Michelin Load & Inflation Tables

[pgchin]

I'll have the bird in this weekend for maintenance so I'll post some part numbers next week. I run 12r's on 8.25's and really do not plan to change. I did contemplate it one time and decided if I did I'd run 12r's on the drives and 315's on the steer and tags and get a set of 9' rims for full weight capacity but since then I put the bird on a diet and the front axle is under about 600 lbs or more on full fuel......fuel is the biggest weight deal on a 95 42' er. Just another solution for you to think about M.R. if you are wanting to get more capacity or a softer ride. Then you can rotate the fronts to the tags when they get older FWIW as well.

[mrkane]

Sleipnir's wheels are Firestone Accu-Forge part number 27471, 22.5x8.25, max cold pressure 120 psi, max load 7000 lbs.

The weight figures given above were taken after filling the fuel tank. I could watch the pricing at the local Flying-J from the campground, and went to get fuel without dumping the tanks when the cost hit a new low.

Weighing was an afterthought, as the coach was expected to be near the maximum load. I estimate both waste tanks were 90% full, fresh water 50%, LPG was 80%, and fuel was 100%. Dumping the tanks before travel is typical for me; therefore, I would expect the coach to lose ~1600 lbs, largely from the drives due to the location of those tanks. Diesel consumption is about 85 pounds per hour.

Recall my steer axle was less than 13,000 lbs actual weight at full loading, so the required pressure with the XZA2 Energy 295/80s is ~95 psi. At 23,000 lbs load, the drive also calls for 95 psi. The original placard calls for 12Rs at 105 psi steers, 85 psi for the rest.

I don't see how going to the 315s, but running at much higher pressures to limit dual spacing issues would result in a better ride?

I rechecked the GAWR and GVWR numbers to verify my earlier numbers are correct. My pick-up also has the sum of the axles greater than the vehicle GVWR: Front GAWR 4800lbs, Rear GAWR 6500lbs, GVWR 9900 lbs. The standard tires on the p/u are LRE, or 3415 lbs at 80 psi, so those ratings are not limited by the tires.

Bottom line is my coach is much lighter than later coaches, and the 295/80 in LRH are a good fit in terms of load capacity, dual spacing, and ride quality.

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

[davidbrady]

(05-22-2013 12:13)mrkane Wrote:  Sleipnir's wheels are Firestone Accu-Forge part number 27471, 22.5x8.25, max cold pressure 120 psi, max load 7000 lbs.

This crosses to Alcoa part number 88311 which has an outset of 6.66" which gives you a dual spacing of 13.32". Add to that the thickness of a nylon spacer and you may be very, very close to the 13.5 inches required.

(05-22-2013 12:13)mrkane Wrote:  I don't see how going to the 315s, but running at much higher pressures to limit dual spacing issues would result in a better ride?

No, it won't. It will only help if you can run the pressures spec'd earlier for the 8.25" wheel after achieving the 13.5" dual spacing required.

[pgchin]

(05-22-2013 12:13)mrkane Wrote:  Bottom line is my coach is much lighter than later coaches, and the 295/80 in LRH are a good fit in terms of load capacity, dual spacing, and ride quality.

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

Yeah, I agree. The solution I proposed will get you to 90lbs on the front but you'd have to mix rim size and tire size. 5lbs does nothing for ride quality. You could gain or loose 5lbs on a 10 degree temperature variant alone. I think you got the best price performance and most flexible solution! Good iuck!

[davidbrady]

(05-22-2013 12:21)davidmbrady Wrote:  This crosses to Alcoa part number 88311 which has an outset of 6.66" which gives you a dual spacing of 13.32". Add to that the thickness of a nylon spacer and you may be very, very close to the 13.5 inches required.

I need to add a caveat to my calculation. Doubling the wheel's outset dimension only works if you're running the same wheel on the inner dual. This is obvious, but bears mentioning. Also, if you are running a steel inner wheel then it's probably a good assumption that it's outset matches the outer aluminum's outset but it should probably be checked. Add to this the fact that these coaches are old and you never know what a previous owner did in terms of wheel replacement. It's interesting that if you go out and buy a late model Prevost XLII you'll get steel inner dual wheels. Prevost only put aluminum on the outside. Cost cutting??? Or ride quality??? I'd venture a guess that steel wheels ride softer; remember the inner wheel does most the work.

(05-22-2013 13:21)pgchin Wrote:  5lbs does nothing for ride quality.

I'd argue over this Pete. Maybe it's coach specific, but on my LXi 5 psi makes a difference. If I can keep the hot tire below 105 psi, then the ride is remarkably smoother than if the hot tire is 110 psi. Luckily for me, my cold settings are such that my hot steer tires run at 105 psi - the typical heat increase from rolling resistance increases my steer pressures by 10 psi. Now, the sunny side on a hot Arizona afternoon will heat up more, in this case I slow down. I try to keep my tires running cool which I measure by noting pressure increases.

[pgchin]

(05-22-2013 13:36)davidmbrady Wrote:  I'd argue over this Pete. Maybe it's coach specific, but on my LXi 5 psi makes a difference. If I can keep the hot tire below 105 psi, then the ride is remarkably smoother than if the hot tire is 110 psi. Luckily for me, my cold settings are such that my hot steer tires run at 105 psi - the typical heat increase from rolling resistance increases my steer pressures by 10 psi. Now, the sunny side on a hot Arizona afternoon will heat up more, in this case I slow down. I try to keep my tires running cool which I measure by noting pressure increases.

I'd counter with its model,brand and geographic specific. With the brand and belt package I run ( not Michelin) 5 degree's is nothing is the south given the summer and spring day road temps are well above 105 degree's ( hence my post of the IR tool) Cooler road temps and your brand, model and belt package I would agree with you, so it depends on your use case again and where and when you drive! There's that nasty word again use case!

[DonB]

(05-22-2013 12:21)davidmbrady Wrote:  

(05-22-2013 12:13)mrkane Wrote:  Sleipnir's wheels are Firestone Accu-Forge part number 27471, 22.5x8.25, max cold pressure 120 psi, max load 7000 lbs.

This crosses to Alcoa part number 88311 which has an outset of 6.66" which gives you a dual spacing of 13.32".

Mine are 883623. Current model is 88367x, which is 6.60 or 13.2 dual spacing.

The 88362x are rated 7300 lbs, while the current 88367x are rated 7400.

[davidbrady]

Thanks Don, that helps round out the picture a bit. I uploaded a copy of the 2013 Alcoa Product Spec Guide which spells out the dimensions for all of their current and probably most of their discontinued wheels. It can be found in our Document Library under Document Library > Chassis > Tires and Wheels.

[mikebulriss]

To show BB product supplier consistency, my 91 has Accuride aluminum wheels. Accuride part number 27471 (8.25 x 22.5, 7250 lbs at 120psi, outset 6.59). Part 24741 is an obsolete number which crosses to a current Accuride part number28615.

FWIW.

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