Best Economy - Cruise Control use or not ?

[Kiwibacon]

As most of the people here have said, cruise control is less economical. If you keep your foot at a steady level, the cars speed will dip slightly as the road rises and rise slightly as the road falls. With CC on it'll give it beans any time the road heads upwards, this uses a lot more fuel than letting those 5-10mph bleed off and regain on the way back down.

Can someone explain how neutral is dangerous and risking an engine conk out? I go through neutral every time I change gear.

BTW, when set to km/l the instantaneous readout goes to --- above 60 km/l. Is it the same for MPG? My car is using around 0.5 litres/hour of fuel. Coasting at 100km/h that's 0.5 litres per hundred km or in km/l that's ---. It would be around 200km/l if the gauge read that high.

[Kiwibacon]

Eccles. The difference between coasting and engine braking is ~0.5-1 litres per hour. But the momentum you lose takes more than 1 litre per hour to regain. Hence coasting in-gear (engine braking) is worse for fuel economy than coasting in neutral.

VW themselves know this, the Lupo they made for high mpg would freewheel on the over-run.

[RainbowFire]

No it doesn't. With the car out of gear, the engine needs fuel to idle.

You only see '----' when the car is in gear, with no throttle. The momentum of the car keeps the engine turning, so fuel is shutoff (indicated by '----').

It's also illegal to coast in Neutral as you are not considered to be in proper control of the vehicle.

lol, try it and see what your readout says.

Not sure what 1/2 you post pertains to either :S

"With the car out of gear, the engine needs fuel to idle." - no dispute here. However the car is in motion at 60mph. Engine idle + 60mph < 199mpg = ---- on display. (Watch the display when you put your foot on the clutch to change gear too) The display has a maximum it will show, above that, it will show ----. The display will show a figure when in-gear and no throttle too.....try it. Leave the car in 1st and just use the clutch and brake in traffic.

Maybe you're confusing "gallons per hour" with "miles per gallon"?

Not something I would do at all. Not necessary on modern anyone's and dangerous if you conk out......

another lol.

If you "conk out"....you should get your car checked out, if it's stalling when idle you have problems, and could also conk out at any moment whilst driving. :| Imagine your engine shutting down whilst in-gear and doing 70mph in the outside lane. I'd get that looked at pronto if I were you. :|

If you "conk out".....re-engage a gear and bring the clutch back up......just like a bump start.

Foot off throtle, in neutral downhill and the instantaneous readout will show (on my 1.8TSi) 0.7 to 0.8 litres per hour - ie the fuel needed to maintain tickover

Foot off throttle in gear downhill and the instantaneous readout will shoe 0.0 litres per hour - ie the wheels are driving the engine and the management system has cut off the fuel.

Lucky you for having a "per hour" readout :-p

"The management system has cut off the fuel" ? Really? So the wheels are driving the engine then? The engine has no fuel and is "off"? Isn't that dangerous? The weight of an off engine will slow the car down immensely. (Again feel how heavy the car feels when you're bump-starting it)

An engine in-gear, no throttle will slow itself down to a mechanical point, even downhill. Idle in 5th on the octy will get about 30mph (I believe DSG hits 6th at 32 when no throttle is applied) If the ECU has shut off fuel because you have taken your foot off the throttle the car will come to a (rather abrupt) halt. (A stall).

An engine out of gear has no "engine/gearbox braking" effect and will go far further as there is less resistance.

Using CC downhill will waste fuel. If you're going downhill at 60mph in 5th and you take your foot off the throttle, the car will start to slow down. If you have CC engaged it will push fuel into the engine to keep at 60mph. If you're pushing the throttle, you'll do the same. You can actually feel CC playing against the gearbox if you're on a long enough hill (Bluebell Hill in Kent for example). Costing down Bluebell Hill usually results in the car gradually gaining speed at tickover.

What does close the throttle right down (apparently) is using the brakes, which is why left-foot braking in an Octy is exceptionally hard. The brake pedal over-rides the throttle pedal, giving undesirable results. To this end, I seem to recall those purveyors of much "played with" programming, Shark, produced some coding that doesn't shut the throttle off when the brake is applied.

I find that the most interesting thing about CC (or speed limiter), especially in SPECS zones, is how inept humans are at keeping the car at a constant, fixed speed.

