Community Forums

rdurham1954 · 10-08-2015, 03:03 PM

For those who may be digging for information, here's some great information
from my tire guy who just does RV and truck tires:

"Your coach is basically a fancy big rig truck. The coach builders who supply you with owners manuals give THEIR recommended tire pressure which is always lower than the manufacturers. That's because they want your coach to ride as soft as possible so you feel like your driving a car, which it absolutely isn't. The tire manufactures engineers are the experts on your tires and the coach manufactures are not.

I recommend max pressures because of several reasons. You tires will wear more evenly. Your tires will run cooler. Your tires will be able to withstand more load carrying capacity. It will be in your benefit if there is ever a warranty problem or accident because if you run them under inflated the manufacture will hold that against you and not warranty your tires or use it as a defense in a civil suit.

There is 2 ways to go about it. Either run max pressure OR completely load your coach like your going on a trip, water, fuel, food, beer, propane, toys, some water in your waste tanks, car if you tow one, I mean everything. Then take it to a truck scale and get it weighed. You dont need to pay for a certified wieght ticket unless you want to for your own records. Just get your weights. You want to wiegh each axle individually and record it and get a gross weight of the entire coach and tow vehicle.

Then when you get back home and get everything put away get out a calculator and a piece of paper and do the math.

Here is an example:

Let's just say your front axle weighs 12,000 pounds. And your tires on the front each are rated to carry 6,500 pounds at 125 psi.
You take 6500÷125=52. That means for every pound of pressure that one of your front tires has it will carry 52 pounds of weight. So your axle weight was 12,000 pounds so you need to be able to carry AT LEAST 6,000 pounds per front tire. 6,000÷52=115.38 pounds of pressure needed at a minimum. Turn it around and round of for easier math, 52 x 115=5,980, so almost the 6,000 pounds you must carry at a minimum. So you figure, ok, I can drop them down 10 pounds, but then take this into consideration. What happens when your going down a hill and applying your brakes? Is more weight being transfered to the front tires? Or when you are going through a curve, or braking downhill through a curve......the answer is yes. Considerably more weight is being thrown forward onto that axle. So wouldn't it just make sense to be at max pressure so that the tires can carry those loads especially when it's a more tense situation if you were to loose a tire?

You can use the same mathematics on the rear axle and tag axles as well.

I will email you separately a couple of links to help you with more info and a way to write down and keep your axle weight for future reference. (See attached)."

Mr_D · 10-08-2015, 03:16 PM

Country Coach now says:

Quote:

Tire Industry Changes
The tire industry, as a whole, has changed its traditional stance on adjusting cold tire inflation pressure for RV tires installed on recreational vehicles and busses. Previously, tire manufacturers supported a policy where tire inflation could be adjusted according to the actual loaded weight of the vehicle. Now, the major tire manufacturers recommend that medium duty truck tires be maintained at the pressure that corresponds to the Gross Axle Weight Rating for the axle to which they are mounted. To make this recommendation uniform across the industry, tire manufacturers strongly urge the consumer to keep all tires inflated to the pressures recorded on the Federal Tire Label.

Tire Inflation
Country Coach recommends that the cold tire inflation pressures should at all times be maintained at the inflation pressure(s) recorded on the Federal Tire Label. There are no acceptable circumstances where tire inflation pressure(s) should be reduced below that pressure recorded on the Federal Tire Label.

MJFZ · 10-08-2015, 04:47 PM

Michelin states:
"Axles & Tire Pressure

Michelin displays tire loads per axle end in the load and inflation tables. We recommend weighing each axle end separately and using the heaviest end weight to determine the axle's cold inflation tire pressure. For control of your RV, make sure tire pressures are the same across an axle, while NEVER exceeding the maximum air pressure limit stamped on the wheels. "

Since I ride on Michelins I plan to use their recommendation.

Mike

Mr_D · 10-08-2015, 05:16 PM

Quote:

Originally Posted by MJFZ

Since I ride on Michelins I plan to use their recommendation.

Our Magna also rides on Michelins but Country Coach supplies the weight ratings for the whole RV, and they have the final say under Federal Law.

Up until we got the Magna I've done what Michelin said because that's also what the MH manufacturer said, and Country Coach used to say go by what the tire manufacturer said. But as I posted above, the thinking has changed.

BTW: Toyo also says not to go by the charts and run the minimum pressure to support the maximum weight rating for the tire but then publishes tire weight/pressure charts. So it seems even the tire manufacturers don't agree with each other or themselves.