what effect do roof racks have on mpg?

how much do they hurt if at all? just a regular roof rack with the bike carriers i'm wondering about. thanks

Enough that I leave mine off unless I am actually hauling bikes or skis around. Your mileage may vary.

I have a Thule box and it probably costs me about 2 MPG. I used to carry snowboards on my Audi w/o a box and they were much noiser and cost me 4-5 MPG. I bet bikes are worth that much.

Take 'em off when you aren't using them!

From my experience, the roof rack it self does not reduce mpg much at all, but when you start putting items on the rack is when the mpg really goes down. The worst item for mpg are bikes traveling on the highway. It slaughtered my mpg from around 50mpg down to around 33-36mpg travelling at 70mph or so. With a thule box (without a LOT of weight, don't put more than about 50lbs in it though) mpg only drops about 4-5mpg.

Have a Thule evolution 16 cubic feet. Cuts fuel consumption about 10 percent at highway speed (i.e. 90 mph!)

I average 44mpg with the racks and fairing on my '98. With the bikes on top i get about 41mpg. Better than the GTI which gets about 27mpg with bikes on top.
I hate hypermilling which is why i only get 44.

Going from Portland to Bend with 2 bikes and a yakima box I averaged 46 mpg on one tank.

Just the roof bars (no accessories or luggage) 38MPG doing about 70MPH. Took the bars off for the return trip and got 49MPG. I did hit a bit of a storm so had to slow to 55MPH for about 100 odd miles on the return trip. This was back when car was almost new and going across Wyoming and Montana for New Years.

Jason

PS: Went from Missoula,MT in western Montana to Laramie, WY in eastern Wyoming. Couldn't make it on one tank with bars on, but made it back with fuel to spare with them off.

I would slip from 42-43 down to 40 every time I went skiing in the winter and the racks were only on the car for 1/2 a tank most times... so figure 4 mpg at least.

yakima crossbars, fairing, and 2 viper fork mounts on my 2011 TDI have cost me about 1 mpg...no big deal. I haven't gone on any trips long enough (usually only 10-20 miles) with the bikes on to give an accurate indication there.

I would imagine that the speed you travel has a lot to do with what kind of hit you will take. Slower you go, less of a hit. Stick a rack and some bikes up there at 80 or 90 mph and I'll bet it is huge!

you guys drive at 90 mph? really? wow

West Texas speed limit is 80 mph. Quite a few at 90 mph.

Theory question here:

If your 2003 Jetta TDI Wagon loses MPG with a rack and bikes, what will happen with the same set-up on a 2003 Jetta 2.0 Wagon? Will it drop the same MPG, will it drop the same percentage, or will it drop differently?

Thoughts, theories, thesises?

I have found adding a front fairing / deflector really helps move the air up and over the cross bars. I do take off the bike trough when on long trips and get pretty close to 48-50mpg running it that way. Guess that is why the bars and deflector live on the car! (Thule bars, deflector, Yakima troughs...mutant goodness).

I have the vw bars, I find they were a bit noisy and I lost about 4-5 mpg on average.