Prevost Front Axle Weight Rating

[wracinti]

On the Newmar owners forum there is an ongoing thread(23 pages and 313 posts!) concerning the new 2016 Dutch Star coming off the line too heavy for the front axle rating. Newmar engineers intial response was carry only half tank of fuel, no water, and limit number of passengers. Not kidding. Anyway, my question is, what concerns, if any, are there with the prevost front axle and what it can handle? And how close to max capacity are you typically running?

[dale farley]

They are all different. Many of us have weighed each wheel of our bus and checked the weight against the axle capacity. A few have been over the recommended weight, but most are well within the specs. Sometimes, just changing the flooring can make a significant difference in the overall weight of the bus. Slides also have an impact.

I have had three Prevosts (Marathon, Country Coach and American Carriage), and I had all wheels of them weighed separately to get an accurate weight. I always weighed with full fuel tank and water tanks, and I have always had plenty of room left on my axles capacities.

[Joe Camper]

If I may add a couple observations. Being a extrucker and lifelong mechanic there is not too much that worries me in terms of weight because of what I see in the size and mass of components on the front axles on the IFS prevo front ends compared to their counterparts in the trucking industry. We have abundantly larger bigger and stronger pieces that would be obvious to even the novice.

However the weak link, if it could be defined as such, is the rims and tires because even with the 365s 20000lb is very very close to their limits.

Another 2 aspects of the front end on our IFS that is unique to prevo is IFS on air. I have not seen either on other heavy front ends on trucks maybe 1 in 1000 on air and never IFS, 1 would be just as uncommon as the other.

The thing that I noticed that gave me pause about the IFS is the amount of air pressure it takes in the front bags on IFS that it takes to get the bus to ride height 90+ psi compared to a similar weight on a staight axle with air ride carrying the same 20000, 60psi, that results in additional pressure to get there.

Ive concluded the geometry of the IFS is pulling the rims and tires very slightly together as it goes up a situation that does not happen on a air ride straight axle.

Ive never searched what manufacturer's limits for air pressures on our front bags r it would be interesting to learn.

Having had the opportunity to put enough miles on both air ride front ends I've concluded the feel is noticeably different. IMHO the straight axles ride softer than their more geometricly complicated counterpart the IFS but that's another topic.

I guess if these issues have an owner worried or if lack of recourse limits proactive and comprehensive component choices and their ongoing service these buses may not be a good fit. It's all a big part of it.

On a side note I recently had the opportunity to get under a new fire truck. A very very large ladder. It had IFS with tortion bars. Great big massive bars. And knore-bremse Bremse disc brakes. Very cool.

[Gil_J]

I don't think Newmar was the only traditional Class A RV manufacturer to deliver an over weight coach. When I bought my 42-footer I intentionally avoided the 40-footers as too many of the single rear axle coaches of that length were pushing the chassis manufacturer's specifications.

Although there are some Prevost conversions that are over weight, most are due to owner upgrades. Non Prevost slides and non carpeted forward flooring are likely the cause on most over weight conversions. The X-3 chassis also proved challenging for some converters that insist on some heavy weight bling and tile flooring throughout.

What's in an axle rating anyway. I've heard a few Prevost conversion owners say it's okay to exceed the rating as the ratings take into account the life of the axle. For me that doesn't hold water. Although likely true, at what point in the life of the axle is the over weight condition really over weight? There's a lot that goes into axle weight ratings and it's not just the axle.

-- Tires and/or wheels can be the weakest component. As such, moving to a more capable wheel and/or tire COULD allow the axle weight rating to be exceeded.
-- Braking capability could be another weak link. The braking system was not engineered to exceed the combine weight rating. Keep in mind, all safety systems are engineered to exceed the specifications, but not in the worse case scenario.
-- Axle weight ratings are generally not stated as being greater than federal limitations. So, the Feds limit a single axle to 20,000 and tandem (as our is set-up) to 34,000. I believe there use to be a single axle limit, regardless of the tandem of somewhere around 20,500. BTW, Newell does subscribe to limiting their stated axle ratings to federal limits. They have a coach with a GVW rating of 63,300 pounds with a combined drive and tag rating of 44,600 pounds! I'm pretty sure 44,600 pounds exceeds the federal bridge limit for a tandem axle.

Before someone can safely exceed the stated axle ratings you would have to determine how that rating was determined and which components could possibly be changed to increase that rating. In some cases, that could be as simple as changing wheels and tires. This is easy to see when Prevost changed to the 365 tires from the 315s. I don't think any other axle components were changed to effect the increased axle rating specifications. This was true on my 10RR Roadmaster chassis. The axle rating was exactly the maximum rating of the 295 series tires the axle was equipped with. Although Motorhomes are seldom targeted by law enforcement for weights, you would likely still be ticketed if you exceeded the axle ratings on the identi-plate, even if you installed heavier components.

For your own peace of mind and safety, all owners should have their coaches weighed when fully loaded. Fully loaded means full tanks, maximum number of passengers you carry in the positions they would sit, and the maximum weight of personal items you would carry and placed where they would be placed. Converters generally do a good job of balancing the coach side-to-side, but you still need to weigh the coach at each wheel position.