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Bus Discussion => Bus Topics ( click here for quick start! ) => Topic started by: Bob & Tracey on December 13, 2019, 05:31:17 PM
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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
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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
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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.
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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 :'(
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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! 8)
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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.
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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
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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
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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.
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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
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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.
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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
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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.
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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
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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.
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Make sure you don't run the pressure in the duals that they have sidewall rub over rough or uneven surfaces on road.
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The tire deal is a personal preface,all owners are different and it's their money so they do what works best for them regardless of what internet experts think or do ;D
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I think monitoring tire temperature might be the ultimate way to find the ideal tire pressure. The question is, what is the ideal temperature range for tire safety and life? From what I can find on RV and truck forums, up to 50 degrees above air temperature is normal, the air pressure monitors that record temperature have alarm points in the 150's, and one source said that tire failure can occur at 180-200 degrees F. Looks like tires should not be hotter than a safe two-stroke temperature. For each bus there should be an optimum temperature/pressure level that results in good tire life and a less harsh ride. I rode on a current Greyhound MCI last spring, and the fronts were set at 130 psi. You could feel and hear every crack and expansion strip. :o
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I want to run a tire pressure that results in the best comfort for my tire weights that doesn't result in premature tire failure. Tire pressure may have had nothing to do with my sidewall blowout, but I'll never really know. I know I didn't hit a curb or something like that as it was the inside dual.
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I've heard that it is common to run about 10% over the chart pressure but have no way to confirm that. However it would seem that would aid in blowout protection without unnecessary harshness.
Jim
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At the Prevost factory back near where they assemble the axle units there is a guy that mounts tires on the wheels all day every day. When we were buying new buses we specified and underlined on every order what pressure we wanted. No matter, every tire on every coach came out with a different pressure, quite often with huge spreads in between. Oh well...
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...I have nothing nice to say about FMCA and anything technical...
Happy coaching!
Buswarrior
The guy I was talking about isn't working for FMCA. Roger is a tire engineer. Here's his site with lots of good information, based on data he's collected over the decades he's done this. http://www.rvtiresafety.net/
I've heard that it is common to run about 10% over the chart pressure but have no way to confirm that. However it would seem that would aid in blowout protection without unnecessary harshness.
Jim
That's what Roger from from rvtiresafety.net recommends.
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Bus Warrior,
I have never tried running 70lb. The ride is still a bit harsh at 90Lb but it it really sucked at 120lb...
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Bob 70 psi is low - even for a back dual. 90 sounds good for the front. 120 psi is way too much psi for your conversion. Remember. When reading a specific tire pressure load chart to see if the column your reading the psi from is for a single or dual tire set up. We run about 5 psi heavier than the actual psi called for on a particular load. That gives some safety net not to be running "soft" (they run hotter that way).
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I had BF Goodrich tires on my 5C for several years. I ran them at 70 psi. That was the sweet spot for them. Now my no name Chinese tires run best at 80 psi. Same bus, same weight.
JC
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My Toyo's run great at 85 up front and 80 in the back and the book says 90 all the way around. :)
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I assume with the transition from nylon bias to steel belt radials - running a tire on the soft side for comfort shouldn't be an overheat problem as much as it used to be. Coupled with the change in tire pressure, replacing all the shocks on the bus made the two AK road trips like night & day
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Ahhhhhh. Good old nylon cord tires. Flat spot when parked. Took ten miles to get them round again till parked.
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Ahhhhhh. Good old nylon cord tires. Flat spot when parked. Took ten miles to get them round again till parked.
It about the same when the tires of today get 5 years old they ride like a rock and pickup the road noise,as far the heat a tire has to dissipate the heat it generates (equalibiruim) some do a better job than others in the radial tires
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Plus the hardening of the strut bushings as they age. Few ever replace them. Several years ago, we worked on a Ford F350 4x4. Rode like a cement mixer over bumps. It was brutal. Did other work, but replaced all the rubber bushings in the front end. Wow! Couldn't believe the improvement in ride quality. It was incredible.
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Radius rod bushings should always be replaced with good ole' soft rubber not hart plastic or nylon.
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OK guys, I'm new here and going to be a new 4106 owner in a few weeks. I am getting 6 new tires installed when I pick it up in CA. Where can I find a chart to see how much pressure to run in the tires? I will get it full of fuel, water and weigh it before heading out home. Would like to start out with close to the right pressure.
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Congrats on the new-to-you bus.
The inflation chart should be available from the tire manufacturer. Probably can find one on their website.
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If you run them in the 80-90 lb. range you should be just fine.
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If you run them in the 80-90 lb. range you should be just fine.
Not saying you're wrong, but what are you basing that on without knowing the tires or the weight of the bus?
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90,000 miles on 2 different brands of tires and i am pretty sure my MCI 5A weighed more than a 4106 does. :)
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It's best to run pressures from the specific chart to your specific tires. A simple google search of your specific tire should reveal a load chart for that tire from it's manufacturer. That's only half the equation. Then you need to know the axle weights of your bus when traveling. The weight of the axle will bring you to the proper area of psi on the tire load chart. Don't forget to differentiate for dual or single tires on the axle - it will show dual or single tire psi on the load chart. Of coarse if a steer axle is 12,000 lbs. each tire is loaded with 6,000 lbs so you'll look on the chart for the closest psi for 6,000 lb single. On a dual tire axle that's weighing in at 16,000 lbs. you'll look on the chart for the closest psi for 8,000 lb dual. Always run the next higher psi # so you're not running any softer than the chart dictates. A little harder (more psi) will keep it safer & run a bit cooler. All this coupled with good shocks will make your bus ride as comfortable as it was designed for.
