Tandem vs single…. - Fiberglass RV


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Old 01-26-2014, 08:29 AM   #1
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Tandem vs single….

A recent thread here is discussing the benefits of remaining small and nimble if given the choice to have any camper available at no cost. This got me thinking about the pro and con of the single axle versus dual axle set up being discussed. Several members feel the single axle simplicity and agility is what they want. Having towed both I feel there are some benefits to the dual axle set up. Safety being the prime reason, as the extra margin of safety the dual axle allows. In addition they also tow straighter and are less prone to wind shifts. I have left a coffee cup sitting on the counter and it was there 60 miles later. I have not had any issues with campsites and ease of backing in of dual vs single axle. Some people complain about the inability to stow items for in flight, it seems everything ends up on the floor. The horror stories about the refer coming open or the upper cabinets spilling their contents. These are single axle attributes. The dual torsion axle set up is smooth and stable and a lot easier on the trailer and it contents. The trailer does not bounce around like a ballon following the string. It merely follows where it is pointed.
Now the extra weight of course is the negative result but I feel the positives out weigh the negatives.I read someplace that an extra 1000# will cost you 10% gas, so instead of 20 mpg you will get 18 mpg or over 20,000 miles a year it may cost you another 100 gallons. What do you think?
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Old 01-26-2014, 08:38 AM   #2
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The only other downside I can think of is the increase in cost of tolls and ferries, when the charge is by the number of axles.
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Old 01-26-2014, 10:26 AM   #3
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Originally Posted by cpaharley2008 View Post
A recent thread here is discussing the benefits of remaining small and nimble if given the choice to have any camper available at no cost. This got me thinking about the pro and con of the single axle versus dual axle set up being discussed. Several members feel the single axle simplicity and agility is what they want. Having towed both I feel there are some benefits to the dual axle set up. Safety being the prime reason, as the extra margin of safety the dual axle allows. In addition they also tow straighter and are less prone to wind shifts. I have left a coffee cup sitting on the counter and it was there 60 miles later. I have not had any issues with campsites and ease of backing in of dual vs single axle. Some people complain about the inability to stow items for in flight, it seems everything ends up on the floor. The horror stories about the refer coming open or the upper cabinets spilling their contents. These are single axle attributes. The dual torsion axle set up is smooth and stable and a lot easier on the trailer and it contents. The trailer does not bounce around like a ballon following the string. It merely follows where it is pointed.
Now the extra weight of course is the negative result but I feel the positives out weigh the negatives.I read someplace that an extra 1000# will cost you 10% gas, so instead of 20 mpg you will get 18 mpg or over 20,000 miles a year it may cost you another 100 gallons. What do you think?
A couple of points...
The ride quality has more to do with axle capacity matching trailer weight. Our single axle trailer has ridden for years with a paper towel roll standing in the corner of the countertop.

Trailer attitude becomes much more important for tire load and wear with a tandem axle.Tongue too high loads the rear axle,too low loads the front axle.

Tire scrub and side loading become an issue with tandems when cornering.
I don't really see the safety issue,since a flat tire on either setup is not likely to cause an accident. In fact trailer damage is often caused by the driver not noticing a flat until the tire disintegrates and starts tearing up the wheel well. (twice the number of tires means twice the number of tire failures.)
The number of axles needed rests more with issues such as overall weight(and load distribution) and trailer length (and distance from hitch to axle).

