[Archived]

Or, you can click on Links in the PC site and get this:)

Prevost/Michelin Tire Chart

[Bernie]

Those charts are what you look up to get P_max and W_max.

Then you do the calculations. Of course you can also look up the pressure on the charts also.

[Archived]

I should have quoted this, by Jon:

“The problem with the tag axle is almost all of us with 365 tires on the tag really don’t know the correct pressure because the charts do not go below 80. For example if the axle weight calls for a pressure not even on the chart because it is below 80, the best we can do is extrapolate and maybe come up with a reasonable estimate. Maybe the correct pressure is 70, so theoretically 20% less would be 56, in which case if the tire still had that much pressure it would be OK.”

The Michelin link only goes down to 80 psi as well.

You can also get W_max and P_max from the tire sidewall.

[Dick]

If I did the calculation accurately my tag tire pressure calculates to about 67 PSI.

That is well below the 80 PSI minimum inflation pressure listed and while it may be mathematically accurate I would not feel comfortable with that pressure without approval from the tire manufacturer. I am sure a certain minimum pressure is required just to seat the bead and eliminate breaking the bead when hitting potholes or curbs.

Extrapolating based on the numbers on the chart yields an inflation pressure close to the calculation so the pressure seems valid but despite arriving at it from two directions I still would want the manufacturer’s blessing.

[Dan]

I guess this fact throws the fact out that the foot print of a tire isn’t important. to low of pressure causes the tire to flex/heat to much. Any belly at all would cause this with the excessive foot print on ground causing the tread to flex more. Talking about ground contact area including length. Has to be a minimun pressure to prevent that from happening. Just a old school concept. Would rather air on high side and maintain full tread width on ground. If it is off their chart (min) there is a reason? Opinions are mine and I defer to mfg chart. If it looks wrong =question it. Bob

[Larry & Diane]

I’m with Bob, and I do use the chart. plus 5 PSI to give me a slight margin. I don’t have anywhere near the axle weight that calls for 80 PSI on the tag but I have treated the 80 PSI as a minimum unless I learn otherwise from Michelin.

[needtocamp]

Why do they put 365’s on the tag? Would a 315 suffice?

[Tim]

When Prevost went ot the 18,000 lb front axle in 2004 we began using the Michelin 365/70R22.5 tire on a 10.5 inch wheel. The tires were necessary for the front axle rating but as you state they are not needed for the tag axle weight we carry on the shells. It was done so that there would be a spare tire to use if you lost a front tire for any reason. The 365 was less available then than now and Prevost was the only manufacturer using the tire.

The reasoning was that you could move a tag tire to the front axle and then install a 315 on the rim of the damaged tire to get you home. Or you could have the tire service bring you a 315 mounted on a 9 inch steel wheel, also to get you home safely. While it may seem that the 315 would not fit on the 10.5 inch wheel, Michelin told us it was possible for those times when a 365 was not readily availbale and you had to continue on.

This was also the time we changed the wheels from “stud- mounted” to “hub-mounted” style that Michelin required on the 365. It also changed us to the more common truck tire setup (hub-mounted). That is also why the studs on the hubs need to be changed when you go to the 365 tires.Presently all the wheels are hub mounted on all axles.

Safe Travels!!!!

[Tom]

Good info, thanks Prevost!

The Hub mounted are much easier to deal with IMO. I would like to have mine changed to hub mounted on the drive, but I’m sure that’s not easy or in-expensive to do.