[CROSS CANADA WITH 8]

I just registered with ecomodder, and I wanted to ask some of you experts a question about car top carriers.

I have a Toyota Sienna, 2004 that I fill up with six kids and two adults. This summer, we plan to drive from Nova Scotia to British Columbia to see my wife's parents. We will be going about 15,000 kms (9,000 miles) in total.

With all those people, we need a car top carrier. We currently have one of the hard shell type-- rather boxy but rounded with a bit of taper to it-- the kind you can get at sears. It is 18" tall and 36" wide and 48" long. I have considered getting a shorter, narrower, longer style to decrease wind drag, but I have no idea how much difference it would make.

Would any of you be able to give me some idea of how much difference it might make in my gas mileage? I don't need to know exactly, just a rough idea.

With the van all loaded up (so much weight that it rides low) on previous trips with the car top carrier in place, we have averaged between 26 and 27 mpg (which interestingly is the same mileage we get driving around town without the carrier or a load). I ordinarily drive about 5 mph over the speed limit with cruise on which often means 70-75 mph. I do look ahead and coast when I can.

I would really appreciate any help you could give us. Finances are tight with such a large family, so every bit helps.

Thanks so much.