MPG with C/Control on

[hawk20]

This is the definitive answer from someone obviously well qualified in the subject and without wanting to sound like a "trekkie" you cannot change the laws of physics which apply here, hence CC has a negative Impact on Fuel economy. Nuff said.

Wrong. It is nonsense wrapped up as pseudo science. To do a steady 70 mph takes the same fuel whether you adjust the accelerator or the cruise control does it for you.

 

[st4]

Wrong. It is nonsense wrapped up as pseudo science. To do a steady 70 mph takes the same fuel whether you adjust the accelerator or the cruise control does it for you.

Read the post again and think about the feathering of the throttle.

 

[hawk20]

Read the post again and think about the feathering of the throttle.

I have. It's rubbish.

To keep a steady 70 uses the same fuel whether you do it or cruise.

 

[st4]

Going to have to agree to disagree on this one. It comes down to personal preferances and experiece I guess.

 

[rf065]

I have. It's rubbish.

To keep a steady 70 uses the same fuel whether you do it or cruise.

Sorry, you are wrong on this one.
Anyone who still has usable brain is smarter than your cruise control.
I'll have to agree to disagree with you also.

Russ

 

[Mactech]

I have. It's rubbish.

To keep a steady 70 uses the same fuel whether you do it or cruise.

I have proved to myself many times that I can drive more economically at a constant speed than the cruise control. I also understand the physics involved, and so I will have to disagree

 

[Dieselman]

How much of a difference do you find there to be, Mactech.?

 

[wemorgan]

I have proved to myself many times that I can drive more economically at a constant speed than the cruise control. I also understand the physics involved, and so I will have to disagree

If you drive at constant speed and the CC drives at constant speed then the difference should be near zero.

Please explain the physics that shows your human constant speed is more economical that the CC constant speed. Thanks.

 

[Mactech]

How much of a difference do you find there to be, Mactech.?

As has been discussed (at some length!) is dependent on many factors including (but not exclusively) gradients, wind conditions, overall vehicle load and surfaces.
In my experience it varies from 1 to 3mpg over the journey distance with Mercedes cars.
Interestingly the gain is more when using a less refined system (eg Vectra DCTi)
In that car you can really feel the ‘square wave’ coarse throttle on/off.

 

[Diesel Benz]

The opinions at the thread start to be pretty hot, not sure if I dare to comment and if it makes sense but I'm afraid the observed fuel savings from driving with brains is from fooling the brains in the sense that you don't push the pedal as hard as the cruise when there is temporarily higher load (wind or gradients) and you don't gain it back later to reach the same average speed. You would save with cruise versus cruise too if you drive at lower speed with the cruise on.

As we do not have any more levers in the cabin to control fuel mixture, ignition timing, not to mention intake manifold control or valve timing etc. the computer anyway is doing all of this. It is odd that the same computer is so poor when the "speed signal" is coming from the throttle potentiometer compared to the case when it comes from the CC control unit.

I just hope we respect everyone's opinions even if some are absolutely contradictory. Most important that each owner feels happy with his own style of driving.

 

[stevesey]

Wrong. It is nonsense wrapped up as pseudo science. To do a steady 70 mph takes the same fuel whether you adjust the accelerator or the cruise control does it for you.

That would only be true if you and the CC adjusted the throttle in exactly the same and that isn't the case - they are two entirely different feedback loops.

 

[Dieter]

Hi,

Cruise control does exactly what it says on the 'tin'...it allows one to cruise...it doesn't switch of your brain or paralyse your feet and as was mentioned before it takes some skill to maintain c.control in traffic...try it on the M25 in the rush hour

and I don't believe any manufacturer has claimed it does anything else.

If fuel consumption is your over riding driving priority, find out what suits you best and stick to it.....or buy a more fuel efficient car .

I find that I use the least fuel when my car is parked on the drive .

Cheers,

 

[Number_Cruncher]

Are modern cruise control systems analogue, or digital devices?

 

[stevesey]

Are modern cruise control systems analogue, or digital devices?

Digital - but even then I doubt if they are much more than a simple PID feedback loop, not bang-bang type digital control.

 

[JohnnyRob]

Jeremy Clarkson managed to acheive higher mpg than the cruise could on the Audi London-Scotland-London on a single tank of diesel challenge...

I found the cruise to be very beneficial in terms of mpg on my old 2001 e39 523, but so far am not convinced on the MLs cruise.

 

[whitenemesis]

Use it for what it s, a convenience aid... Not an economy option.

 

[Dryce]

Digital - but even then I doubt if they are much more than a simple PID feedback loop, not bang-bang type digital control.

The more modern ones understand the concept of braking if going downhill.

The difference in refinement between a R170 (mid/late nineties) and W211 (early/mid noughties) is quite noticeable.

 

[Dryce]

Jeremy Clarkson managed to acheive higher mpg than the cruise could on the Audi London-Scotland-London on a single tank of diesel challenge...

He stated that he was not using CC for that reason. Which isn't the same as demonstrating it to be true or false.

 

[rf065]

He stated that he was not using CC for that reason. Which isn't the same as demonstrating it to be true or false.

Do you think Top Gear just decided to drive from London to Scotland & back on a full tank of fuel without researching or analysing how it was likely to turn out?

The fact that they made the decision not to use cruise control would have been made after consultation and/or trial runs to determine the best method of obtaining maximum mpg figures before filming started. Which kind of proves what the more enlightened among us have been saying, CC was never meant to increase your fuel consumption and if it does, it's because you had an uneconomical driving style to start with.

Russ

 

[JohnnyRob]

He stated that he was not using CC for that reason. Which isn't the same as demonstrating it to be true or false.

But it does point towards it being true; well at least in the case of the big Audi Diesel.