Do you ‘coast’ in your EV? Is it just a complete waste of time and energy or a useful option?

[Dr Dave]

I am a firm advocate of coasting in ICE cars for maximising fuel economy. As far as I can see, the associated risks are no greater than other negligent driving activities (such as being in the wrong gear at a junction etc).

BUT I haven't (yet) done it in the electric car (except for one exploratory attempt at low speeds) for the simple reason that I am not sure what would happen if you inadvertently stuck the car into reverse whilst turning the knob too far anti-clockwise in the process of trying to select neutral. It's a real possibility and could have disastrous consequences. Has anyone any experience of this? I have more experimentation to do on this but I'm not in any great hurry as I believe that you are unlikely to get much (if any) advantage by coasting in an electric vehicle with regen. Also I need to understand the drive system better to make a judgement. Nevertheless my left hand still wants to reach out and push the gearbox into neutral on downhills

In modern fuel injected vehicles coasting actually uses more fuel.

How Neutral Could Save Your Life—Really

Sometimes, putting a car in neutral is the best way to avoid an accident. But most automatic drivers have an aversion to shifting while in motion, afraid that they'll damage the engine or put it in reverse by mistake.

www.popularmechanics.com

 

[Cocijo]

You cannot coast in the ZS EV like an ICE car as regen is always on even in the lowest setting. If you are on the motorway set the KERS to the lowest setting though to maximise downhill stretches. Either or, you will never visibly see any difference to your range. You can however coast downhill in an ICE car in gear and it will use absolutely no fuel as the vehicle momentum is what keeps the engine running.

You’ve raised some interesting points. I think that the general consensus for defining coasting is rolling with no driveline or powerplant connected. For example in an ICE car this is rolling (uphill, downhill or on the flat) in neutral or in a manual gearbox with the clutch dipped and the engine disengaged. The engine will be at tickover under this condition. Historically this has been frowned on, but does come from a time when braking and steering systems were much less advanced and brakes in particular prone to fading quickly.
The situation you describe in an ICE is not coasting but overrun, where the kinetic energy from the car through the vehicles connected driveline turns the engine. There is engine braking under this condition. Most modern cars also have a fuel cut off that stops wasting fuel under this condition.
in the EV things are slightly different. However there has been considerable discussion about selecting N neutral when travelling along and it’s impact on things like control, electric motor and efficiency. MG in the owners manual seem to suggest not to do this. Some do and so this thread is discussing members thoughts, general theories and votes.

 

[Adee]

In modern fuel injected vehicles coasting actually uses more fuel.

How Neutral Could Save Your Life—Really

Sometimes, putting a car in neutral is the best way to avoid an accident. But most automatic drivers have an aversion to shifting while in motion, afraid that they'll damage the engine or put it in reverse by mistake.

www.popularmechanics.com

Yes, I'm aware that modern (fuel injected cars) stop fuel flow altogether when decelerating. But under these conditions the engine is essentially braking the vehicle and hence impeding forward motion. It is not quite as simple as the article suggests - for one thing, it is incline dependent. Take an incline where the slope is exactly matched by the car in top gear with no accelerator and a sensible speed is being maintained. In other words if you are going downhill at an acceptable speed of say 40mph with your foot completely off the throttle, then you are progressing at 40mph and using no fuel. Great. But if you now push it into neutral, the car will speed up (because the engine is effectively braking the car when you are not coasting), so the car will be going faster but now it is using fuel (to power the idling engine). It is a trade-off between the two scenarios.

Looking at it another way, take the case of a moderate incline where the car is happy coasting along in neutral (admittedly using fuel due to idling) at, say 50mph. If you now put the car into top gear with no throttle it will gradually slow down because of engine braking (admittedly using no fuel in the process). So you are using no fuel, but eventually you will stop altogether and get nowhere until the injectors kick-in again.

The criteria I always used was that if you push the car into neutral and it can maintain an acceptable speed on a slope, then you are better off than having to put the car into top gear and then having to apply a small amount of throttle to achieve the same speed, because as soon as some throttle is applied you then have to support the rotation of the engine (using fuel in the process). Another good tip is that if you do need to brake because of excessive coasting speed, then put it in gear and use the engine to brake you as this then does cut off the fuel supply (and saves your brake pads ).

