Tire Inflation Question

[VegasDogMan]

Weighed my coach today 42980 Lbs full Water & Fuel -
15660 on front axle
27320 on Rear Axle plus Tag

Tires are Michelin XZA-1 315 80 R22.5

According to Michelin Chart -
http://www.michelinrvtires.com/michelinrv/tires-retreads/load-inflation-tables.jsp
Front tires 7830 lbs ea should be at 115 PSI

How do I figure load on Duals and Tag? 2/3 and 1/3 ?
If I divide rear weight by 6 I get 4553 Lbs for Tag and doulbe that to get 9106 lbs for Duals
Both of these weights fall below 85psi on the michelin inflation chart.

Is it wise to run front at 115 PSI and Dual/Tag at 85 psi?

I'm confused!

[dale farley]

Lee, To get a weight that will really give you the info you need, each axle should be weighed separately. This way, you will just go by the dual chart for your drive wheels, and all the others will be figured as singles.

To be most accurate, you could weigh each side of each axle, but not many setups have that capability. Most of us just weigh the three axles.

Based on your weight, 115 is what you should be running on the front. Your weight will normally not be equally divided between your drives and tags, but you will probably be safe to run 85-90 in all the rears until you get a more accurate weight. I currently have 85 in my drives and 95 in my tags based on the axle weight. Dale

[VegasDogMan]

Dale:
How do I weigh the Drive and Tag separately?

[garyde]

Go to www.rvsafety.org These people have portable scales which weigh individual wheels . The scales a very thin and small and you drive onto them. I had mine weighed at a FMCA rally here in California recently.

[Joe Cannarozzi]

As a driver of almost 30 years now IMO you guys are over complicating this issue slightly.

I know that most of the newer buses are real heavy on the steers so more air there is understandable. At 115 cold those tires will grow to somewhere around 130 driving on a hot day. I might go with 110 cold because of that.

For the 2 rear axles and in the name of simplicity, uniformity, ride and mileage it's 100 for all.

We have a 42000 pounder with 12200 up front and run 100 in all 8 tires.

Case in point; Any spread axle semi trlr is carrying 40,000 (20,000 per axle) on 11-22.5 tires (one weight classification DOWN from 12-22.5) at 100lbs of air. Folks like Yellow and Roadway with the wiggle wagons and all that light bulky freight 100lbs in those tires too.

[Jon Wehrenberg]

Joe, with all due respect you are mixing the apples with the oranges.

We do not have loads that vary so unlike the typical truck we can get our axle or even individual tire weights, determine what our pressures should be, and air up our tires accordingly. Unless we change our loading we only have to look up the appropriate pressures once. My front to rear is 105, 85, 90 with all pressures five pound over the recommended pressures to give me a small margin for error. Interestingly the Goodyear seminar presenter at our rally suggested 10 pounds so there is a basis for doing so.

The Goodyear guy also made it very clear that if we are not vigilant, and we run our tires at 30% less pressure than what is called for we have run the tire "flat" and it must be trashed. Kind of emphasizes the importance of running the right pressures and checking tires.

In the case of a trucker, there is no other option other than to assume the heaviest weights based on axle limits. Unless the trucker carries a constant load (such as your gravel truck) there is no other way to select the correct pressure.

The pressures affect the ride as well as tire life so when they are inflated according to the tire manufacturer's charts we end up with the best compromise for comfort and safety.

[dale farley]

Lee,

The easiest way to get your weight for the three axles is to go to a truck stop. Many of them weigh each axle when you drive upon the scales. It cost me $11 to get a printout from my local truck stop for all three axles.

Jon, I think the Goodyear spokesman said if we run our tires 20% low, they are considered "flat" and should be trashed. I too, run each of mine 5 lb over what the chart says. And as Joe said, I have noticed on my tire monitor that the 110 lbs on my front tires turns into 126 lbs when they get hot. I assume that lattitude is built into the tires.

[MangoMike]

As I recal, The Goodyear man said that the pressure at a cold reading took into account increased pressure at road temperatures. You're not supposed to compensate.

Mike

[VegasDogMan]

Checked mi tires Cold this AM - All were at 100 PSI

Drove a few hours - checked again and all were at 115 PSI

For my front axle load the 115 PSI is the required pressure (Cold I presume)

The 100psi for drive and Tag should be appropriate - they're not 20% underinflated..

I will see if I can get a 3 axle weight somewhere...

In the meantime, should I pump up my front to 115psi Cold?

[JIM CHALOUPKA]

Checked mi tires Cold this AM - All were at 100 PSI

Drove a few hours - checked again and all were at 115 PSI

For my front axle load the 115 PSI is the required pressure (Cold I presume)

The 100psi for drive and Tag should be appropriate - they're not 20% underinflated..

I will see if I can get a 3 axle weight somewhere...

In the meantime, should I pump up my front to 115psi Cold?


Absolutely, Lee. ( cold )

Whatever the chart says, and if you know your gage is on the money, you may want that pressure, for a smoother ride.

Some though are going 5 to 10 psi over as a safety measure.

[merle&louise]

Lee,

How much psi does Newmar recommend? Give them the actual weights of each axle and see what pressures they recommend?

[truk4u]

Excess air pressure = rough ride, not smooth!

[garyde]

I think I mentioned this before, but when I had new Michelins installed on my tag and my drives @ Prevost, they inflated all to 120lbs. My 365's up front are at 110 lbs. I really don't feel much difference in the ride but I'm not in the back.

[merle&louise]

I had my coach weighed last week; each wheel separately. Full fuel and water & gear without passengers. The Goodyear rep @ Sevierville told us to use the higher of the two weights per axle to use the charts.

Front: P/S 8320 D/S 8410
Drive: P/S 11760 D/S 11450
Tag: P/S 4660 D/S 5310

My tire chart shows: Front @ 8410 I should run 125
Drive @ 11760 I should run 105
Tag @ 5310 I should run 80

Newell recommends: Front 130 Drive 110 Tag 80

I am going to continue running the additional 5# per tire to cover the weight of the beer on board for LSU games.:D

Last night was not fun:eek:

[phorner]

Tuga,

That seems like a lot of weight on the front axle. What's the front axle weight rating on your coach?

I think mine is rated at 16,500 lbs and my actual weight was 15,450 lbs last time it was weighed.

[merle&louise]

The front axle is rated at 17,640# and the actual weight is 16,730 for a CCC of 910#. Not bad for a coach with 2 slides:D