[mr_awol]

It seems that some people know better than the police, the DSA, the IAM, ROSPA and basically every advanced driving organisation who all agree that coasting downhill is either wrong, dangerous or both.

Can someone explain how neutral is dangerous and risking an engine conk out? I go through neutral every time I change gear.

Neutral doesn't 'cause' a stall, but if you do stall when in neutral you will lose braking and steering assistance. If in gear this wont happen.

another lol.

If you "conk out"....you should get your car checked out, if it's stalling when idle you have problems, and could also conk out at any moment whilst driving. :| Imagine your engine shutting down whilst in-gear and doing 70mph in the outside lane. I'd get that looked at pronto if I were you. :|

If you "conk out".....re-engage a gear and bring the clutch back up......just like a bump start

A stall can happen for several reasons - and often occurs in an emergency stop if the driver dips the clutch too soon (or too late lol). You even later go on to state that this will happen

What does close the throttle right down (apparently) is using the brakes, which is why left-foot braking in an Octy is exceptionally hard. The brake pedal over-rides the throttle pedal, giving undesirable results. To this end, I seem to recall those purveyors of much "played with" programming, Shark, produced some coding that doesn't shut the throttle off when the brake is applied.

As for re-engaging a gear if the car stalls, that's all well and good if it just conks out and you want to start it again. If you're trying to do an emergency stop then it might be too late by the time you drop it back in gear.

:

Edited 19 November, 2012 by mr_awol

[Kiwibacon]

Mr_Awol.

You haven't explained how it is bad, dangerous or wrong. You have simply repeated the assertation. Which does nothing to further your argument.

If you can't explain how this is bad, dangerous or wrong, then your argument has no support and instead becomes more like a superstition.

You also haven't explained how it is an engine conks out or stalls when in neutral.

BTW, should your engine cease to turn while driving at speed (say mechanical failure) you will find that steering at speed with no power assist is very little different to steering at speed with power assist. It's mainly when parking that power steering is necessary. Vacuum brakes are also good for several applications before they run out of vacuum and stop assisting.

If I was on the motorway and experienced sudden engine failure, a related thing has happened to me before, I'd be pulling it into neutral and coasting to give me as much distance as possible to find a safe stopping place. If I were to obey the back seat police and keep it in gear, then I'd grind to a hald pretty quickly, compounding any engine damage and dangerously disrupting the traffic behind me.

[TDIum]

There's lots of things in life that may be bad, dangerous and wrong but folk still do them!

[Kiwibacon]

I just worked out why cycling in traffic is so dangerous. It's not the drivers on the road, no, it's because they freewheel into neutral when you're not pedalling.

[mr_awol]

Mr_Awol.

You haven't explained how it is bad, dangerous or wrong. You have simply repeated the assertation. Which does nothing to further your argument.

If you can't explain how this is bad, dangerous or wrong, then your argument has no support and instead becomes more like a superstition.

You also haven't explained how it is an engine conks out or stalls when in neutral.

BTW, should your engine cease to turn while driving at speed (say mechanical failure) you will find that steering at speed with no power assist is very little different to steering at speed with power assist. It's mainly when parking that power steering is necessary. Vacuum brakes are also good for several applications before they run out of vacuum and stop assisting.

If I was on the motorway and experienced sudden engine failure, a related thing has happened to me before, I'd be pulling it into neutral and coasting to give me as much distance as possible to find a safe stopping place. If I were to obey the back seat police and keep it in gear, then I'd grind to a hald pretty quickly, compounding any engine damage and dangerously disrupting the traffic behind me.

Apart from the facts that you risk losing braking efficiency if the engine stalls whilst out of gear, and that the car does not handle in the same manner when not in gear, there was my point that the police, the DSA and all advanced motoring bodies ALL say not to. But hey, you know better so go for it

I just worked out why cycling in traffic is so dangerous. It's not the drivers on the road, no, it's because they freewheel into neutral when you're not pedalling.

This, and your motorway example, are the reasons i wont be typing a lengthy reply to explain it to you properly.

http://webcache.googleusercontent.com/search?q=cache:XP0h0osZWbgJ:www.advanced-driving.co.uk/forum/viewtopic.php%3Ff%3D2%26t%3D2084%26start%3D0+COASTING+DOWNHILL+ROSPA&cd=3&hl=en&ct=clnk&gl=uk

The above has a sensible discussion on the matter

http://www.k79.com/uk-driving-theory-test/uk-dsa-car-driving-theory-test-preparation-road-and-traffic-signs.php?category=Vehicle+Handling&question=Vehicle-Handling-020.xml

The above shows that you and your ignorance would fail at least one part of the theory test.

