I think this may be like the long discussions we have had here about central heating - on twice a day or breakfast until bed-time - there will be differing opinions!
I have just done 390 miles in my 2 litre petrol Focus, of which something over 300 were done on motorways with the cruise set at 70 mph sat nav speed. I averaged 56 mph overall and got 39.8 mpg. That seems to good to me in any event but might I have got more (or less) without using cruise?
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The 320d has cruise, combined with an analogue instant mpg gauge.
If I'm driving at a constant speed, and I turn the cruise on and release the accelerator, the mpg gauge instantly climbs by about 20 mpg. I cannot match the instant readout figures with manual throttle control that I get using cruise control. Why this should be the case, I have no idea, but I can reproduce this phenomenon at will, so it's not just my imagination.
That, and you get a significant fuel saving when you go downhill. It's natural to allow the car to speed up when encountering a downhill stretch on a motorway. With the cruise on, the way it backs the power off to keep the speed constant is much more noticeable than it would be if I were doing it myself, which of course will also boost fuel economy.
Last edited by: DP on Wed 22 May 13 at 12:39
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>> but I can reproduce this phenomenon at
>> will, so it's not just my imagination.
>>
But is the gauge accurate? How do you know it is actually measuring mpg correctly, not just sensing something that is presumed to be a measure of mpg?
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But equally it won't back off the accelerator on hills when slowing down slightly gives improved economy.
I sketched out an idea for a variation on cruise control a couple of years ago that targets fuel economy over speed (within margins). So if you set it at 70mph, it'll increase to a maximum of, say, 75 when doing downhill and drop as low as 60 when going uphill. Basically, it's looking for the target fuel economy at 70mph and varying the speed to keep it as close as possible.
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My car handbook says that my computer read-outs include instantaneous fuel consumption but I can only find "Average" so I can't make the same check that DP mentions.
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In the modern era of cruise control I can only speak for my 1.6HDi 2009 C5 Tourer where the cruise control would increase the fuel consumption by a large amount. It spent far too much time flat out up inclines and regaining speed after being slowed by traffic.
Perhaps the smaller engine working hard in large body effect?
Never tried cruise on the Alfa as it's not the type of car that spends long at the same speed.
Last edited by: Fenlander on Wed 22 May 13 at 13:31
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When we had our SEAT Alhambra tdi it was noticeable that using cruise control sensibly lowered fuel consumption.
It also made long distance driving much more relaxing and even had it increased consumption I would have considered it worthwhile.
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Spot on Roger. Mirrors my experience in the Landcruisers.
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>> But is the gauge accurate? How do you know it is actually measuring mpg correctly,
>> not just sensing something that is presumed to be a measure of mpg?
>>
Good questions, and I don't know. All I can say is that's what the gauge does. It doesn't make any sense at all, so I suspect it's telling lies.
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The cruise control in my car backs off going down motorway hills to maintain the chosen speed. Then it has to come down heavily on the gas to maintain that speed up the next hill, in a manner absolutely characteristic of the classical 'law'-obsessed mimser. If I am driving myself, I allow the speed to increase going downhill to give the jalopy some momentum to climb the next one without the need to press harder on the pedal.
I don't know whether I am more economical than the cruise or not (there certainly isn't much difference), but since the cruise drives in what I consider a perverse and inelegant way except on more or less flat and level roads I seldom use it.
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>>If I am driving myself, I allow the speed to increase going downhill to give the jalopy some momentum to climb the next one without the need to press harder on the pedal
Pre-cisely what I was a'thinking ... if I had gorn and got this ere blimmin fire from the cester of Glou, I would have stuck the cruise control on and then had a kip in the back for 3 hours.
But, I would have over-ridden the c/con so as to progressively increase my speed (hey man!) down hill and sort-of glide up hill on fresh air, hopefully.
Many hills in the West country - so my actions would have paid orf, I'll wager.
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Thing is Doug, I'm probably already going as fast as I am able / is safe, so the opportunity to speed up going downhill probably isn't there.
Equally, I am probably driving at the speed I want to drive at, so slowing down going up hill isn't desirable either.
Consequently, for me, its a competition between me and the machine as to who can do the most efficient job of maintaining a constant speed - and I think its the machine.
If speed/time isn't important I guess speeding up going down and slowing down going up is the most economic.
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Driving by numbers is essentially inelegant and boring, so probably more dangerous. Far too many people are blind to the aesthetic component in driving, the 'flow'.
