Is engine braking good or bad?
Discussion
7db said:
jbsportstech said:
There is a thinking that changing down through intermediate gears is unnecessary in the approach to a hazard.
There's certainly some thinking that it sometimes sounds rather fruity to heel and toe down through all six...
On the motorway I try as hard as I can to avoid the brake pedal, as I know cars behind will always brake harder than I have, causing the ripple effect. In fact whenever I get on the brakes on the motorway I have one hand hovering over the hazard switch just in case of coming to a complete stop sharpish.
^^^ is that why, when you brake hard in some cars (like the Fiat 500) the hazards come on?
I learnt to heel and toe in my Citroen AX when the 2nd gear synchro started to rumble. You can't heel and toe a Series II Land Rover unless you have size 16 feet and legs like tree trunks, the pedals are too far apart as they're designed to be drivable if your wearing wellies and the brakes aren't servo assisted.
HustleRussell said:
OP, if you want to select lower gears when slowing to avoid fighting the engine or shunting about at very low engine speeds (and show your brake lights while you do it), then perhaps heel and toe is worth learning?
I've started resting my foot on the brake pedal just enough to bring the lights on or changing down to third and then braking.I learnt to heel and toe in my Citroen AX when the 2nd gear synchro started to rumble. You can't heel and toe a Series II Land Rover unless you have size 16 feet and legs like tree trunks, the pedals are too far apart as they're designed to be drivable if your wearing wellies and the brakes aren't servo assisted.
jamieduff1981 said:
I think that's rubbish. If light signals were not considered to be important then vehicles would not be required to have them and driving around with defective lights wouldn't be an offence.
It's far from the only thing people rely on, but it is an excellent early warning system.
Everyone should be aware that human depth perception is extremely unreliable and cannot be trusted. It works by measuring very small angular changes between your eyeballs as they converge on a nearer target. Huge differences in distance are needed for tiny changes in what your brain perceives to be distance. When not relying on depth perception itself, you rely on the image itself changing (i.e. relative movement). That again consumes precious time as you watch for a picture to evolve.
Brake lights (should, if the brakes are used) offer a clear and instant indicator that the car in front is slowing giving everyone else much more time to react in a safe manner. By not using your brake lights you are absolutely assured (even with your superhuman advanced driver techniques) to consume more time and allow a greater speed differential to develop with less space between you before you even acknowledge that the situation is changing.
Frankly, anyone who does not appreciate the advance warning that brake lights provide are the ones that worry me on the road, because they clearly place far, far too much trust in a human system which is scientifically accepted to be very approximate and slow to update at best.
Are you one of those people who constantly applies the brake pedal on a journey? May I say you're a flipping nuisance if you are. It's far from the only thing people rely on, but it is an excellent early warning system.
Everyone should be aware that human depth perception is extremely unreliable and cannot be trusted. It works by measuring very small angular changes between your eyeballs as they converge on a nearer target. Huge differences in distance are needed for tiny changes in what your brain perceives to be distance. When not relying on depth perception itself, you rely on the image itself changing (i.e. relative movement). That again consumes precious time as you watch for a picture to evolve.
Brake lights (should, if the brakes are used) offer a clear and instant indicator that the car in front is slowing giving everyone else much more time to react in a safe manner. By not using your brake lights you are absolutely assured (even with your superhuman advanced driver techniques) to consume more time and allow a greater speed differential to develop with less space between you before you even acknowledge that the situation is changing.
Frankly, anyone who does not appreciate the advance warning that brake lights provide are the ones that worry me on the road, because they clearly place far, far too much trust in a human system which is scientifically accepted to be very approximate and slow to update at best.
heebeegeetee said:
jamieduff1981 said:
I think that's rubbish. If light signals were not considered to be important then vehicles would not be required to have them and driving around with defective lights wouldn't be an offence.
It's far from the only thing people rely on, but it is an excellent early warning system.
Everyone should be aware that human depth perception is extremely unreliable and cannot be trusted. It works by measuring very small angular changes between your eyeballs as they converge on a nearer target. Huge differences in distance are needed for tiny changes in what your brain perceives to be distance. When not relying on depth perception itself, you rely on the image itself changing (i.e. relative movement). That again consumes precious time as you watch for a picture to evolve.
Brake lights (should, if the brakes are used) offer a clear and instant indicator that the car in front is slowing giving everyone else much more time to react in a safe manner. By not using your brake lights you are absolutely assured (even with your superhuman advanced driver techniques) to consume more time and allow a greater speed differential to develop with less space between you before you even acknowledge that the situation is changing.
Frankly, anyone who does not appreciate the advance warning that brake lights provide are the ones that worry me on the road, because they clearly place far, far too much trust in a human system which is scientifically accepted to be very approximate and slow to update at best.
Are you one of those people who constantly applies the brake pedal on a journey? May I say you're a flipping nuisance if you are. It's far from the only thing people rely on, but it is an excellent early warning system.
Everyone should be aware that human depth perception is extremely unreliable and cannot be trusted. It works by measuring very small angular changes between your eyeballs as they converge on a nearer target. Huge differences in distance are needed for tiny changes in what your brain perceives to be distance. When not relying on depth perception itself, you rely on the image itself changing (i.e. relative movement). That again consumes precious time as you watch for a picture to evolve.
Brake lights (should, if the brakes are used) offer a clear and instant indicator that the car in front is slowing giving everyone else much more time to react in a safe manner. By not using your brake lights you are absolutely assured (even with your superhuman advanced driver techniques) to consume more time and allow a greater speed differential to develop with less space between you before you even acknowledge that the situation is changing.
