Tire question for Bus Warrior

Bob & Tracey · December 13, 2019, 05:31:17 PM

I did not want to change the discussion to the tire question for a 4104 so I will ask here. You bring up tire pressure in your response and this is an ongoing issue between me and some "friends". We are running 12R22.5s on our 4104 and if I use the weight per axle and use the manufactures tire chart I would be running 70lbs per tire but my extra smart friends say to run at max rated pressure at all times. I have asked around, tire shops, repair shops and anyone I feel might have an answer and get sooo many different opinions so I have compromised and am running with 90lbs. Can you please expand on you thoughts?
Thanks, Bob

buswarrior · December 13, 2019, 06:09:35 PM

The tire manufacturer knows best. The load chart for the specific tire is the way to go.

Not one from someone else, not something posted in a manual, not something someone's fleet used to do...

The maximum on the tire sidewall is just that, a maximum. Not a rating to run the tire at.

A bus conversion doesn't usually load up as badly as a service coach does.

For the other readers, get the coach ready for operation, fuel full, fresh water full, and put it on the scales and get each axles's weight, then do the math with the chart.

That gives you a place to start. If the chart doesn't go low enough, i wouldn't go below the lowest pressure on the chart without something in writing from the tire manufacturer's technical people.

90lbs has been used by lots of GM folks.

Now, with that said, making some small adjustments to sort out "the feel" is just as valid as doing so with your automobile.

But, you will be working from a much better base line.

Did you try 70 lbs and see how it felt?

Happy coaching!
Buswarrior

dtcerrato · December 13, 2019, 06:50:23 PM

On our first (2016) road trip FL to AK we were running 120 psi (max rated pressure for our tires) IT WAS AWFUL! After sifting though the tire manufacturers load chart as BW explained. We ended up with 90 psi on the front & 75 psi on the rear duals. The ride difference was like night & day.

windtrader · December 13, 2019, 07:30:30 PM

Quote from: dtcerrato on December 13, 2019, 06:50:23 PM
On our first (2016) road trip FL to AK we were running 120 psi (max rated pressure for our tires) IT WAS AWFUL! After sifting though the tire manufacturers load chart as BW explained. We ended up with 90 psi on the front & 75 psi on the rear duals. The ride difference was like night & day.

What a revelation! Thanks Dan. For some dumb reason I had been setting the same tire pressure for all my tires. The light just went on that the rears and fronts are going to run different pressures. Kicking myself

dtcerrato · December 14, 2019, 05:13:15 AM

That's one of the penalties for not reading the specific charts because it always gives pressure for "single" & "duals". Tag axles may be trickier - I have no experience with that. Glad I can light someone's bulb!

richard5933 · December 14, 2019, 05:33:28 AM

The tire guru over on the FMCA forum recommends using 53% of the axle weight for each end of the axle rather than half. This is to account for the fact that very few coaches are balanced side to side. Seems reasonable to me.

Then of course you would use that number to find the proper pressure, always rounding up to the chart weights and not down. To accommodate day to day temperature swings and weight variations, he advises to add 10% to the pressure shown in the chart.

I've been following this method for the time we've had buses, and it seems like a good compromise between ride quality and having a safety margin.

luvrbus · December 14, 2019, 06:17:32 AM

Quote from: windtrader on December 13, 2019, 07:30:30 PM
What a revelation! Thanks Dan. For some dumb reason I had been setting the same tire pressure for all my tires. The light just went on that the rears and fronts are going to run different pressures. Kicking myself

Keep in mine RV owners are after the ride not the longevity of the tire ,commercial carriers and truck are usually at about 10psi below the max,it nothing to see the 45 ft Prevost and MCI and others with a 130 psi on the front axle with 315/80/22.5 tires and last around 80.000 miles or a year

TomC · December 14, 2019, 06:18:44 AM

Pure and simple-weigh your bus then run what is recommended in the tire inflation tables for your tire size. DO NOT run the maximum tire pressure imprinted on the tire-all you'll get is bus that rides like a fork lift, tire wear in the middle of the tire, and the tire not fully seated on the pavement. With the proper tire pressure, you'll have a nice riding bus, tires wearing well, and the maximum tire pattern on the pavement for maximum traction. Good Luck, TomC

belfert · December 14, 2019, 06:33:00 AM

My bus only needed 75 PSI on the duals per the inflation charts. That was based on the unloaded axle weight. I actually ran the duals at 80 PSI to account for all stuff loaded in the bus for a trip. A few years ago I had an inside dual tire blow out the sidewall. When I went to get a new tire the tire guy was shocked I would run at only 75 or 80 PSI. Since then I run 90 or 95 PSI (Don't recall right now.) and no difference I can tell in how the bus rides.

