Best Fuel economy: cruise control ON or OFF?

[ItalianTuneUp]

I'm interested in people's experiences with driving with cruise control.

Did turning it on give better fuel economy or not ?

Also, what effect do hills or flat terrain have on fuel economy with cruise on?

 

[Deleted member 65149]

I've never done an accurate comparison, but on long and relatively flat roads I get the distinct feeling that economy is better with cruise on. Depending on how much you prepare for what's ahead, I would think it's better with cruise off on hilly runs because you can gently accelerate in preparation for a uphill and ease right off the throttle downhill where the cruise would apply the brakes to maintain speed.

 

[tombo5609]

I'm interested in people's experiences with driving with cruise control.

Did turning it on give better fuel economy or not ?

Also, what effect do hills or flat terrain have on fuel economy with cruise on?[/QUOTE

In my experience driving 1000s of miles in US it is more economical but obviously not as relaxing with cruise control off.
With it on your car will try and maintain the given speed whatever the terrain, even downhill and will try and reduce your speed to the set figure.
If you have it off you will just come off the gas.
On a flat road, if such a thing exist it may be marginally better but with a head wind possibly worse.
I detect an interesting debate developing, no fisticuffs please.

 

[ItalianTuneUp]

That sounds like it makes sense.

Does cruise control apply the brakes on downhills or simply starve the fuel supply?

 

[ItalianTuneUp]

My reply was too knighterrant...didn't refresh/update.

 

[artyman]

Mine seems the throttle in the first instance, but if the hill is steep enough it does apply the brakes, thus losing any potential momentum gain. I usually tap mine off then flick it back on again when the speed uphill drops to the target figure.

 

[BTB 500]

Does cruise control apply the brakes on downhills or simply starve the fuel supply?

I think it depends on the model. There have been various discussions about it here in the past - run a few searches if you're interested. It would need a reasonably steep hill for brakes to be required (unusual on a motorway).

As already mentioned the difference between economy with cruise on/off is based on the fact that people don't actually maintain a set speed without CC, no matter what they think. They go slower on bends (even gentle ones on motorways) and up hills. I use CC all the time, for convenience rather than economy. It also helps stop the speed creeping up!

 

[ItalianTuneUp]

@tombo: that's interesting. Your info seems to concur with some other people who say cruise off is more fuel efficient.

Cruise on definitely helps with avoiding foot/leg ache, so I wonder if a combo mixture of cruise on & off would be the best compromise: cruise on when flattish terrain, and flick it off when hills approach? Saves leg ache for the most part, and gives good economy for hills. Also cruise off when dense traffic.

 

[ItalianTuneUp]

I think it depends on the model. There have been various discussions about it here in the past - run a few searches if you're interested. It would need a reasonably steep hill for brakes to be required (unusual on a motorway).

As already mentioned the difference between economy with cruise on/off is based on the fact that people don't actually maintain a set speed without CC, no matter what they think. They go slower on bends (even gentle ones on motorways) and up hills. I use CC all the time, for convenience rather than economy. It also helps stop the speed creeping up!

Interesting. Perhaps cruise off is more efficient, if it is, due to this slowing down effect? Slower speeds are usually more efficient.

I agree with you, I tend to have cruise on on long journeys to save leg ache aggro. And there's another reason to keep it on, apart from mere comfort/convenience: speed cameras. How many people here who usually have cruise off 'because it's more efficient', have received speeding tickets? That would be a fascinating poll in itself: number of tickets received for cruisers on versus off.

If more tickets received due to cruise off, then the savings made due to fuel efficiency may well be a false economy?

 

[baxlin]

I think it depends on the model. There have been various discussions about it here in the past - run a few searches if you're interested. It would need a reasonably steep hill for brakes to be required (unusual on a motorway).

As already mentioned the difference between economy with cruise on/off is based on the fact that people don't actually maintain a set speed without CC, no matter what they think. They go slower on bends (even gentle ones on motorways) and up hills. I use CC all the time, for convenience rather than economy. It also helps stop the speed creeping up!

