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I was driving on I95 and I saw a beautiful Mountain Aire being pulled by a white Dodge DRW. The rig had just pulled into a rest stop after crossing the Delaware River Scudder Falls Bridge from New Jersey. What struck me about the fifth wheel was the axle configuration. It had double axles with dual wheels. Never, ever saw anything like that before. What would be the advantage to something like this?

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I have a Newmar Kountry Aire - similar to the Mountain Aire that you saw - and mine also has dual wheels on 2 axles.


One thing, I'm told is that it is easier to back up than with a tri-axle trailer. Also, with 8 tires each bearing weight, you can get by with lower load range tires, and if one were to blow out, you can still safely drive (at a slower speed, I'd hope) for a time if needed.


I don't know this for sure, but in the end it just seems safer to me. Too bad that Newmar quit making 5th wheels several years ago.


With all of that said and done, I towed my 5 th wheel less than 50 miles this past year, and almost all of that distance was to go to the tire store and buy those 8 new tires!

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Newmar put the dual axles under the Mountain Aires and Kountry Aires for a number of years. Only mfg. that I know of that did this. There are pros and cons. As MT Flyfisher said there is virtually no scrub on the tires during tight turns when backing and there is a wider range of tire choices. I have 8 tires supporting the 20k fiver versus 6 on a triple axle. Instead of three 6k axles, we have two 9k axles. To me that make more sense. With 6 Michelin XPS ribs we would be right at max capacity with 80 PSI; with 8 of them I can run at 65 PSI with plenty of reserve capacity.


One less axle saves on tolls in a number of places, but the big advantage is towing stability.


The narrower frame causes very little problem, there is no intrusion on inside floor space as the slides go out over the tires on both sides. It does provide three extra storage compartments outside the frame rails in addition to the generator compartment, and our pass through storage has a deeper space about 18 inches wide on one side. Only draw back for us is that the BigFoot jacks are closer together so slightly less stable when parked.


We have towed our Mountain Aire over 80k in the last seven years and it is a dream to tow. Personally I think it is a superior design.

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Tandem Dual configuration has only 4 brake assemblies compared to 6 for a triple single configuration.


Tire scrub is present is both configurations. In the tandem dual configuration, the pair of tires bolted together means one of the two will scrub in the thread direction in a twist maneuver as the outer tire has more distance to cover. In the singles, the tire scrub in more in the across the tread direction.


The narrow frame can be an issue when installing hydraulic levelers as outriggers are needed.

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Then there are the toll states that count pairs of tires (ex: NY, Illinois)


Not quite in Illinois. From a Chicago Trib article:


Trucks and trailers will be categorized in three categories: small truck, two axles with six tires; medium, three to four axles; and large truck, five or more axles, said tollway spokeswoman Jan Kemp.


From Tollway website:

Passenger Cars: Auto/Motorcycle 2 axles - four or less tires; auto, SUV, motorcycle, taxi


Trucks and Vehicles with Trailers:

Small Truck: 2 axles - six tires; single unit truck, buses

Medium Truck: 3 and 4 axles vehicle or combination; truck, bus, auto/SUV with 1 or 2 axle trailer

Large Truck: 5+ axles vehicle or combination; trucks, auto/SUV with 3+ axle trailer



So with 4 axles and 14 tires we are still a "medium truck" for Illinois tolls instead of a "large truck". That is an over $12 difference going the length of the Tri-State. There is no RV classification last time I checked. Only place duals are counted is the "small truck" classification. Weird huh? BTW, "small truck" pays passenger car rates.


We do have hydraulic levelers and no need for outriggers. They are actually installed inside the front frame rails since it was an aftermarket installation and they had to work around the pre-existing factory jacks. Like I said above, slightly less stable, but not so we notice.


Obviously I don't know the thought process, but I expect that Newmar's reasoning for going to what is probably a more expensive configuration was tire capacity. The fact that they built their own frames might have been a factor as well.


In the end it is pretty much a tomato / tomahto situation.

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We had a triple axle 40' Newmar Kountry Aire and a 40' dual axle dual wheels Newmar Kountry Aire and the dual axle dual wheels was hands down easier to back/park and towed nicer. Newmar came out with the dual axle dual wheels setup in 1998. If I remember right it was only offered in the Mt Aire, Kountry Aire and London Aire models back then. It was an option on the Mt Aire and standard on the Kountry Aire and London Aire.



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