Is changing down through the gears a bad habit

[james_gt3rs]

S. Gonzales Esq. said:

I've always understood 'coasting' (sorry - COASTING) to mean travelling in neutral, rather than in gear with the clutch disengaged.

Same thing? Still no drive to the wheels so you are freewheeling.

[Reg Local]

Pressing the clutch for the last few yards of travel when you're coming to a stop in a high gear, to prevent labouring the engine is not coasting.

Coasting is allowing the car to travel either in neutral, or with the clutch depressed unnecessarily. Removing drive from the wheels does result in the loss of an element of control which could affect a vehicle's balance around a corner, for example, or allow it to gather unnecessary speed on a downhill run.

When coming to a stop in gear, it is necessary to press the clutch to prevent labouring, so this isn't coasting.

[gp1699]

Reg Local said:

Pressing the clutch for the last few yards of travel when you're coming to a stop in a high gear, to prevent labouring the engine is not coasting.

Coasting is allowing the car to travel either in neutral, or with the clutch depressed unnecessarily. Removing drive from the wheels does result in the loss of an element of control which could affect a vehicle's balance around a corner, for example, or allow it to gather unnecessary speed on a downhill run.

When coming to a stop in gear, it is necessary to press the clutch to prevent labouring, so this isn't coasting.

In my Porsche the revs will drop down to idle if I let off the throttle when cruising. im guessing it disengages the drive some how. is this not safe?

[Reg Local]

Some modern Porsches do have a freewheel function to help with efficiency.

I'm not entirely sure how they work, but my stepson is a Porsche technician, so I'll have a chat with him at the weekend and find out how the freewheel function links to throttle application, downhill coasting in gear etc.

[gp1699]

Reg Local said:

Some modern Porsches do have a freewheel function to help with efficiency.

I'm not entirely sure how they work, but my stepson is a Porsche technician, so I'll have a chat with him at the weekend and find out how the freewheel function links to throttle application, downhill coasting in gear etc.

That would be interesting!

I'm wondering why they are allowed to introduce these measures to improve economy and reduce potential emissions if generally they are considered unsafe. Such as my Porsche having an in built coasting function and my BMW telling me to slow down without using the brakes.

[IcedKiwi]

I guess the difference with the car disengaging the drive is that if it needs to be reconnected for stability reasons it can do so. If you've knocked it into neutral yourself, I doubt you'd have the ability/response times required to do so.

From the manual said:

Driving in gliding mode
Through attentive driving, fuel can be saved in gliding mode. The vehicle rolls with the engine disengaged and at idle speed without engine braking effect.

Preconditions for automatic gliding mode
– Driving in selector lever position D
– Gliding mode is switched on. Indicator light on the button is off.
– Sport and Sport Plus modes are switched off
– PSM is active
– Cruise control is not active
– Engine, transmission and battery are at operating temperature
– Calm/economic driving style
– Slight uphill or slight downhill gradients

> Slowly take your foot off the accelerator.
The engine is disengaged and runs at idle speed. The vehicle rolls with no engine braking effect.

Gliding mode is recognisable by the idle speed indicated on the tachometer.

Information
In the case of a sporty driving or when swiftly releasing the accelerator pedal, gliding mode is suppressed to allow targeted use of the engine braking effect. On more pronounced uphill gradients, "gliding" is also prevented as the gliding phases are very short due to the gradient and no significant fuel savings can be achieved. On more pronounced downhill gradients, gliding is suppressed because here, the vehicle does not slow down, despite the engine overrun torque and no fuel is consumed in this driving situation due to utilisation of the overrun shut-off.

Ending gliding mode/utilising engine braking effect
> Press the accelerator or brake pedal or
Operate a shift paddle or a shift button or Shift gear using the selector lever.

Initiating gliding mode manually
– Driving in selector lever position D or driving in selector lever position M

When gliding mode is suppressed, e.g. in the case of sporty driving, sudden release of the accelerator pedal or excessively low engine temperature, gliding mode can be initiated manually.

> Take your foot off the accelerator pedal and shift past the highest possible gear with the shift paddle, one of the shift buttons, or with the selector lever.

On the hybrids, it goes one step further and switches off the engine - I assume because you have to motor to do torque fill whilst you wait for the engine to fire up.

