[DON]

Dan, This is a real simple topic to explain from my perspective. The size of components selected by Prevost is to meet the needs which usually are part of what is required for certification by the DOT.

It would be far cheaper and easier for Prevost to only stock one size brake chamber but then they would have to come up with a design that balanced the braking forces some other way. I am sure the engineers have determined the sizes required for each axle is what is needed to insure each axle will have the same braking forces so no one axle or wheel can lock up prematurely.

The tag axle on your coach does not have ABS so if you do a maximum brake effort stop I can imagine brakes larger locking the tag.

[Dave]

My guess is, since our old beast don’t have ABS, they don’t want the rear tires/brakes locking up when the streets are slick(rain, etc).

Have you weighed your coach? Most truck stops have CAT scales. I’ve weighed mine.
My Tag = 8,880 Lbs, its max cap = 12,000 Lbs.
My Steer = 13,120 Lbs., its max cap = 14,600 Lbs.
My Drive = 19,000 Lbs, its max cap = 20,400 Lbs.
My Total = 41,000 Lbs, max cap(GVWR) = 47,000 Lbs,
plus I can tow another 10,000 Lbs giving my bus a “combined gross wt rating” of 57,000 Lbs.

On four other tag axle MHs(SOB) that I’ve owned, I was able to easily adjust how much wt the tag axle supported with a adj regulator in the engine compartment. I set it and forgot about it. Two of the four MHs had ABS but not on the tag axle brakes.

Prevost I’m sure had a good reason.

[Mark]

Steer left: 6234 right: 7115 total: 13349

Drive left: 10589 right: 10125 total: 20714

Tag left: 6752 right: 6441 total: 13193

Total. 47256

Jeff’s jacks, already subtracted the weight of the forks. Don’t remember water and fuel, could cause a 3000 lb swing.

Since the tag and steer are very close in static weight, justifying the use of a brake chamber nearly twice the size on the steer vs tag must be dynamic weight transfer under braking.

Most of the difference between Don and I is the tag which makes sense to me as we can see the rear overhang difference on the 40 vs 45 footers.

[Archived]

Dan, what engine is in your bus? and what are the MAX capacities of each axle?

[Archived]

Engine is 12.7 liter S60. Don’t know how to find max weight axle rating.

[Archived]

On Liberty coaches the Prevost data plate that lists design weights is on the panel to the left of the driver’s seat about 12″ off the floor.

[Rocky And Tonya]

Thanks Jon, never noticed that plate. It says:

Gross vehicle weight rating 45,000

Steer axle 14,500. 105psi cold

Drive axle 22,500. 95psi cold

Tag axle 11,000. 85psi. cold

So the sum of the individual axle ratings is > than GVW.

[Bernard]

Dan, a couple of things standout to me.
1) When the max weights are added up on your metal placard next to the driver seat they equal 48,000 lbs, not 45,000 GVWR which is undoubtedly on the placard?????? What’s up with that somebody? Like yours, when I add up the max weights on my placard the total is 47,000 lbs, but mine placard also reads 45,000 lbs GVWR.? I have another official Prevost document that states that the GVWR for my specific bus, S-5665, is 47,000 Lbs? Do Canadians not know how to do math in English? Is this French math? 😉

2) Your tag axle is severely over weight. This is probably caused by improper ride height adjustment. I believe the ride height on your bus should be 11.25″, give or take .25″, between all drive and steer axle air bag upper and lower mounting plates. If the rear ride heights(2 ride ht valves)are set to low, or the steer axle ride height valve is set too high, the tag axle will get extra load. When you had it weighed, and became apparent that something was not right, what attempt was made to remedy the situation?

[Michael]

The overall weight rating may be chosen with consideration to factors beyond axle weights. For example, the overall braking/acceleration performance of the vehicle may limit GVWR, but not necessarily GAWR. There are federal requirements for stopping distance, regardless of how much load the axles can handle.

So you have some “play” with how you distribute your weight when your combined axle ratings exceed the GVWR.

[Archived]

Yes the plate definitely says 45,000. Don’t know why, but I always thought it was more like 52,000.

Although I have over the years replaced all the air springs and had Jeff replace the three height control valves, no height adjustments have ever been made. But have never measured distance between top and bottom spring plates either. It appears to be ok side to side and front to rear.

When it was weighed, was not cognizant of the overweight, so did no remedies.

Interesting: The owners manual that Liberty puts together for customers says to run 115psi tire pressure in all positions. Inconsistent with the data plate. But Prevost’s numbers may be preconversion and Liberty’s post conversion.

Interesting II: The owners manual signed by the then president of Prevost, Andre Normand (son of Paul Normand who bought the Prevost assets in 1957), says “thank you for buying the H3-40”. So losing faith in the accuracy of some factory references. And did not use any information from this manual in this thread.