|
If you are driving at 30mph for 10 miles and return 35 mpg, it still saves more gas than driving at 60mph for 10 miles and return 30mpg. Mpg is miles per gallon, no time factor. But in reality, we will put the time factor in consideration, which is save money vs save time. That's it!!
Engine has its own power curve. Usually, lower rpm saves more gas because it rev less = less cycle per min = less # of gas injected cycle per min. However, less gas = less power. If the engine doesn't produce enough power at low rev, you need to burn more gas in each cycle. In this situation, lower rpm may burn more gas than higher rpm. What makes this situation happen is controlled by your right foot. If your foot is light enough and the gas injected is just enough to maintain the speed, then you save gas. However, if you have a heavy foot, more gas injected, but may not have enough power to reviv up the rpm, it looks like cruising at the same speed, but you are burning more gas.
In some situations, we have to shift down to maintain the low speed, like going uphill at low speed. I won't drive 25 mph with top gear. Engine can't produce enough torque at such low rpm. Driving with that combination won't save you gas and probably bad for the engine. In that situation, use 3rd gear or 4th gear, whatever gives you the best mpg. That is our ultimate goal, right?!
__________________
|