Best Fuel economy: cruise control ON or OFF?

[E55BOF]

Interesting...... How much better? 5%? 10%? A fraction? And on what car or cars?

 

[ItalianTuneUp]

I do not have current experience on a Merc but I have a CC on my 911/997 (manual) and my observations are
1. Super important where you have average speed cameras... Love it in those situations
2. Only useful in UK when travelling very early morning or in the middle of the night when roads are empty and traffic is light. Most of the other times you can not use it effectively
3. During long trip in Europe the CC was great. Doing a 3-4h without stopping in France with CC on is a joy. Traffic in the motorways in France (anywhere not around Paris) is perfect for CC. And it does affect fuel economy about 10% better
4. Fuel economy is better with CC because the control is with the CC and not with you. I can manage similar MPG without it but need to concentrate hard to do so. With CC I just set the speed and look ahead do not have to look at the speedo etc.
5. With CC on is better to adjust the speed up and down with the stick as the increments are small and that maintains good fuel consumption

Theo

Ahhh the 997...lovely car
Gen 1 or 2?

Like yourself, I find CC helps reduce mental strain on long journeys and like dieselman says, it helps avoid running into speeding issues.

I find that CC is still possible during daytime motorway drives unless it's heavily congested. Just flick it on and off as required.

What mpg do you get with the 997 on a motorway run?

 

[theogeor]

Ahhh the 997...lovely car Gen 1 or 2? Like yourself, I find CC helps reduce mental strain on long journeys and like dieselman says, it helps avoid running into speeding issues. I find that CC is still possible during daytime motorway drives unless it's heavily congested. Just flick it on and off as required. What mpg do you get with the 997 on a motorway run?

Is a mid/late Gen1 . Had it for 5 years now and love it... Great all around car...

The maximum I got on long motorway driving with CC been used most of the time in Europe was 29MPG. In UK for clean runs I get 25-26MPG and when traffic is bad and weather is very cold I get as low as 15MPG. When in heavy traffic I get 10-12. Average over long term is around 19-20MPG
On a trip I did last June all the way to Stuttgart for a visit with other fellow 911 drivers to the Porsche Museum and factory I got 22MPG average but with speeds reaching 150-175MPH and average speed including stops around 87MPH. One of the best drivers I have done for years and would highly recommend it to any AMG owner

Saying that the fuel consumption is the least of my concerns Never bought the car for fuel efficiency....


Regards

Theo

 

[ItalianTuneUp]

Sounds like a fun run to Stuttgart. Must have been quite a sight, a procession of 997s whizzing down the autobahns.

 

[theogeor]

Sounds like a fun run to Stuttgart. Must have been quite a sight, a procession of 997s whizzing down the autobahns.

Yes it was fun. It was not just 997. We were a mixture of 993/996/997s all different to be honest (Turbo, GTS, C2 C4S etc) but on the autobahns we were a fast train. We were lucky that traffic allowed us to drive at high speeds. We also drove the famous B500 in Baden-Baden area which is another great reason to visit the area
Anybody who loves driving and has a fast car that wants to enjoy it without been illegal then I would highly recommend a 4-5 day trip in Stuttgart. The Porsche and Mercedes museums should be visited and if possible you should arrange a visit to the Porsche factory... It was a great experience.. And then allow 1/2 a day for a drive int he Baden-Baden area

We are planning to repeat the trip with the group I went to next year


Theo

ps: We did not use CC at all at that trip by the way....

 

[ItalianTuneUp]

Nice trip! Despite working in Stuttgart and surrounding area many times, I never managed to visit the Porsche factory and museum.

Using CC on a 911 seems a little crazy, but on a long journey, not in Germany, I expect I would use it from time to time.

 

[BTB 500]

My in-laws live near Leonberg (not far from Stuttgart) and there's some sort of Porsche facility nearby. Took a picture a few years ago (below) ... not sure whether it's the factory or not but it certainly sounds like they have a test track there!

 

[flango]

I can answer the question based on my experience of Volvo V70 T5's and over 250,000 miles of motoring. For 5 years I used to do a 600 mile weekly commute to Scotland on numerous occasions I tried it with CC on and then off over a lot of miles and 4 cars on this particular run without fail driving with CC off would consistently return 3 - 4 mpg better than with cruise on. I never use CC and its one of the things that annoys me I would never spec it on a car, yet you can't delete it or swap it for something more useful.

Top tip for use of CC never use it when you are speeding its too easy to get caught

 

[ItalianTuneUp]

Your results seem to confirm what V12 also experienced: 3 to 4 mpg less with cruise on.

 

[BTB 500]

For 5 years I used to do a 600 mile weekly commute to Scotland on numerous occasions I tried it with CC on and then off over a lot of miles and 4 cars on this particular run without fail driving with CC off would consistently return 3 - 4 mpg better than with cruise on.

Would be really interesting to know if that was simply because you had a slightly lower average speed (over the whole trip) when driving with CC off.

 

[ItalianTuneUp]

I also suspect this may be the reason. Additionally, 'the gain' from downhills with no CC.

 

[geraldrobins]

It seems that many members say CC isnt as economical as varying your speed. Such as lifting off a bit for hills and increasing speed on downhils or straights to assist going up hill.
But if you wish to drive at a constant speed say 70 as opposed to 65 -75 then surely there is no difference with CC on or not.

 

[HumberMart]

It seems that many members say CC isnt as economical as varying your speed. Such as lifting off a bit for hills and increasing speed on downhils or straights to assist going up hill. But if you wish to drive at a constant speed say 70 as opposed to 65 -75 then surely there is no difference with CC on or not.

