Load limits

[dashonthedash]

OK, now I'm confused.

The placard in my new motorhome says that the front tires should be inflated to 95 pounds for a front limit of 12,000 pounds, and the rear tires should be inflated to 100 pounds for a rear limit of 7,000 pounds.

The GVWR of the coach is 18,000 pounds.

I just checked the tire pressures, and they are all about 85 pounds. According to the Continental website, this should equate to a load limit of 3315 pounds single, or 6630 pounds front, and 3115 dual, or 12460 pounds rear, for a total of 19090. The recommended pressures on the placard would equate to a load limit of 14860 pounds rear and 7280 front. At first, I thought the tires were underinflated but, based on the overall distribution of weight and storage, the current inflation is probably about right. Anybody here know the reason for the discrepancy?

[LadyWindrider]

Manufacturing changes occur even faster than Superman can keep up. This is in the RV World and the tire plants also. Just watch the wear on the tires, and change pressure according how they wear, until you get it figured out. And when you get the next set of tires, be sure and start all over.

[starburst2]

Hi Dash
I composed a lengthy response but it got hung up in the forum protocol and I lost it. Essentially it said.

• I'm not surprised.
• I had the same experience.
• If you dont already have one buy yourself an IR temperature testing guauge.
• Check all your tires every time you stop for a two week period while travelling as well as check the temp of the pavement
• Make a table showing all these temps.
• If you are finding temperature variences of more than 5 degrees take your table of readings and go to an expert like the manager of a truck tire shop which carries your brand of tires.
• Ask him what thew data suggests and ask him for his opinion on what inflation pressure you should be using.

On my last coach I went through a couple of sets of steer tires due to premature and irregular wear. No matter how meticulosly I paid attention to keeping the coach steering alignment checked and adjusted and no matter how dutiously I checked the inflation pressures each morning, I was getting irregular wear which resulted in front end vibration. I weighed the tires on each of the quadrants of my coach and followed the Goodyear inflation chart suggestions for my tire make and size. To make a long story short, after two sets of steer tires went bad I ask the manager of the largest goodyear tire dealer in Western Canada what,. in his opinion was causing my problems. He looked at the wear and told me it appeared to him that my tire problems stemmed from running them underinflated. When I told him I was following the charts on the Goodyear website he said I must have made a mistake. I rechecked the website and there was no mistake.
I followed his advice and ran the tires at 97 PSI in the steer tires and 95 in the duals. I had no more problems. I had been running 85 in the front and 80 in the rear in accordance with Goodyear's company charts. Those few extra pounds of preassure made all the difference in tire wear in my case.
The moral of the story is; who knows what to believe anymore.
As I said above, do yourself a favor and get an IR temp gauage. Check the temp of each of the rear duals each time you stop. It only takes a few seconds and it alerts you immediately if there is a problem or if a problem is developing. That is the only way you can detect an inflation issue short of testing the tires each time with an air pressure gauage.
Don't believe the old wives tale that you can check your duals by thumping them with a hammer. Get an IR temp testing device. They are only about 50 to 75 dollars and they enable you to check the tire temps in a few seconds. It will give you more than $70 worth of "peace of mind".
Lloyd

[Herk7769]

EVERY component of your vehicle has a Gross Weight Limit associated with it.
The TIRES (variable based on rating and inflation pressure)
The AXLES (based on axle strength, length, Springs and hardware)
---) Front has a different GAWR than back due to construction
The FRAME (C Beam, I Beam, Box beam all have different load capacities)
The BRAKES (the 2500HD has a smaller brakes than the 3500HD)
The Gross Vehicle Weight rating is based on the LOWEST of the above.

The TOW rating is what you can PULL (NOT CARRY OR STOP). The Tow rating is ONLY based on ENGINE, TRANSMISSION, Drive Shaft, and REAR RATIO. (Period) This is why my 2008 GMC 2500HD with diesel has the same tow rating as the 2008 3500HD AND the 2008 3500HD Dually.

The GROSS COMBINED WEIGHT involves all the above. Above the GCWR, "there be dragons." You are exceeding the design specifications for ALL components. You will damage the drive train in very short order.

Hope that helped.

[bend302]

When I bought my used MH, the dealer said to keep the tires at 85psi.

Since the tires were 6 yrs old, I went to a Goodyear dealer and bought 6 new ones. He put in 95 lbs. and there I have been with no issues and at 4,000 miles so far, no apparent wear.

I check psi regularly and they seem to go up to 100 when warm but that hasn't scared me (yet)

[prof_fate]

Tire pressure affects all sorts of things - load capacity, ride comfort, tire wear, vehicle handling, contact patch on the road, tire longevity, fuel mileage and perhaps others.

Like everything there are always compromises. The tire folks want the tires to wear a long time so you buy them again and the car folks want them to ride nice so you buy this car over that one. And of course different brands/types of tires change everything all over again.

The air supports the vehicle and provides cooling for the tire which is why running a tire low on pressure can cause it to fail from overheating.

I tend to run my tires on the higher end of things and IMO never get the mileage claimed by the tire manufacturers. But from my understanding i've got a smaller contact patch on the road so have more PSI on the road and more grip in the wet, get better MPG too. Higher pressures add to harder sidewalls for better handling too. My tires wear even on all my vehicles, just don't seem to last '40k' or '60k' as claimed. YMMV of course.

My TV has overkill for tires on it - Load range E - and ride like a haywagon, but my neighbor noticed and raved how great they'll be for towing and stability. We'll see. So far I've just been around the block in the 'hood to set the WD/sway and check that the brakes work.

[johnnypal]

Ive been running the same Michelan tire 245x22.5 on my last 3 coaches.The tire pressure Ive always used is 100 front 95 rear. Never had A blowout or for that matter had A tire wear out.Get yourself A good pressure guage and an AC powered tire inflator check tires often in the morning while its cool and keep those pressures constant.You will never have any trouble.

[Los Popes]

I've been running mine at 90 PSI. Based on the advice on this thread I think I am going to go to the scales and weigh each corner and make some adjustments. I only have about 9k on these tires - no unusual wear yet. I also bought an IR thermometer at CW a month or so ago and will start using it to check the tires.
Thanks all for the advice.