Roof-mounted bike racks are common fare for outdoor enthusiasts, but you might be surprised how driving with the bike rack increases your fuel consumption.
To prove this, Consumer Reports took a 2013 Honda Accord and drove it with no rack, an empty bike rack, an empty rack with a wind deflector and then a bike rack with two bikes and a wind deflector, to measure the incremental affects on fuel consumption. The car was driven on the same course for each test, which consisted of highway driving at 65 mph and a simulated city scenario.
In testing with no bikes or bike rack, the car returned 42 mpg on the highway, a great number even for a four-cylinder family sedan. When just a bike rack was added, fuel economy sunk by five mpg, bringing the highway average to 37 mpg. When a wind deflector was added to the empty rack, an extra two mpg was lost bringing the car down the 35 mpg. Finally, the car was tested with the wind deflector and two bicycles, which sunk the average to 27 mpg.
That represents a 15 mpg discrepancy between a car with no rack, and a vehicle with a wind deflector and a roof-mounted bike rack packed with two bikes.
[Source: Consumer Reports]