Bike racks - gas mileage

[GLC1968]

Depends upon your car and how aerodynamic it is. If you're talking a squarish SUV or minivan, probably not much; if you're talking a Prius or Honda Insight, you could see a considerable drop.

I drive a Prius and mileage dropped from 55mpg to around 40mpg with the rack and 2 bikes. Just the presence of the rack dropped mileage. We've since learned how to get both bikes inside the car if we're transporting for any distance.

This.

We saw our Prius drop from 48 mpg to 33 mpg on the windy highways of Kansas and Colorado with two bikes on the back rack (ours is a hitch rack - but same idea). We moved the rack/bikes to our Matrix which is boxier and has a more powerful engine and the mpg drop was 2 or 3 mph - even crossing the continental divide. It really depends on the car!

ETA - I used to use my Saris bones on my Mini Cooper with little to no mpg difference and it held very well. The longest ride I ever used it for was about 2 hours and I was carrying two bikes (one very heavy one).