Rooftop ski racks or cargo box for best gas mileage?

[fuzzybabybunny]

Did I screw up? I'm skiing by myself and driving cross country to do it, so I bought the Yakima round poles and Big Powderhound Ski Racks.

I'm now concerned about the decrease in gas mileage of the ski racks because they are really just flat upright surfaces directly facing into the wind.

Should I get something like a Thule Dynamic roof cargo case? Would that have less impact on gas mileage?

 

[xSkyDrAx]

I heard roof racks impact mileage pretty significantly though not sure about cargo cases. I would image they would do the same.

 

[NutBucket]

I really don't think it makes much difference. Either one is bad.

 

[The Boston Dangler]

if you're so concerned about fuel savings, cross country ski across the country

 

[herm0016]

cd is a function of a lot of things, one of the largest contributors is cross sectional area.

i think the racks will be better than a box. do you have the diverter for the front? those also help.

 

[Sheep221]

If you travel in very high speed yes it will consume more gas over a time. But if you do it several times in winter, I wouldn't be bothered about it much. Don't ever carry the skiing stuff inside the car.

 

[Meghan54]

From my experience with roof mounted bike and roof cargo carriers, the increased drag is a major hit on your gas mileage. No way around it. That's one reason I switched to a rear hitch mounted bike carrier.

But in your situation, probably no other choice. Going to have to just suck up the drop in mileage.

 

[fuzzybabybunny]

I did a lot of reading on aerodynamic shapes last night and I'm bummed out by the shapes of boxes. They are not optimized very well for aerodynamics.

You would think that something this sleek would be the most aerodynamic out there...

http://www.takboxar.nu/wp-content/uploads/2012/11/IMAG0044-1024x682.jpg

http://www.tuning-market-ural.ru/files/cat/thule-dynamic-800-bez-imeni-2442921374804.jpg

The front is thin and should cut into the wind like a knife right?

Nope. The back is flat which creates a lot of turbulence in the rear which is what actually contributes to drag.

https://www.youtube.com/watch?v=1exOXa-5WYo&feature=youtube_gdata_player

That tail turbulence at 0:54? Not good at all.

http://exploration.grc.nasa.gov/education/rocket/shaped.html

Instead of a sleek bullet shape they need to have a tapered back end.

http://ecomodder.com/forum/showthread.php/most-aerodynamic-cargo-box-18000.html

The gist is to mount as far back as possible and to mount the boxes *backwards* so the tapered end is pointing towards the back.

 

[Greenman]

Honestly, if a few bucks worth of gas is going to make a difference in your life, you shouldn't be driving cross country to ski. If it's just that you're that frugal, the same advice applies.

 

[_Rick_]

Just drive a bit slower.

 

[heymrdj]

They aren't designed with as much aerodynamics because usefulness is inversely proportional to aerodynamics. Think about it, how are you going to store suitcases or anything on the roof it it's like 2" high. If you need more space you suck up the loss in mpg. Or you sacrifice what you carry. Those are your two options, you'll have to live with them.

 

[996GT2]

Why is this even an issue? You can afford a cross-country skiing trip but can't afford to spend an extra few bucks on gas?

 

[JulesMaximus]

Your gas mileage will suck with either one.

 

[skyking]

don't you have room inside for skis? you had room to sleep.

 

[fuzzybabybunny]

Damn guys, forget I asked.

I got my answers from a ski forum from people who actually have experience with this stuff.

The cargo cases are better gas-wise. Some only decrease mileage by 1mpg. Most people get only 2-3 mpg lower and the case is vastly superior to a rack anyway because it stores a whole lot more than just skis.

And some people in certain cars have even gotten better gas mileage than even *not having anything on the roof* because the box creates a smoother air flow in the back, reducing overall drag.

Reviewing basic aerodynamics confirms that smoothing out the air flow in the back as the air rushes past the object can sometimes be more important than smoothing out the front of the object.

I'm going to sell my racks and get a cargo box.

 

[Capt Caveman]

Driving cross-country with a Thule Roofbox twice, I discovered that the roofbox caused me to lose 2 mpg. The combination of the roof rack and roof box, causes a lot of drag.

And due to your vehicle being fairly small, in order to be able to open up your rear hatch, you'll need to move the roofbox forward quite a bit. The roofbox willl probably end-up hanging over your front windshield which will even cause more drag.

 

[Zorba]

FYI, if you mounted the box backwards and then added a spherical nose to it, it would be fairly aerodynamic.

Also remember that just the bare bars will cause quite a bit of drag, sometimes putting something on it will reduce the drag of just the bars.

 

[monkeydelmagico]

The amount of money you just lost selling the brand new Yakima rack would probably have covered the gas.

You honestly think a box top with probably 10x the frontal surface area compared to the powder hounds is going to be more fuel efficient?

 

[fuzzybabybunny]

The amount of money you just lost selling the brand new Yakima rack would probably have covered the gas.

You honestly think a box top with probably 10x the frontal surface area compared to the powder hounds is going to be more fuel efficient?

Uh, yes. Read around. Boxes get better mileage than racks plus they protect your gear from damage and road grime and can be used to store a lot more stuff and are multifunctional versus being a unitasker.

Powderhounds are cheap. Not much money lost there after selling them. And the boxes hedge against equipment damage.

I can buy a good Thule box for $200 used.

 

[KoolAidKid]

Honestly, the wind noise of the rack bothered me more than the reduced gas mileage. I took it off for that reason.