Most people miss the whole point here.

In trying to sustain a fixed speed on CC, the car is constantly applying short bursts of fuel. Unlike when you sit with your foot in a static position on the pedal.

The CC will try and overcome effects from wind, drag, slip stream, different road surfaces, standing water, plus of course inclines.

So even in Lincolnshire and East Anglia CC uses more fuel.

In hilly areas the cost of cruise can be significant.

 

[geraldrobins]

If you sit with your foot in a constant position on the pedal then your speed will vary with inclines wind etc as you say. CC is a convenience of course but I have yet to hear a reason why CC is using more fuel when driving at a constant speed. I do agree it can waste fuel if you allow it to brake when going downhill, but only marginal unless its a long steep slope. How far do you go though in driving economically? Engage neutral downhill?
Everyone has an opinion but I can continue to use CC and enjoy a relaxing drive.

 

[rothbury]

If you sit with your foot in a constant position on the pedal then your speed will vary with inclines wind etc as you say. CC is a convenience of course but I have yet to hear a reason why CC is using more fuel when driving at a constant speed. I do agree it can waste fuel if you allow it to brake when going downhill, but only marginal unless its a long steep slope. How far do you go though in driving economically? Engage neutral downhill?
Everyone has an opinion but I can continue to use CC and enjoy a relaxing drive.

The answer is in the previous post to your last one! Also you can use the speed limiter to prevent fines. I agree in the US or continental Europe CC can help save an comfortable leg on occasions but in this country the traffic on the motorways makes it ill advised most of the time from the safety point of view. I never feel quite as much in control with it on .

 

[Deleted member 65149]

I'm sure that with a lot of care for every second of the journey, fuel consumption will be less with CC off. But it's flippin hard work thinking about easing off the throttle marginally once you've attained your desired speed, and then keeping that right foot balance perfectly throughout the journey. CC does that for you. My previous car (W208 CLK 230K) would return around 40mpg at an average speed of around 70mph on long runs (>200 miles) on a mix of A & B roads and motorways using CC whenever possible. My C350 Sport returns around 37mpg for similar trips, again with CC on most of the time. Remembering that we're talking here about petrol cars with large engines, I think those figures are indicative of how effective CC is at providing good consumption.

 

[Deleted member 37751]

Cruise control has always affected my mpg negatively, I'd say an average of 10% loss.

As an example I did a 200 mile round trip in my Q7 4.2 V8 TDI and on the way there I used my C/C as much as possible with the speed set at 72mph and achieved 28.7mpg. On the 100 mile journey back I didn't use the C/C at all and drove as I normally do (keeping up with traffic up to 80) and achieved 33.1mpg.

 

[HumberMart]

I'm sure that with a lot of care for every second of the journey, fuel consumption will be less with CC off. But it's flippin hard work thinking about easing off the throttle marginally once you've attained your desired speed, and then keeping that right foot balance perfectly throughout the journey. CC does that for you. My previous car (W208 CLK 230K) would return around 40mpg at an average speed of around 70mph on long runs (>200 miles) on a mix of A & B roads and motorways using CC whenever possible. My C350 Sport returns around 37mpg for similar trips, again with CC on most of the time. Remembering that we're talking here about petrol cars with large engines, I think those figures are indicative of how effective CC is at providing good consumption.

Not hard for millions of drivers without CC.

It's just intuitive. You become oblivious to worrying about the slower up hills and quicker descents. In fact if you use CC on a road with lots of concurrent rise and falls it tends to feel like the car is accelerating on the up hills, even though it's not. Most drivers without CC keep their foot pretty still and avoid the consistent squirts of fuel that CC uses to maintain a fixed speed.

Like AC, just accept it uses more fuel but it's worth it for the comfort.

 

[Dryce]

Most drivers without CC keep their foot pretty still and avoid the consistent squirts of fuel that CC uses to maintain a fixed speed.

My observation is that many drivers not using CC vary their speed a lot more significantly than they realise. And they're not consistent. Some speed up on inclines others slow down. Some seem subconsciously want to speed up when being overtaken.

And for those using CC. It's not unusual to see cars that had been keeping pace shooting past towards the end of a DC or motorway and brake hard - or catch up a vehicle in front and brake. I'm pretty sure that a fair number of people who do this are basically not disengaging their CC until they have to brake.

So on that basis I think the effects of CC on or CC off no fuel consumption vary. Switch your brain off when using CC and it probably costs. Just like switching your brain off with CC off. And my theory is people switch their brains off inconsistently.

I've always reckoned I got slightly better consumption using CC. But I hardly ever use brakes to disengage it. And if I'm going up and over a hill with a steeper descent I'll disengage it before cresting to use the momentum. And then re-engage.

 

[ItalianTuneUp]

@dryce
I find myself agreeing with pretty much all of what you say here.

At the end of the day, it seems it's possible to save a few mpg by turning CC off, but the reasons for this saving are not obvious, but may be due to driving slightly more slowly, and taking the foot off the gas on downhills to capitalise on gravity.

Due to the substantial benefits in reducing tiredness on long journeys, I'll stick with using CC. However, if I remember and can be bothered, I might capitalise on hills by knocking CC off before crest of hill and getting the downhill gravity gain.

By keeping a good distance behind the car in front, I rarely find myself using the brake, I look for trouble ahead and then flick the CC off to slow naturally without the brake, reserving the brake for times when it is needed. Seems to work for me, and means the brakes should last longer.