Edited by IcedKiwi on Thursday 23 February 12:18

[Gary C]

Reg Local said:

Coasting is allowing the car to travel either in neutral, or with the clutch depressed unnecessarily. Removing drive from the wheels does result in the loss of an element of control which could affect a vehicle's balance around a corner, .

sort of see what your saying but dipping the clutch can be useful if you need it.

While there is a torque on the wheel, either positive or negative, some of the tyres grip is being used other than lateral grip, ie the slip angle is increased.

Disengaged from the drive and without brakes a tyre actually has the highest amount of cornering grip. Feathering throttle does very similar, but lifting with engine braking does apply a torque to the wheels, often small but it does.

Dynamic grip control (Ie driver controlled weight transfer) is reduced true but that's only really for the track.

[Speary8]

Re coasting / freewheeling or whatever manufacturers call their system.
To disengage drive and let the engine idle as you coast long uses fuel
To be in a high gear with the throttle closed uses no fuel in a modern car. In a high gear you will get low engine braking so shouldn't be vastly different to coasting, especially down hill

[anonymous-user]

Speary8 said:

Re coasting / freewheeling or whatever manufacturers call their system.
To disengage drive and let the engine idle as you coast long uses fuel
To be in a high gear with the throttle closed uses no fuel in a modern car. In a high gear you will get low engine braking so shouldn't be vastly different to coasting, especially down hill

So you are saying the manufacturers have got it wrong??


Well they haven't. What they realise is that parasitic engine friction is a HUGH component of the overall losses, so downspeeding, taken to the extreme with the latest gliding systems is important. if you want to STOP then yes, you may as well do that in gear, with zero throttle in DFSC, but if you don't want to stop, you want to GLIDE!

[Gary C]

Max_Torque said:

Speary8 said:

Re coasting / freewheeling or whatever manufacturers call their system.
To disengage drive and let the engine idle as you coast long uses fuel
To be in a high gear with the throttle closed uses no fuel in a modern car. In a high gear you will get low engine braking so shouldn't be vastly different to coasting, especially down hill

So you are saying the manufacturers have got it wrong??


Well they haven't. What they realise is that parasitic engine friction is a HUGH component of the overall losses, so downspeeding, taken to the extreme with the latest gliding systems is important. if you want to STOP then yes, you may as well do that in gear, with zero throttle in DFSC, but if you don't want to stop, you want to GLIDE!

OR

Don't give a st and have a manual and choose exactly how and when you want to disconnect the drive from the engine.

[BricktopST205]

I always use gears to slow down than brakes. Engine braking is far more efficient than using brakes which is wasted energy unless you have kers. It is all about judging what is in front of you.

[Dr Jekyll]

BricktopST205 said:

I always use gears to slow down than brakes. Engine braking is far more efficient than using brakes which is wasted energy unless you have kers. It is all about judging what is in front of you.

So if you change to a lower gear for increased engine braking, where does the energy go?

[pingu393]

Dr Jekyll said:

BricktopST205 said:

I always use gears to slow down than brakes. Engine braking is far more efficient than using brakes which is wasted energy unless you have kers. It is all about judging what is in front of you.

So if you change to a lower gear for increased engine braking, where does the energy go?

Heat.

When the clutch is disengaged and the brakes are applied, the following parts are being worn / used
a) Brake pads and discs. This is the heat that is slowing the car.
b) Clutch release bearing
c) Clutch cable
d) As the accelerator pedal is not being touched, there is only a limited amount of fuel being injected per cycle.

When the gears are used to slow the car (assuming speed matched gear change)
a) As the accelerator pedal is not being touched, there is only a limited amount of fuel being injected per cycle, but fuel consumption will be increased over the braking option as the revs will stay higher for longer.
b) The compression stroke is being used to heat the mixture and this is the heat that is slowing the car.


Arguments for changing down

a) Less wear on brakes
b) Assuming good downshifts, Less wear on clutch components (plate and release bearing)
c) You will be in the correct gear with everything ready to go when lights change

Arguments for using brakes rather than gears

a) Better control both for car balance and emergency as foot is already applying brake
b) Most downshifts involve some clutch drag, so less wear on clutch plate
c) Better fuel consumption(*)


What swung it for me was RegLocal's car control argument and I am now attempting to change my muscle memory from thirty years of slowing down with the gears.



