Front end allignment

[Sid Tuls]

After my recent trip I notice my front passenger tire had excessive tire wear on the outside. The driver's side tire is fine. My question is this can a good truck shop do this for me? Or do I have to bring the bus to Prevost? I only have 30,121 miles on it. and I'am the only driver I Ididn't hit anything like curbs or pot holes. There are a few rough spots on the Interstate 40. Thanks

[Joe Cannarozzi]

Sid any good truck tire supplier should be able to point you to the right shop.

Almost sounds like a warranty issue:confused:

[Loc]

Sid,

I had the same issue on my XLII with 45K miles. I took it to a truck aligment shop in Houston. They did a great job (Josam Laser Alignment Equipment). They even gave me a before and after print out that showed how out of alignment the front passenger tire was. My experience was Prevost was that they called a mobile guy out to their lot. I prefer to go to their shop where they have all the equipment and tools. Prevost can probably recommend a shop in your area.

Loc

[Sid Tuls]

Loc & Joe, talk to a truck shop and will go down there with the info you guys sent me. Talking to him he said we can take the front's and put them on the tags and the tag's on the front. He does work on charter buses. Also called Prevost Mira Loma and they told me this afternoon that it takes about a half a day to do a bus. So is there something I'am missing? The truck shop said it was just a toe out problem and if we switch tires looking at a 3 hour time table. Thanks for the input!!

[hhoppe]

Sid: I have found a very reliable service company located in Sacramento. I had my 89 Prevost aligned there and they have an excellent front end man for rigs like ours. I recently had them do complete service on my 2000 Prevost and they were very thorough in every way. They service a lot of Fire Trucks and trucks of all sizes. They have the largest truck frame straightening device on the West Coast. Call Rick Tracy @ 916-371-6100 or Cell 916-825-7422. West Coast Frame & Collision Repair, Inc. They'r easy to find and have plenty of room for your rig. Call me if you want to discuss them.
530-273-9124 Jeff did my bus service work and knows his busses.

[mikedee]

Sid,
I had my 2001 done in Mira Loma. Took all day and they did a fine job.

Set the front and tag as well as check the drivers, adjusted ride height, found an repaired a road damaged ride height control rod from my night fight with a monster road gator.

All for $600.00 even including parts.

[0533]

If you are going to invest in a front end alignment I would recommend a 3 axle alignment, which my be what the folks who went to Prevost are referring to. This cost about $600, but is well worth the expense given the price for new Tires.

They place the bus up on 6 steel tables, use a laser device and then go through the entire process of aligning each axle. It is important to make sure that the steering wheel (correct position) is checked before completion, straight that is. and also test drive the bus before signing off on the alignment.

[merle&louise]

After my recent trip I notice my front passenger tire had excessive tire wear on the outside. The driver's side tire is fine. My question is this can a good truck shop do this for me? Or do I have to bring the bus to Prevost? I only have 30,121 miles on it. and I'am the only driver I Ididn't hit anything like curbs or pot holes. There are a few rough spots on the Interstate 40. Thanks

Sid,

Is there any similar wear on the inside of either tire?

[Sid Tuls]

Sid,

Is there any similar wear on the inside of either tire?

No just on the outside of the passenger tire. The drivers side is perfect. Going to a truck shop tomarrow and will post the results.

[merle&louise]

Sid,

I have the same symptoms, but it is on both of my front tires. My driver's side tire has the wear on BOTH sides of the tires. The passenger side only on the outside. I presently have Toyo tires on the front with 25,000 miles on them. I had Michelins previously and they did the same wear pattern. I had the front end aligned by TCI (Tire Centers, Inc.) after the Toyos were installed. It appears that the front end alignment didn't fix the problem.

Someone told me that I should have installed STEER tires on the front; they have extra rubber on the edges. Hope that this has helped you.

[Gary & Peggy Stevens]

Someone told me that I should have installed STEER tires on the front; they have extra rubber on the edges. Hope that this has helped you.

Mel, I think someone was pulling your leg about " Steer Tires" ? :eek:

I could be wrong but I don't think there is an actual tire that is made specificly for the steer tires ? :confused: I think that is just a terminology made for the front tires. As in: I moved my steer tires to the tag, and replaced the fronts with NEW tires ? :)

As a side note, you should have called when you first came into Houston, instead of on your way out. You and your friend could have played golf at my course "Greatwood" and had lunch at my house. I make a great grilled turkey / cheese sandwhich.Maybe next time?
Gary S.

