Kia Forum banner

1 - 20 of 36 Posts

·
Registered
Kia pro ceed 3 2013
Joined
·
271 Posts
Discussion Starter #1
Has anyone tested cruise control against careful accelerator control over a fixed distance with regard to fuel consumption? I have tried it myself using the average mileage consumption figures and much to my surprise, find the difference so small it’s hard to establish any figures. Even on our local empty roads I had to drop out of cruise control at times, but not enough to make a big difference. I know the forum has its fuel consumption experts who may have done a more careful test than mine and wonder if they can inform me how big the difference actually is?
 

·
Registered
Kia Ceed
Joined
·
281 Posts
The official line is any driver can get better mpg not using cruise control, reason given is the driver can anticipate gradients, traffic etc and lift off earlier than cruise would.

However, in the real world that most of us inhabit I have found that it makes no difference, yes I can anticipate the road ahead better but I cannot keep up the constant speed that cruise control can and any variation of speed wastes fuel either when I overspeed or have to accelerate back to the speed limit..

Even if it did use extra fuel it would be worth it, after a 400+ mile holiday run mostly on motorways I still feel fresh which is down to having one thing less to concentrate on i.e. keeping to a constant speed.
 

·
Registered
Joined
·
943 Posts
I agree with SWCeed, In the real world there is little difference in fuel consumption. I would use CC even if there was a consumption penalty, and would not buy a car that did not have CC fitted. My car averages 50MPG at a steady 70MPH (satnav speed, 75 on the spedometer). I live in a light traffic area with motorways.
 

·
Registered
Ceed 1.6crdi ('07)
Joined
·
648 Posts
Has anyone tested cruise control against careful accelerator control over a fixed distance with regard to fuel consumption?
John, you obviously know by now that this sort of question has a Pavlovian response on me. No, I don't have cruise control...

I know the forum has its fuel consumption experts
...or bluffers?
who may have done a more careful test than mine and wonder if they can inform me how big the difference actually is?
On any such comparison, the first place to start is to perform a sanity check to see what might be achievable.

Theoretically, fuel consumed at speed is primarily dependant on aerodynamics so I will work on the known principle that drag is a function of the square of the speed.

So let's say, two cars do a 120 mile journey at an average speed of 60mph, and the cruise control car uses 2 gallons of fuel.

If the driver in the other car does 66mph for 60 miles and 55mph for the other 60 miles, the fuel used is (66/60)^2 + (55/60)^2 or 1.121+0.84 = 2.05 gallons (+2.5%). (Although the driver would normally oscillate around 60mph due to inclines and foot fatigue, for simplicity assume two speeds.)

So I suggest that any difference inherent in the car itself is just too far below experimental accuracy to identify. A person doing the experiment over two journeys would not be able to separate out the effects of other traffic, wind & weather and fuel variation. And is their driving genuinely consistent, other than the ability to maintain steady speed?
 

·
Registered
Cerato
Joined
·
692 Posts
I've thought about this a bit, but never tested it. As Ace Demon has calculated, the differences will be small.

I do note that some CCs are better than others. There is one section of highway that I regularly travel which is hilly with a speed limit posted at 90km/h. I wouldn't normally use CC on that road, but in one test, my car varied between 85 and 100 km/h because the CC seemed to be rather "lazy", and I'm sure that the fuel consumption was adversely affected. A previous car with manual transmission and more power would have kept a more constant speed, because the CC was more "aggressive". Somewhere in between (e.g. careful driver with no CC would be better for fuel consumption on this section).

On most flat and straight highways, I wouldn't be without CC.
 

·
Registered
Kia Ceed, MGTF, Various Jeeps new and old, FIAT 500
Joined
·
268 Posts
I never considered the role of CC as being to save fuel. However, I find that practically CC does save me fuel as without CC on long motorway drives my speed creeps up. So although I intend to do 70mph suddenly find that I am over 80mph. With CC this does not happen. Given I travel about 35,000 miles a year even small differences matter.

Sent from my ZTE-BLADE using AutoGuide App
 

·
Registered
Kia pro ceed 3 2013
Joined
·
271 Posts
Discussion Starter #7
Thanks Gents for the replies. It seems CC is more efficient than I had imagined. It’s a bit of a culture type shock as I expected, with anticipation, to beat the CC hands down. To read my peers quoting my efforts would not make much difference has confirmed my dodgy road test. I will use it more often now. Trundling along with my caravan it is a Godsend I would hate to be without. Sorry RT:D
 

·
Registered
Many, KIa Ceed 1.6 crdi auto at the moment
Joined
·
103 Posts
I have tested CC on four cars and could see no differance in MPG even I have been told by one Agent that it does.
I use CC about 90% of the time now even if I am going through a town I lock it on at 30 MPH
John, do you know that if you turn it off CC by the switch or touching the foot brake, it will go back to the original speed if you push the CC switch up
 

·
Registered
Kia Ceed
Joined
·
281 Posts
even if I am going through a town I lock it on at 30 MPH
That is a very dangerous practice, CC should not be used in town. Suggest you stop it immediately.