(*)The best fuel consumption and reduced wear scenario would can be achieved if the car is allowed to slow naturally and you downshift at around 1100 rpm in each gear (using perfect rev-matching and ideally not using the clutch) until you are doing 1100 rpm in 1st and disengage the clutch and roll to a stop and apply the handbrake using just enough force to hold the car stationary, but this would be totally impractical in most circumstances.

[cmaguire]

Why don't you just use the gears and the brakes to slow down. You'd save yourself a lot of thinking.

[IcedKiwi]

pingu393 said:

What swung it for me was RegLocal's car control argument and I am now attempting to change my muscle memory from thirty years of slowing down with the gears.

One of his points was that using the gears to slow meant you would only be slowing down using 2 wheels (in most cases) compared to all 4 wheels when applying the brakes which could potentially lead to instability in extreme cases. Along with the foot on pedal ready to go and ABS/ESC functions.

[cmaguire]

IcedKiwi said:

One of his points was that using the gears to slow meant you would only be slowing down using 2 wheels (in most cases) compared to all 4 wheels when applying the brakes which could potentially lead to instability in extreme cases. Along with the foot on pedal ready to go and ABS/ESC functions.

Is there truly a magical driver that uses only the gears to slow down? Show me I'm wrong, but I would assume there are drivers that use the gears and brakes together to slow down and those that avoid the gears (for whatever reason).
In any event, whatever choice the driver makes it is of little consequence unless the vehicle is at or close to the limit of adhesion. Which is likely to be highly unlikely if the driver pays any notice to the speed limits. I can't get past this, because beyond the need to use your eyes to observe your surroundings, at or below the speed limit there is very little need to be too concerned with anything except staying awake.

[pingu393]

IcedKiwi said:

pingu393 said:

What swung it for me was RegLocal's car control argument and I am now attempting to change my muscle memory from thirty years of slowing down with the gears.

One of his points was that using the gears to slow meant you would only be slowing down using 2 wheels (in most cases) compared to all 4 wheels when applying the brakes which could potentially lead to instability in extreme cases. Along with the foot on pedal ready to go and ABS/ESC functions.

These were the reasons that swung it for me.

[pingu393]

cmaguire said:

IcedKiwi said:

One of his points was that using the gears to slow meant you would only be slowing down using 2 wheels (in most cases) compared to all 4 wheels when applying the brakes which could potentially lead to instability in extreme cases. Along with the foot on pedal ready to go and ABS/ESC functions.

Is there truly a magical driver that uses only the gears to slow down? Show me I'm wrong, but I would assume there are drivers that use the gears and brakes together to slow down and those that avoid the gears (for whatever reason).
In any event, whatever choice the driver makes it is of little consequence unless the vehicle is at or close to the limit of adhesion. Which is likely to be highly unlikely if the driver pays any notice to the speed limits. I can't get past this, because beyond the need to use your eyes to observe your surroundings, at or below the speed limit there is very little need to be too concerned with anything except staying awake.

I used to slow almost to a halt without the brakes and only used them if I needed to stop. Most of the time you don't need to stop. In fact, while I was driving in the Army, I was encouraged never to stop as it can be quite hard getting 70+ tons rolling again can be quite an effort.

If you ever get to the limits your training (and muscle memory) take over. Although I felt that I was 100% in control doing what I did, RegLocal has convinced me that it was only 99%. Now I would rather cover the brake than the accelerator when the limit unexpectedly appears.

I revert to my old ways when I am deliberately finding the limit, but my feet are like Fred Astaire's when I'm doing that

[pim]

Very rarely use gears to slow down.Maybe in winter on a icy road when driving slow.Don't know if this is a bad habit or not.

On a straight stop before lights I tend to put the gearbox in neutral just before braking.Instead of depressing cluch the last minute.To safe on brake pads by using engine braking can't see the point.

[Pica-Pica]

Dr Jekyll said:

BricktopST205 said:

I always use gears to slow down than brakes. Engine braking is far more efficient than using brakes which is wasted energy unless you have kers. It is all about judging what is in front of you.

So if you change to a lower gear for increased engine braking, where does the energy go?

Basic law of thermodynamics, heat is work and work is heat. All braking generates heat.