MPG with C/Control on

[st4]

You indicate and change lane.

You might need to speed up to do that safely

 

[fyonn]

You might need to speed up to do that safely

cruise control does not prevent you from doing this

 

[hawk20]

off the top of my head yes

The car infront of you is doing 60 MPH its 500 yds away but, you're gaining on him quite rapidly, in your mirrors the queue of traffic is gaining on you, you need to accelerate to pull out in front of them or face being boxed in until they pass.

If you are doing 70, they will only pass you if they are exceeding the speed limit. So you should let them past anyway or to stop them you must exceed the limit too. If you've seen them coming well in advance, you can pill out long before they reach you, if you really need to.

But this has nothing to do with cruise and economy!

 

[crockers]

Cruise set at 70mph =

I wonder how those very impressive figures would be if you did the same journey using speedtronic to limit your top speed to 70 mph but let yourself control the accelerator..

 

[rf065]

I think Glojo has summerized it correctly in post 27, worth reading if you have not already done so.

Cruise Control is designed to maintain a constant speed, nothing more, nothing less. If you get more MPG using it, then you have not been driving in a fuel efficient manner to start with.

If you get more MPG because it stops you starting a journey at 70mph but ending it at 80 or 90mph, then using the speed limiter and driving efficiently without cruise control will result in even better mpg.

If you use it for convenience and to make your journey more enjoyable, fine, but don't be fooled into thinking it will save you fuel as it cannot think for itself and does not have a "fuel saving mode" programmed. Flat deserted motorways are great for using cruise control, using it on congested roads can make it downright dangerous and hilly terrain turns it into the greatest fuel wasting driver aid ever put into a vehicle.

I use it rarely in the UK unless the roads are quiet, but find it ideal in certain states of the US where fuel is much cheaper and roads can be a hundred miles long with no hills and very few cars around you.

Russ

 

[Dieter]

Quote: "I drive it, it doesn't drive me"

Hi,

What a load of rot.

As with all things related to driving on today's modern roads you adapt your driving to the conditions.

C.control is just another driving aid as is the accelerator or the brake...both of which you can use in exactly the same fashion whether c.control is on or off.

This thread was about c.control and fuel efficiency and unfortunately most of the comments are either anecdotal or hypothetical.

Mpg can change just as easily depending upon the wind direction, the volume of traffic etc. etc. so unless you are willing to carry out a controlled trial (as mentioned earlier in this thread) then it's each to his own I would suggest.

Cheers,

 

[Dryce]

Cruise Control is designed to maintain a constant speed, nothing more, nothing less. If you get more MPG using it, then you have not been driving in a fuel efficient manner to start with.

Tosh.

 

[Diesel Benz]

I think Glojo has summerized it correctly in post 27, worth reading if you have not already done so.

I agree what glojo says at post #27 but in my opinion the complex traffic scenario that asks for anticipation is not where CC fuel efficiency should be compared to driving without cruise. Theoretically one could drive at the same speed pattern with CC as you would do without it, it just isn't practical.

In my opinion CC fuel efficiency should be compared at scenarios where other traffic does not ask for changes to your speed. When you want to get good fuel efficiency and relaxed driving, I suggest driving with cruise on straight legs where traffic is not an issue and once driver's anticipation is needed, disengage cruise and drive with your brain.

I believe the main debate in this case would be if CC burns more or less fuel on an a hilly road when it keeps constant speed while a driver would typically adapt speed differently for uphill and downhill sections.

This thread was about c.control and fuel efficiency and unfortunately most of the comments are either anecdotal or hypothetical.

Because of this, I thought I'd ask some physical background for different arguments for and against CC.

I assume we do not expect real difference in fuel consumption on a flat road at constant speed, with CC compared to without? Then I'd suggest limiting the calculations to the case of "no other traffic" but a road with uphill and downhill sections (my assumption is that the complex scenarios in practise cannot be driven with cruise anyway).

When doing the maths, we have to assume the same time spent on the trip (I've seen discussions challenging this assumption which is crazy).

Assume a road with 1 mile of uphill driving at a fixed inclination, followed by another mile of downhill at the same inclination (ignoring the sign).

I don't want to put figures and I don't even have all but I would give a few points that should be considered.

1) when you drive slower the uphill section to save fuel, say 80 mph, you have to drive the downhill section at 133.3 mph to make it at the same time as if you were driving 100 mph all the way.

2) most of the force needed to make the car move are linear to the car speed, making the energy spent on both options the same but air drag grows by the square of the speed. Even if you would drive a shorter time at the higher speed, the energy spent is higher on the average.

3) we can assume all modern cars handle the trip at the highest gear, even the uphill section. The engine efficiency then changes for the three different speeds (80 mph, 133 mph and 100 mph). One should find out appropriate efficiency figures for the different speeds and taking into account the change of potential energy up and down. The engine efficiency would increase for the uphill section and on the downhill section the engine would run at worse efficiency (modern engines get the best efficiency close to the maximum load at any speed basically, absolute best would be close to the max torque rpm but isn't relevant here).

