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davidbrady · (This post was last modified: 05-11-2013 18:02 by davidbrady.)

Has anyone else noticed that Michelin has changed their Load and Inflation Table numbers for the 315/80R22.5 LRL XZA1 and XZA2 Energy's? For example, if you need a 15220 lb load capability in 2009 you'd have to run 110 psi in your steer tire, whereas in 2013 you'd only have to run 104 psi.

The fact that the 2013 curve is linear makes interpolating easy. The formula for the steer axle is: PSI = (Axle Weight - 2740)/120.
I'm at 14227 lbs on my steer, so doing the math puts me at (14227-2740)/120 = 95.7 psi. Which is great for me because I find that if the hot tire stays below 105 psi, the ride is MMMmmm Smooth! Smile

I run 95 psi on the steers and 85 on the drive and tags.

Here's the table from 2009:

Here's the table from 2013:

Here I graphed the two for you:

***Arcticdude*** · 05-11-2013, 19:44

That's a great find! Thanks Big D! Big Grin

cmillsap · 05-12-2013, 00:49

Sooo, David,

Does this mean a 2013 date coded tire will carry more weight than a 2009 date coded tire? Are they saying that a 2013 tire is better constructed tha a 2009?

davidbrady · 05-12-2013, 11:07

Hi Chuck,

I think it's a standards thing. I think they slightly tweaked how the tables should be reported or how measurements are taken. My guess is that there hasn't been any change made to the tire. Nonetheless, it's our job to conform to the tables which is exactly what I plan to do! LOL Smile

Here's what Michelin says:
"Industry load and inflation standards are in a constant state of change, and Michelin continually updates its product information to reflect these changes. Printed material may not reflect the latest load and inflation standards."

***mbulriss*** · 05-12-2013, 18:06

One cautionary point of note here since I just bought new front tires - the Load and Inflation Chart being referred to here is valid for the default 9.0" wide wheel. While I know most of the later model mid-90s onward have the 9" wheel, the earlier ones have 8.25" wheels. The Michelin 'alternate' acceptable 8.25" wide wheel has much lower load factors. The max load on that tire/wheel combo is 8,000 lbs at 130, going from memory. One of the Michelin Tire Application Charts has a footnote that basically says something like: Contact Michelin before installing 315/80R22.5 LRL XZA2 Energy on 8.25" rim. Of course the 8.25" rims are rated for anywhere from 7200-7300 depending on when manufactured! Since I was curious about that footnote, I called them. They just wanted to make sure users were aware there was a different Load and Inflation Chart for the 8.25" wheel and that the load ratings were much lower.

As I alluded to, it's all kind of a moot point for earlier Birds, since the axle and wheels are rated for 14,600/14,500 prior to mid-90s depending on which wheels you have. I went with the 315s anyway due to much better general availability versus 12Rs, they are about $60 each cheaper than the 12Rs, and the higher load rating (for safety), even if I don't get the full benefit of it.

FWIW,

Mike Bulriss
1991 WB40 "Texas Minivan"
San Antonio, TX

DonB · (This post was last modified: 05-12-2013 19:32 by DonB.)

(05-12-2013 18:06)mbulriss Wrote: The max load on that tire/wheel combo is 8,000 lbs at 130

The 8.25-inch rim is only rated for 120, so it is 8000 at 120.

Michelin puts the 8.25-inch table in each book, and I happen to have 2007, 2010, and 2013 books on hand, so images for the 315s on 8.25-inch rims are attached.

A cursory reading does not indicate any weight changes, except 75PSI values were added between 2007 and 2010. They also changed the minimum spacing from 13.2 to 13.5 inches between 2007 and 2010.

My drivers have 13.0-inch spacing. I would not have put 315s on there, but Chuck did, and I'm not going to replace new tires, so I run 100PSI on them when 80 is nominally enough. As I recall, Shane has been doing that for years.

cmillsap · 05-12-2013, 21:20

(05-12-2013 19:30)DonB Wrote:
(05-12-2013 18:06)mbulriss Wrote: The max load on that tire/wheel combo is 8,000 lbs at 130
The 8.25-inch rim is only rated for 120, so it is 8000 at 120.

Michelin puts the 8.25-inch table in each book, and I happen to have 2007, 2010, and 2013 books on hand, so images for the 315s on 8.25-inch rims are attached.

A cursory reading does not indicate any weight changes, except 75PSI values were added between 2007 and 2010. They also changed the minimum spacing from 13.2 to 13.5 inches between 2007 and 2010.

My drivers have 13.0-inch spacing. I would not have put 315s on there, but Chuck did, and I'm not going to replace new tires, so I run 100PSI on them when 80 is nominally enough. As I recall, Shane has been doing that for years.

Don,

I think that as long as the tires do not touch, all's well. Obviously, low tire pressures could allow the tires to touch; so maintaining proper inflation is important.

DonB · 05-12-2013, 21:53

It probably isn't an accident that they raised the separation minimum at the same time they added a lighter weight/pressure (75PSI). It would imply that higher pressures need less separation, but it is hard to know what pressure is correct for my 13.0 inches. When I get down there and look at the bulge there is about 1/4-inch of separation, which likely means they touch when I hit a bump.

I've got my Truck Systems pressure monitors to let me know that I don't get down on pressure.

mrkane · 05-20-2013, 01:08

How does one measure the wheel separation spacing with tires mounted on the coach? Is it the edge-to-edge distance?

M.R.Kane
1987 PT40 'Sleipnir'
currently near Elmo, TX

DonB · 05-20-2013, 01:48

It is any point on one tire to the same point on the other tire. With straight-tread tires, particularly if they are fairly new, it is easy. Just hook a tape measure in a tread on the inner tire and measure out to the same side of the same tread on the outer tire. Do a few to make sure it is consistent. Mine were 13 inches every time.