Coasting to save fuel

[keithh44]

Is it illegal to throw the car out of gear and coast to save fuel and if so where do we stand every time stop/start kicks in?

[Ootohere]

Just dim to do it if you have a manual. 

Only going to get questioned as illegal if you lose control and are involved in an accident maybe.

'Simply Clever' to use 'Coasting Function' with vehicles that have that.  Usually those with DSG.

 

'If everything in life was as reliable as VW intended VW's to be!'

Or if all VW's worked as VW Advertising would lead you to believe.

 

 

Edited 10 August, 2019 by Roottootemoot

[Guest]

1 hour ago, keithh44 said:

Is it illegal to throw the car out of gear and coast to save fuel and if so where do we stand every time stop/start kicks in?

 

Very simply answer - you won't save fuel by coasting.

 

Stop /start ?  Auto engine stop has nothing to do with the engine running at idle, rather what speed the car is travelling at. So if you knock your car out of gear at the top of Kirkstone Pass in the Lake District. the engine will cut out about 7km later 

Edited 10 August, 2019 by Guest

[Danny 57]

You will I believe find, if you look at the trip data (it does on mine) use more fuel out of gear than by allowing the car to coast in gear and by dropping down gears as you need to as you slow down.

[AGFalco]

A car coasting with the engine running uses fuel if the car is not in gear.

A car in gear with the revs above 1400 ( in my Fabia ) and the throttle off uses no fuel.

Look at the instant fuel consumption on the MDF, if you have one.

 

Thanks AG Falco

[Ootohere]

You certainly can save fuel or get more range from vehicles if you use 'Coasting Function' and take your toe off the accelerator and let the DSG change from Showing D7 or D6 to just D.

Not difficult to find out, just brim your tank and do your usual journeys with Coasting Function' enabled and driving with it, 

then another time do your usual without enabling it.

Do it through the year / seasons, and see the difference to the 'range' you might get from a tank fill.

 

For me with 63 litres of diesel 730 miles is the usual when thinking about 'coasting' and using the function and 630 or so when not, 

journey times are all much the same.

Edited 10 August, 2019 by Roottootemoot

[Guest]

I don't know what 'coasting function' entails but 'coasting' as it's generally known ( no gear selected ) uses more fuel in modern cars. Well when I say modern, I mean those who's fuel supply is managed by computer.

 

Basically when a car is in neutral, the management system sets the fuel input to idle, however if there's no input on the accelerator when the car is in gear, the computer will cut the fuel supply to the cylinder.

Edited 10 August, 2019 by Guest

[Ootohere]

Time moves on, the use of words or terms move on and with some 2 pedal auto / automated manuals the fuel consumption using the tech can be better than the figures they get on rolling roads.

[Sanqhar]

I like coasting.

With coasting on a level road the slowing is governed by rolling and wind resistance. Without coasting the slowing is governed by the the same as well as the alternator electric recovery and the fuel shut off.  At some point you will need to open the throttle earlier, compared to coasting, to get back up to speed thus using fuel to do this. It’s a trade off between the two.

With coasting switched on just a light touch on the brakes will cancel it so you are always in control regarding switching between the two systems. 

 

Tom

 

[Guest]

On 10/08/2019 at 16:29, Roottootemoot said:

Time moves on, the use of words or terms move on and with some 2 pedal auto / automated manuals the fuel consumption using the tech can be better than the figures they get on rolling roads.

 

 

I'm none the wiser...  what does coasting function do? How does it operate?

[Guest]

8 hours ago, Sanqhar said:

I like coasting.

With coasting on a level road the slowing is governed by rolling and wind resistance. Without coasting the slowing is governed by the the same as well as the alternator electric recovery and the fuel shut off.  At some point you will need to open the throttle earlier, compared to coasting, to get back up to speed thus using fuel to do this. It’s a trade off between the two.

With coasting switched on just a light touch on the brakes will cancel it so you are always in control regarding switching between the two systems. 

 

Tom

 

 

As per Root's reply, I'm still none the wiser...  Is a gear engaged when coasting?

 

BTW - excuse my ignorance but "with coasting on a level road" ?   What's the point of that?

[Ootohere]

Simply it disangages the gears and coasts when drive is not required as happened when drivers took a manual gearbox car out of gear.   Just it happens seemlessly.  Touch the accelerator or brake and it is back in gear.  All legal and safe. 

Point of it is fuel saving. 

[Gerrycan]

On 10/08/2019 at 22:36, keithh44 said:

Is it illegal to throw the car out of gear and coast to save fuel and if so where do we stand every time stop/start kicks in?

Not sure why a '1.6 Yeti Greenine' owner is asking this question in the Karoq section? I'll put it down to you being a newbie and some Hot Fuzz moderator will transfer to an appropriate section if necessary.

 

It has been many years since I looked at the UK Highway Code but my understanding is that it is illegal to coast out of gear in a manual car, but it is not illegal to disengage the clutch, which is also what the DSG box does when coasting. In reality coasting out of gear in manual is unlikely to be a problem unless there is an accident and it can be proven to be a factor. 

