Cruise control efficiency comparison.

[Konrad C]

Yesterday I was driving around the M25, and was using the cruise control. I decided to look at the instant readout (guessometer). At roughly 70 mph, the display was showing  half way. With the gauge displaying upto 90 mpg, with two marks at 30 and 60 mpg, the car was doing 45 mpg. Occasionally it went to 60 mpg if on a downhill section or speed correction. I then disengaged the cruise control and see if I could match it. No I could not! It was either down to 30 mpg or when lifting off upto 90 mpg. Basically the gauge was all over the place. It was though the throttle was all or nothing. My driving style on the motorway is lift to cruise, so I do get good fuel economy. I did post on a similar subject last year - 

Does this means the cruise control is more efficient on the motorway? 

[Mr Wolf]

11 hours ago, Konrad C said:

Yesterday I was driving around the M25, and was using the cruise control. I decided to look at the instant readout (guessometer). At roughly 70 mph, the display was showing  half way. With the gauge displaying upto 90 mpg, with two marks at 30 and 60 mpg, the car was doing 45 mpg. Occasionally it went to 60 mpg if on a downhill section or speed correction. I then disengaged the cruise control and see if I could match it. No I could not! It was either down to 30 mpg or when lifting off upto 90 mpg. Basically the gauge was all over the place. It was though the throttle was all or nothing. My driving style on the motorway is lift to cruise, so I do get good fuel economy. I did post on a similar subject last year - 

Does this means the cruise control is more efficient on the motorway? 

The disadvantage of using cruise control is that going up any inclines it will ensure that the set speed is maintained thereby using more fuel than if speed was manually allowed to reduce. I suppose it would also be a disadvantage to use CC on downhill stretches as it would limit the speed and not allow momentum to increase the distance travelled. So on the face of it it seems that CC would be less efficient fuel wise. Another factor would be how journey times might be affected. Who knows whether manual reductions in uphill speeds would be compensated by increased momentum/speeds going downhill and whether it would be favourable compared to CC. To be honest I'm not bothered.

I use CC because I find it more relaxing and comfortable for longer journeys and am not concerned that arguably it might be a little less fuel efficient (or not, if that's the case!).

 

[Willss]

Haven't got precise figures but I've done a similar test over about a 40mile stretch of my local dual carriageway.  One time used CC at 65mph, next time without CC.  Did this over a few days with and without a number of times.  By my reckoning CC on gave about  3mpg difference (lower) than without.  Obviously weather, road conditions, driving style, traffic, number of hills etc will affect mpg with/without CC on but it is not as efficient in my opinion with it on - markedly so but not massively (very scientific)!!!

That said I use CC due to comfort etc.