[Kiwibacon]

Mr_Awol;

We are still waiting for any logical reason why an engine should stall out of gear. In fact any explanation of how that is physically possible would be a start.

The only way I know of to stall an engine is to connect it to a stationary gearbox at too low rpm. A situation impossible to achieve at road speed.

The UK theory test question is an extremely badly worded one.

It doesn't put more wear and tear on the tyres.

It doesn't damage the engine.

Picking up speed downhill is only wrong if you don't intend that to happen.

Your braking and steering control are no different.

The discussion is also full of people who don't understand the fuel economy implications of drag being greater than fuel savings. There is a hilarious quote in there that while coasting you are relying solely on tyre friction to keep you on the road.

I'm sure I'm not the only one who knows the tyre friction is all there ever is keeping you on the road.

The only argument in there, is being able to rapidly accelerate is sometimes required. Now if driving downhill, why would you need to suddenly accelerate?

I couldn't get to page two, forum down for maintenance. But in summary, there is no logical argument presented there on why it is unsafe, bad or wrong.

So please. Backup your argument in a concise and logical manner so we can understand your viewpoint.

[RainbowFire]

Apart from the facts that you risk losing braking efficiency if the engine stalls whilst out of gear, and that the car does not handle in the same manner when not in gear, there was my point that the police, the DSA and all advanced motoring bodies ALL say not to. But hey, you know better so go for it

Ah, you've gone from "illegal" to "don't do it". If you want to go back to illegal, please state relevant statute that coasting infringes. Highway code usually relevant laws when listing the rules. Rule 122 refers to no such statute. Maybe it's a printing error?

Not that long ago the "experts" said smoking was good for you too.

http://www.k79.com/u...andling-020.xml

The above shows that you and your ignorance would fail at least one part of the theory test.

.....and when entering "fuel consumption will be higher", you're told that is not correct. So, according to your source, fuel consumption will not be higher. If it's not higher, what are the other options? :|

Also, how is "picking up speed" (one of the "correct" answers) wrong? If you put your foot on the throttle will you not pickup speed too? :S

OMG! Less steering control too! How does that one work? :o

Do this one, and fill in "it will cause the engine to stall" and see if you're right.....

http://www.k79.com/u...andling-022.xml

Also this one, and fill in, "use more fuel" and see if you're right......

http://www.k79.com/uk-driving-theory-test/uk-dsa-car-driving-theory-test-preparation-road-and-traffic-signs.php?category=Vehicle+Handling&question=Vehicle-Handling-061.xml

I'd really like to know how you get a well-maintained engine to stall too.

[mr_awol]

I'm not gonna feed the trolls much longer, but would point out that:

1) I haven't gone from illegal to anything, never mind back again.

2) the Highway Code isn't law

3) nowhere have I said being in neutral 'causes' stalking - but that being in gear will prevent some of the negative effects.

The links to additional theory test questions are the most riddiculous yet - as they all support my statement that coasting is considered bad practice.

I'd suggest reading the posts in this thread and if you still can't get it then do your own research. Failing that just carry on with your own misconceptions - I'm not that fussed either way TBH........

Edited 20 November, 2012 by mr_awol

[lfc958]

I luuurve this discussion, & the fact that NOBODY picked up other stupid comments about the tank refilling itself etc.

based on this i think it was said as a JOKE !!!!!!!

[Jockdooshbag]

Regarding "coasting" as discussed here, the new autos on the likes of BMW etc actually fully disengage drive on the overrun to achieve better mpg. Is this not coasting?

On CC and MPG i couldnt care less about a small mpg deficit for using CC as its far more convienient ans relaxing. My knee kills me after a short while so i need to adjust my leg position from time to time and can only do thios properly with CC. My kness are pretty knackered hence why CC is essential for me but even if my knees were fine i would still prefer it.

I do enjoy extracting maximum MPG on country roads and in town as its strangely satisfying but on motorways its just boring so i flick CC on as soon as im on one.

