When I got my motorbike it had a non-standard rear sprocket with two extra teeth. I decided to swap it for a standard one. I expected to get a better overall mpg, but it didn't change noticeably. So... An engine has a red line at 14000 rpm. Peak power is delivered at 12000 rpm. Driving along in top gear at 70 mph, the revs are at 6500 rpm. Because maxmimum power is delivered at 12k, surely this is the point where the engine is most efficient, and getting the most power from the fuel? So, when cruising at a constant 70mph would it use less fuel if you changed down a gear or two, to get the engine revs as close to 12k as possible? Or is it better to drive in a high gear, keeping the revs as low as possible? Why?