[MangoMike]

Tuga,

I checked a couple of tire shops around Houma and was able to find you a couple of Steer Tires. The dealer says they will only fit a Newell.

3756

mm

[JIM CHALOUPKA]

I can see why you wouldn't use them on the drives:cool:

[0533]

I have these steer tires on my bus, every friday evening, medium rare. think Mango's on to something here.

I also agree with Gary, I do not think that steer tires are an actual tire designed for turning etc or even for the front of the bus. I do know that the use of the 365's on the front will make a difference and they do have 19/32 of tread and are 14.3" wide, a really good choice if you want better handling and more tread, see link below. The 315 80R 22.5 XZA2 are 12.5" wide and have 17/32" of tread, not quite as robust. So if you want the added tread life and width, I would highly recommend the 365 Upgrade tires from Michelin.

365 70R 22.5 specs: http://www.michelinrvtires.com/michelinrv/tires-retreads/tireInfo.do?tread=XZA

315 80R 22.5 specs: http://www.michelinrvtires.com/michelinrv/tires-retreads/tireInfo.do?tread=XZA2%20ENERGY

[Sid Tuls]

Just had my bus alignment done at our local truckstop they use the "BEE LINE EQUIPMENT". They took my tag tires balanced them and moved them to the front and then did the alignment. The problem was my right front was 2 degrees out. I hope thats how you say it the left front was good. Took it for a ride down the hwy and rode no differant but knowing that the fronts are good gives peace of mind. The bill came to $250.00 and I'am a happy camper!

[Ray Davis]

Good job, Sid. Let us know after next trip if the tires are wearing evenly!

Ray

[Sid Tuls]

Good job, Sid. Let us know after next trip if the tires are wearing evenly!

Ray

Ray, How was your fuel milage going cross country. I logged on about 5200 miles and got 5.9 and thats towing an going an average of 70 mph.

[lewpopp]

I do recall that the tire companies came out with a tire for UPS years ago for the front end. It had a special extra grouve about a half inch from each side. It was to absorbe the turns and wear would be less than the wide flat surface on most tires.

I think the Michelin XZE tires are the ones with the extra wear rib. There is a name for that grouve but I cannot think of the exact nomenclature .

I also think the extra rib is made with a harder wearing compound.

I know the tires have been around for years with the extra ribs. But shit, who am I? Let the guys who buy tires every 6 minths just so they can keep the moths out of their wallet.

[Orren Zook]

Just had my bus alignment done at our local truckstop they use the "BEE LINE EQUIPMENT". They took my tag tires balanced them and moved them to the front and then did the alignment. The problem was my right front was 2 degrees out. I hope thats how you say it the left front was good. Took it for a ride down the hwy and rode no differant but knowing that the fronts are good gives peace of mind. The bill came to $250.00 and I am a happy camper!

Sid,

Was that "2 degrees out" caster, camber or toe in/out? Did the shop provide you with before and after data? Just curious

[Sid Tuls]

Sid,

Was that "2 degrees out" caster, camber or toe in/out? Did the shop provide you with before and after data? Just curious

That was toe out. Yes they supply me with a before and after sheet. It had a bunch of numbers so I just asked for the short verson. I'll more than happy to fax them to you if you like.

[Loc]

Tuga,

I don't know what you herd, but those steer tires are no bull. I am not sure how to cow-ch this, but it is udderly important to use the steer tires as you can really tail the difference when you moove. I would get on the horn and see if you can corral some quickly and then hoof it on down to the tire store. I always pictured you as a cattle-ist for change. I think I have milked this one for most of what it is worth. You can run but you can't hide from the bad puns. Dont give this much thought because it may cause mental angus. Yes Jerry there was a "g" in angus.

Sorry, it was a late night and a early morning here in NYC.

SpongeBob,

There is really such a thing as steer tires. Most tire companies now call them all position tires instead of steer tires (made for the steer axle). On the bus I have steer tires or all position tires all the way around. There are lug or traction tires made for better traction on the drive axle (think of a logging truck application) which most companies now call drive tires. A lug tire is not ideal for a steer axle application. Let me know how the slide repair turns out. The steer tires are really popular in Austin.