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Addendum: for optimal fuel economy at any speed, what counts is steady, unchanging throttle opening, not steady speed.
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IIRC I posted a while ago about a Corsa I hired in Minorca that had cruise control. Hardly an ideal place for CC.
I noticed I couldn't achieve the same economy figures by driving manually that the CC could.
I presumed the CC knew the optimum throttle input for speed relative to the engine management characteristics.
I thought I could drive economically, having once achieved 90-odd MPG out of a 1750 Austin Maxi on a fuel economy run.
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>> Addendum: for optimal fuel economy at any speed, what counts is steady, unchanging throttle opening,
>> not steady speed.
Yes, I'm sure that there are many people out there that believe that they are getting good economy by getting into top gear as soon as possible, irrespective of the speed that they are doing at the time. So they are into top gear by 30 mph, then trying to maintain that speed or accelerate with a heavy throttle opening and putting stress on the crank, rather than higher revs and a much lighter throttle opening.
You only have to ride a bike to see how much energy is used in both scenarios.
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...there are many people out there that believe...
We still have a few in here, me old crow. I remember my dad - an engineer, albeit mostly civil, but who never rode a bike - labouring his Maestro round corners in absurdly high gears.
Last edited by: WillDeBeest on Wed 22 May 13 at 19:03
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>> ...there are many people out there that believe...
>>
>> We still have a few in here, me old crow. I remember my dad -
>> an engineer, albeit mostly civil, but who never rode a bike - labouring his Maestro
>> round corners in absurdly high gears.
>>
>>> THIS THREAD IS USELESS WITHOUT NUMBER CRUNCHER <<<
It puts no more stress on the flywheel than flooring it in a lower gear. If the acceleration is the same, or greater, then more power is being transferred through the crank than labouring the engine at low revs.
Less, technically, since the engine generates less torque at lower RPMs. Doesn't feel like it, though
Last edited by: Fursty Ferret on Wed 22 May 13 at 20:44
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>>> THIS THREAD IS USELESS WITHOUT NUMBER CRUNCHER <<<
Why? We may value him for what he can tell us, but it isn't always interesting or valuable and doesn't always make sense. That crap about half g corners the other day for example.
I noticed one or two here were frightfully impressed. Really it was utter garbage.
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>> >>> THIS THREAD IS USELESS WITHOUT NUMBER CRUNCHER
I was enjoying it despite the absence of this character you hold in such great reverence.
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>> It puts no more stress on the flywheel than flooring it in a lower gear.
If I can feel it through my hands and bum, then believe me your DMF and everything else mechanical is is feeling it pretty badly too.
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I'm specifically thinking of the A30 through Bodmin Moor/Dartmoor, Martin, some serious long and steep declines/inclines, I actually drive like that so as not to labour the engine more than a concern for the saving a few teaspoons of petroleum spirit.
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>>I'm specifically thinking of the A30 through Bodmin Moor/Dartmoor, Martin, some serious long and steep declines/inclines<<
So am I now:)
It's surprising just how fast a fully freighted lorry, limited at 56MPH, can go down those hills;)
Pat
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So it was YOU was it!
:-D
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Yup, and I did enjoy it!
Brings back memories of before speed limiters;)
Pat
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Hmm, an Aussie road train sniffing your behind in whichever lane it fancies on a freeway where everyone is doing exactly 100 or 110Km/h is pretty unnerving, limiting trucks to a speed something less than cars and banning them from the third lane seems eminently sensible to me I must admit, but then I'm not a truck driver.
As to cruise controls, I find that on motorways cruise control is actually more economical than DIY provided the road isn't too hilly and the traffic is light. It saves your license in contraflows and speed restricted areas too.
Going off-piste, the braked cruise control on my E91 330d was marvelous and I miss this function on our current Golf which merely changes down the DSG gears to try to stop you exceeding the cruise control speed on down hill sections with limited effect. I wonder why braked cruise control isn't more commonplace, surely it can't cost much more than the non-braked variety given that it's all done through sensors and actuators these days ? IIRC it was only fitted to 6Cyl BMWs with the 4Cyl variants having a conventional setup.
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I'm not sure it makes any real difference.
