Motorhome weight and tire pressure

[burgmark]

I just had my motorhome weighed for the first time, pretty much fully loaded as I was off for a 42 day trip. Front was 9900 lbs and the rear (no tag) was 19520. I was not able to weigh each corner. My tires are Michelin 275/80R22.5 LRH X Line Energy Z XZE. Since I don't have corner weights, I divide the front weight by 2 and the rear weight by 4 to get the per tire amounts and then add 10% since I don't have the corner weights. That gives me 5,368 lbs for the rear and 5,445 for the front. According to the Michelin charts that translates into tire pressures of 85 PSI for the front and 92.5 PSI for the rear (extrapolated). That 85 PSI seems pretty low to me, I've been running 100 PSI in all 6 tires. I'd really like to know what pressures others are running.

[Arch Hoagland]

Michelin recommended 80 for my fronts and 85 for my rears. I went with 90 all the way around.

I did not do corner weights.

[Crasher]

The scales don't lie. If you used the correct load inflation chart, you are good to go. What does the placard near the drivers seat say?

[Dodge Guy]

I would run 90 frt and 95 rear.

[paddler1954]

You really need the corner weights. Dividing the axle weight by 2 gets you into a ballpark but that's about it. On my rig, there is a 600 lbs. difference between my front tires. Dividing the axle weight, would put me 15 lbs. low on the heavy side. Something to consider.

[Ray,IN]

Go by the Federal Tire Placard inside the MH and you don't need to be concerned.

[burgmark]

Originally Posted by Crasher

The scales don't lie. If you used the correct load inflation chart, you are good to go. What does the placard near the drivers seat say?

120 PSI all the way around, which is simply the max for the tires. But the weight rating at that inflation level is way more than the RV chassis is rated for at 12,400 front and 20,000 rear.

[burgmark]

Originally Posted by Ray,IN

Go by the Federal Tire Placard inside the MH and you don't need to be concerned.

That would be overinflated for the weight the tires are carrying. Here is a reply from Michelin concerning appropriate inflation of their tires.


Thank you for your recent inquiry seeking information on proper inflation of our products on your RV. The load inflation tables we have listed on our webpage is designed to give the maximum performance of our products based on the load they are carrying, so they are specific to each vehicle and load. By following these suggested pressures you will maximize the overall performance of the product in all areas, including fuel efficiency, ride quality, and safety.

If a tire is used over-inflated to its load capacity, it can impact the safety of the product by reducing traction and will ultimately wear unevenly, greatly affecting the life of the tire. This will also affect the ride quality of the product by creating a rougher ride to the driver and passengers.

If a tire is used under-inflated to its load capacity, the product will gain excessive heat from the additional friction on the road surface. This greatly affects the over all integrity of the product and could shorten the life of the product exponentially.

As under-inflation has much greater impact on the safety of our consumers, we recommend that your air pressures be checked frequently and adjusted based on the load it is carrying. This may mean that your optimal pressures will change depending on the number of passengers, cargo, and fuel and water levels. We recommend our consumers to have their vehicles axle end weights acquired at the peak of the cargo level before each trip. If you are unsure of the correct pressure your load is requiring, we do recommend that you inflate the tires to the maximum cold pressure until you can acquire a proper reading of the weight and distribution of the load.

[NXR]

Originally Posted by burgmark

120 PSI all the way around, which is simply the max for the tires. But the weight rating at that inflation level is way more than the RV chassis is rated for at 12,400 front and 20,000 rear.

That's not adding up. By law the sticker inside needs to show the minimum pressure in the OEM-installed tires to fully support the GAWR, gross axle weight rating, of each axle.

Have the tires been changed so they are different from what was originally installed?

Ray

[NXR]

Originally Posted by paddler1954

You really need the corner weights. Dividing the axle weight by 2 gets you into a ballpark but that's about it. On my rig, there is a 600 lbs. difference between my front tires. Dividing the axle weight, would put me 15 lbs. low on the heavy side. Something to consider.

That's why he said he added an additional 10%.

Ray

[Crasher]

Originally Posted by burgmark

120 PSI all the way around, which is simply the max for the tires. But the weight rating at that inflation level is way more than the RV chassis is rated for at 12,400 front and 20,000 rear.

I guess I'm not surprised. In most MH, the placard would give the pressure needed to support the maximum axle ratings. Mine was no different. It called for 110# all the way around. That amounted to the steer axle being underinflated by 5 psi and the drive was over by 25# and tag was over by 30+# for the pressures to support the actual weights. As I have said before several times, the MH manufacturer is concerned about covering any potential liability related to underinflation. Hence, the placard is higher than required for the correct pressure. The tire manufacturer says to weigh each position and use their Load inflation table to get the most optimum pressure for performance and safety. Since the tire is the only thing between me and the road, I'll take their advise.

[High Road Travelers]

I think that the maker of the tire knows more about the proper tire pressures for it than anyone else, and would go with what the maker states in the tire inflation chart for that tire.
IMHO it seems that most people want to over inflate them.
Thanks,

[NXR]

Originally Posted by Crasher

... In most MH, the placard would give the pressure needed to support the maximum axle ratings. Mine was no different. It called for 110# all the way around.

That amounted to the steer axle being underinflated by 5 psi and the drive was over by 25# and tag was over by 30+# for the pressures to support the actual weights. ...

Hence, the placard is higher than required for the correct pressure. The tire manufacturer says to weigh each position and use their Load inflation table to get the most optimum pressure for performance and safety. Since the tire is the only thing between me and the road, I'll take their advise.

Sorry, would you please elaborate a bit? I agree with what you wrote but it seems your front axle weighed in at its GAWR or perhaps a tad more. Is that correct? Or was that 5 PSI a bit of extra pressure you added to account for expected temperature variations in your travels?

Obviously 5 PSI is almost within the accuracy variations of many tire pressure gauges so it's not much.

Ray

[dbircky]

Curious if anyone, after getting a 4 or 6 corner weighing, adjusts their pressure by tire load per corner. For example, putting 95 psi in the passenger front and 110 psi in the driver front - if those pressures align with the tire manufacturer charts for a given load. If not, why bother with getting an exact weight on each corner? I am really confused as to the logic of following the tire manufacturer charts but then adding some arbitrary percentage if each tire loading is known. If the tire manufacturer wanted the higher psi, wouldn’t they reflect that in their charts? Perhaps that is already factored into the charts and by adding some arbitrary percentage, the tire is overinflated by that percentage leading to increased wear and reduced performance. I don’t add a percentage to my medicine above what my doctor prescribed, she’s the expert. I think the same way about the tire manufacturer charts. They know their tires and recommend those pressures for a reason.
It really makes me wonder why some follow Michelin’s recommendations to replace tires after a certain number of years, why not add an arbitrary percentage to that time too?