Purpose of Full Rear Cap

[Kevinc2011]

We see semi trailers on the road here with flaps on the rear doors that mimic the rear cap. It is based on fuel economy, same as the skirts from the landing gear to the tires.

[mds1]

I had been watching a walk-around video where it was mentioned a certain manufacturer designed the front and rear cap to work together providing a 2 or 3 mile per gallon benefit from the aerodynamics. That was the reason I posted the question regarding the reasons for the fancier full rear cap. I've been everywhere looking for the manufacturer to have listed this claim on their website and have not found it listed. I purposely did not name the manufacturer to avoid upsetting anyone.

[Cummins12V98]

"I purposely did not name the manufacturer to avoid upsetting anyone"

I am upset because you did not mention the manufacturer!

[wa8yxm]

I never considered the effect of the rounded v/s square corner on fuel economy but logically it might make a tiny improvement.

However use of the full rear cap has two major advantages that I can think of

1: Makes it way easier to wire the tail lights and such.. Way way easier. also makes it easier to work on them if needed.

2: When (not if) you back into a tree and crack it.. Well a whole lot easier fixing the rear cap than fixing the rear wall.

[jacknife]

Any aerodynamics added is a plus. A rounded nose is a definate plus over a square one. Why do Motor homes get such poor mileage because they have the aerodynamics of a cinder block !

[wingnut60]

So "a certain manufacturer designed the front and rear caps to work together providing a 2 to 3 mpg benefit from the aerodynamics"
And you believed this...?

[JBurg]

I could use a 33% improvement in fuel economy.

[mds1]

The only thing I might believe is that front cap design would make a difference in fuel economy. I was thinking on the lines the mileage improvement of 2 to 3 miles per gallon would be compared to those with lessor designs. As for back cap I have been looking for reasons why the extra expense is justified and I've appreciated the reasons given by others who replied.

My guess is back cap design has no bearing on the fuel economy.

[IC2]

I suspect that the purposely designed full front and rear cap 5er that's being alluded to is a Glendale Titanium. They were discontinued in 2010.

As far as improved fuel mileage - maybe - though my V10 F350 never got more then 7.4 mpg (gas, not diesel)

[Dasmoeturhead]

There is supposed to be small fuel advantage in having a front and rear cap designed for this purpose. If it's 1 gallon a tank for, I'd be happy. Semi trucks and there trailers are using this advantage as well.

[easdsa]

I've been told that the most aerodynamic shape is an egg (leading with the big end). Unfortunately that isn't a very practical shape for an RV. I would imagine that anything a manufacturer can do to approach that shape would be a help in the fuel economy department.

For the past few years it seems that most manufacturers have gone to rounded front caps rather than the flat fronts of the first 5'ers. Part of that may be more attention to wind resistance and part may be a way of gaining a few more cubic feet of interior space. The rear caps may be more of a styling exercise than anything else, with perhaps a bit of added fuel economy for good measure.

BTW, do you know why most new cars all look alike? They are all wind tunnel tested, and an aerodynamic shape gives the best fuel economy, and every manufacturer is being forced to improve economy. I wonder how long it will be before RV manufacturers will have to do their part, too.

[jacknife]

The back cap looks better period !