Roof box mileage

[daught]

I am looking in to buying a roof box for my avant. I am really curious how it affects fuel efficiency. I am very happy with it's fuel efficiency right now on long trips. I can stuff four people with a week worth of backpacking gear in the car as it is, but for convenience sake if it's not too big of an efficiency penalty I would like to get one.

[Luxus Panzer]

I looks arpprox 5-10% with a full size (11Cubic feet) Thule.



I get even better mileage when I use this device...

[B-Time]

Boxes are used more often in the winter, and winter fuel can be less efficient. And snow tires are less fuel efficient. So keep that in mind when trying to quantify mpg loss.

[chad99]

I get even better mileage when I use this device...

Lol

[daught]

Boxes are used more often in the winter, and winter fuel can be less efficient. And snow tires are less fuel efficient. So keep that in mind when trying to quantify mpg loss.

My winters get way better mileage. 215/55R16 Altimax arctic vs 235/45R17 pilot sport AS/3. Weird, I know.

5-10% does not sound bad at all. Of course speed can have a big impact. At 140-150ish it probably gets pretty bad, not that I ever go that fast.

[B-Time]

My winters get way better mileage. 215/55R16 Altimax arctic vs 235/45R17 pilot sport AS/3. Weird, I know.

Interesting. Have you weighed each setup?

[old guy]

Interesting. Have you weighed each setup?

Even if both set ups weighed the same the 16" wheels will give you better gas mileage. It has to do with the moment of inertia. The further out you place the mass on the same diameter the more energy is required to accelerate/decelerate the mass. Here's a quick visual:

[B-Time]

Even if both set ups weighed the same the 16" wheels will give you better gas mileage. It has to do with the moment of inertia. The further out you place the mass on the same diameter the more energy is required to accelerate/decelerate the mass.

Understood, thanks. For that comparison to be completely apples to apples, you would have to have the same type wheel and tire. Winter rubber is generally heavier that summer. And winter wheels are often of a lesser quality, therefore heavier. In my case, same size winter setup is substantially heavier and I can feel it.

[egovreau]

Obviously you'll take a hit. I guess you could try testing it by tying the neighbor kid to your roof and taking it for a spin.

Sent from my SAMSUNG-SGH-I337 using Tapatalk

[customa4]

Obviously you'll take a hit. I guess you could try testing it by tying the neighbor kid to your roof and taking it for a spin.

Sent from my SAMSUNG-SGH-I337 using Tapatalk

Haha! Not sure you'd get the same turbulence if he's laying down. Maybe the suggested method might be with the kid sitting up or possibly standing?

[egovreau]

Haha! Not sure you'd get the same turbulence if he's laying down. Maybe the suggested method might be with the kid sitting up or possibly standing?

Good point. That could work. Or try and find two.

Sent from my SAMSUNG-SGH-I337 using Tapatalk

[daught]

I ended up getting the behemoth horizon xl. The dude got it with his van and did not have a key to open it so he took it off with the Dodge crossbars. I had to use the $7 conversion kit. Kinda jealous minivans come with nicer crossbars than audi original.



Definitely improves my stance.





Sent from my clear iPhone 31SS

[daught]

Sooo... Can these boxes take 150kmh speeds and aggressive mountain driving? Seem pretty flimsy to me.


Sent from my clear iPhone 31SS

[Luxus Panzer]

I ended up getting the behemoth horizon xl. The dude got it with his van and did not have a key to open it so he took it off with the Dodge crossbars. I had to use the $7 conversion kit. Kinda jealous minivans come with nicer crossbars than audi original.



Definitely improves my stance.







Sent from my clear iPhone 31SS

If I saw zip ties holding on a roof box.....we would have a talk ;)

[daught]

Screw the roof box. I am taking my open ski rack from toronto to BC and my fuel consumption is ridiculous. Weather is pretty bad and very windy, but it's waaaay over the usual by a few liters. Now I wonder if open racks are worse for fuel milage than a closed box.

The rack is a flat huge air dam.



I am considering replacing it with. Should be way better, no?




Sent from my clear iPhone 31SS

[yasiu_k]

I have Thule 1700 and works perfect. I don't see any difference on the fuel efficiency.

Sent from my SM-G900V using Tapatalk

[daught]

Bump. I got back from the rockies trip and I tried my roof box. Way better than a ski rack. Mileage and comfort wise. My only issue is not being able to open my trunk all the way. Is there a reason the rails are marked where the crossbars should sit? I want to move them forward. Only issue I can see is the sunroof clearance. I could pull that fuse to be sure it does not open and crack the glass.