Loc

[truk4u]

Spongebob,

Steer tires are common in the trucking business, so I think you stepped on your winkie!:p

[merle&louise]

PunMan,

Love those puns keep them coming! I emailed Michelin last night asking about the steer tires - will post as soon as I hear back from them. Have fun in the Big Apple. Is the Millenium parked on Fifth Avenue? (Like Jeff Bayley)

[Gary & Peggy Stevens]

Spongebob,

Steer tires are common in the trucking business, so I think you stepped on your winkie!:p


Well then I sit corrected ?

But I'll bet there is not one person on this site, that orders a specific "STEER" tire to put on the front of his bus, when he replaces tires? :p

If so what is the difference in the tire code designation to show that it is a steer tire, and not just a tire for all axels? LOC prove this one to me!

Bet you can't !

Gary S.

[Jon Wehrenberg]

Gary, the opposite is true. We order tires that are acceptable for the steer position as well as the other positions. If we were to order "snow tires" with agressive lugged tread none of us would allow those tires anywhere except on the drives.

Tires have changed significantly from our first coach. The Michelins of the time on all buses I saw wore on the outside edges on the steer axle. The tire was apparently designed for less weight than our front axles carried and a new tire would quickly show more wear on the outsides even with air pressure equal to or in excess of the recommended pressures.

If the tire was not balanced the outer edges would scallop and the only recourse was to put them on the drive axle to true them back up. The tag axle would eat up a pair of scalloped tires in a few thousand miles. The newer tire designs never show the wear patterns like that anymore. That scalloping is what got me started with Equal and the elimination of scalloping when Equal was used was impressive. A tire balanced with weights would start to scallop within 5000 miles.

The newer tires are nowhere near as sensitive to uneven wear or scalloping.

Loc.......how much of your company's time was spent writing your puns? No wonder AIG is in the dumper.

[Ray Davis]

Ray, How was your fuel milage going cross country. I logged on about 5200 miles and got 5.9 and thats towing an going an average of 70 mph.

Sid, I got about 6.3MPG over 4500 miles, towing. Generally I tried to keep it around 65. At one stretch after a fill up I had gotten 9+ for about 100 miles! (I guess we were going down hill?)

This new bus has a ProDriver DC console in it, which I really like.


Ray

[Sid Tuls]

Sid, I got about 6.3MPG over 4500 miles, towing. Generally I tried to keep it around 65. At one stretch after a fill up I had gotten 9+ for about 100 miles! (I guess we were going down hill?)

This new bus has a ProDriver DC console in it, which I really like.


Ray

Ray what is a ProDriver DC ??

[0533]

I have logged about 12,500 miles since my purchase last fall. I reset the unit when I purchased it. When I look at the Pro Driver III readouts I see all activity for the entire period 12,500 miles. I averaged 7.19 miles to the gallon over the entire 12,500 mile period. Now as you know this includes idle times as well which can represent a good portion of the total. When I look at the Pro Driver while running down the road It reads out around 6.5 MPG at 70MPH while towing on Economy transmission mode, the rest is combo of idle hours I guess. The Pro Driver III is a great tool.

[Gary & Peggy Stevens]

Jon forgive me for being so "DENSE" ? I understand the resaon behind using a balancing agent like Equal, but I still don't see a definitive answer to the question?


Is there a specific tire or tire code you sould ask for if you were needing to replace the front tires? "Steer Tires"


Or as I see it, any of the quality brand & proper tires rated for load for your bus are all you need to ask for to mount on the front ? :confused: Sorry for being such a nubie!

Gary S.

[0533]

Jon forgive me for being so "DENSE" ? I understand the resaon behind using a balancing agent like Equal, but I still don't see a definitive answer to the question?


Is there a specific tire or tire code you sould ask for if you were needing to replace the front tires? "Steer Tires"


Or as I see it, any of the quality brand & proper tires rated for load for your bus are all you need to ask for to mount on the front ? :confused: Sorry for being such a nubie!

Gary S.
Gary, I think the answer depends somewhat on what you feel your bus needs based on existing factors and how much you want to spend. The short answer is I do not think there is a tire that is only designated to the steer position.

I also feel that if you have a heavy front end or do not like the ride with your air pressure at 120 lbs. then you might consider the 365 70R 22.5 upgrade. This will offer a higher weight limit, lower air pressure, wider tires, deeper tread and a better overall ride, but it all comes with a price.

