We have a request to re-post this topic re: Tire inflation: MPG versus comfort
Here it is!
https://www.busconversionmagazine.com/forum/index.php?topic=11710.0 (https://www.busconversionmagazine.com/forum/index.php?topic=11710.0)
Hope this helps, Phil
Why would anyone post a thread that has been beat to death from 2009..???>>>Dan
There is only one true way of finding out what inflation you tires should be. Weigh the bus by axle on a Cat scale at your local truck stop when the bus is fully loaded. Then obtain the tire inflation table for your exact tires and tire size. Inflate to what is suggested during winter. Run 5psi higher in hot weather. No other way is accurate. Good Luck, TomC
One has to pick a happy spot for himself on tire pressure axle weight is not always the best most converted buses are heavier on one wheel or the other, I have watched converters weighing each wheel and if they get the weight with in 500 to a 1000 lbs they call it good,Best to add air pressures to compensate for the heavier wheel weight I was told,Prevost converters add pressure to the manufacture's tire specs.My Country Coach uses 130 PSI on the 315/80/22.5 on the front tires and that is max rating and I don't see any difference in tire wear or wandering and the rear and tags are 105 psi only difference I see is a rough ride on the front axles with the IFS @ 130 PSI.I am pondering the idea if I have the clarence of using 365's on the steering like Prevost for less psi and a better ride
315/80-22.5 are rated for 75mph, but only at 18,000lb. 20,000lb is 55mph. I would seriously consider going with bigger tires in front.
Quote from: TomC on November 12, 2022, 09:00:33 AM
315/80-22.5 are rated for 75mph, but only at 18,000lb. 20,000lb is 55mph. I would seriously consider going with bigger tires in front.
I am heavy my GCWR is 67,000 lbs that is only16,000 lbs less than a 18 wheel truck and trailer,my weight is around 50 to 51 thousand lbs.the ISX does a good job with pushing and pulling the weight to I can average 7.5 mpg every day @ 70 MPH,I do worry about blowing a tire on steers though
The 365 on the front sure do like to wander around, following whatever imperfection is out there.
What is your steer axle weighing now?
Happy coaching!
Buswarrior
Quote from: buswarrior on November 12, 2022, 11:14:54 AM
The 365 on the front sure do like to wander around, following whatever imperfection is out there.
What is your steer axle weighing now?
Happy coaching!
Buswarrior
17,800 lbs
Quote from: luvrbus on November 12, 2022, 11:34:53 AM
17,800 lbs
That is obscene! It actually weighs that on the scales?
An entire GM 5307 weighed 23k empty...
Happy coaching!
Buswarrior
Quote from: luvrbus on November 12, 2022, 11:34:53 AM
17,800 lbs
Wow! Thats the Equivalent of 712,000 oreo cookies! Your coach needs a diet Clifford! ;D
Quote from: buswarrior on November 12, 2022, 01:37:51 PM
That is obscene! It actually weighs that on the scales?
An entire GM 5307 weighed 23k empty...
Happy coaching!
Buswarrior
Yep it has a 18,000 lb rating .I have a 18ft slide on the passenger's side and 14ft slide on the drivers side and both have some heavy duty framing plus the 12.5 generator is ahead of the steers in a hush box it is heavy.
Given the painful bill at the fuiel pump, I decided to up the pressure all around on my bus.
It weighs in around 32k, I think about 12 on the steers 20 in the back. I just put 100 all around, well withing spec.
The ride is firmer, not harsh, nothing is really hard riding on air. As to improved MPG that will take a few tanks to figure out because much of my travels are up and down so hard to get a good average reading.
I am inclinded to go back to the more accurate lower settings if the increased comfort is "worth it"?
As to steering, no difference in wandering or feel, drives the same at both pressures.
interesting of note: couple weeks ago, i drove car from Sacramento, elevation 50 up to Tahoe, over 7500 at pass. got about 32mpg on that leg. On the trip back, there is a big sign warning about downlill grades for the next FORTY miles. Got about 45mpg on that leg. lol
Higher tire pressure for the average drive, ie: smooth asphalt is hardly noticable but do the extreme as in the far NW corner where pot holes, frost heaves, & wash boarding is common - dropping to the proper load rated pressure is like night & day both for comfort & handling. Oh & good shocks make a big difference in the same condition differential.
Good luck seeing ACTUAL mpg improvement. Driving 5 mph slower would yield better results for most except Clifford and others with lots of overdrive.
Quote from: windtrader on November 13, 2022, 08:26:52 AM
Given the painful bill at the fuel pump, I decided to up the pressure all around on my bus.
It weighs in around 32k, I think about 12 on the steers 20 in the back. I just put 100 all around, well within spec.
Don -I'm going to speculate that you're not going to see any difference in your fuel mileage, or at the most, decimal points different.
As has been pointed out earlier, just take your bus to a truck scale in full, ready-to-roll condition, pay the $15 and get the weights on each axle, instead of guessing. Then set your tire pressures to the load/inflation table for your tire size and manufacturer. Just do it right and you, mama and the bus will all be happy campers.
FWIW & HTH. . . ;)
RJ
You never get it perfect ,the data plate on a vehicle will tell you one thing and a tire manufacture will tell you different
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
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
Quote from: Jim Blackwood on November 14, 2022, 07:31:55 AM
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
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
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.?
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
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
Quote from: Jerry W Campbell on November 14, 2022, 01:38:13 PM
. . .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.
Quote from: windtrader on November 14, 2022, 11:48:49 AM
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
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
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
Quote from: windtrader on November 15, 2022, 05:42:13 PM
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
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. ;)
Pull into a dot inspection site when they arent busy. Have them check every wheel weight. They may have interest in bus conversions.
Quote from: chessie4905 on November 16, 2022, 03:32:30 PM
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