When the cruise backs off downhill, the vehicle uses less fuel, courtesy of the closed throttle. That saved fuel is then burned maintaining speed on the next upgrade. The effect of gravity on the downhill stretch is still being taken advantage of, but is being used to save fuel rather than increase speed. The only way that there would be any serious advantage were if energy available from gravity on the downhill stretch were being "wasted", e.g. by application of the brakes, which is something that cruise control does not do.
I suspect it's nigh-on a zero-sum game when compared to "faster down, slower up".
If anything, the greater aerodynamic resistance of the higher speed achieved on the downhill stretch with the manual approach may well have a detrimental effect. As aerondynamic drag is non-linear as it increases with speed, the effect of this in increased fuel consumption will be greater than that of the reduction experienced in travelling more slowly uphill.
One for the "Mythbusters" I suspect.
Finally, I have the privilege of driving regularly for long distances on European motorways where, due to the lower traffic volumes, cruise control is more useful. The car returns marginally better consumption figures on cruise than I get doing it the hard way.
Plus I don't get cramp in my right leg.....
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One thing in favour of manual economy would be the opportunity to anticipate. i.e. don't bother to maintain speed up hill because you'll need to slow anyway for the truck you're gaining on.
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Surely CC is manual control, the alternative being pedal control.
};---)
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Best economy = constant and focused foot control
Easiest & second best economy = cruise control.
Worst economy = foot control without focus
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Best economy - thinking driver and anticipation.
Many drivers: last minute braking, tailgating, zero anticipation.
(see approaches to roundabouts and traffic lights at red)
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s'wot I said.
CC is a convenient aid to those who are not obsessively attentive - i.e. Me.
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People who do economy runs for sport and enjoyment (yes such people exist) never use cruise control.
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Never use cruise control anywhere north of Calais or south of Preston.
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>> People who do economy runs for sport and enjoyment (yes such people exist)
I read a piece about it once, and it sounded to me like long drawn out torture.
It was from the carb days. You tuned the car as lean as it would go, changed into top at 10mph or so and floored it until the car reached 30. Then you turned the engine off until it was down to 10mph, jump started it and did the same thing all over again, and again, and again. Ignoring the gross pinking.
Bad for the car too.
Last edited by: Armel Coussine on Wed 22 May 13 at 20:17
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>>It was from the carb days. You tuned the car as lean as it would go, changed into top at 10mph or so and floored it until the car reached 30. Then you turned the engine off until it was down to 10mph, jump started it and did the same thing all over again, and again, and again. Ignoring the gross pinking.
You forget, charging the battery the night before and not running any electrics to reduce alternator load. The windows were kept shut even on the hottest days. I'll never forget the staccato of numerous starters when several of us turned up at the same traffic lights together.
Coasting in neutral with the engine off would get you disqualified on an observed event.
I haven't competed in one for decades and haven't heard of any being run in recent years. Do they still exist?
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>> to reduce
>> alternator load.
Generator
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>> I'll never forget
>> the staccato of numerous starters when several of us turned up at the same traffic
>> lights together.
It must be similar now when several start-stop cars turn up at the same traffic lights together.
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>>Best economy = constant and focused foot control
Easiest & second best economy = cruise control.<<
Best economy with minimal effort = cruise control and autobox.
Or, as I have discovered recently, cruise control and autobox plus the dreaded diesel.
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>> It must be similar now when several start-stop cars turn up at the same traffic lights together.
It is indeed Gastropod. Becoming commonplace in and around London.
One assumes these jalopies have some sort of evolved or brushless starter motor. A stop-start Skoda Estelle would have got through a lot of starters.
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Did RMS Queen Mary I have cruise control?
A Danish workmate recently returned from a conference aboard her and was amazed by the level of engineering that went into the construction of the propulsion systems. She even had a reduction gear that continued to turn the props at 1 rev/hr while she was moored, to stop the bearings being damaged by static weight.
27 boilers produced 160,000 HP and a cruising speed of 28.5kts.
You'd need a decent limit on your credit card to fill her up though. Her tanks held 2,398,000 gallons and avg. fuel consumption was 13ft/Gal.
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I remember seeing Clarkson doing a piece on a Mille Miglia celebration. He was going round Italy with the Bentley Driver's Club and had been lent a then new Mulsanne for the job.
At one point he stopped for fuel. As he pulled in, on the other side of the pumps was a Blower Bentley with the nozzle in its slab tank. He filled up, went to pay, came out and there was the other car, still with the nozzle in its tank.
"You're still filling up? How much does it hold?"
