Requested Link: Tire inflation: MPG versus comfort

[luvrbus]

You never get it perfect ,the data plate on a vehicle will tell you one thing and a tire manufacture will tell you different   

[buswarrior]

I would think really hard about lowering the tag axle tire pressure to match the load.

Many an MC8 have torn the tag structure loose from the frame, manymany have had welded repairs. No need to be pounding it with a hard tire.
(That was how i acquired my old parts bus, the entire tag structure let go and pushed everything up into the top of the wheel well. Instant scrap value)

You will likely find the tag axle only bearing down around 4000 lbs, if all is right pneumatically, so minimum air pressure on the tire chart,  historically, fleets i drove with would set an MC8 tag tire at 75 lbs.

How old are the shocks?

Happy coaching!
Buswarrior

[Jim Blackwood]

If you set the tag on an MC8 at 75, what would be appropriate for the tag on a 102DL-3? Are they the same or different?

Jim

[buswarrior]

If you set the tag on an MC8 at 75, what would be appropriate for the tag on a 102DL-3? Are they the same or different?

Jim

VERY different!

The tag on a 45 foot coach carries a load, the old 2 stroke 40 footers, it was there as a token effort, as they were just a little too heavy for 2 axles.

Until you get it weighed, air it according to the build plate rating.

Better too much than too little until proper measurements can be taken.

Happy coaching!
Buswarrior

[luvrbus]

You need to watch the tag weight on 45 ft buses they are not your dads Oldsmobile,I had a time trying to balance my DL3 to much pressure would load the front axle on a already heavy front axle to little would load the drive axle but take weight of the front axle ,tag axles on the DL3 carry a lot more weight than a older MCI 8,I am going to reduce the weight on my CC tags just for the front axle weight lol adjusting a 45ft converted bus can be a challenge,My DL3 was almost a 1000 lbs heavier on the passenger's side,I found that with portable wheel scales not on a truck scale   

[windtrader]

All good details especially when in revenue service and tire tread gets run out. In my  and most of our cases they'll age out so tread wear is not a real factor. Safety is of course. I did get the bus weighed, front and rear, just was too lazy to pull the exact numbers for here. But I never did go the extra step to get the actual mfg. spec for the actual weight. I just kept them all around 90 and life was good.

Just this summer was when I pushed them up to 100 and it did seem a slight difference but as was mentioned there is far greater savings by just running slower than 75. You think that is why my mileage sucks.?

[Jerry W Campbell]

Hello friends,
  Years ago I did research tire pressure but it's been so long ago I don't remember what, where or when I got the info. For about 20 years I've been running 100 in the fronts and 105 in the rears. The tire wear is even, The axels are 12K+ on the front and 20K+ on the rear. GVW is 32,600, I am at about 28,000. Tires are 12/22.5. Both front and rear are under the weight limit. I don't think I could be getting better mileage but if I run over toothpick I can feel it. I put new shocks on when I first bought the bus. These old Crowns are not known for their suspension. I'm wondering if I go a little less on the tire pressure if it would smooth the ride enough to matter or just leave well enough alone?
Thanks
Jerry

[luvrbus]

You can set all tires by size for air pressure, you need to know the rating on the tire like G,H and so on I see bus people ruin new tires by setting the pressure to low because the tires carry different weights by rating and pressure for the same size tire,People read I run 80lbs and have no idea what the person is running for tires,You see the trucks and buses running the wide base tires (super singles) they use 1 setting for air pressure and that is a 115 psi     

[RJ]

. . .The axles are 12K+ on the front and 20K+ on the rear. GVW is 32,600, I am at about 28,000. Tires are 12/22.5.

Jerry -

Up until Sept 2018, I owned an MC-5C with similar axle weight ratings - 12K front, 20K rear, running the same size tires, 12R22.5s.  When I first picked up the coach, the PO had all six tires pumped up to 120 psi, and the air-suspended bus rode like a steel-wheeled skateboard!

First chance I got, with full fuel and fresh water tanks, I ran it across a CAT scale, where the coach weighed 28,000 exactly.  Going to the Michelin load/inflation tables, I was able to drop the fronts to 85psi and the rears to 80psi. HUGE difference, with virtually no change in the fuel economy.

Just this summer was when I pushed them up to 100 and it did seem a slight difference but as was mentioned there is far greater savings by just running slower than 75. You think that is why my mileage sucks?

Don -

Since your MCI has the aerodynamics of a brick, something to ponder is that wind resistance goes up by the cube of the speed. Simple physics. . .

FWIW & HTH. . .

RJ

[Jerry W Campbell]

Thanks Guys,
The tires say a load rating of "H".
I think I will try a lower psi for the trip home in the spring and see what happens.
Jerry

[windtrader]

Yes. Fully aware of drop in mileage as speed goes up. I hate that MPG gauge in the passenger car. Even though it is farily aerodynamic, you can watch the efficiency decline once you get even over 60's. by the 70's there is like 10% loss.

If that meter was on the bus, I'd be hauling @$# at 55. lol

[luvrbus]

Yes. Fully aware of drop in mileage as speed goes up. I hate that MPG gauge in the passenger car. Even though it is farily aerodynamic, you can watch the efficiency decline once you get even over 60's. by the 70's there is like 10% loss.

If that meter was on the bus, I'd be hauling @$# at 55. lol

When you see the Silver Leaf on my coach say a rolling 2 mpg you watch to see if it going to change  and it does

[Van]

The most acurate way to weigh the coach is each wheel position individually all at the same time, a local FOB  can help you with that.

[chessie4905]

Pull into a dot inspection site when they arent busy. Have them check every wheel weight. They may have interest in bus conversions.

[luvrbus]

Pull into a dot inspection site when they arent busy. Have them check every wheel weight. They may have interest in bus conversions.

ADOT has a interest at the rest area on I 17 south bound before Rimrock they had a couple of buses with trailers pulled in,looked to me like it was a couple of vendors headed for Quartzsite with kitchen trailers, one didn't fare good he must have had some tires that didn't pass because Loves roadside had it up front and rear on the GM bus installing new tires lol I told Sonja the price of fried Twinkies just went up