The Michelin 315/80 22.5 Energy is a great choice as well, great highway tire and can be placed on all 3 locations, the tag, drive and steer position. The 365's can only go on the steer and the tag position because of the width, and stud pattern. There is no way to mix and match the 365 70R 22.5 with the 315 80R 22.5 at the drive position.

So it really depends on your bus, your driving patterns and your pocketbook.

[Ray Davis]

I also feel that if you have a heavy front end or do not like the ride with your air pressure at 120 lbs. then you might consider the 365 70R 22.5 upgrade. This will offer a higher weight limit, lower air pressure, wider tires, deeper tread and a better overall ride, but it all comes with a price.

Bruce, can you give me a ballpark on this upgrade? Both of my XL2's have ridden a little heavy in the front, and I think I would benefit from the lower air pressure.

In fact, on my recent trip I noticed in the mornings when it was very cold, that the ride was definiately smoother than later in the day when the tires heated up.

Ray

[0533]

That is interesting Ray. When I picked my bus up in Coburg I noticed the same problem. Each morning when I first started out on my trip back east I would notice that the tires felt hard and the ride felt uneven almost out of balance for a bit until the tires heated up. When I changed all of my tires out this past spring we noticed that all tires had used the silicon power material for balancing. The tire guy at Prevost said that in the morning and when the moisture builds up the powder can get clumped up in places until the tire is heated up and the ride feels funny for a while.

I do not get this feel at all anymore with the new Michelin tires balanced with weights.

Anyway this does not answer your question. The 365 upgrade costs about $4K. for each position (some dealers are charging $5.5K for this upgrade) Depending on your bus. Don't forget though that to make the complete transition you should add the 365's to the Tag position as well, so double the price. The cost includes New studs, new stud pattern and install, new wheels and of course the tire and install. I would make certain that I had this done by Prevost (they warrantee the install for one year) and make sure it was done by a technician who has installed several upgrades. Its a little tricky wiggling the tires into the wheel wells. The tires are about 2.5" wider than the 315 80R's and look like they will touch your fender wells but they do not. There is ample room for proper turning radius as well. I also took the time to have my ride height adjusted, and a three axle alignment at the same time just to be sure.
I also had my upper and lower bushings replaced while the tires were off.
With the 365 on and depending on your front end weight load you will be able to run with about a 105lbs reducing pressure by as much as 20lbs. Just to make sure though, I would check with Prevost to see if they recommend the upgrade on your year, I suspect they will say yes.

[Jon Wehrenberg]

I'll not express any opinion regarding improvements to the ride, but as one who has had to deal with tire issues while on the road a word of caution.

It is bad enough trying to replace a 315 (or even a 12.00) while on the road. If you are lucky you can get one. Luck being the key word here.

On two occasions when I have had to replace tires unexpectedly (once a 12.00 and once a 315) I was unable to get either size within a reasonable time (I'm talking days, if not weeks) I ended up getting the closest possible rolling diameter and juggling tires around putting the new replacement on the tag. I then ran those oddball sized tires (I cannot remember the sizes now) on my tag axle until I had to replace my tires. They have to be close because your ABS will not like different rolling diameters.

Once you have 365 tires on the steers you are screwed if you have a failure that requires replacement. Find out the availablity of 365 tires. Then consider what happens if one fails on the road. They look neat, they may have a ride that someone with a sensitive butt can describe as smoother, and having them puts you in big boy league. But it will not change the fact that any tire failure, anywhere on the coach once you have 365's on both the tag and steers puts you in a world of hurt. Have a plan if you upgrade as to what exactly you will do if you have a tire failure at any position on the coach.

[0533]

I guess I have a sensitive butt, but Jon I thought about the question of availability as well. My conclusion was that Greyhound uses 365 on their H models that make up a large part of the fleet, all later H models use 365 on both Steer and Tag positions. Prevost has no problem providing tires and Michelin seems to have a good supply as well.

I do not think the decision to use a certain type, size or quality of tire should rest solely on availability but rather on the tires ability to match the needs of the bus, the driver and be able to last longer, ride better and be overall safer tire that does not need to be replaced as often or prone to the stress that the 315's are placed under on our heavy buses running down the road with 125lbs of air.

