Tire Pressure Sanity Check

[DeWat]

Originally Posted by Clifftall

That 90 lbs on the placard is relevant if you have the chassis maxed out at ( in your case ) 22,000 lbs. weights lower than that should go by the tire chart with a few extra lbs for good measure.

Originally Posted by Tony Lee

Big problem because each stage in the manufacturing process adds their own CYA requirements and they get compounded at each stage. Then the owners get their turn.



Even after the chassis manufacturer and the powerplant manufacturer and the MH manufacturer have done their best to confuse and cloud the issue, the dealers and the owners get their chance to add to the confusion by adding all sorts of after-market bling like extra solar panels and 8 extra batteries and a 64" TV and washing machines and driers and basements full of toys - all of which make the placard a total work of fiction even if the manufacturer had got it right in the first place.
Then of course the hapless owner poses a question on a public forum and gets as many different advices as there are replies.

This unscientific approach contrasts with that of the tyre manufacturer which sells a the-buck-stops-here product with the final responsibility for vehicle handling, comfort and safety and who has been manufacturing and testing tyres for a hundred years. If they say weigh each corner and air them up according to their scientifically and real-world-testing derived figures, why would anyone bother going by a bit of stamped aluminium fixed to the door pillar 10 years ago.

While I fully understand what both of you are saying, the point is that even Michelin states that when the weight pressure is less than the placard pressure, to use the placard pressure.

[CLIFFTALL]

Originally Posted by DeWat

While I fully understand what both of you are saying, the point is that even Michelin states that when the weight pressure is less than the placard pressure, to use the placard pressure.

Here is the Michelin RV Tire guide.

http://www.michelinrvtires.com/asset...esBrochure.pdf

I couldn't see the part about their policy as it relates to the placard. Would you be kind enough to direct me to that page or the material that you read about that.
Thanks

[Tony Lee]

Fairly common - but perhaps illegal - for people to put tyres on that have a different load rating than the alternatives normally shown on the placard or other manufacturer's documentation and if the load rating on the new tyre is substantially higher than the original, inflating to placard pressures might result in an unduly harsh ride.

[DeWat]

Originally Posted by Clifftall

Here is the Michelin RV Tire guide.

http://www.michelinrvtires.com/asset...esBrochure.pdf

I couldn't see the part about their policy as it relates to the placard. Would you be kind enough to direct me to that page or the material that you read about that.
Thanks

I knew someone was going to call me to task on this one! Not that I feel accused of lying, but because it is so unbelievable. I still have a hard time, so here it is... take a look at the first paragraph under "What inflation
pressure to use" on page 5...

EDIT: Oops... I see that my attachment didn't take. I also wrongly blamed Michelin, it was the Bridgestone brochure.

[Dr4Film]

Originally Posted by Scotter

Places to weigh outside of truck stops.

large Farms
Seed corn companies
feed mills
grain elevators
farm chemical outlets
some concrete plants
weigh stations
any more you know of?

I believe that Moving Companies have scales that can weigh big rigs.

Dr4Film ----- Richard

[CLIFFTALL]

Originally Posted by DeWat

I knew someone was going to call me to task on this one! Not that I feel accused of lying, but because it is so unbelievable. I still have a hard time, so here it is... take a look at the first paragraph under "What inflation
pressure to use" on page 5...

EDIT: Oops... I see that my attachment didn't take. I also wrongly blamed Michelin, it was the Bridgestone brochure.

Thanks for clarifying that. I see you have a new Winnebago. Are they using Bridgestone Tires ?

[DeWat]

Originally Posted by Clifftall

Thanks for clarifying that. I see you have a new Winnebago. Are they using Bridgestone Tires ?

Nah... it has the 22.5 XRVs. What made me trip across that statement was after I weighed and discovered that I should be running 70-75 psi based on the charts. Not knowing which to believe, I started searching everywhere for an answer before just firing off a question without checking. I happened to have the PDF stored in the "Motorhome" directory on my computer due to its help on weights and weighing. With all that said and even though it was Bridgestone and not Michelin, I still can't understand why they tell you to run the placard pressure when it is substantially above their own recommended weight pressure .

[MandG-Fun]

I'm gonna go with the 5 psi over the recommended pressures based on the Michelin chart and see how the coach rides. I may even go a bit more considering all of my water tanks are presently empty. Then I'll try and find a scale that I can weigh each corner. Dr4Film made a good suggestion... I think the moving company near here has a scale, I'll see if theirs will accommodate individual wheel placement.

