Tire pressures

[bruc]

Please excuse my ignorance, but as a newbie I would like to know if any motorhome owners out there inflate their tires the same psi all the way around using the tire manufactures max. rating or just under depending on weight. It seems hard for me to believe that the majority of class A owners drive up onto scales a weigh each wheel and inflate accordingly. There has to be rv'ers out there that have had good results with standard air pressures all the way around. Any comments or experiences would be greatly appreciated. Thanks in advance , Bruc .

[FlyingDiver]

Originally Posted by bruc

Please excuse my ignorance, but as a newbie I would like to know if any motorhome owners out there inflate their tires the same psi all the way around using the tire manufactures max. rating or just under depending on weight. It seems hard for me to believe that the majority of class A owners drive up onto scales a weigh each wheel and inflate accordingly. There has to be rv'ers out there that have had good results with standard air pressures all the way around. Any comments or experiences would be greatly appreciated. Thanks in advance , Bruc .

Never a good idea to use "standard" weights or pressures. Getting weights done once is not that hard to do, and it's not likely to change all that much over time.

[seasonedsole]

There are a lot of ill handling motorhomes out there because of inflating to max on the sidewall. I someone doesn't want to get it weighed, or hasn't been able to, they should inflate to recommended pressure on the sticker by the driver. Good luck, be safe.

[JFXG]

Originally Posted by bruc

....would like to know if any motorhome owners out there inflate their tires the same psi all the way around using the tire manufactures max. rating or just under depending on weight. It seems hard for me to believe that the majority of class A owners drive up onto scales a weigh each wheel and inflate accordingly. There has to be rv'ers out there that have had good results with standard air pressures all the way around. Any comments or experiences would be greatly appreciated. Thanks in advance , Bruc .

Hi, and Welcome! Do not apologize, as everyone starts knowing nothing. The only stupid question is the one unasked.

The fact is that motorhomes are different from cars. There is no standard pressure. I remember back in the '60s when virtually all cars had the same size tires, and it was simple gospel that you inflate car tires to 28 lbs. Those days are gone forever.

Most motorhomes (and their tires), particularly those that fulltime, live their whole life at or near max gross weight. This means the tires are constantly stressed, making proper inflation all the more important, and under-inflation all the more dangerous.

You could inflate all to the max and know you're safely inflated, but you'd likely then have to suffer a much stiffer and harsher ride than necessary. But you don't need to be constantly weighing your coach, either.

The fact is when heavily loaded, tires are very pressure sensitive-- mostly to underinflation. The first step is to get weighed, four corners if possible. Then you inflate all tires on a particular axle to the proper pressure for the heaviest side of that axle. Its important for handling that each axle be balanced laterally. Example: your front left weighs 5000 lbs, front right weighs 5300 lbs. Inflate both front tires to the proper pressure for a 5300 lb load, according to the inflation tables provided by your tire manufacturer. Your left rear weighs 10100lbs, your right rear 9400lbs. Inflate all four tires on that axle to the recommended pressure for 10100lbs, again according to the inflation table.

If all you can get is the basic axle weights, just cut that weight in half and use that number. That will work ok, but you're better off with the four individual weights.

Once you've been properly weighed, there's no need to weigh again soon unless you shift a lot of weight around or add (or remove) a lot of weight to the coach. Since we tend to accumulate "stuff" in the coach without realizing it, its probably a good idea to reweigh annually.

I'm sure there are some folks who just pump in some arbitrary air pressure and go blithely about their business, but their continued good health and fortune is more a matter of happenstance than prudent operation, and its a testament to the quality of modern tire design. As their tires age their risk will elevate exponentially regarding tread wear, internal structural failure, and handling reliability.

Good Luck!!

[Peterd503]

The tire inflation number is the minimum air for the maximum load. I have always used this number with no obvious handling issues. My tires are the original tires to the coach which was built in Nov of 1999. I just got home yesterday from a 3000 mile trip with no issues. Heat is the number one killer of tires and reduced air pressure is one of the main causes of heat.