Until you drive a bus (our vintage with 365's on it ) I would not make any assumptions. The 14.4 inch wide tire at 105 lbs is a really great improvement, a much better handling ride, and a softer less stressful overall experience. With the added 2/32nds of tread the tire is a better choice for Prevost Buses in my humble opinion, a great upgrade and a good investment for an older bus.

[Ray Davis]

thanks for the info bruce. I probably should have considered it when I put 8 new tires on the bus before picking it up. $10k is a bit steep, but may be something to consider long term.

I'm not sure if I explained my ride "feelings" correctly. I have balance masters, so I don't have a problem with moisture disturbing the balancing. What I do have is a heavy front-end, and rough roads (doesn't even need by horribly rough) can sometimes be unpleasant.

What I discovered is that when I started early morning, with temps down in the 30's and 40's (i.e. tire pressure was lower than normal), the ride was smoother. I attributed this to the lower tire pressure at the time. As we drove, and the tire temperatures raised, it seemd to get a bit bumpier.

ray

[Jon Wehrenberg]

Uh...Ray....Aren't we supposed to put the required pressure in the tires before we drive? If it is cold in the morning it sounds like you allow low pressure in the hopes your tires warm up and reach the required pressure.

[garyde]

Hi Ray. I have the 365's on my front steer. I keep them at 110 lbs. Probably a litte higher than the suggested. Irregardless, I still feel every bump on a crumy road. I don't think lowering the tire pressure is going to reduce that very much. On the other hand, I get a great ride on good roads.
Even in California.

[Sid Tuls]

Bruce, can you give me a ballpark on this upgrade? Both of my XL2's have ridden a little heavy in the front, and I think I would benefit from the lower air pressure.

In fact, on my recent trip I noticed in the mornings when it was very cold, that the ride was definiately smoother than later in the day when the tires heated up.

Ray

Ray, could you tell me what is Pro Driver?

[truk4u]

The problem with the 365 is if your in Podunk or even near a major city, your in for a surprise. Remember, we couldn't even get a 315 while at Spearfish and the closest source was Minneapolis and 3 days transit time.

[merle&louise]

Hi Ray. I have the 365's on my front steer. I keep them at 110 lbs. Probably a litte higher than the suggested. Irregardless, I still feel every bump on a crumy road. I don't think lowering the tire pressure is going to reduce that very much. On the other hand, I get a great ride on good roads.
Even in California.

Ray & Gary,

Ray, I love my Smart Tire system; it is amazing to see the temps on the tires 140-150 degrees. Unbelieveable!

I run 130 in my STEER tires and I can feel every bump on the rough and I mean jaw bone rough roads in Louisiana. You haven't lived until you ride on US 90 between Houma and Lafayette, LA. I-10 is a cake walk compared to that bad mammy jammy!

[Jon Wehrenberg]

Hey guys, in case none of you have noticed you are driving a bus.

This ain't an S500 or even a Chevy Malibu. It has the suspension of a truck. It rides on tires made for commercial use. You are likely to feel the bumps.

I think 365s look way cool. I drive a Corvette and it has fat wide tires too. I love the look. But even with my 315s I have a serious issue if I get a blowout. But at least I can stick an alternate size on my rims. My last tire failure was in St. Louis. I could not get a 315 tire there for 2 days. I went with an odd size that I put on the tag. Forget about getting one from a bus company. They lease their tires, so even if they wanted to help you they cannot because they don't own their tires. The closest tire was Prevost in Nashville.

I guess everything in life is a compromise. To get the 365 ride and look you risk sitting wherever you are until a tire shows up if you have a blowout.

[JIM CHALOUPKA]

Sid, I don't like to see your question ignored, so instead of incurring Lew's ire over not knowing what I am talking about here is a link describing the Pro Driver. :rolleyes::D

http://www.busconversions.com/bbs/index.php?action=printpage;topic=9854.0

http://www.heavytruckedr.org/diesel.html

http://www.analysis-inc.com/electronic_control_modules.php

These links are not complete in the explanation of the Pro Driver, but I think it is enough to get others to post about it.

The last link is for a cartridge for the Pro Link scanning tool. Read the menu of functions to get an idea of the Pro Driver capabilities.
By reading about what it does, you can form your own opinion about, "What is a Pro Driver?".

