Tire Pressure

[Jon Wehrenberg]

We were going to mention something to you about the tire marks...............



But it was more fun talking about Jeep parking.

[CAPT MOGUL & Sandy]

I have had my current coach for more than 6 years and haven't lifted the tag yet.[/QUOTE]

Jon,
Ed wants to know if your switch for the tag works?

When we were at Prevost, they lifted the tag every time a bus was moved (per Ed).

[Jon Wehrenberg]

If I were to say yes it would be a guess.

However, the automatic system that dumps air on my coach along with the stabilizators that keep the rear from dropping when my wheels are turned to the extreme, left or right works, and because of that I do not need to manually lift the tag. If I were to manually lift the tag the stabilizators would not function and the rear would drop until the drive axle air bags were filled with air to raise the rear to the normal height.

Most Prevost techs are not familiar with that system that was designed for and used on early 45 foot coaches to minimize tag axle tire scuffing as an alternative to the "steerable" tag axle that was supplied on MCI coaches around that time. I think that feature was discontinued and it is my understanding that some converters even went so far as to disable the system if the coach had it installed.

Aren't you glad you asked?

See you guys in Kerrville, where I hope Ed allows you in the bed instead of the fiddle.

[Orren Zook]

Here's something interesting that I ran across in the September 2010 issue of Heavy Duty Trucking magazine regarding tire air pressure. "Pressure will increase by about 2 psi for each 10 degree change in temperature. A properly inflated tire that is up to operating temperature (one or more hour of operation) will typically run about 60 degrees hotter than ambient temperature - adding about 12 psi to that tire."

[Jeff Bayley]

So I guess the easiest way to check if my tag locks in position and ignores the request to lift is to turn the wheels tight , pull the tag and observe. ?

[Jon Wehrenberg]

Jeff,

When the 45 foot coaches were originally built in 94 the tag axles automatically dumped air when the steering wheels were turned to the extreme in either direction. I don't know when or how the stabilizator system to prevent the rear of the bus from dropping came into being but several buses owned by POG members have that feature also.

Having said that I heard but do not have any way to confirm this that Prevost and some converters were disabling those features so it is my opinion you may or may not have either of the systems and if you do they may or may not work.

While you or Stephanie turn the wheel hard left or right, the other should stand next to the tag axle and see if the rear of the coach drops a little from the driving height, or if air is heard to escape from the tag air bags. That's the easiest way to know how your bus is currently set up.

If the rear does drop and air escapes from the tag air bags then the automatic dumping of air from the tag axle air bags works and you do not have to dump air manually. If air escapes but the rear of the bus does not drop it is probable you have the automatic air dumping feature and the bus is equipped with stabilizators. I doubt if it is, but it is possible due to the vintage.

[Jeff Bayley]

Over the weekend I had the chance to get some service with someone that was real knowledgeable and competent. Among the things I learned, he finished explained about lifting the tag further to what is in this (not too far off topic) thread creep I started related to tire wear here. I now believe my tire wear on the tag is because of my lifting the tag so regularly though turns in town. I learned that the tag takes far too long to lift off the ground waiting for the drive axles to raise the coach up again. Even 3 minutes was not sufficient and when it finally came to it's end it was still around an inch shy of height with the tag. This was translating into my tires rubbing MORE, not less because there is less weight on them so they scrub easier. I had a driver of an entertainer give my some driving tips a few years ago. He was a 25 year man with Greyhound and was an instructor towards the end and he told me to train myself to use the tag often in town. I've also had at least one Prevost tech say similar. Guess I can't always listen to the "experts". I now believe my tires wore on the tag prematurely as a result of pulling the tag often. It was the latest opinion of this technician that lifting the tag gives negligible tighter turn radius and is only practical in the most necessarily help needed in a turn.

The more I learn the more I realize how much I don't know.

[michaeldterry]

The more I learn the more I realize how much I don't know.

Welcome to the club I've belonged to for years!

[Jon Wehrenberg]

Lifting the tag does have some impact on turn radius. Lifting the tag even though it does not come off the ground also reduces the tire wear due to scrubbing.

When the tag is not "lifted", the term meaning in this context that air has been dumped from the tag axle air bags, but the rear has not raised enough to lift the tag tires from the ground, it reduces the turn radius slightly by moving the pivot point of the rear axles forward slightly. The simple way to prove this is to find a large empty parking lot and go around in a circle with the tag down. Measure the circle. Then repeat the process with the tag "lifted". There will be a slight decrease in the diameter of the circle.

Any time weight is removed from a tire that is being scuffed sideways the wear on that tire will be reduced. Start a turn with the steering wheel to the extreme and once the turn is extablished step outside the coach and look at how much side deflection the tag tires have. Repeat that with the tag lifted and you will see much less side deflection because the tire tends to slide sideways more readily.

But lifting the tag when cornering is really not required because over the life of the tires, if they are inflated properly tag axle tires are not being scuffed sideways any more than the steer tires are during turns. I don't know this for sure, but I would suspect steer tires on average have a shorter lifespan than tag axle. When we turn the front wheels to alter the path of the bus those steer tires are resisting the forward motion of the bus and are being scrubbed sideways as the bus turns.

[merle&louise]

I have seen some Prevosts lift the tag tire a couple of inches OFF OF THE GROUND. Is this a converter option? Or does the 40' Prevost lift off the ground and the 45' Prevost does not?