What else needs to be taken into account? Who would be willing to post some figures, the result may be a bit surprising (I've actually seen the maths done at another forum).

Or do forum member feel these things are not supposed to be calculated at all? If not, then I ask all the discussions reconsidered for Distronic Plus as opposed to standard CC only.

 

[glojo]

I think we can all learn a lot from my old sergeant.

You can tell a person their breath stinks

You can tell a person they have bad breath

You can tell a person their partner\wife\husband\dog is ugly

But you can never

NEVER tell someone they are a bad driver.

It is a piece of cake to get less mpg when not using cruise control Just don't look ahead, don't plan your drive and do not anticipate potential hazards correctly and most of all, have a heavy right foot.

Job done. Less mpg than when using cruise control.

The skillful bit is getting more mpg. No not skillful, but being more appreciative of your surroundings.

Cruise control has no idea about what it is doing, when the speed drops it will accelerate positively to get back to its correct setting. If it is going too fast it will immediately take corrective action.

Under perfection conditions with no variables, and by that I mean a variation of wind speed or direction, or a road that goes either up, or down, then and only then will cruise control keep the vehicle at its set speed at hopefully a constant engine speed. When this perfect situation arises then I cannot see how a driver can manually do any better.

However in the real World this will never happen. There will always be head winds, cross winds, gradients and other hazards. It is the early anticipation of these that will sort the men from the boys and the ladies from the girls.

We can discuss this until the cows come home but if one driver with a C220CDI travels along the M6 and gets a better fuel return when travelling at approximately the national legal limit with Cruise Control disengaged and six drivers of the same car, under the same conditions get less, then I'm sorry the answer is obvious. It's not the six that are right, because if one person can do it then with better training, we all can.

Apologies for doubting the skills of some of us but just remember my old sergeant

If we disagreed with him, then it was 30 push-up's

 

[w211 custom]

All good points.. but has anyone found a good use for the limit function on c/c, it is just to make sure you don't creep over 30mph n busy camera infested roads...? any other suggested as to what it would be used for...?

*good point crockers...

 

[BTB 500]

I have never personally used the limiter. In SPECS zones etc. the normal cruise control works fine for me.

 

[oorjim2]

I have never used the limit function as yet but will have to give it a try some day once I find out how it works.

Jim.

 

[stevesey]

All good points.. but has anyone found a good use for the limit function on c/c, it is just to make sure you don't creep over 30mph n busy camera infested roads...? any other suggested as to what it would be used for...?

*good point crockers...

Used mine a fair bit recently - been driving around unfamilar parts south of the river (son's living in Camberwell for 2nd year at Uni), so used it from the 60 zone on the M4 to there and back a couple of times. Set the limiter at 5mph over the limit. No problem keeping up with (most of) the traffic and no worries about cameras. Also borrowed my Dad's Tom Tom, so didn't have to read the signs, just watch the other traffic and get in the right lane.

Actually this was my first experience of Sat Nav. My brain handles topology very well, so I'm nomally the one look at a map and I'm off person - but round an unfamilar city, especially south of the river where I find there is very little in the way of landmarks/features (apologies) it was brilliant.

 

[Dieselman]

Set the limiter at 5mph over the limit.

You can go in 1 mph increments. I usually go 1-2 mph over the posted limit.

 

[hawk20]

Cruise Control is designed to maintain a constant speed, nothing more, nothing less. If you get more MPG using it, then you have not been driving in a fuel efficient manner to start with.

If you get more MPG because it stops you starting a journey at 70mph but ending it at 80 or 90mph, then using the speed limiter and driving efficiently without cruise control will result in even better mpg.


Russ

No reason at all why using the limiter should give better mpg. Depends entirely on how fast you accelerate when regaining speed after being forced to slow down.

As I said earlier, best way to use cruise for economy is to flick it off when held up by traffic, resume cruising speed yourself by accelerating gently, and then flick cruise back on. Easy. And no logical reason can then be given for anyone getting better fuel economy if they are seeking to maintain,say, 70mph whenever possible.

Why? Because once back to cruising speed, no driver keeping to a steady speed of, say, 70 mpg can possibly get better economy than cruise at the same speed. Doing a constant 70 uses the same amount of energy whether you control the fuel input yourself or let electronics do it for you.

 

[stevesey]

You can go in 1 mph increments. I usually go 1-2 mph over the posted limit.

Mine only goes up in 5's (unless there's a way of changing that).

 

[Shude]

Mine only goes up in 5's (unless there's a way of changing that).

Pull the lever towards you.

 

[Dieselman]

Pull the stalk towards you, it goes up in 1 mph steps then.

 

[stevesey]

Pull the lever towards you.

Weird - yesterday, for some odd reason, my brain started thinking "when in limit mode does the lever do anything when you push/pull it?" And know I know (haven't had chance to try it becuase SWMBO is away and I'm driver her car to even up the miles and save a bit of petrol).

 

[whitenemesis]

Pull the stalk towards you, it goes up in 1 mph steps then.

Surely that recalls the last speed set?

I thought it was press up (increase / down (decrease) to the pressure point for 1mph and beyond pressure point for 5mph?