:)JIM

[0533]

Uh...Ray....Aren't we supposed to put the required pressure in the tires before we drive? If it is cold in the morning it sounds like you allow low pressure in the hopes your tires warm up and reach the required pressure.
Jon, what you have just stated above is more important info than tire size and tire availability and raises some interesting questions.

OAT has always been an interesting factor in the decision to add/reduce air pressure or wait until the temps rise.

I use the following theory when considering adding air. I call it the "HomePort" approach. Example: In So. Florida the average temps are about 75 to 80º in the winter months by 2 pm.. I check my air around this time (before driving) and allow some difference for the sunny side of the bus.

Here is the big question: It has been colder here now with the addition of cold fronts coming down from CA, (relative terms for you Northern Boys) 50's in the morning. Rising to 80's by 2 pm.

I Had to take the bus to the Fort lauderdale Boatshow last week, before heading out I checked the air pressure, the OAT was around 65º and the tire pressure was about 5lbs low all around. I had checked them the week before and the air pressure was perfect all around, and the OAT was 80º (baseline OAT for So. Florida) so I decided that by the time I got up to speed on the road and by 12 noon I would see proper air pressure again. ( Here is an added question, The tire gauge was also very cold, metal was ice cold can this affect the result)

Yesterday around 2 PM I took the bus for a ride to the Fort Pierce Pilot Fuel plaza at exit 129 off 95. (fuel price $2.98 P/G) Checked the tires before leaving, all pressure is where it should be based on Michelin specs and bus weight, OAT was 82º. I have not added air for a very long time to any position on these tires since I have been back in So. Florida.

What I am hearing from you is that if one sees lower air pressure no matter what the outside temps, no matter where you are you should add/reduce air pressure to get the air pressure back to specs before driving off ???

I did however readjust the pressure for each region of the country, New England in the summer has cool nights and warmer days and average temps are 70's in the summer about 10º lower than Florida winter, I add air while in these climates. I add air if I see a difference over several days of checking, (subject to a huge change) check air everyday before driving) On the road for the summer 8K miles of driving across the East coast.

I have always been careful about checking air (comes from flying I guess) but I do not want to be a slave to the changing OAT on a daily basis and adding and reducing air pressure every few days unless I am spending some period time in the changing environment, lower temps etc.

What is the answer Jon???

[Jon Wehrenberg]

I am making a huge assumption here, so take my opinion with a grain of salt.

The tire companies know that heavy vehicles like ours travel north to south, south to north, they start driving when it is cold and getting warmer and they start driving when it is warm and getting colder.

If they felt that the cold tire pressure (meaning a tire that has not been recently driven) needed to reflect the outside air temperature they would have given us temperature correction values, or the charts would reflect the pressures at specific temperatures.

But they did not. They took a lot of time to develop these charts. Anyone that has looked at the charts can see clearly that they are set up in 5 PSI increments and 400 to 500 pound weight differences. If you extrapolate the weights you can get the correct pressure to the exact PSI. If they thought temperature was important there would be a note about the correction factor or like on our plane POH we would see columns for pressures based on weights and outside temperature.

So you are making a huge leap of faith by figuring when it warms up outside that the underinflated tires you started with will be at the correct pressure when it gets warm. If you want to be consistent then it follows that if you are departing FL in January, heading to the north, you should overinflate your tires. My guess is you do not do that.

I don't know the exact change in pressure per degree of temperature rise, but I would always feel more comfortable bringing my tires up to the proper pressure while cold. I know when I start out at 32 degrees with tire pressures set per the chart that when I am at 75 degrees the next day my pressures will read high, but unless I am remaining in warmer temps for a long period I will leave the tires "overinflated". I will not bleed them down if I am going back to the cold because I know they will be below the recommended pressures.

[0533]

I am making a huge assumption here, so take my opinion with a grain of salt.

The tire companies know that heavy vehicles like ours travel north to south, south to north, they start driving when it is cold and getting warmer and they start driving when it is warm and getting colder.

If they felt that the cold tire pressure (meaning a tire that has not been recently driven) needed to reflect the outside air temperature they would have given us temperature correction values, or the charts would reflect the pressures at specific temperatures.