These are just my views which I believe to be correct and I think the article is over-simplified in just saying that an engine uses no fuel when engine braking is in operation. It's true if you actually want the engine to brake the car. Otherwise it's more complex.

 

[Deleted member 3150]

I can’t believe this is a serious conversation. Please don’t coast - ever
From the MG Manual
Shift Control Knob Position
Do NOT turn the shift control knob to either P or R from the D position whilst driving or whilst the vehicle is in motion. This will cause severe damage to the electric drive system or cause an accident.

Highway Code - Coasting in Neutral Gear​

Rule 122: Coasting is a term describing a vehicle when it travels in neutral gear. You can also achieve coasting by depressing the clutch pedal. Coasting in a car can reduce driver control because:

• Normal engine braking is usually eliminated.
• The vehicle speed will increase quickly downhill.
• An increased use of the footbrake can reduce its effectiveness.
• Coasting can affect the steering response (particularly on corners).
• It may be difficult to select the appropriate gear when required.

ICE advice below but for An EV the concept is simply ridiculous

What is coasting and why is it bad? | startrescue.co.uk

Find out what is coasting, why coasting is a potentially dangerous practice and why in a modern car it won’t actually reduce your fuel consumption.

www.startrescue.co.uk

 

[Adee]

I can’t believe this is a serious conversation. Please don’t coast - ever
From the MG Manual
Shift Control Knob Position
Do NOT turn the shift control knob to either P or R from the D position whilst driving or whilst the vehicle is in motion. This will cause severe damage to the electric drive system or cause an accident.

Highway Code - Coasting in Neutral Gear​

Rule 122: Coasting is a term describing a vehicle when it travels in neutral gear. You can also achieve coasting by depressing the clutch pedal. Coasting in a car can reduce driver control because:

• Normal engine braking is usually eliminated.
• The vehicle speed will increase quickly downhill.
• An increased use of the footbrake can reduce its effectiveness.
• Coasting can affect the steering response (particularly on corners).
• It may be difficult to select the appropriate gear when required.

ICE advice below but for An EV the concept is simply ridiculous

What is coasting and why is it bad? | startrescue.co.uk

Find out what is coasting, why coasting is a potentially dangerous practice and why in a modern car it won’t actually reduce your fuel consumption.

www.startrescue.co.uk

Interesting that the highway code defines coasting, lists some of the supposed disadvantages but does not then forbid it (unless the snippet is incomplete?). I can counter most of these quoted disadvantages......

* Normal engine braking is usually eliminated - of course that's the whole point and per se I don't see how it reduces control. Just because you are coasting does not imply that you have to speed!

* The vehicle speed will increase quickly downhill - as above - the point of coasting is to make the most of the momentum of the vehicle, but does not have to include travelling at excessive speeds. A good coaster will use the gearbox to control the speed of the vehicle before using the brakes.

* An increased use of the footbrake........ - see previous comment, engage engine braking first, and then you use the same amount of footbrake as any other driver.

* Coasting on corners - when coasting (using no drive) the car is at it's MOST stable. There is no drive or braking to the wheels so the grip will be maximised. I don't see how coasting can affect steering response.

* This final point is valid but no more so than when changing between gears with a healthy gearbox and clutch.

I think we are all entitled to our views. I really don't see that it is harmful to safety or to the mechanical integrity of the vehicle (provided that some degree of mechanical sympathy is employed). If someone feels more in-control keeping a car in gear then they shouldn't coast.

 

[JodyS21]

Regarding coasting in an ICE - knocking it out of gear/clutch down, it uses more fuel than not doing it in any recent car, an ICE car has to burn fuel to keep the engine turning over if it isn’t engaged with the moving wheels, modern cars know not to burn any fuel if not wanting acceleration and the engine is being turned over by the engaged wheel momentum.
Re EV are we actually talking about engaging the actual “Neutral gear”? It doesn’t actually uncouple the motor from the wheels does it in an EV - I presumed it just de-energises the motor so it’s free to turn with no resistance? So in effect that is the same as just taking foot off accelerator pedal, but is there anyway to stop any KERS from occurring - I presume KERS 1 still does mild regen?

 

[Cocijo]

From my (limited) experimenting, selecting N when travelling means there is no regen. The motor obviously keeps spinning, but you effectively coast to a halt. Not sure what impact a spinning motor with disengaged regen might have. It is all pretty pointless in my view.

