the tongue wieght of towed vehicle?

newmarpusher · 04-05-2015, 04:45 PM

Quote:

Originally Posted by RattVader

Thanks guys. Ok I think I've got it..minimum pressure to support maximum load. And the placard was drivers side wall near floor. Newmar suggests 100psi for both axles..single front-dual rear. Fords sticker right underneath suggests 90 psi for same setup. Maybe I'll split the difference!! Last question(yeah right). Does the TOTAL weight of my toad count towards TOTAL overall wieght of combined cargo and motorhome or is it just the tongue wieght of towed vehicle?

In lieu of knowing your exact corner weights, you should go with the Newmar placard. Those will be the pressures assuming you are carrying the maximum load the RV is designed for.

Once you get weighed, you will then know how much under you the max load you are carrying. In that case you should consult the Michilein charts and dial in those pressures, which will be less than the Newmar placard. This will provide a better ride, handling and contact patch for the weight you actually have on board.

lanerd · 04-05-2015, 04:50 PM

No. The toad weight is not applicable to the mh's tire pressures...only the weight directly applied to each tire. Most toads will have a tongue weight (including tow bar) of less than 100 lbs.

Ron

Algoma · 04-05-2015, 05:38 PM

There are two acronyms you need to know. One is GVWR (gross vehicle weight rating), this is the maximum weight of the motorhome including all the stuff you carry with you. The other is the GCWR (gross combined weight rating), which is the GVWR + the weight of your toad. GCWR - GVWR is usually 5,000 or 10,000 lbs depending on the size of your rig. This determines the size of vehicle you can tow.