I've read conflicting opinions on this, but haven't been able to use 'science' to conduct my own test.

The idea is that if you drive off the 'instantaneous mpg' you should lift off a bit when you go uphill and plant it a bit more going down hill; this is allegedly more efficient than than the steady speed the cruise control maintains, which I used to assume was more efficient since if you just use your right foot you are always speeding up or slowing down (surging) a bit like a sine wave* which is less efficient?

*Yes I know the computer does that too but it is far better at it than a human.

I drove over 400 miles yesterday in my Golf TDI, and averaged 56 mpg (which I am fairly happy with but I used cruise maybe 90% of the time). I think I could have got better than 60 mpg but I was making good progress* to save some time. Plus I had the AC on too.

*Not in anyway over 70 mph officer

Scooby owners with no cruise control please ignore.

 

Decrease .... the Cruise Control is far more accurate than anyone's right foot.

I get 72mpg with the Cruise on ..... about 65mpg with my own foot and eye combination.

Although, I grant being Scooby owners, those figures are cosmic ..... so, maybe, when you are only getting 20mpg the difference doesn't matter?

 

Is that on motorways Pete? That's pretty damn impressive. If I drop to 60 mph I might expect that but it's too slow for me.

 

Mine general decreased when cruise control is on but then it is a ****ing ****e car.

 

decrease, definitely.

In our Astra, you can watch the range INCREASE as you switch on c/c and drive a few miles.

 

Motorway's Tony, yes.

And set at around 65MPH .... sensible, like

 

Unless you are able to drive with a "soft" foot on the accelerator, cruise control will be more economical.

Les

 

I tried this before when I was doing a lot of motorway miles every day. In my experience, I got a higher average mpg figure without cruise control, but I probably couldn't be bothered putting that effort in all the time.

 

I can get better economy than cruise control, but then I'm a very good driver.

 

Decreases unless you're very good

But then you'd have to be a total nerd

 

I used to travel alot of motorway miles a few years back and could always get better fuel economy myself. It's the uphill that lets CC down, if you plan ahead you can keep momentum much easier using your right foot.

 

http://movieclips.com/EYUh-rain-man-...ellent-driver/

 

I can get marginally better fuel consumption in our 1.6 TDCi Fiesta - that thing is amazing on fuel - and R32 Golf driving "manually" than the cruise control, maintaining a constant and similar speed. In the Golf I can get it to be significantly better, my record so far is 35mpg on a local run though on the same journey in similar conditions on cruise it managed 29mpg.

Basically I coast down hills whereas the cruise control will continue to accelerate or brake the pounds away, and up hills I give the throttle little blips and use the weight of the flywheel to carry the car up without effectively wasting fuel to maintain a couple of miles an hour. It obviously depends on what car you have, diesel cars have a lot of torque and usually a heavy flywheel that pulls the car along better (compared to my last Impreza which would probably grind to a halt in top going down the side of the Eiffel Tower).

Going off the realtime readout can also be very helpful. It is painstaking to do though, it is much easier to just hit cruise on the motorway and pay more attention to the idiots who don't look before changing lanes etc.

As for cruise control in the Impreza, the dash readout has been largely at ø20.1mpg since I got it, I'm sure if I had a realtime readout or really wanted to save half an mpg it would be better to switch the cruise control off but to be honest I didn't buy the car for that and reeeally can't be arsed

 

Depends on the driver...and the cruise control system.

For example modern BMWs (at least F-series BMW) have cruise control systems that activate the brakes if the car over-speeds past the set speed down a steep hill. Now, brakes waste fuel. As the extra momentum gained going downhill can't be used to go back up the hill after reaching the bottom. So in this case its not the best of cruise control systems...however handy for avoiding hidden speed cameras in the Navarre mountains

So in the case of current BMWs or any other car with advanced cruise control (Merc, VAG etc) it could be wasteful.

I noted this on the past 2600mile jaunts to Spain and back: 40.2mpg average in a 2 ton car with a 3.0litre engine...deactivating cruise control on the long downhill stretches (and using gears on the mega steep declines, to save wearing out the brake pads ).

The other issue is the throttle pedal. The pedal movement is not always linear to the engine's torque/power output, notable on some old cable driven cars (Classic Impreza) as well as some drive-by-wire cars. Where a small pedal movement at motorway speeds can translate to the engine producing alot more power...and using alot more fuel as a result. The car's speed slowly keeps creeping up, meaning the driver has to make loads of tiny pedal movements to prevent accelerating and decelerating. A car that is constantly accelerating/decelerating on a flat road, even by a few mph will use a hell of a lot more fuel (basic physics). And lets face it, most drives can't maintain constant speed on a flat road, let alone on a hill!

Then there is a good number idiot drivers that tend to overcompensate and accelerate up a hill then slow down on the flat/down hill sections For these types of driver...cruise control is a must if they want to conserve fuel.

 

As a certified hypermiler you can get better mpg without the use of CC...

Contrary to what Pete thinks,your brain/eye/foot combo is a LOT better than any cars CC system..

 

I'm not 100% on which is actually better at the same speed in my car. BUT, I use a lot less fuel using the CC as it prevents me from creeping up to speeds that would be higher than I normally set the CC to (about 68MPH)

Good for keeping the licence clean as well.

 

"It depends"

For most people, most of the time, a good CC will be more economical.

For those who want to try and extract every last mpg (and don't mind that they're not holding a constant speed) they can probably beat a good CC most of the time.

The difference between the two however is probably not worth it in real terms most of the time.

 

I drive a Forester 2.5XT PPP with cruise and it's definitely slightly more economical on cruise. To be honest it's probably only because everything is kept nice and smooth, the throttle mapping on that car is definitely not linear and it's a bit tiring around town as it's just too eager at low speeds.

Came back from Center Parcs yesterday and used cruise all the way up the A1 and on the M62 (past Leeds in the worlds longest and most stupid roadworks, 50 in 5th for a long time). Well up on my normal tank range but then I suppose I would be anyway.

 

When I was doing loads of miles i'd use the mpg as a means of entertainment and could definitely get more mpg than any cruise control system, but it was a few years ago so maybe things have improved, just like anything it just requires concentration and practice.

The key to good mpg is planing ahead, and when you spend some time driving heavily laden non turbo diesel vans you get plenty of practice.