I live in an area with medium hills…
In: 5
It can but you’re better off understanding torque vs speed if it’s because of hills and downshifting. It does a better job saving gas on a highway, keeping speed constant at high gear.
Yes, because the computer has much more precise control over the throttle position than your foot can provide. It is constantly watching the speed and the variation as well as rate of variation, and a well designed system will always only give as much throttle as needed to maintain your set speed. People are always wobbling their shit and keeping a sort of constant state of acceleration which requires more fuel than just maintaining speed.
In my experience, yes it saves fuel, the main problem of cruise control is if you have to change speed all the time
YES
take into consideration that a big factor of fuel consumption is: Acceleration aka change in speed. The less change there is the more efficient is the engine power driving the wheels.
i.e. going 0-60 in 10 sec. wastes more fuel that doing it in 15 sec.
With lots of hills, not always… depends on how much speed you are willing to lose going up hill compared to how hard the cruise control will fight to keep speed up… as well as how aggressive the cruise control is going downhill to reduce speed.
Usually, though, cruise control is better.
Eli5 verson: Think you go to the store. what makes you more tired?
– constantly switching between running and walking. run, walk, run walk and so on
or
– walking normally
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!
This is heavily dependent on your habits as a driver and what the driving conditions in that area allow. In hilly terrain that goes up and down its best to accelerate lightly on the downhill letting gravity assist and coast/slow down a bit on the uphill so you aren’t fighting gravity to maintain speed.
If you practice that as a driver then cruise control is likely to give you worse mileage. Cruise control is trying to maintain a static speed. So it will throttle down on the down hill and lose the advantage of the gravity assist to maintain a static speed and accelerate on the uphill to fight against gravity.
If you are consciously practicing that though, cruise control is likely going to do a better job of maintaining speed and fuel efficiency. Many drivers wait until they’ve slowed down significantly and then heavily accelerate back up to their desired speed, whether on uphill or downhill. Its very inefficient and cruise control works better than that.
With hills I tend to do about 3-5 mpg better in my car than the cruise control does.
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.
If you’re on flat or flattish roads yes it will save fuel for the same average speed. It minimises the amount of fuel you spend accelerating having accidentally slowed down.
However. Dropping down a gear and going a bit slower on an uphill will save you fuel because your engine will probably be working more efficiently uphill in a lower gear with a bit more revs.
Finally – on a long highway run almost all your fuel is spent overcoming air friction drag. Slowing down by 5mph will save you more fuel than using cruise.
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