luvrbus · December 14, 2019, 06:54:42 AM

Quote from: TomC on December 14, 2019, 06:18:44 AM
Pure and simple-weigh your bus then run what is recommended in the tire inflation tables for your tire size. DO NOT run the maximum tire pressure imprinted on the tire-all you'll get is bus that rides like a fork lift, tire wear in the middle of the tire, and the tire not fully seated on the pavement. With the proper tire pressure, you'll have a nice riding bus, tires wearing well, and the maximum tire pattern on the pavement for maximum traction. Good Luck, TomC

School buses and transit authorities all run their tires about 10PSI below max ,there no way in hell will I run a 315/80/22.5 $700.00 Michelin tire at 75 psi.I have a SilverLeaf monitoring inside the tire every 10 psi I add to the Michelins will drop the temperature about 10 degrees I found that out bringing it home from Texas when I thought the tires where to hot to touch with 80 psi .Every time I blow a Michelin tire the 1st they say was to low of air pressure

belfert · December 14, 2019, 08:49:43 AM

Quote from: luvrbus on December 14, 2019, 06:54:42 AM
School buses and transit authorities all run their tires about 10PSI below max ,there no way in hell will I run a 315/80/22.5 $700.00 Michelin tire at 75 psi.I have a SilverLeaf monitoring inside the tire every 10 psi I add to the Michelins will drop the temperature about 10 degrees I found that out bringing it home from Texas when I thought the tires where to hot to touch with 80 psi .Every time I blow a Michelin tire the 1st they say was to low of air pressure

School bus operators and transit authorities care more about tire life and MPG than passenger comfort. A fully inflated tire will have a slightly higher MPG that a bus nut will never notice, but a transit authority spending a few million a month on fuel wants every bit of MPG they can find.

I no longer run my tires at 75 or 80 PSI since it cost me $550 for a new tire when the one blew out. Luckily, no damage other than the tire from the blowout.

buswarrior · December 14, 2019, 02:59:40 PM

Geezus... we aren't loading our buses.

We don't usually need the air pressure that a loaded bus needs.

All the commercial tire guys know is loaded heavy, they don't know what to do with us.

We are wierd ducks, running commercial equipment light.

And no insults intended, but tire changer is way down the food chain in the shop. If all of us, with internet connections and lots of enthusiasm to read stuff, don't know what to do with tires, what makes you think the tire changer does?

He gets told to fill 'em to the max, and gun those puppies on as tight as the friggin gun will go. And he has trouble getting that right...

I have nothing nice to say about FMCA and anything technical...

Pick your poison, choose a Deity, pray that you have made the right choices?

Happy coaching!
Buswarrior

chessie4905 · December 14, 2019, 03:24:04 PM

Spend the coin to get the coach weighed in your normal running condition. Full fuel and water tanks and all your normal junk. Get all wheel locations weighed, not just front and rear axle. Then you can run what is recommended or what YOU prefer. Either way, tpms should be considered seriously, especially for those that actually use their coaches extensively. Although those members usually take close care of their tires and pressures.

luvrbus · December 14, 2019, 05:22:33 PM

Tire manufactures are well represented at the FMCA gatherings they will tell will you straight up if you ask the question I find and not hear say from the internet,things have changed in the tire industry that why you buy tires every 6 or 7 years now and not 15 years like in the past

belfert · December 15, 2019, 05:49:42 AM

Quote from: buswarrior on December 14, 2019, 02:59:40 PM
Geezus... we aren't loading our buses.

We don't usually need the air pressure that a loaded bus needs.

All the commercial tire guys know is loaded heavy, they don't know what to do with us.

I was never told to run my tires at max. The tire guy just said that 75 PSI is too low so I went up 10 or 15 PSI which is still well under max. It sure isn't going to hurt to run the tires with a little more air and hopefully saves me from another sidewall blowout.

I figure the guy who sells tires for a living knows at least as much as I do about tires and hopefully more so. It wasn't the guy doing the work stating the PSI was too low.