I've done many a trip over long distances in my ford ranger, both with a traditional cap and without. if there was any difference in mileage I couldn't tell it, and I'm kind of nutty about keeping track. one experiment I did was to add a piece of aluminum across the back of the shell to deflect wind. it's low profile and has a curve in it to shoot the wind down across the back window. after many more thousands of mile on trips (15k last year ) it has consistantly gotten 2mpg better. I'm figuring it's breaking up the wind on the back and creating less vacuum on the backside. now the problem is, I've been reading too much on this site and I'm thinking about doing a kammback design to see if that does any better. you people are causing me a lot of work.
