What effect does the Thule roof rack have when loaded at highway speeds and when empty at city speeds?
I had a big Thule box on my minivan and it actually gave me better mpg!! But it fit perfectly on it and was a little narrower than the van and its shape must have done some magic lol. On a C, I'd expect to lose 5 mpg. That is just a guess, but when you think of it, small car; low power; the unnatural shape of the rack and losing its "natural" round roof shape...plus the stuff you'll put on it. -Expect to get better mpg than most vehicles on the road anyway.
On my previous HCH I had a Thule rack briefly until I figured it was costing me about 0.7litres/100km fuel or about $2 day because of my 70mph commute to work. At lower speeds the effects will be much help less pronounced. It was loud too. I switched to a hitch bike rack that didn't make a difference fuel wise. Nexus 7 ? HD