On a tandem axle utility trailer, tandems gain advantage due to a greater tolerance for a variety of loads (even empty)and their distribution. This is less important with an RV since it is pretty much the same load and distribution every time, so once you've got it engineered and loaded right you're good with either design.
Axle alignment (not wheel alignment) is much more critical with tandems since they must be in exact relation with each other and with the frame to prevent scrubbing and tire wear even when going straight.
Dog tracking doesn't really affect a single axle and it doesn't have a second axle with which it must share alignment.
Truly each type has its place and advantages, depending on the application and engineering acumen.
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Old 01-26-2014, 10:30 AM   #4
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The only other downside I can think of is the increase in cost of tolls and ferries, when the charge is by the number of axles.
Here in BC the tolls for ferries and bridges is based on length only.
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Old 01-26-2014, 10:36 AM   #5
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Twice the amount of tires also means twice the cost when it's time to buy new tires. Plus if you want fancy wheels... well, that's more cost. Two more sets of bearings to maintain. An additional axle to replace when THAT time comes. Leveling side-to-side comes with it's own issues on tandems; easy-peasy on a single axle.

I didn't buy the classic Escape 5er because it didn't have tandems any more than I AM buying the new TA 5er because it does. It is what it is and all things considered, for me, it's about many other reasons.
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Old 01-26-2014, 10:55 AM   #6
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Jim, if I was shooting for a larger and heavier trailer, I suspect a tandem would just come as part of the package and I wouldn't give it much thought. I just hope I'm smart enough to figure out, like others have, how to keep stuff from flying all over the place when I go over washes and other bumpities and such. I've already solved the fridge door opening issue. My "small and nimble" mentality is just a mindset, a control issue for me I suppose, and time will tell if it's silly or not. What I'd REALLY REALLY like is Donna's upcoming 5th wheel with an escalator to the top bunk, or a standard 20-footer with a button to shrink it up lengthwise when I'm towing. I know, I know. Women, sheesh.

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Old 01-26-2014, 11:18 AM   #7
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I think that the entire discussion on single v. dual axles is a moot point.

One usually selects a trailer based on the size of what's needed and that will, in almost every case, determine if you get a single or a dual axle. The builders usually select the axle configuration based on how much tire carrying capacity they need.

It's not like we have many opportunities to get the size trailer we want and then have to determine the number of axles, it is what it is.

And, as mentioned, dual axle trailers, at least in FGRV's are always the heavier ones, that's why they need 4 tires.

A good example is the 17' vs. the 19' Bigfoot. That extra 2 feet and a second axle adds over 1000 lbs.
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Old 01-26-2014, 11:35 AM   #8
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Or in the case of the 19' Escape, it doesn't really need tandem axles, but consumer demand dictates the design.
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Old 01-26-2014, 11:41 AM   #9
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At close to 4000 lbs loaded wouldn't a 19' Escape be a bit towards the upper limit of just two tires, espcially 2 tires that were 5 years old?????
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Old 01-26-2014, 11:46 AM   #10
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Don't know. I just know that tandem vs. single was up for discussion at one point in the design. A major consideration was that the consumer expects tandem on a trailer of that size.
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Old 01-26-2014, 12:14 PM   #11
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One more factor - tandem axle means twice as many tires on the ground, twice the friction, more drag resulting in poorer fuel economy.
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Old 01-26-2014, 12:42 PM   #12
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If I were seeking validation as an adherent of the safety-first school, I'd look at the curb weight, wheelbase, suspension, horsepower, gearing, and braking capacity of the tow vehicle and let em put the trailer over the number of axles they deem necessary.

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Old 01-26-2014, 01:21 PM   #13
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Tandem axles give the advantage of either smaller wheel boxes, or even a flat floor, for a given floor height, since their wheels can be smaller.

Tandem axles probably give a little less drag. The rolling resistance will be much the same single.v.double since rolling resistance is a constant times vehicle weight and does not depend on the number of tires. If the tires on a tandem axle are narrower, that will cut a little bit of aero drag - and most folks forget how important aero drag is.
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Old 01-26-2014, 01:38 PM   #14
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The rolling resistance will be much the same single.v.double since rolling resistance is a constant times vehicle weight and does not depend on the number of tires.
And, what is the "constant"? Could it be resistance of the wheel to turn? So, shouldn't that be 2 X the "constant" since there are twice as many wheels?
Do tires on tandem axle trailers last twice as long as tires on single axle trailers?

I don't have the answers, just the questions.
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