"It's a 70 gallon tank."
"I see. What fuel consumption do you get out of it?"
"On a run like this, I'm doing very well and getting about 8-10 miles per gallon. It does drop into gallons to the mile around town though......"
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I have just got in from choir practice. On the way home I managed to keep the cruise set at 32mph (its very quiet out there tonight) and the average mpg increased by 0.2 over the 10 mile journey. Not much of a difference, but a difference nonetheless.
TBH the only reasons I turned it on were a> to make sure it still works and b> to help keep to the speedlimits - indicated 32mph is spot on 30mph after checking against the satnav
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>> indicated 32mph is spot on 30mph after checking against the satnav
I wonder what mine would be indicating at that speed... I don't usually get impatient and irritated following someone in a real 30 limit (not a ludicrous Surrey Sussex PITA goddam rural 30) if my own speedo reads a bit over 30. But 35-37 is better and I have always got away with it so far I think and hope, fingers crossed.
30 limit is pretty silly almost everywhere given the grip and braking of modern cars. Granted there are some places and times, but not all that many. The 30 limit dates from the 1920s, cart suspension, skinny crossplies, drum brakes... 40 or 45 would be the modern safety equivalent. But never fear, no one will listen to me even though I drive safely and don't have a lot of crashes or near-misses.
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>> I ................... don't have a lot of crashes or near-misses.
Just several, maybe?
;>)
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I have indeed had several over 55 years of rough motoring. But the last crash was many years ago and not my fault to any great extent. Near-misses are decently rare.
I wouldn't trust a driver who'd never had a crash to know what he was doing on the road frankly. I would see him as hopelessly inexperienced and naive.
I wish Rattle would get on with it (no fatalities or serious injuries though please Sheikha).
Last edited by: Armel Coussine on Wed 12 Jun 13 at 23:44
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30 limit is pretty silly almost everywhere given the grip and braking of modern cars...
...and the awareness, reactions and ability to see round corners of modern drivers? A 50 percent increase from 30 increases reaction distance alone by the length of a car, and the kinetic energy the brakes have to convert increases by 125 percent.
Do - within reason - what you like out in the wilds of Sussex, but the driver most likely to elicit a muttered 'onanist' as he passes is the one who negotiates a road lined with pedestrians or houses at significantly more than 30. I doubt my Porsche-driving, pressure-washing neighbour reads this but if so...
I wouldn't trust a driver who'd never had a crash to know what he was doing on the road frankly.
Substitute 'admitted to making a mistake' and I'd agree with you, AC. It's possible - indeed necessary - to learn from the mistakes we get away with as well as those we don't.
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The reason we have 30 mph limits is, as WDB says, due to thinking times and deceleration rates.
At the point where a car doing 30 would have stopped, the car doing 40 is still doing 25 mph. That's why.
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>> At the point where a car doing 30 would have stopped, the car doing 40
>> is still doing 25 mph. That's why.
>>
I don't doubt what you say, but I'd be interested to see your mathematics. I found this information on the subject, tinyurl.com/87andlq , but it doesn't say what speed the 40mph car would be doing when the 30mph car had stopped.
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>> >> At the point where a car doing 30 would have stopped, the car doing
>> 40
>> >> is still doing 25 mph. That's why.
>> >>
>>
>> I don't doubt what you say, but I'd be interested to see your mathematics.
I should have been more specific and asked what thinking time and what rate of deceleration you had assumed in your calculation.
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Hi L'Escargot,
I used a graph and calculation from Brake's (the charity) website:
www.brake.org.uk/facts/speedscience.htm
The specific graph (collision speeds):
www.brake.org.uk/assets/images/facts/Collision_speed_graph.jpg
Look at the graph and note where the 30mph line reaches 0. Move vertically upwards until you intercept the 40mph line and then move horizontally back to the vertical axis. The point of interception is the speed the 40mph car is doing at impact, which in this case is about 27mph.
While they've probably erred on the side of caution in these figures (it doesn't help their campaign to go the other way), I should think they're broadly accurate.
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There's another way to approach this question - by taking the total stopping distances given in the highway code, one could imagine video recording two cars stopping from the same point, one going at 30, the other at 40. If you then play the recording backwards, the 40 mph car would appear to accelerate from rest in reverse until it crossed the 30 mph car.
This speed at the cross over point is then very easy to estimate using a constant acceleration assumption (which is quite reasonable as the effect is effectively integrated and therefore smoothed).
