first, you acutally use less gas (and 0hp!) if you leave your car in gear (manuals only that is) while rolling than you do if you were to roll in neutral. so if your going down a hill and u pop it into neutral, you're actually wasting more gas than you would if you were just to leave it in gear, no matter what gear it is too! (as long as its under redline that is!) the drivetrain generates the power for the engine to keep going, so its creating its own energy. but if its in neutral, its acutally using about 2-3 hp just to keep the engine running, which obviously = more gas.
Which brings me to number 2. RPM is not really what matters when it comes to mpg, its throttle position. when cruising on the highway, when im at a higher RPM, it takes less effort for the car to create power. so that means I do not have to open up the throttle as much to pass or just keep going from that matter. yet, when at a lower rpm, it takes longer, the car needs more power and therefor uses more gas. So if I am at 45 mph on a road and want to get to 50, if im in 3rd the car is at lets guess 4800rpm(?), to get to 50 i only have to open the throttle up a bit and i will get there faster (1-2 seconds). yet, if im in 5th at around 2500rpm and want to go to 50, its gonna require me to push down further on the gas and is gonna take like 7 seconds in our car (sad
).
hopefully this makes sense!
