Roof rails effect on fuel economy

[BobF13]

Anyone have any hard data as to the effect of the roof rails on fuel economy? I have a 2014 Touring with roof rails but no crossbars, a coworker has a 2014 Grand Touring without roof rails. We both track our fuel economy using Fuelly, and he seems to consistently get about 2 mpg better than I do. I realize there are plenty of other variables affecting fuel economy, but I was just wondering how much of a contribution the roof rails might be.

 

[Kedis82ZE8]

I'd be looking at what their commute looks like... flat, speeds, use of control. IMO even with crossbars it probably is not anything more than like 0.25 MPG. Now loaded and used....thats a whole different story.

 

[flyfisherdon]

I just returned from a 489 KM journey, mixed driving, mostly highway, including going over the Malahat (Mountain with repairs going on ) twice, there and back.
I figured out the mileage on my return, it was 36.5MPG. Typically with a 2007 Hyundai Tucson with 2.7 V6 I was lucky to get 30-31MPG.
Our CX5 only has 1500 KMS.
I DO have roof rails.
Don

 

[robertmazda]

Some answers from a simple Google search. The answers really surprised me.

http://www.consumerreports.org/cro/...ow-bike-racks-can-ruin-your-mileage/index.htm
http://www.edmunds.com/fuel-economy/we-test-the-tips-part-ii.html
http://auto.howstuffworks.com/fuel-efficiency/fuel-economy/roof-rack-affect-mgp1.htm
http://www.cartalk.com/content/guide-better-fuel-economy
http://www.terrapass.com/science-technology/conservation-ti-3/

 

[Kedis82ZE8]

I agree roof baskets & carriers have an effect but rails alone the loss will be minimal IMO.

 

[rjdee]

The rails alone have almost nothing for added drag. There is no frontal area to them. Any difference is going to be due to driving style, tires, tire pressure, road conditions, etc. Adding crossbars will add a bit of drag but it's barely noticeable. Adding accessories to the bars will definitely affect mileage. Baskets are the worst followed by cargo boxes. Bike mounts, kayak and ski are all about the same.

With my setup I get about 33-34 mpg with crossbars and no mounts (all around, city and hwy). 29-30 with the long and skinny Yakima Skybox 12 on top.

 

[Bcdad182]

I would think that the mudflaps would add more drag than roof rails -- especially those rear ones, they're huge and flat, just what you need to cut through the wind. Seriously, if the roof rack is empty it adds very little drag. The only way to get a fair comparison between two cars is to switch drivers - driving style and route have a huge impact on fuel economy.

 

[ALafya]

Thank you for the links, they were helpful.

I too am considering installing roof rails. So far, I did not because the concern of increased fuel consumption, I rarely really need them and because the car looks so much better without them.

With my previous vehicle I used a Thule roof rack, with fairing and ski carrier attachment, which I had installed only when needed, removed when I was done with them. Driving even without skis I could feel the extra drag on the vehicle and with skis the fuel economy dropped by ~5 MPG. Granted, the Thule were bulky and had pretty bad aerodynamics compared with the original CX-5 rails.
If I'd get the rails, I'll probably drive without the cross-bars most of the time anyway.

 

[NinjaNoises]

Kudos to you guys for using "effect" and "affect" correctly. lol.

 

[MikeM.]

Thank you for the links, they were helpful.

I too am considering installing roof rails. So far, I did not because the concern of increased fuel consumption, I rarely really need them and because the car looks so much better without them.

I agree completely. Another side benefit is the car will be quieter on the highway with clean airflow over the roof.