I agree, convenience not economy - but very important in m-way roadworks speed limits.

My C220 is the first car I've had (first MB but that's irrelevant) that has any cruise engine braking, and I find it's quite disconcerting if set at say 65, but I accelerate to overtake, it brakes quite sharply when I ease off the throttle.

As CC keeps a steady speed, I often find I'm playing 'overtake tennis' on motorway, with cars obviously not using CC, and who tend to slow down on inclines.

 

[artyman]

I agree if you come across a limited section on the motorway with average speed cameras it's easy to just let cruise deal with it.

 

[ItalianTuneUp]

I agree, convenience not economy - but very important in m-way roadworks speed limits.

As CC keeps a steady speed, I often find I'm playing 'overtake tennis' on motorway, with cars obviously not using CC, and who tend to slow down on inclines.

Yes CC very important for speed cameras.

I know what you mean about 'overtake tennis'

Also, knowing physics and human nature (hills, bends, slip roads joining), anticipation helps greatly in being proactive for a smooth, safe, economical gliding experience.

 

[ItalianTuneUp]

Anticipation & safety were the main things I took away from the advanced driving course I took many moons ago. A very worthwhile course to take.

 

[Teflonso]

If you are a complete mpg compulsive, then cruise control isn't the best way to go.

Typically, for example on a motorway, the mpg freaks will allow speed to build going downhill and decay when climbing at the other side. In maintaining constant speed cruise control throws away the "gain" of downhill but opens the taps on the climb so consumes more juice. There's lots of other similar situations.

There's a similar arguement for the claimed mpg figures of automatic transmission versus the equivalent engine with manual gearbox. Even CVTG and double clutch gearboxes with no torque converter are unable to predict what terrain is next. To get the very best out of an auto you need to be flicking paddles and changing up earlier than would otherwise be the case.

At the end of the day, I don't expect that cruise will be dramatically worse (or better) than the "average" driver bumbling along thae motorway and A roads but it's vcertainly more relaxing.

.

 

[ItalianTuneUp]

If you are a complete mpg compulsive, then cruise control isn't the best way to go.

Typically, for example on a motorway, the mpg freaks will allow speed to build going downhill and decay when climbing at the other side. In maintaining constant speed cruise control throws away the "gain" of downhill but opens the taps on the climb so consumes more juice. There's lots of other similar situations.

There's a similar arguement for the claimed mpg figures of automatic transmission versus the equivalent engine with manual gearbox. Even CVTG and double clutch gearboxes with no torque converter are unable to predict what terrain is next. To get the very best out of an auto you need to be flicking paddles and changing up earlier than would otherwise be the case.

At the end of the day, I don't expect that cruise will be dramatically worse (or better) than the "average" driver bumbling along thae motorway and A roads but it's vcertainly more relaxing.

.

Thanks.

So, it seems cruise off best to achieve max economy. I find CC very relaxing so I'll continue using it for the most part.

But flicking it off for hills saves a bit.

Your point about changing up earlier is interesting though, so would the C or S setting give best economy? I suppose this saves little for the majority of same speed driving on motorways though, as there's little gear changing taking place?

 

[V12]

Hi Simon (guessing it's you from the other thread I just read)
I think you know my stance on cruise control.
I live with it on.
Does it negatively affect my mpg? Possibly.
Is it a sacrifice I'm willing to make for a relaxing drive? Yes.

The difference in the real world for my driving in the s class is 2 or 3 mpg.

 

[BTB 500]

When we drive to/from Germany the CC is a big help with the varying national speed limits on the motorways. Set it as you enter each country (where there are typically signs giving the limits on different road types) then you just have to 'resume' each time conditions are appropriate.

 

[ItalianTuneUp]

Well, 2 or 3 mpg isn't anything much to bother about. And CC is so relaxing, I know

 

[theogeor]

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

 

[Dieselman]

I find economy better with Cruise Control set on, as I normally set it to an indicated 75 and let it run. Without CC set speeds can vary and tend to creep up somewhat...