Proper hypermiling sounds boring but there is a strange gratification from easing off the throttle at the exact moment to be able to coast up to a junction with just enough speed to check its clear and then pull out without stopping or from keeping up with traffic flow and negotiating corners with zero braking whilst maintaing a sensible average speed.

I must be getting old but at least its one aspect of motoring you can legally enjoy these days plus speeding with the missus in the car and the wee one gets quickly nipped in the bud and me nipped in the lug.

[cs.rogers]

From the Highway code:

122

Coasting. This term describes a vehicle travelling in neutral or with the clutch pressed down. It can reduce driver control because

engine braking is eliminated

vehicle speed downhill will increase quickly

increased use of the footbrake can reduce its effectiveness

steering response will be affected, particularly on bends and corners

it may be more difficult to select the appropriate gear when needed.

I don't think its illegal as such, but if you lose control of the vehicle while coasting, I'd suggest the police could do you for dangerous driving. Unless there is a genuine reason for it, i.e. burst fuel line (happened to the father in law a couple of weeks ago on a Range Rover) or a failed fuel pump (my dad's Peugeot 406 a load of years ago) or a. n. other disaster.

[RainbowFire]

I'm not gonna feed the trolls much longer

Run away, run away! You backed your argument up with nothing and now need to retreat because it's been questioned. Again, like several others on here, running away under the cry of "troll troll!". It's what happens you've been asked questions that you can't answer, don't feel bad about it, just run away.

You've got up from the table and walked out the room because you've been asked to back up your comments.

2) the Highway Code isn't law

Didn't say it was, I said it quotes the law where where relevant

3) nowhere have I said being in neutral 'causes' stalking - but that being in gear will prevent some of the negative effects.

Didn't say you did. We asked what would cause it to stall when in neutral, big difference. You were happily banging on about "what happens if you stall", you were simple asked what would cause a well-maintained engine to stall. You obviously can't answer that.

The links to additional theory test questions are the most riddiculous yet - as they all support my statement that coasting is considered bad practice.

Best you go back and read them then. If the questions are answered as you advocate, you are told you are wrong. If you're unhappy with the information your source states, don't invite people to use it. :|

I'd suggest reading the posts in this thread and if you still can't get it then do your own research. Failing that just carry on with your own misconceptions - I'm not that fussed either way TBH........

Have done own research

Something you have failed to do.

[cs.rogers]

Oh and MPG? if its such an issue, don't touch cruise control.

[RainbowFire]

I luuurve this discussion, & the fact that NOBODY picked up other stupid comments about the tank refilling itself etc.

based on this i think it was said as a JOKE !!!!!!!

Would driving backwards mean I'd arrive before I left too

[Jockdooshbag]

Would driving backwards mean I'd arrive before I left too

No driving in reverse winds the odometer back. Have you not seen Ferris Bueller's Day off?? Everyone knows this.

[mr_awol]

Regarding "coasting" as discussed here, the new autos on the likes of BMW etc actually fully disengage drive on the overrun to achieve better mpg. Is this not coasting?

On a standard car? As far as I know this only happens on the hybrid models as the electric motor acts as a generator during overrun or braking, which gives the car the stability it would be lacking if truly coasting.

[Jockdooshbag]

On a standard car? As far as I know this only happens on the hybrid models as the electric motor acts as a generator during overrun or braking, which gives the car the stability it would be lacking if truly coasting.

No i read this will be a common feature on all new autos. It maybe wasnt BMW now i think about it. It might have been the new range rover. Doesnt really matter which car it is, the point was that the car will effectively be coasting.

[RainbowFire]

then do your own research.........

Well as you come to mention it.............

Same hill (Bluebell Hill, just North of Maidstone, Kent - use this hill monday to friday) same approach speed, same entry and exit points, same objective: maintain at least 60mph.

Three different runs: One on cruise, one being driven, one coasting. (Done one three separate days, in light traffic). Speed indicated by GPS.

Run 1) Well as, expected, the cruise could be felt fighting against the engine braking effect. As cruise has to keep putting fuel into the engine, overrun cannot be engaged.

Run 2) Hit the entry point at 60mph, in 5th, foot off throttle, within 100 yards or so, the car s doing 50mph (overrun engage conditions should have been met). To return to 60mph, throttle applied (oh, there goes overrun)

Run 3) Entry point, 60mph, neutral applied, engine is now at idle. Within the same distance that the car took to bleed off 10mph, we've increased speed. By the time the exit point is reached the car is approaching 75 mph.

