How much does a bike rack reduce your MPG?

I've seen lots of speculation but no definitive answers. I think it's a little too tricky to pare out all the noise in such a comparison, so you'll hear a lot about "1 or 2 mpg" or maybe "no difference."

I think a tail hitch might be better though as you can pull your rack off when you're not using it and not introduce extra drag that a permanent roof rack would cause. Just try remember not to use that hitch to tow anything

 

<div class='quotetop'>QUOTE(burritos @ Mar 1 2007, 08:51 AM) [snapback]398520[/snapback]</div>

Thule did a test of ski racks on cars a few years back and came up with 10% mpg reduction on a Mercedes sedan at Autobaun speeds ( tested in the Mercedes wind tunnel ). I do not notice any difference around town with my racks but take them off if taking a road trip without my kayak. The speed you drive will make a huge difference on the road with a roof load. I drive no faster than 65mph with something on the racks. We take the mini van on road trips so I don't have any direct data on the prius yet.

The Thule racks fit better on the Prius than the Yakima because Thule makes a custom clip and pad for each individual car. The Thule rack also has a patented movement when tightening that clamps the rack solid to the car. They have a new aerodynamic aluminum bar available which is quieter and lighter in weight. You can also use a fork mount bike rack, put the front wheel in the trunk to reduce the bike's profile.

http://www.thuleracks.com/thule/product.as...&sku=400XTR

 

When I had my Thule rack + fairing on the car, mileage went down about 3-4 mpg. Not too bad. However, on a long highway trip with a bike *actually on the roof*, it went down enormously. Driving across NH on the highway at 70mph in the summer, I got an average of 32mpg for the tank. The tank before the bike went on, I was at 42mpg. The tank after the bike went on, I was at 51. I haven't put the rack on since and instead put the bike in the back with a towel covering the oily bits (being a road bike, it's not too bad usually).

 

<div class='quotetop'>QUOTE(HappyPig @ Mar 1 2007, 12:49 PM) [snapback]398682[/snapback]</div>

One of my major reasons for getting a Prius is the hatchback easily fits my road bike. I have to use a rack on my Impreza, and the hatchback is better in every way, more theft proof, rain proof, and no decrease in mpgs. Last year on the way to the LA Marathon bike tour, I saw a nice mtn bike laying in the middle of the Hollywood Freeway. I know my bike will never fall out of the car, but it could fall "off" the car. I never had more than one bike in the car, but it could be done if you remove the front wheels. B)

I forgot to mention that I actually melted a bike tire from having it too near the exhaust on my trunk rack. Inside the car is better!

 

<div class='quotetop'>QUOTE(subarutoo @ Mar 1 2007, 04:01 PM) [snapback]398691[/snapback]</div>

fwiw, my experience: with a rear rack sitting on the bumper and hatchback (the ordinary kind with 2 horizontal arms), no difference noted with rack on but no bike, when bike mounted on rack, then mpg reduced to 49 from 51, driving on hwy 65 mph.

 

2001 Prius with Yakima rack and 'ankle biter' bike holder; most recent mpg compilation:

45.5 mpg w/o roof rack etc. (87500 miles)
36.5 mpg w/ roof rack etc. (9000 miles)

Not a totally fair comparison because when the bike is on top, the car is usually more heavily loaded as well.

The mpg impact increases rapidly with speed. At speeds below about 40 mph, the roof rack effect essentially disappears. Note that above that speed is also where the front rack bar audibly howls. I built my own fairing to remove the howl, not wanting to buy the Yakima one.

 

<div class='quotetop'>QUOTE(Ichabod @ Mar 1 2007, 11:56 AM) [snapback]398523[/snapback]</div>

FWIW, if you're running department store bikes or entry level a hitch carrier might be a good option....but if you've got $10K tied up in a couple of high end bikes then you might not want some moron to take them out with what would be a pretty mild rear ender. I'm pondering my options now and think I'll go with the roof option. I typically carry the bikes in our Element but need a second option.

 

I use a Yakima rack with the fairing and switch between bike rails and the Mako Kayak carrier with hully rollers. Without the bike or Kayak on top, my mileage dropped 6-8 mpg, consistently. I remove mine in the winter and am getting ready to re-install it for the summer. It's a significant difference, but still much better than my 04 Element did.