How much MPG can I expect to lose carrying a roof cargo carrier (Thule, X-Cargo, etc.)?

I'm going to be buying a roof cargo carrier for my Chevy HHR. I currently get between 29 mph and 32 mpg on the highway, depending entirely how fast I go.





I'm going to be travelling soon, and for the extra cargo carrying capacity I'm going to get a roof-top cargo carrier, like this one (http://www.sears.com/shc/s/p_10153_12605鈥?/a> and I'm curious to know if anyone out there has one, and how much of a hit you take on your MPG?





Assuming my normal MPG is 30 mpg, what do you think my MPG will be with a cargo carrier on the roof rack?|||There is no way to be exact, it depends on how fast you drive, how you handle your starts (jack rabbit starts, etc.) do you have cruise control (this helps MPG if used), is your car carrier areo dynamic, etc. Just to take a guess, if you are getting 30 MPG without the car carrier, with the car carrier and an extra 100 lbs, I would estimate your mileage to be around 26 MPG.





melscybergarage.net


melscybergarag@gmail.com |||Consumer Reports %26amp; Edmunds tested a Thule roof box and roof basket. Both tests determined the loss depends on speed and car. The MPG hit was 17% to a whopping 25%. Roof mounting burns more fuel and decreases MPG significantly. We use AeroPACK which is easy to use and save gas.

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|||It would depend entirely on the disruption to the air flow your carrier would make. Some of the better ones are aerodynamic with a cover, and the weight you plan to add.