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...On a dual tire axle that's weighing in at 16,000 lbs. you'll look on the chart for the closest psi for 8,000 lb dual...
Be careful with the dual wheels on the charts!!
What Dan mentions sounds like the RV tire charts for Michelin which list the dual tires by AXLE END and not by each individual wheel. On other charts, you would take that 16,000 lbs and and divide by 4 to get the weight per wheel to use on the chart.
Read the charts carefully!
One other twist to make the math more difficult...
A tire industry guy on another forum recommends that unless individual corner weights are known, it's best to assume that each end of an axle carries 53% of the total axle weight. This is done to account for the fact that most coaches are out of balance side-to-side, and one side is likely carrying more than half the total weight. So with Dan's example, the weight per wheel would be calculated like this:
Front: 12,000 x 0.53 = 6,360 lbs per wheel
Rear: 16,000 x 0.53 = 8,480 lbs per axle end OR 16,000 x 0.53/2 = 4,240 lbs per wheel
Not a huge difference from Dan's math, but enough that it may put you in the next column in the manufacturer's chart.
90,000 miles on 2 different brands of tires and i am pretty sure my MCI 5A weighed more than a 4106 does. :)
Really hard to know what another coach weighs. Take ours for example... A 4108 converted by Custom Coach that weighs in at 30,000 +/- a few hundred lbs. I would guess that we are heavier than most DIY 4108 conversions by a long shot. CC was fond of making their cabinetry of 3/4" plywood, and their interior walls are made of double layer 3/4". Makes for a heavy coach with how much cabinetry they put inside. We also carry large tanks and an old-school heavy generator. You never know by looking at the model or at the outside of the bus how things are configured.
Changing just the size of water & waste tanks can vary weight by up to 1,000 pounds, and generator choice can also vary weight 500 pounds or so.
Again, I don't know that you're wrong or right. But I know that since he's getting his coach weighed it's easy enough to check the charts. Odds are he'll end up within 5 psi of your recommendations, but depending on tire size it could be much more.
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Richard's examples are point on & I covered that in a different way by stating to go to the next higher not lower psi cell. We personally run 3 to 5 psi higher than what the load chart calls for for a safety margin. At any rate running closer to chart ratings is a world better than running max tire psi. Easier on the bus AND its occupants. :)
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Truckers would have a hard time going by the charts all truckers I know run with in 10 or 15 psi of the max for 150,000 miles then buy new tires
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Truckers would have a hard time going by the charts all truckers I know run with in 10 or 15 psi of the max for 150,000 miles then buy new tires
Apples and oranges...
Truck owners are trying to get the max number of miles from their tires. Ours will age out long before we get near the max miles.
Truck owners have to set pressure based on the max load they will carry. We know what we weigh and can set for a much more specific load.
Truck owners don't care how comfortable their load is. If we bounce our occupants around on hard tires we may be driving alone.
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Speaking for one truck driver, I am concerned about my load because things can shake apart if the ride is too hard. In some cases, the load can wiggle around and shake the truck. When I drove a tanker hauling hot acid, the company required that all tires be inflated at 90 lbs. on every position, and checked and reported daily. The gross load was always 75,000 to 80,000 lbs, which divided by 18 wheels was 4444.44 lbs per wheel, average maximum. Considering that it was an open chamber tank with no baffles, the load could move around a lot with wave action, loading some tires up quite a lot. That pressure worked because it provided decent traction whether loaded or empty, and the tires wore evenly. Greyhound puts 130 lbs. in their steer tires currently, and I assume that it is for fuel mileage primarily. A conversion on eight wheels puts about the same weight on each tire as the tanker.
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Greyhound puts max pressure in their steers, same as every other modern bus company, because the steers are going to see max LOADING.
Front axle weights of +14k lbs is not uncommon for the 45' coaches. Neither is 14k lbs on the tags.
These ain't your father's Oldsmobile...
That's why they have the big 315 tires... in revenue service, they need 'em.
Weigh your coach, buy and set tires according to the manufacturer ratings.
Save money if you need to, don't put heavy rated tires on a coach that doesn't need them.
Happy coaching!
Buswarrior
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About all the 45 ft buses run the max on the front axle with the 315/80 some even use the 365/80 on the front,like BW said it is not your fathers Oldsmobile the suspension system and air bag location on the newer buses they really don't care what pressure you run it doesn't affect the ride one way or the other
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My thoughts on PSI is simple, too low and you can have a catastrophic failure, too high and it’s a bumpy ride.
When at the tire load rating you don’t have much safety margin. If you have a TPMS I suppose you’d know of a leak sooner and it’s less of a risk. I check every fuel stop / extended stop.
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For Hankook AH37 11R-24.5 14 ply, my front axle is 10,500lbs which is suggested 85psi. Rear axle is 20,500lbs which is suggested 80psi. I run 90psi all around for ease of checking and having a bit of leeway. Good Luck, TomC