Eli5 – Does using cruise control save fuel?

Question

I live in an area with medium hills…

In: 5

Answer 1

Nowhere near as much as just driving 5mph slower.

Pretty much, you’re using the same amount of energy no matter what you’re doing, uphill hurts, downhill gives back, but accelerating on the downhill and not on the uphill doesn’t “save” anything, the same forces still apply.

But just set your cruise control to 5mph slower and you’ll definitely save fuel. The losses on aerodynamics, road friction, etc. come back to bite you and running the engine nearer its peak torque is always more efficient. In almost all cars, that’s far nearer 50mph than 70mph.

Any modern car with a live MPG statistic will show you this, with only a few minutes experimentation.

If you want to save fuel, cut A/C (not always an option in some countries, but certainly don’t open windows… that’s even worse, the aerodynamics are destroyed when you open a window), drop the revs to something lower (close to peak torque) and drive smoothly (where cruise control can help, but also don’t change speed, by predicting the road ahead, smoothly changing lanes in plenty of time, etc.).

Peak torque for my car is 1600 revs, that gives me something around 50mph in top. Whenever there’s an “average speed camera” area on a motorway with a 50 limit, that’s when I get peak MPG. No idiots fighting to get past and cutting in, no point going any faster, and the engine is at its most efficient workload.

Also: If you’re driving an American car, just don’t. You guys haven’t caught up with the rest of the world.

In the US, they sell the Ford Fusion. In the EU/UK they sell the Ford Mondeo. They are the SAME CAR, same chassis, same parts, etc. The only difference is that in the EU market, the engines go from 1500cc to 2000cc. In the US market, the engines for the exact same car START at 2300cc and go up to 3500cc.

That’s what years of “cheap” fuel did to you – they screwed you over by giving you engines that you can’t sustain when the price rises. Now you’re paying the price of that designed-in, allowed-by-legislation inefficiency.