 

As to the discussion whether coasting is actually worthwhile compared to using engine braking then it does vary by car and driving environment.

I'm based in Australia and we use metric measurements which is a bit easier than working the fathoms, chains, furlongs, pints of the old country.

When I first got a mk2 1.9pd diesel I was pleasantly surprised that the consumption display showed a low consumption at tickover of 0.5L/Hr. I expected it to be good but not that good, but when I subsequently got a 1.4tsi mk3 I was amazed that it matched that consumption at idle . In both cases they were warmed up and with no ancillaries turned on and neither car had stop/start.

 

Now if you raise the revs to 1500 and hold it there then consumption increases to over 1L/hr and 2000 rpm incurs close to 2L/hr. These are approximate figures as it is a while since I took the higher rev measurements on my car

 

The relevance of these figures is that if coasting out of gear/clutch disengaged at say 20kph consuming .5L/hr then you are getting 40km/litre which is 2.5L/100 (113mpg). At 100kph with 0.5L/hr consumption represents 200km/litre or 0.5L/100 (564mpg)

 

If you are going down a hill steep enough to require engine braking then you are not going to use any fuel.

Let's now imagine we have the cruise control engaged at 100kph and the gradient is insufficient to overcome aerodynamic resistance and engine braking, then the system will feed sufficient fuel to allow the set speed to be maintained at say 2000rpm. If, however the gradient is enough to match aerodynamic resistance then coasting will be more fuel efficient.

 

The point at which coasting works best will vary from car to car depending on aerodynamic factors (brick-like on Yeti, but much better on a Karoq) and engine braking provided by the unit. In my experience even small diesels (1.9pd and a Kia 1.6d) provide far more engine braking in top gear than my 1.4tsi, and I'd assume the 1.5tsi is similarly low.

 

Personally I have found coasting to be particularly useful in motorway congestion with slight gradients where you are not actually stationary but progressing in bursts of up to 40kph. Of course it does mean leaving a bigger gap in front than normal for this to be effective and any gap in an adjacent lane seems irresistible to BMW drivers to dive into (without indicating) .

 

It is just a question of picking the tool that works best for you in the circumstances and the instant consumption display is a reasonable indicator of effectiveness.

Edited 12 August, 2019 by Gerrycan

[Sanqhar]

12 hours ago, Scot5 said:

BTW - excuse my ignorance but "with coasting on a level road" ?   What's the point of that?

 

The car coasts in a no throttle situation, it may still slow down because of rolling and win resistance but not as much as in a conventional closed throttle in gear state. 

 

You reach your cruising speed and lift off, the car does the rest. What it does is decided by the settings you use. I just prefer one way. 

 

Tom

 

 

[Ootohere]

You soon see how seldom a road might be level / flat or goes up or down by how often the gear indicator does to 'D' and the gears are disengaged, 

and if you are carrying speed / momentum down you might carry that speed along the flat then up an incline again and not need to re-engage gear.

In traffic you might choose to slow by shifting down a gear with the shifter or paddles and not touching the brakes or the accelerator then change back up a gear and you are back in 'D' and coasting.

[Guest]

13 hours ago, Roottootemoot said:

Simply it disangages the gears and coasts when drive is not required as happened when drivers took a manual gearbox car out of gear.   Just it happens seemlessly.  Touch the accelerator or brake and it is back in gear.  All legal and safe. 

Point of it is fuel saving. 

 

If it's out of gear then how does the computer know the intent isn't to idle?  How does it distinguish between the two?

Edited 12 August, 2019 by Guest

[Ootohere]

I would assume by the speed you are going at and the RPM is down to idle.

They did engineer it and evolve it over the past years. 

 

 

Edited 12 August, 2019 by Roottootemoot

[Guest]

56 minutes ago, Sanqhar said:

 

The car coasts in a no throttle situation, it may still slow down because of rolling and win resistance but not as much as in a conventional closed throttle in gear state. 

 

You reach your cruising speed and lift off, the car does the rest. What it does is decided by the settings you use. I just prefer one way. 

 

Tom

 

 

 

Thanks for the explanation - I'm still wondering what the point is, but that's just me.

 

If Root is correct, and the gear disengages when you take your foot off the accelerator...    I'm now struggling with the fact the clutch (or clutches as it is in DSG) must be in contant use if everytime you lift your foot off the accelerator the car goes in to this coast mode.

 

Who am I to argue - haven't a clue how the system works or ever heard of that term, but it doesn't sound right to me. Oh well, can't teach an old dog new tricks I suppose.

 

Edit - My single brain cell is thinking again...  what's the point coming out of gear, why would that save fuel? Why not cut-off fuel whilst in gear as happens in a manual?

Edited 12 August, 2019 by Guest

[Ootohere]

ACT / COD gave Cylinder deactivation, and you can also have 'Coasting Function'  

 

Mony a mickle maks a muckle. 

