Tests show bike racks can ruin your mileage

We're in the thick of summer travel season and vacationers are packing up their cars for getaways. Bringing bikes on vacation is a great way to get exercise and save gas touring your destination. But, our tests show that taking bikes with you will exact a fuel economy toll.

To find out how much fuel economy is actually lost with a bike rack, we tested various setups on a 2013 Honda Accord. We ran our traditional highway fuel tests with no rack, an empty rack, empty rack with wind deflector, and a rack with two bikes and deflector. The results were dramatic.

To test fuel economy, we use a precise fuel-flow measuring device spliced into the fuel line, then run two separate circuits. One is on a public highway at a steady 65 mph. That circuit is run in both directions to counteract any wind effect. A second is a stop-and-go simulated city-driving test done at our track. CR's overall fuel-economy numbers are derived from those fuel consumption tests.

The Accord LX four-cylinder used for this testing is exceptionally fuel efficient, earning 30 mpg overall--good enough to rival many small cars.

As we cruised at 65 mph in the Accord with a pair of bicycles on a roof rack plus wind deflector, our highway fuel economy plummeted by more than a third, from a miserly 42 mpg to a miserable 27 mpg. The rack alone wasted 5 mpg. Keep in mind that a car filled with people and cargo will also have an effect on fuel economy, so pack as efficiently as you can.

Going across town, this may not be a concern. But if you're planning a multi-state family road trip this summer, a mounted bike would have a real impact on your fuel costs. Plus, it may create some annoying wind noise.