But they did not. They took a lot of time to develop these charts. Anyone that has looked at the charts can see clearly that they are set up in 5 PSI increments and 400 to 500 pound weight differences. If you extrapolate the weights you can get the correct pressure to the exact PSI. If they thought temperature was important there would be a note about the correction factor or like on our plane POH we would see columns for pressures based on weights and outside temperature.

So you are making a huge leap of faith by figuring when it warms up outside that the underinflated tires you started with will be at the correct pressure when it gets warm. If you want to be consistent then it follows that if you are departing FL in January, heading to the north, you should overinflate your tires. My guess is you do not do that.

I don't know the exact change in pressure per degree of temperature rise, but I would always feel more comfortable bringing my tires up to the proper pressure while cold. I know when I start out at 32 degrees with tire pressures set per the chart that when I am at 75 degrees the next day my pressures will read high, but unless I am remaining in warmer temps for a long period I will leave the tires "overinflated". I will not bleed them down if I am going back to the cold because I know they will be below the recommended pressures.
I would not read into the Michelin (or any tire chart) tire chart the lack of info about the need to compensate for OAT. My guess is they just do not know how to accurately articulate this info in their chart to reflect changing temps and driving distances across changing temperatures. I would be very interested in hearing how over the road truckers handle this question on a daily basis. Maybe this contributes to the many blowouts we see on our highways ??

If I understand you correctly, you feel that over inflation is a better bet than risking driving away with under inflation and hoping for the tires to heat up while underway. This is a safe way to handle the question I guess, but lets examine a sample trip for a moment and draw some agreed conclusions. Do you agree that it is a certainty that the tires will increase pressure as you build speed and heat over time at highway speeds ???

Trip "A". Leaving So. Florida for No. Dakota Dec 1 2008: Temps are 80º in So. Florida (why am I leaving So. Fl>) Fargo No. Dakota is 13º I leave with proper air pressure, check the pressure daily, by the time I get to Kansas City I am 5 lbs low, this is when I would start adding air, and would continue adding every other day until I arrive, and depending on my stay I would adjust the pressure for Fargo. I would reverse the trend on the return trip.

Is it safe to use a 5 lb margin up/dn of normal for this trip planning verses running with over inflated tires all the time. What is the margin up or down?

[merle&louise]

On my previous coach the tire size on all axles was 11R24.5 and they were availabile at most truck stops. Things sure were simple in those days.

As times passes on, will 315 and 365s become more availabile since more and more vehicles will be using them? Hope so!:)

[BrianE]

Bruce, Over the road truckers are seldom in one place long enough to fool with tire pressures. Most of them simply thump the tires and press on. I personally only air up when in home average temp conditions unless planning on extended travel in a hot or cold extreme. I think tires are a lot more adaptable than we give them credit for.

[Jon Wehrenberg]

I would not read into the Michelin (or any tire chart) tire chart the lack of info about the need to compensate for OAT. My guess is they just do not know how to accurately articulate this info in their chart to reflect changing temps and driving distances across changing temperatures. I would be very interested in hearing how over the road truckers handle this question on a daily basis. Maybe this contributes to the many blowouts we see on our highways ??

If I understand you correctly, you feel that over inflation is a better bet than risking driving away with under inflation and hoping for the tires to heat up while underway. This is a safe way to handle the question I guess, but lets examine a sample trip for a moment and draw some agreed conclusions. Do you agree that it is a certainty that the tires will increase pressure as you build speed and heat over time at highway speeds ???

Trip "A". Leaving So. Florida for No. Dakota Dec 1 2008: Temps are 80º in So. Florida (why am I leaving So. Fl>) Fargo No. Dakota is 13º I leave with proper air pressure, check the pressure daily, by the time I get to Kansas City I am 5 lbs low, this is when I would start adding air, and would continue adding every other day until I arrive, and depending on my stay I would adjust the pressure for Fargo. I would reverse the trend on the return trip.

Is it safe to use a 5 lb margin up/dn of normal for this trip planning verses running with over inflated tires all the time. What is the margin up or down?

Bruce,

Lets enter this discussion with some things I think we agree upon.

The tire pressures listed in the charts based on weights and tire size are those pressures necessary to maintain a column of air of sufficient pressure to keep the tire at a given height (in other words the less pressure, the closer the rim comes to the ground, and vice versa) and to maintain the tire foot print (too much air and the center bulges, too little air and the tire cups).