I assume there is no safety issue running at the recommended pressure or higher and since the guys at TCI that installed the tires were the ones that inflated the tires to 125 front 90 rear in the first place. The only downside of running significantly higher is a rougher ride. The benefit of running higher being lower rolling resistance and better fuel mileage. So somewhere in between is the best balance of minimum safe operating pressure and comfort.

Here's a question for you physics guru's out there. I live at almost 7,000 ft. If I fill my tires to 80 psi are they still at 80 psi when I go to sea level?

[beaverjim]

Originally Posted by MandG-Fun

I just weighed my coach today, the front axle is 10,400 and the rear is 18,240. I have Michelin XZE2 275/80-22.5. According to the Michelin pressure chart for my weights I should be running 85 psi front and 80 psi rear. The tire pressure sticker in the coach says 125 front and 95 rear which is what I have been running since getting the new tires a month ago but the ride is definitely harsh.
Anyone have any thoughts on the recommended pressure on the Michelin chart? I definitely don't want to run under inflated.

Glenn

glenn, I may have missed it but are your xze 2"s lr g or lr h rated? big difference in lcc. jim

[rdkng88]

I inflate 100 PSI in the front 110 PSI rear with no problems. My tires call for 120 PSI max pressure for max load I'm not going to take chances with under inflated tire that is just asking for trouble. I'll take a little rougher ride for the safety factor especially pulling a trailer that adds additional load to the rear axle. I just don't have time or a place to weigh each corner every time I leave the driveway I'm not loaded the same each time. I say be safe don't take a chance on under inflated tires.

[MandG-Fun]

Originally Posted by beaverjim

glenn, I may have missed it but are your xze 2"s lr g or lr h rated? big difference in lcc. jim

Jim,
They are G's.

[MandG-Fun]

Originally Posted by rdkng88

I inflate 100 PSI in the front 110 PSI rear with no problems. My tires call for 120 PSI max pressure for max load I'm not going to take chances with under inflated tire that is just asking for trouble. I'll take a little rougher ride for the safety factor especially pulling a trailer that adds additional load to the rear axle. I just don't have time or a place to weigh each corner every time I leave the driveway I'm not loaded the same each time. I say be safe don't take a chance on under inflated tires.

I figuring the 4 corner weighing to be a one time task. My weights are not going to change by a significant amount. The biggest variable will be how much water and fuel I am carrying. Normally I'll be either flat towing a Jeep or a Miata so that is just pulling weight, not weight on the axle. Other than that is the difference in a couple cases of beer and food.

I agree, don't want to be under inflated. Just trying to understand what under inflated means for my situation.

[Hooligan]

Originally Posted by Tony Lee

Fairly common - but perhaps illegal - for people to put tyres on that have a different load rating than -- shown on the placard ---

Replaced my XRV 235/80R22.5 (LR G) tires with G670RV 275/70R22.5 LR H).
I gain over a 1000# margin on the front axle and over 3000# on the rear axle and run 90/85 psi vice 105. Legally complies with tire mfgr tables..

Another consideration on proper tire pressure, both over and under inflation reduce the contact patch of the tire.

Altitude has little effect, the psi changes about 1/2 pound per 1000 ft of altitude. Decrease altitude decreases pressure. However as you decend to the flatlands, Temperature rises, and every 10 deg increase adds 2 psi to pressure.

[MandG-Fun]

Originally Posted by Hooligan

Replaced my XRV 235/80R22.5 (LR G) tires with G670RV 275/70R22.5 LR H).
I gain over a 1000# margin on the front axle and over 3000# on the rear axle and run 90/85 psi vice 105. Legally complies with tire mfgr tables..

Another consideration on proper tire pressure, both over and under inflation reduce the contact patch of the tire.

Altitude has little effect, the psi changes about 1/2 pound per 1000 ft of altitude. Decrease altitude decreases pressure. However as you decend to the flatlands, Temperature rises, and every 10 deg increase adds 2 psi to pressure.

For me, getting an increase in load rating is secondary. My coach is built on the standard Dynasty chassis but is the smallest that they built in 2000. It is designated 34' with only one slide. My total weight without water is 28K lbs. I can't see ever hitting 30K so I'm still well under the max chassis weight and tire ratings.