Do you find that you get better fuel economy with or without cruise control?

I have a VRS and from a bit of reading I've heard differing opinions as to whether it is more or less efficient, especially if the car has a turbo.

Does anyone have any real experience of this?

The fuel economy is significantly worse on cruise control for the simple reason that it never fully closes the throttle. When you close the throttle (lift off completely) and keep your left foot off the clutch, the engine is turned over by the movement of the wheels on the road and the ECU totally cuts off all fuel to the engine.

The cruise control VERY rarely does that, so the fuel economy is much worse.

When would that situation happen?

I use my cruise on the motorway and on most dual carriageways when it's free enough and any occasion i can think of where i'd be off the throttle i've generally braked anyway knocking the cruise off :S

I find cruise actually imrpoves my economy as it tailors throttle to keep constant speed rather than a steady foot which keeps contant throttle whatever the situation.

I also find the benefits of a constant cruising speed on the motorway adds hilarity when you overtake or get overtaken by the same car with fluctuating speed for the 5th time

Edited 17 February, 201115 yr by PastyBoy

I frequently drive Leeds to Nottingham using A1, M18, M1.

Driving down there is generally heavy traffic so I don't get to use cruise. I drive back late at night at similar speed but can use cruise most of the way.

Fuel consumption on the computer is always 1-3mpg better coming back but that may be down to less slowdown/acceleration cycles in the lighter traffic.

The big advantage with cruise is that your speed doesn't gradually creep up over long distances so you stay at a more economical speed.

Cruise control does totally shut off the fuel going downhill if it is steep enough - just look at the instantaneous fuel consumption to see it reach "--- mpg".

The fuel economy is significantly worse on cruise control for the simple reason that it never fully closes the throttle. When you close the throttle (lift off completely) and keep your left foot off the clutch, the engine is turned over by the movement of the wheels on the road and the ECU totally cuts off all fuel to the engine.

The cruise control VERY rarely does that, so the fuel economy is much worse.

I'm open to be proven wrong but I can't see why that would be the case? If I go down a hill with CC on there seems to be just as much engine braking as when CC is off.

I had always presumed (this isn't based on any concrete evidence, just educated guess work) that on long flat roads, cruise control is more economical because it can hold the throttle steadier than you can with your foot, and therefore avoid unnecessary acceleration.

I would think where it's less economical, though, is when the road is a bit hilly. The cruise control is often dim-witted and slow to react to a change in the gradient of the road, meaning it then has to use extra fuel to over compensate and get back up to speed. When you're in control, you can see the hill and predict the necessary increase in throttle to maintain speed. I would think in this case, driving normally would be more economical.

Do you find that you get better fuel economy with or without cruise control?

I have a VRS and from a bit of reading I've heard differing opinions as to whether it is more or less efficient, especially if the car has a turbo.

Does anyone have any real experience of this?

IMO it depends on your driving style as to whether it's better or not. If you are consistent and light on the loud pedal the results are similar to cruise. I find that on or off I average about the same, but I like using cruise control to keep me away from speeding fines!

The fuel economy is significantly worse on cruise control for the simple reason that it never fully closes the throttle. When you close the throttle (lift off completely) and keep your left foot off the clutch, the engine is turned over by the movement of the wheels on the road and the ECU totally cuts off all fuel to the engine.

The cruise control VERY rarely does that, so the fuel economy is much worse.

I, like others, don't accept this response.

I suspect there's very little difference in reality between either mode of driving...

Personally, I doubt if the ECU cuts off all fuel to the engine when you lift off completely as the engine would cut out, like trying to bump start a car that won't fire.

I find cruise control best on clear dual carriageway and motorway only. As soon is gets busy you have to keep adjusting your speed and cruise is then a PITA. Not great for the roads in the UK unless you drive alot early in morning or late at night IMO.

Cheers

Simon

The fuel economy is significantly worse on cruise control for the simple reason that it never fully closes the throttle. When you close the throttle (lift off completely) and keep your left foot off the clutch, the engine is turned over by the movement of the wheels on the road and the ECU totally cuts off all fuel to the engine.

The cruise control VERY rarely does that, so the fuel economy is much worse.

This isnt the first time i`v read this. People have tested to see what MPG they can get with and without cruise control, and it is possible to get better by doing it yourself.

Matt

Interesting responses and thanks for commenting. I'm having it fitted by BigStu on Saturday so will see for myself soon enough and will test it properly on a road trip to the south of France in summer!

mpg is 2-3 mpg worse as the car cant change itself down up big hills so uses a load of fuel to maintain speed...

far better on long drives tho

I frequently drive Leeds to Nottingham using A1, M18, M1.

Driving down there is generally heavy traffic so I don't get to use cruise. I drive back late at night at similar speed but can use cruise most of the way.

Fuel consumption on the computer is always 1-3mpg better coming back but that may be down to less slowdown/acceleration cycles in the lighter traffic.

The big advantage with cruise is that your speed doesn't gradually creep up over long distances so you stay at a more economical speed.

Cruise control does totally shut off the fuel going downhill if it is steep enough - just look at the instantaneous fuel consumption to see it reach "--- mpg".

next time you do that trip mate you'll also notice that from nottingham to leeds for the vast majority of the time it appears your going uphill dont you think?? i go from leicestershire to sheffield quite regularly and i always average a better MPG coming home because i feel its all or mostly down hill on the M1

Generally cruise control is a bit agricultural and it's certainly no match for a human brain.. If you really can't be bothered to concentrate on driving economically then cruise will see better results as it keeps things consistent. It will however, never match someone with a bit of common sense trying to drive with a light foot.

+1 for preventing your speed creeping up.

The incidence of "big hills" on a journey is few and far between. On a long journey I doubt if there's more than 1-2% difference EITHER way. It's just that cruise is so much more relaxing...

It's also impossible to check since conditions will vary day to day.

Edited 18 February, 201115 yr by DRJ

I find cruise adds a discipline to my driving I normally lack. i.e. with my foot on the accelerator, I tend to drive faster and more aggressively. Also, I feel more analytical and less stressed when driving on cruise.

I'd guess that I drive tend to drive 10 MPH faster, OFF cruise. I live in the SE, so that "tend" often gets interrupted by something. So as well as driving slower, there's less slowdown, accelerate cycles when I'm on cruise, and I'm going slower anyways, so I have more time to adjust speed to suit hazards (less braking and smoother acceleration).

Best MPGs I've had have been mid-summer with air temps around 25 degrees, tootling along a busy M25 at around 60mph. I think air temperature plus the summer/winter diesel thing will have more effect than cruise does. I've seen short term averages of 62.1 mpg in summer, never over 55 in winter.

J.