So you're driving down a long fairly straight stretch of road and when you finally stop for fuel and check your consumption rate, it is several points above its usual average. How can that be? And then you remember that you had a tail wind coming straight at your back for the last few hours. On another day on the some road, you had to stop for fuel long before you expected to and your rate was way down and, come to think about it, you never did quite get up to the speed limit. Yep, you guessed it, a head wind was responsible. Pretty straight forward—the wi