>> % From Highway code
>> % from 30 mph, thinking distance 9m, braking distance 14m = total 23m
>> % from 40 mph, thinking distance 12m, braking distance 24m = total 36m
>> % assuming 0.7g deceleration - reasonable for a tyre on a dry road
>> a=0.7*9.81;
>> % using v^2 = u^2 + 2as i.e., assuming constant deceleration
>> v=sqrt(2*a*(36-23)), % veloctiy (m/s)
v =
13.3620
>> vmp=v*3600/1609.3
vmp =
29.8907
So, nearer 30 mph!, the 25 mph is both reasonable, and if anything plays the speed down a bit.
(Yes, I don't believe the 4 decimal places either - that's just what the software I use reports, and I'm not faffing around rounding it)
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>> and the awareness, reactions and ability to see round corners of modern drivers?
Awareness is the one that counts.
A good driver in my book is one who virtually never needs fast reactions because he or she is already doing whatever is necessary having seen the situation coming. All this learned guff about car lengths and what speed you will be doing when you hit the ped is just faff. I will only hit the ped if the carphound absolutely insists by walking into my car.
As for roads lined with pedestrians or houses, it's always obvious when the pavements are so narrow and crowded that caution is required. Wide pavements and wide road, no problem surely?
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Spot on AC.
>>A good driver in my book is one who virtually never needs fast reactions because he or she is
>> already doing whatever is necessary having seen the situation coming.
About twice a year, somebody is surprised by the narrow hump backed canal bridge down the road (there since 1814), gets there to find somebody coming over it towards them, and demolishes the parapet.
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>> >> and the awareness, reactions and ability to see round corners of modern drivers?
>>
>> Awareness is the one that counts.
>>
>> A good driver in my book is one who virtually never needs fast reactions because
>> he or she is already doing whatever is necessary having seen the situation coming.
I agree. A newly qualified driver might be good at going through the motions of actually driving the car but they tend not to see hazardous situations developing soon enough.
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>> I wouldn't trust a driver who'd never had a crash to know what he was
>> doing on the road frankly. I would see him as hopelessly inexperienced and naive.
I agree. Until a driver has been involved in an RTA, they're liable to think that RTAs are something which only happens to other people.
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And the important thing they don't realise is how swiftly disaster can overtake you when something goes amiss.
You're a brave bloke, AC...
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>> a brave bloke
Hackspeak for foolhardy idiot Mike?
It's crucial to be ahead of the game so that the chance of anything 'going amiss' is minimised. Narrow blind corners and humpback bridges are cases in point: only a kamikaze will approach them in the hope that nothing is coming the other way.
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>> >> I wouldn't trust a driver who'd never had a crash to know what he
>> was
>> >> doing on the road frankly. I would see him as hopelessly inexperienced and naive.
>>
>>
>> I agree. Until a driver has been involved in an RTA, they're liable to think
>> that RTAs are something which only happens to other people.
>>
Hope you don't apply this policy to public transport...
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>> Hope you don't apply this policy to public transport...
They aren't always perfect FF, not by a long way. But buses are so big and heavy that injury to passengers is quite rare.
I've been involved in a small crash with a London double-decker driven by someone who was either careless, or arrogant, or both. It was a long time ago though, when I was less restrained myself than I am now.
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>> ........ but might I have got more (or less) without using cruise?
If I activate cruise control at, say, 30mph the car accelerates faster to the set speed than if I'd been in control of the accelerator. For that situation I'd probably get better fuel consumption when not using cruise control.
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>> If I activate cruise control at, say, 30mph the car accelerates faster to the set
>> speed than if I'd been in control of the accelerator. For that situation I'd probably
>> get better fuel consumption when not using cruise control.
>>
I'm sure I remember seeing a view that accelerating hard to a known cruising speed and then cruising may actually use less fuel than accelerating slowly to the same speed and then cruising. Maybe NC or someone else who understands the physics could comment.
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>> I'm sure I remember seeing a view that accelerating hard to a known cruising speed
>> and then cruising may actually use less fuel than accelerating slowly to the same speed
>> and then cruising. Maybe NC or someone else who understands the physics could comment.
But you have to take into account you use more fuel to accelerate fast.
Never yet seen a definitive answer with proof to back it up.