Was not even aware CC worked at such a speed and not about to try it.
 

·
Registered
Many, KIa Ceed 1.6 crdi auto at the moment
Joined
·
103 Posts
Thanks SWCeed, I have driven millions of miles in all types of vehicles ( hgv's & buses ) with no accidents and take a driving test every four years, so I think I am capable. Its like driving at 70 MPH you get used to it and I have driven over twice that speed up the M1
 

·
Registered
Kia Ceed, MGTF, Various Jeeps new and old, FIAT 500
Joined
·
268 Posts
That is a very dangerous practice, CC should not be used in town. Suggest you stop it immediately.

Was not even aware CC worked at such a speed and not about to try it.
It works at about 28 and above.

I struggle to see why it is dangerous, if it was dangerous at 30 it would be dangerous at 50. If you are suggesting that by using CC you are not in control of the vehicle, I would disagree. It would be the same no matter what the speed is. I also use my CC to stop me accidentally exceeding the speed limit. I would not use it say in a town centre but in the suburban areas where speed limits can go from 50 to 30 and back to 50 then its a godsend.

Interestingly here in France it is not sold as Cruise Control at all, but as "limiteur de vitesse" literally meaning speed limiter and the car mags etc here actively encourage its use as speed limiting system to avoid fines in towns where most speed traps are, rather than as a motorway crusie control. The "limiteur de vitesse" sold in France is not a speed limiter or alarm such as fitted in Saab's but the same system sold as CC in the UK.
 

·
Registered
Kia Ceed
Joined
·
281 Posts
At 70 mph on the motorway with reasonable traffic conditions and good separation between cars CC is fine and safe. In town where you are closer to other traffic and people are likely to jump off the pavement its not.

If you cannot drive through town at 30mph without CC I say you should not be driving.

Dads car has a speed limiter and its bloody dangerous. Would stop you accelerating out of trouble should the need apply, its now disconnected. CC does not stop you accelerating should the need be there, you just press the throttle.
 

·
Registered
Kia Ceed
Joined
·
281 Posts
Thanks SWCeed, I have driven millions of miles in all types of vehicles ( hgv's & buses ) with no accidents and take a driving test every four years, so I think I am capable. Its like driving at 70 MPH you get used to it and I have driven over twice that speed up the M1
No matter how many miles you have driven bad practice is bad practice.

Admitting you have driven at 140mph on the M1 should mean a lifetime ban IMHO.
 

·
Registered
Joined
·
943 Posts
Once again I agree with SWCeed, I use CC at any speed I want to maintain if the circumstances make it safe. It is not when you use it, it is how you use it.
 

·
Registered
Kia Ceed, MGTF, Various Jeeps new and old, FIAT 500
Joined
·
268 Posts
Once again I agree with SWCeed, I use CC at any speed I want to maintain if the circumstances make it safe. It is not when you use, it it is how you use it.
That's the point I think deeps its not when but how you use it. I happily use it in town but what I mean is on a dual carriageway or similar in a city where there is 30 or 40mph speed limit not say on a congested road in a city centre where to be honest speed is never an issue because you only manage about 10mph :(
 

·
Registered
Kia Ceed
Joined
·
281 Posts
That's the point I think deeps its not when but how you use it. I happily use it in town but what I mean is on a dual carriageway or similar in a city where there is 30 or 40mph speed limit not say on a congested road in a city centre where to be honest speed is never an issue because you only manage about 10mph :(
That is very different to the way your first post read and perfectly acceptable IMHO.

I have used CC many times on pieces of motorway and dual carriageway when there have been 40mph average speed cameras present during roadworks.

Need to check if ours works as low as 30mph the next time I am driving on a suitable piece of road, sure I had read 37mph in the manual but that in the car and the Mrs is out in it.
 

·
Registered
Many, KIa Ceed 1.6 crdi auto at the moment
Joined
·
103 Posts
Speeds and CC's

SWCeed, I live in the country and some of the roads are straight and they are 30 MPH and that is when the CC is used and it operates any speed above25 MPH.
Why should I be band for doing twice the now national speed limit for it was when there was no speed limit on the M1.
I have also driven a 40 ton vehicle at 100MPH around a test track, is there anything wrong with that
 

·
Registered
Cerato
Joined
·
692 Posts
CCs that I've used don't work below 40 km/k and cancel-out preset once you stop. Can't agree that using CC around town is a "bad practice" (although I must say that I don't do it); you always have the ability to over-ride the CC.

CC used to be only available on automatics. I did have a manual with CC, but it was only useful on long sections where there wasn't much gear-changing, since operating the clutch cancels out CC.
 
1 - 20 of 36 Posts
Top