Smart Weigh

wagwar · September 26, 2012, 08:08:14 AM

Thanks so much for your help and advice! It is very much appreciated. I'll just adjust the tire pressures as recommended by the mfg charts and get on down the road!

wagwar · November 22, 2012, 11:56:51 AM

I'm installing a TPMS and I'm ready to program the sensors for each axle and wheel. I posted an earlier thread discussing "Smart Weigh" and regarding axle weights and adjusting the tag air bags. The advice was to leave the suspension alone. So I did.

Based on the weights below and the charts I found at Firestone, does it make sense to adjust the tire pressures as follows:

Front: 115 psi Drive: 75 psi Tag: 70 psi.

Bus Weights:

The numbers as I understand for a 1981 MCI MC9. My tires all around are fairly new (0409 and 0712 DOT date code) Firestone FS 560 Plus Load range H, running 110 psi in all eight.

GVWR: 36500
Front GAWR: 13340
Drive GAWR: 22000
Tag GAWR: 6000

My weights:
Front GAWR: L front - 7100 R front - 6300 Total - 13400
Drive GAWR: L rear - 9925 R rear 9150 Total 19075
Tag GAWR: L rear - 1800 R rear 1760 Total 3560

Thanks

Oonrahnjay · November 22, 2012, 01:09:35 PM

Is it common to have a 800 Lb difference side-to-side on a front axle? (That's not a complaint or a criticism - just noticed it and am asking the question. Thanks, BH NC USA

bevans6 · November 22, 2012, 01:21:23 PM

He has a slide-out and a generator on the driver's side of the coach. Even though the side to side leveling is through the rear axle, the front springs have to deal with the fact that the center of gravity of the bus is offset to the driver's side, hence higher weights.

Brian

Oonrahnjay · November 22, 2012, 02:29:45 PM

Quote from: bevans6 on November 22, 2012, 01:21:23 PMHe has a slide-out and a generator on the driver's side of the coach. Even though the side to side leveling is through the rear axle, the front springs have to deal with the fact that the center of gravity of the bus is offset to the driver's side, hence higher weights.
Brian

Thanks, I figured that there would be a perfectly logical answer. If someone really cared about balance (or considering a bare bus), would the weights likely be more equal? I guess tanks would have a lot to do with it, too.

Lin · November 22, 2012, 02:54:47 PM

Without seeing the tire inflation chart you are using, no one can verify the pressures you list. However, I would guess since you have looked at it in detail and can do the arithmetic, you would have it right. I personally like to go about 5#'s over what the chart says since it is better to be a little over than under, and I never really trust the tire gauges. The TPMS always says different than my gauge anyway.

Ednj · November 22, 2012, 07:52:00 PM

These are my weights on my Mci9 now.
It was 6000lbs lighter as a shell.

wagwar · November 23, 2012, 09:17:13 AM

I took it from this site: http://www.firestonetrucktires.com/us_eng/load/index.asp

The Medium and Commercial and Light Truck Tire chart - 12R22.5. Unfortunately, I could not find any charts that were specific to my tires: Firestone FS 560 Plus LR H. This generic chart was all I could find.

Thanks for the 5lb + tip. That sounds like a good idea.

belfert · November 23, 2012, 09:34:02 AM

I'm pretty sure that Firestone chart applies to all Firestone tires of that size. I use that chart for my FS 590 Plus tires in the 11R24.5 size. Interesting thing is that I replaced the steer tires with Roadmaster tires. The Roadmaster tire chart has the exact same weight/PSI specs as the the Firestone table for the 11R24.5 tires.