Every little saving helps.  Then regenerative braking etc.   

It has all gone towards getting the sort of WLTP & RDE2 figures that are going to be needed to keep people able to buy heavy cars that might be bigger than they actually need.

[xman]

1st things 1st

 

It is categorically not illegal to coast, and DSG or other gearboxes do not have an exemption or special permission to break a non existent law.

 

Highway code rule 122 is advice only and not a MUST. This rule is largely out of date when it comes to very modern vehicles which have next to no engine braking, have excellent brakes which new learners are advised to use instead of engine braking and as for the other points I think they really only apply to cars built before the middle of the last century.

Rule 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.

 

As to the question of whether coasting saves fuel, no one so far has given the correct answer, just their opinion.

 

The answer is, it depends, it's complicated and depends on many things. Sometimes it can, other times it's better to leave the car in gear, and which gear is the best is again a complex issue. Maybe even part throttle. Many issues at play, vehicle speed, engine friction and pumping losses, engine mapping, efficiency Vs throttle opening Vs rpm, energy recovery systems , rolling and air/wind resistance, road gradients and plenty of forward planning and a few more things beside. 

 

Also the surrounding traffic need to be taken into account. Whether you are intending to slow down, maintain speed or allow the car to speed up downhill and not waste energy though braking, engine or otherwise.

 

A highly experienced hypermiler will learn the best strategy to extract maximum economy in the immediate situation he finds  himself. And some experts can extract mind boggling mpg. Every car, engine and power train combination is different and has different characteristics that the hypermiler needs to learn and be aware in order to optimise.

 

Highway code rules are there to ensure the not very bright driver remains safe and not a threat to others.

 

Its far too complicated to give tips, imo some good automotive engineering knowledge is really required to get a grip on hypermiling.

 

Remaining safe and in control is a priority, I must stress.

 

 

Edited 12 August, 2019 by xman

[Ootohere]

@xman

I did not give an opinion i gave an example of my experience and ability to get more range per tank by using 'coasting'.

It may be anecdotal to you but it is not an opinion it is stating what i can get in the way of fuel saving doing the same journeys and taking the same time to do them and repeated quite a few times over 40,000 miles and 32 months.

Also tried in other vehicles that have 'Coasting Function' available.

 

PS,

i know how to 'hypermile' in the usual old school Automatics, Automated Manuals or CVT's that i have driven for a long time and still do, 

but add in 'Coasting Function' and use it and a TDI or TSI DSG can become pretty economic.

 

Maybe still not as good for low fuel consumption as a 10 year old plus petrol or diesel auto without the extra emissions lowering gubbins / kidology.

Edited 12 August, 2019 by Roottootemoot

[shyVRS245]

Easy to save fuel if you simply lift 300 metres before a roundabout (I have 14 on my commute each way) and either change down to 5th or 4th gear without touching the brakes. The brakes are your real enemy regarding fuel consumption. If you compare the since start of journey readout  you will save at least 0.5mpg per roundabout. Accelerating away from the roundabouts will use less fuel in 4th or 5th gear than accelerating in 2nd or 3rd gear.

[xman]

32 minutes ago, Roottootemoot said:

@xman

I did not give an opinion i gave an example of my experience and ability to get more range per tank by using 'coasting'.

 

 

It was referring to the "Just dim to do it if you have a manual. " comment and other posters.

 

And the first question was as to the legality.

 

And Shy of course gives his influential opinion which, as in most cases, is inevitably suspect, slogging away from a roundabout in a higher gear is highly likely to be less economical intotal amount of fuel used then using a lower gear, unless you are taking a decade to get back up to speed in top gear which Shy assured me he never does, as his cars like to do 0.5g and he still get 64mpg using only 300 of his 4899.96 horses/kangaroo's.

 

25 minutes ago, shyVRS245 said:

you will save at least 0.5mpg per roundabout. 

Given enough roundabouts you might find you topped your tank foc.

 

😁

 

📟📁✏️✏️

[Ootohere]

It would be good if @keithh44 came back and said if they were thinking on getting or have got a Karoq and do they 'coast' in whatever.

Edited 12 August, 2019 by Roottootemoot

[shyVRS245]

27 minutes ago, xman said:

 

It was referring to the "Just dim to do it if you have a manual. " comment and other posters.

 

And the first question was as to the legality.

 

And Shy of course gives his influential opinion which, as in most cases, is inevitably suspect, slogging away from a roundabout in a higher gear is highly likely to be less economical intotal amount of fuel used then using a lower gear, unless you are taking a decade to get back up to speed in top gear which Shy assured me he never does, as his cars like to do 0.5g and he still get 64mpg using only 300 of his 4899.96 horses/kangaroo's.

 

Given enough roundabouts you might find you topped your tank foc.

 

😁

 

📟📁✏️✏️

Last tank 399 miles 45.09 litres (9.92 gallons) average 40.22mpg, not bad for a 335.9bhp car.