The engineers make the pressure determinations so the tire tread contact is optimized, and so the amount of flex the side wall experiences when rolling is not so great that the sidewall heats and fails. They also want some flex in the sidewalls as a compromise between a harsh ride and a likely blowout.

If we can agree on that (assuming my understanding is correct,) then it follows that regardless of outside temperatures the cold inflation pressure is a constant. It has to be a constant because the weight of the bus does not decrease when it is cold outside.

It still requires that imaginary column of air at a given pressure to maintain the sidewall height and to apply even contact pressure with the ground all across the tread.

Truckers may not be the best sources for technical data. I would rather get my tire information from the guys that design the tires. I also don't believe OWTs from pilots. I would rather rely on my POH.

Now let's consider the 5 PSI you are discussing. Just so everyone knows my bias I run 5 PSI over the Michelin charts. Here are my reasons. Tread wear is not likely to be one of my considerations. I expect sidewall cracking before I have worn out my tread. I realize I will get less optimal tire contact with the ground, but I consider the impact to be marginal because I hope to never have to drive at my limits of adhesion. We had the refrigerator door open once. That was enough. When that happened we weren't even close to losing traction.

But on a more serious note, over the years I have had the slow leaks every one else has encountered. I have had nails in the tire, a bad Schrader valve and a leaky valve stem. These subtle leaks are the ones that surprise you. If I were to accept starting my day with tires underinflated by 5 PSI, then according to the 20% loss of inflation statement made by the tire experts as being the point at which you convert a good tire into junk, you have just given up 25% of your margin on your steers and almost 30% of your margin on your rear tires.

By running 5 PSI over inflated I have some room for a leak to occur and not adversely affect my tires or get me into the range where a blowout could occur.

Before trips, even if I know I am going from Knoxville in the winter to the warmer temperatures of the Keys, I still top my tires off to my regular 5 PSI in excess of the Michelin charts.

I do know from the experts that runing a tire at 20% less than the pressure in the charts has ruined that tire. I do know that underinflation is the cause of blowouts. I do know that there is universal agreement that if the pressures are too high it is far better than if they are too low.

If there is any doubt about that look at the Spearfish photos of Terry's inner dual. He had a leaky valve stem, and apparently it was a slow leak, right up until the tire started to come apart.

I agree with you that tire pressures increase as we drive due to the heating of the casing. That is normal and the cold tire pressure charts probably allow for heating of the tires over the full range of ambient conditions. I am just as sure that the engineers contemplated that you put air in your tires at the elevation of Sacramento, and then you went over Donner pass at a much lower barometric pressure.

As to your hypothetical trip, yes I would add air heading north, and no I would not release it heading south until I got where I was going because I am less concerned about over inflation than underinflation.

What we need is someone with a heated shop to cold soak the tires at some low temperature such as zero F, and then bring the bus in the shop and let tire temperatures stabilize at 70 F to see what the actual pressure change will be. I bet it will be within a few PSI. Any engineers capable of calculating it? Peter?

[Darl-Wilson]

Maybe this will put this subject to rest:

Effects of Time and Temperature

Tire inflation pressures change due to time and temperature. Tires lose about 1 psi per month due to air escaping through the rubber as it stretches. If you were to check your tires only every six months, it would not be uncommon to find them under inflated by as much as 6 psi. Tire inflation pressures also fluctuate with changes in the outside air temperature. This occurs at a rate of about 1 psi for every 10°F (plus or minus). So the tires you set correctly with an 80°F ambient temperature will be under inflated by 6 psi at 20°F.

Here is another site that deals with racing tires. (http://www.patentstorm.us/patents/6983209/description.html) :)

[Joe Cannarozzi]

When we leave Chicago for Florida in January I used to panic about the tires in our old Class-C, that was what the dorian system was originally installed on and when I first realized just how much pressures fluctuate under different conditions.

Now I'm with Brian. If it is 0 to 20 outside leaving and my pressures are 90% of where they should be we are out-a-here.

IMO most of you guys over inflate the damn things anyway, little bit a cold air do um a world a good.

[Jon Wehrenberg]

See what I mean about getting advice from a trucker?:D

[truk4u]

The real advise a Trucker would give you about pressure is, "beats the hell out of me, I just count them.":eek:

Geez, set the pressure 5 psi above the chart based on axle weight, check them often and get on the road....

[BrianE]

Hear! Hear!