Security is another issue. Bikes on a rack are more noticeable than bikes inside a vehicle. When I went shopping for my last vehicle, I wanted something that would meet the following requirements:
- Fit 1 bike (tri and/or road) inside the vehicle with the front wheel on.
- Fit 2 bikes (tri and road) inside the vehicle with the front wheels off.
- Have a hitch available as an option, to mount a 2+ bike hitch rack (so other stuff can be inside the vehicle).
- Get at least 40 MPG highway.
The car I wound up with, a 2012 Mazda 3 hatchback with the high-efficiency SkyActive drivetrain, not only met the above requirements, but was also the most fun to drive at a very reasonable cost.
Soon after getting it, I joined a Mazda 3 forum to learn more about the car and its idiosyncrasies. We talked about the mileage we were getting for our various commutes, and how we achieved it. Someone on the forum found a spreadsheet that helped test and compare performance over commutes, and converted it to a Google Docs spreadsheet we could share. For repeatability purposes, the test required us to be on cruise control as much as possible. We plotted our commutes on Google Maps and plugged the elevation profiles into the spreadsheet, to see how elevation changes affected our commute mileage.
We got some great data, with surprisingly consistent results for most of us. But a few folks had much worse results (10-20% lower). The most common factor was a roof-mounted rack (bike, ski, kayak, whatever). Some of them removed their racks, repeated the test for a month, and had results compatible with the rest of us.
The moral of the story, at least for high-efficiency vehicles, is to use a rack as little as possible, and remove it when not in use, especially if it is a roof rack.
I still haven't purchased my hitch or rack. Probably means I don't travel enough.