I live in an area with medium hills…
In: 5
Ultimately if you have similar average speeds over a journey and you keep your speed within a few MPH of constant without cruse and make smooth gradual corrections to speed – its not going to make that much difference. The energy required to propel you that distance will end up about the same and the engine will operate in very similar operating zones where efficiency is very close. The difference may be significant if:
1) You are hard with your accelerating when going too slow. Hard acceleration takes you out of the good efficiency zones of operation.
2) You often end up going too fast and then brake to bring your speed back in check. Going fast uses more fuel, and braking throws away the extra energy you just built up.
3) You allow the car to freely accelerate under gravity on the downhill stretches above your intended speed where the cruse control would engine brake to keep speed constant. The engine braking is throwing away free energy!
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