Whenever overrun conditions are met, the car will slow down under the engine braking effect. To maintain a minimum given speed with the gearbox engaged, fuel has to introduced to the engine. This action is putting more fuel in than when the car is in idle.

There are merits to all three approaches, usually combined over a journey. It's up to the individual driving the vehicle.

There are questions to be raised to the "coasting is bad" brigade:

When does the process of changing gear become coasting?

Do you always change gear at the same speed, regardless of whether it is up or down?

The are short-shift devices the allow you to change gear faster. The must obviously be safer than your slower gear change?

[keith3289]

2) the Highway Code isn't law

If the HC says "must" or "must not" then it is stating law.

[keith3289]

Run 1) Well as, expected, the cruise could be felt fighting against the engine braking effect. As cruise has to keep putting fuel into the engine, overrun cannot be engaged.

There are questions to be raised to the "coasting is bad" brigade:

When does the process of changing gear become coasting?

Do you always change gear at the same speed, regardless of whether it is up or down?

The are short-shift devices the allow you to change gear faster. The must obviously be safer than your slower gear change?

Re run 1, really - why does it have to keep putting fuel in? I would have thought it would just back off until the speed dropped back to the set cruising speed.

Re coasting, and the argument that you go into neutral every time you change gear. Do you also let the revs go to idling speed while changing gear? I would suggest part of the point of not coasting is that you are doing two totally unnecessary gearchanges, so you're not paying as much attention to the road as you might. Also your speed is more likely to increase than when under engine braking - and what's the point of wearing out your brakes to counteract that?

[RainbowFire]

Re run 1, really - why does it have to keep putting fuel in? I would have thought it would just back off until the speed dropped back to the set cruising speed.

If it didn't feed fuel in, you're back into the engine-braking scenario (Run 2) and back to below the target speed. Allowing the car to "drive itself" (for want of a better phrase) - so, downhill, in gear, no throttle applied - it drops to a speed of 50mph. The target speed is 60mph.

Re coasting, and the argument that you go into neutral every time you change gear. Do you also let the revs go to idling speed while changing gear? I would suggest part of the point of not coasting is that you are doing two totally unnecessary gearchanges, so you're not paying as much attention to the road as you might. Also your speed is more likely to increase than when under engine braking - and what's the point of wearing out your brakes to counteract that?

Continuing with Bluebell Hill, at the bottom there is a 50mph limit as it heads into the mess that is the junction with the M20. At a given point, the gearbox is re-engaged to allow engine braking to take effect. If done at the right point, it is possible to arrive at the junction and to have only used the brakes in the last 30 yards (in conjunction with changing down through the gear box) As I've said before, there's not a reliance on one single technique (which seems to be an assumption). Using a combination of techniques, the run I usually do on wednesday or thursday (depending on SWMBO), which is Redhill to Whitstable, I pull up at Whitstable with the overall economy for that run reading 74mpg. This includes the climb up Detling Hill (fairly steep). My usual run home (Redhill to Medway) sees 70(ish) mpg before climbing back up Bluebell Hill. Having had the Octavia for over a year now, and doing the Redhill-Medway run for most of the working days between then and now, I can say I have played with most combinations of techniques. Coasting isn't always appropriate for the road, sometimes dropping the car into neutral slows it faster than leaving it in gear. Sometimes "self-drive" is exactly what is required.

As for needing to pay attention for changing gear, after 20 years of driving, the operation of changing gear is done without thought. (Just ask anyone who has been driving a manual for a long time, how often their left foot goes to move in an automatic ;) ) The human mechanical side of driving a car should really be able to be done without thought, from changing gear, to using flick wipe (Why do you think the controls are basically laid out the same? (Well, except the Japanese). Do you *think* about putting your seat-belt on when you get into the driver's seat, or is it just second nature? Do you look where you put the keys, or already know which way up and where the ignition barrel is?

[Kiwibacon]

Mr_Awol

Why do you think a car needs to be under acceleration or braking for stability reasons?

I am keen to hear your thoughts on this matter. Note the subject of vehicle stability and handling is a magnitude more complex than stalling an engine.

Simple scenario, please explain the difference in stability between these two:

1. Coasting down a hill in neutral and idle.

2. Driving down a hill in gear and maintaining a load on the engine that balances drag in such a way that speed is the same as coasting.