Originally Posted by Velo Dog

This comes up all the time, and nobody ever listens to my expert opinion....
I have a Yakima cartop rack, and I can put it on in about 90 seconds with a helper or three minutes by myself, take it off in 30 with a helper or 60 solo. When it's on, my highway mileage drops from 34 mpg to high 20s, and there's a constant roar from the roof. I can't use the sunroof at all because of the noise, plus the rack is up there getting sand-, grime- and salt-blasted for 2,000 miles a month.
Assuming you have the standard Yakima Q-tower setup, put it on and use a Magic Marker to mark the spots where the clamps go (inside the doorframes where it won't show when the door's closed). Take the rack off and enjoy silent, high-mileage motoring until you want to carry the bike. Then slap the rack back up there, lining the clamps up with the marks you made, lock it down and you're in business.