 

[Cocijo]

Btw - i used to own an old land rover that had free-wheel hubs fitted . Not sure if they were standard or optional. They would disengage the front axle only to reduce wear as i remember it.

 

[Lovemyev]

Btw - i used to own an old land rover that had free-wheel hubs fitted . Not sure if they were standard or optional. They would disengage the front axle only to reduce wear as i remember it.

They where an option, fitted plenty “Back in the Day”.
Along with cabin heaters on the very early ones !.
Can you believe that in this day and age.
Showing my age now !.

 

[LeoRBK]

I think I do and you can too freewheel coast in your MG without engaging N with a very gentle nudge to throttle where you can see that the power meter shows 0. So there is no regen and no power delivered to motor.

In case you need a move on you can continue pressing further, or in case you need to slow down you can ease of the pedal and regen gets back to work.

This works quite nicely for me. Admittently it needs slight practice.
I do not like the thought of having to move a gear knob in case of any emergency manouvre.

 

[MOrr5]

I think the title is misleading
I do not advocate driving in neutral, it is a dangerous risk
But you don't have to in order to remove regen due to a 'failing ' with the current ZS ACC
In the ZSEV you can drive in 'D' and mimic zero KERS and still have full control of the vehicle. all the safety systems are still available to you . A simple touch of the brakes at any time returns you to your preferred regen setting. On longer cruise speed journeys it increases my range by up to 0.5mpkWh .

 

[Johnnib]

You’ve raised some interesting points. I think that the general consensus for defining coasting is rolling with no driveline or powerplant connected. For example in an ICE car this is rolling (uphill, downhill or on the flat) in neutral or in a manual gearbox with the clutch dipped and the engine disengaged. The engine will be at tickover under this condition. Historically this has been frowned on, but does come from a time when braking and steering systems were much less advanced and brakes in particular prone to fading quickly.
The situation you describe in an ICE is not coasting but overrun, where the kinetic energy from the car through the vehicles connected driveline turns the engine. There is engine braking under this condition. Most modern cars also have a fuel cut off that stops wasting fuel under this condition.
in the EV things are slightly different. However there has been considerable discussion about selecting N neutral when travelling along and it’s impact on things like control, electric motor and efficiency. MG in the owners manual seem to suggest not to do this. Some do and so this thread is discussing members thoughts, general theories and votes.

With an eV down hill with no throttle charges the battery, converting the potential energy lost in losing height into potential battery energy (Kwh). On the flat or uphill some throttle is required to move the car converting the potential energy from the battery into kinetic energy. Now reducing throttle on the level charges the battery converting the kinetic energy into potential battery energy. All of these transfers of energy take place when Drive is engaged. What I don't understand is what happens when Neutral is selected while moving (this is what I understand as coasting) The motor is turning but is disconnected from the battery. With a PM and commutator dc motor the open circuit voltage would rise to a no-load value which in most cases wouldn't matter too much but with a brushless dc motor system emf would be generated in the form of an alternating voltage. I have no idea what voltage but at some stage (vehicle speed) I suspect this voltage might be high enough to damage the semiconductor switches that control the motor. For this reason I would be very cautious about selecting Neutral at anything other than very low or zero speed. Since neutral does not allow the motor to take advantage of the potential or kinetic energy resulting from going down a hill or slowing the vehicle I can't see what can be gained from selecting it.

 

[n0de]

...don't see any point in coasting - outcome for the effort required is a broken formula, but this thread did bring back old memories of leaving the car (Vauxhall Nova) in gear and turning off the ignition while heading downhill into the town - turning it back on and blowing my exhaust off (totally worth it)

 

[DriverInNorway]

When you are going down hill or have lifted off the accelerator, the forward momentum of the car drives the wheels that turn the electric motors (that have now become electric generators). You can feel the load placed on the generators in KERS 1, 2, 3. You feel this as 'engine braking'. That load is charging the battery. If you select neutral then there is no load on the electric generators. Depending on how they are designed, placing no load on an electric generator is not recommended, hence the advice in the owners manual.

 

[5teep]

If by coasting you mean switching into neutral and letting the car roll downhill then no I don't think it's worth it. The car needs to be in drive to activate kers charging so the best you could hope for is minimal power usage.