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>>
>> >> I'm sure I remember seeing a view that accelerating hard to a known cruising
>> speed
>> >> and then cruising may actually use less fuel than accelerating slowly to the same
>> speed
>> >> and then cruising. Maybe NC or someone else who understands the physics could comment.
>>
>> But you have to take into account you use more fuel to accelerate fast.
>>
>> Never yet seen a definitive answer with proof to back it up.
Depends how you do it perhaps.
Maximising the torque tends to be efficient - so you are not using full power, just full power at the rpm you are using.
That ties in with AC's description of economy driving above.
I tried it for a while with my CRV diesel, which would accelerate fairly briskly from 1700 rpm, changing up at 2400. It seemed to work, unlike general use of heavy acceleration which hits the economy hard.
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Have only had one car and one pick up with CC, both auto which in the case of the Hilux saw it immediately drop a gear and apply full throttle in order to maintain set speed when it encountered a hill, hence it was seldom used.
Have used lorries for many years now with CC though so feel i can add a little here, whilst weights differ the theory is the same, i dislike CC intently but for keeping to a set speed its the only way.
If i'm running on the limiter at 55mph there is no point at all in using CC apart from saving leg muscles, but in the interests of economy (my own experiment this) i've cut my *loaded* cruise speed to 51 mph which equates to 1200 rpm and despite the vehicle doing its best to revert to auto i override the auto box and drive it manually, i maintain that 51mph on the level by using CC.
In auto on CC the lorry will do as the Hilux did and immediately drop a gear and often a second or third in order to try and keep that set speed on hills, this is wasteful, not only do you lose momentum with each gearchange both ways but the revs go sky high and the vehicles programming (not being Volvo) is so poor that it can't make its mind up which gear it wants.
Auto also holds on to gears too long before upchange again pouring fuel out of the exhaust, on most motorway hills the vehicle in question will quite happily lug down to 900rpm and pull up the hills without needing a change at all = lower revs and no loss of momentum.
Another problem with CC is that unlike a human driving properly it cannot take advantage of terrain by coasting in gear for as long as possible...of which every yard is free, its often possible to cut power before the brow of a hill is reached and allow momentum to slow and the next downhill section to regain full speed for huge distances, all free.
Downhill with CC on as soon as set speed is passed the vehicle will automatically apply the engine brake and will downshift also if left in auto, again this wastes the downhill freeby that you should be taking advantage of coasting for as long and as far as possible before resuming power.
OK now to the nitty gritty, overall the fuel consumption has improved by around 1.5 to 1.8 mpg (around 9.4 mpg avg now and seen over 10 several times) depending on journey, identical sister lorries driven in auto only are struggling to make 8mpg at very best with low 7's regular, what percentage of this is down to using CC to maintain the 51mph cruise on the level and how much is down to knowing when to switch CC off is debatable.
CC is a good tool for limiting your speed, but i firmly believe a competent and conscientous driver can beat it for economy, and without fail in lorries at least overriding the auto box is paying dividends, plus saving brake pads/discs by maximising engine braking but thats for another conversation and isn't applicable to car engines/gearboxes anyway.
** depending on journey i don't always stick to 51 under power when empty as the massive drag from the tyres when loaded isn't such a factor in fuel use.
Last edited by: gordonbennet on Thu 13 Jun 13 at 15:09
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>>Downhill with CC on as soon as set speed is passed the vehicle will automatically apply the
>> engine brake and will downshift also if left in auto, again this wastes the downhill freeby that >>you should be taking advantage of coasting for as long and as far as possible before resuming power.
That explains something I've often noticed which is lorry brakes coming for no apparent reason after cresting a rise. Clearly not all drivers are as interested in the workings of their charge as you are.
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>> That explains something I've often noticed which is lorry brakes coming for no apparent reason after cresting a rise. >>
Scanias in particular and probably some others light up the brake lights even if you only press the exhaust brake button and go nowhere near the brakes, i don't like this i'd rather the brake lights meant business.
I don't *think* my MAN lights up the brake lights with exhaust brake alone, but couldn't swear to that, i'll make a point of checking next month when winter dark mornings start arriving..;)
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The LEC's cruise control has two modes: a conventional minimum-speed one, which doesn't use the brakes, and a maximum-speed one, which does and illuminates the brake lights without my touching the pedal. I'm with GB on brake lights, so this is a feature I use very occasionally.
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Effect of Cruise Control on Fuel Consumption - DP