[gruelens]

Originally Posted by Peterd503

The tire inflation number is the minimum air for the maximum load. I have always used this number with no obvious handling issues. My tires are the original tires to the coach which was built in Nov of 1999. I just got home yesterday from a 3000 mile trip with no issues. Heat is the number one killer of tires and reduced air pressure is one of the main causes of heat.

It is my hope that we are not advocating, to forum members, driving RVs on 15+ year old tires. Too many aged out tires have come apart causing structural damage and accidents.

[Tobias7000]

Had my tires changed recently and Les Schwabb inflated to what the manufacturers plate listed (on the wall left of my drivers seat). My owners manual stresses that I should never run the tires at any other pressure than what the plate lists. I don't know for sure, but I understand the recommended pressure is there by law. So this process of measuring and adjust pressure is news to me (I am new to the motor coach life). Why wouldn't my owners manual discuss this? I am eager for more insight as well and thank the questioner for posting this.

[FlyingDiver]

Originally Posted by Tobias7000

Had my tires changed recently and Les Schwabb inflated to what the manufacturers plate listed (on the wall left of my drivers seat). My owners manual stresses that I should never run the tires at any other pressure than what the plate lists. I don't know for sure, but I understand the recommended pressure is there by law. So this process of measuring and adjust pressure is news to me (I am new to the motor coach life). Why wouldn't my owners manual discuss this? I am eager for more insight as well and thank the questioner for posting this.

The pressures on the plate are for the original tires at the maximum loaded weight of the coach as specified by the builder. If the tires have changed (different manufacturer, different size, load range, etc), or if you're not running at max weight, then the plate numbers are not correct. The tire manufacturer will have a chart specifying what pressure you should have in those specific tires for the weight actually on the tire.

I'm sure that there is a law requiring a recommended pressure. That doesn't mean that the recommended pressure is correct in all (or even most) situations.

I also really doubt the owner's manual says exactly what you think it says. Can you quote the exact passage?

[Ray,IN]

The RMA-Rubber Manufacturers Association states that over 90% of all tire failures are due to underinflation/overloading. It is better to err on the side of higher pressure.

[FlyingDiver]

True, but over-inflating reduces braking effectiveness and negatively impacts handling.

Getting it right by the tire manufacturer charts is the best policy.

[Tobias7000]

Originally Posted by FlyingDiver

Can you quote the exact passage?

There are about six pages on tire pressure and safety. Here are a few paragraphs from the CC Inspire 360 (2008) owners manual.

"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.

Federal Tire Label Information
The motor home's important tire information is contained on the Federal Tire Label (Figure 1.8, page 1.19), which is located on the transmission shift panel near the driver's left knee. This label includes recommended tire size, wheel size, and cold tire inflation pressure for each tire position on the motorcoach. "

From another page...
Country Coach Tire Inflation Policy
" Federal law requires that the tire's maximum load rating be molded into the sidewall of the tire. If you look there, you can see the maximum load allowed and the cold air inflation pressure required to carry that stated maximum load. Less air pressure restricts the tire to carry a lighter load. For your safety, always adhere to the Federal Tire Label for proper inflation numbers. "

This has been a good thread. Thanks everyone!

[Tobias7000]

Another interesting paragraph from the manual.

"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. "

[UFO Pilot]

Winnebago said my tires should be inflated to 105 pounds. The service shop inflated them to 110 per the max on the sidewalls. I had the Coach weighed and the manufacturers tables said I should run 85. I choose to run 95 for a safety factor. The 15 pounds less I am now running sure improved the ride. I also use the Tire-SafeGuard for constant monitoring.

[Triker56]

Originally Posted by Peterd503

My tires are the original tires to the coach which was built in Nov of 1999. I just got home yesterday from a 3000 mile trip with no issues.

What make are those tires? Hard to believe if they are OEM Michelin's XRV's that old and the sidewalls are still good and not dry rotted.
If they are you should be buying some lotto tickets.

Some owners would have have replaced them 2-3 times by now and spent around 6-9K doing it.

On my Aug 98 built 99 I now have almost 9 years on the first replacement(May 2005) G670's put on. Plan on a 2015 replace with them.

For the OP have your RV weighed and use the manufacture of your tires PSI table for weight. Very seldom that the front & rear will take the same PSI.

How to weigh your RV 2MB PDF