Frankly, anyone who does not appreciate the advance warning that brake lights provide are the ones that worry me on the road, because they clearly place far, far too much trust in a human system which is scientifically accepted to be very approximate and slow to update at best.
heebeegeetee said:
jamieduff1981 said:
I think that's rubbish. If light signals were not considered to be important then vehicles would not be required to have them and driving around with defective lights wouldn't be an offence.
It's far from the only thing people rely on, but it is an excellent early warning system.
Everyone should be aware that human depth perception is extremely unreliable and cannot be trusted. It works by measuring very small angular changes between your eyeballs as they converge on a nearer target. Huge differences in distance are needed for tiny changes in what your brain perceives to be distance. When not relying on depth perception itself, you rely on the image itself changing (i.e. relative movement). That again consumes precious time as you watch for a picture to evolve.
Brake lights (should, if the brakes are used) offer a clear and instant indicator that the car in front is slowing giving everyone else much more time to react in a safe manner. By not using your brake lights you are absolutely assured (even with your superhuman advanced driver techniques) to consume more time and allow a greater speed differential to develop with less space between you before you even acknowledge that the situation is changing.
Frankly, anyone who does not appreciate the advance warning that brake lights provide are the ones that worry me on the road, because they clearly place far, far too much trust in a human system which is scientifically accepted to be very approximate and slow to update at best.
Are you one of those people who constantly applies the brake pedal on a journey? May I say you're a flipping nuisance if you are. It's far from the only thing people rely on, but it is an excellent early warning system.
Everyone should be aware that human depth perception is extremely unreliable and cannot be trusted. It works by measuring very small angular changes between your eyeballs as they converge on a nearer target. Huge differences in distance are needed for tiny changes in what your brain perceives to be distance. When not relying on depth perception itself, you rely on the image itself changing (i.e. relative movement). That again consumes precious time as you watch for a picture to evolve.
Brake lights (should, if the brakes are used) offer a clear and instant indicator that the car in front is slowing giving everyone else much more time to react in a safe manner. By not using your brake lights you are absolutely assured (even with your superhuman advanced driver techniques) to consume more time and allow a greater speed differential to develop with less space between you before you even acknowledge that the situation is changing.
Frankly, anyone who does not appreciate the advance warning that brake lights provide are the ones that worry me on the road, because they clearly place far, far too much trust in a human system which is scientifically accepted to be very approximate and slow to update at best.
real4star said:
When driving Dads (1960)Land Rover to Tesco in Strood
I go around the one way system in top gear (4th)
Indicate and turn left into the side road after the traffic lights (at McDonalds).
I back nearly all the way off the power to start slowing down and follow the bumpy potholed road around to the right.
I change down into 3rd (still slowing) and indicate right to enter Tesco.
Double de-clutch down into 2nd (no synchro) and make the turn into the carpark.
Double de-clutch into 1st and pootle around to find a parking space.
As I was walking into the store I was stopped by another customer (who followed me in) and was informed he had nearly run into the back of me because 'your brakelights aren't working'.
I didn't brake until I was parked as the speed of travel can be controlled easily with the gears.
Did I do something wrong/illegal or was he just following too close?
Nothing wrong in what you describe - just a case of the other driver not paying attention to their driving.I go around the one way system in top gear (4th)
Indicate and turn left into the side road after the traffic lights (at McDonalds).
I back nearly all the way off the power to start slowing down and follow the bumpy potholed road around to the right.
I change down into 3rd (still slowing) and indicate right to enter Tesco.
Double de-clutch down into 2nd (no synchro) and make the turn into the carpark.
Double de-clutch into 1st and pootle around to find a parking space.
As I was walking into the store I was stopped by another customer (who followed me in) and was informed he had nearly run into the back of me because 'your brakelights aren't working'.
I didn't brake until I was parked as the speed of travel can be controlled easily with the gears.
Did I do something wrong/illegal or was he just following too close?
Edited by real4star on Saturday 29th December 03:00
Red fergie
Sir Fergie said:
Nothing wrong in what you describe - just a case of the other driver not paying attention to their driving.
Red fergie
Are we going round again? It must be better to proactively communicate than not bother and rely on "he did it Sir" come crunch time. Risk reduction (aka increasing safety) is the prime tenet of Advanced Driving surely?Red fergie
Wouldn't it be far better if the brake lights came on when engine braking is applied, or perhaps some other light that signaled to rear drivers that the vehicle is coasting/gradually loosing speed? (god knows what kind of disco you would get on a motorway).
I quite often slow down via changing gear (was a major part of my lessons in 2011) however if there is some smart driver who thinks its a 0.2 second rule then i will use my brakes as i don't want them going into the back of me.
I wish more drivers were eco drivers. I need better mpg and prefer reducing speed gradually, but sometimes its just not safe to do so (e.g. duel carriageway roundabout/traffic light junctions.
I quite often slow down via changing gear (was a major part of my lessons in 2011) however if there is some smart driver who thinks its a 0.2 second rule then i will use my brakes as i don't want them going into the back of me.
I wish more drivers were eco drivers. I need better mpg and prefer reducing speed gradually, but sometimes its just not safe to do so (e.g. duel carriageway roundabout/traffic light junctions.
timtoo2 said:
Wouldn't it be far better if the brake lights came on when engine braking is applied, or perhaps some other light that signaled to rear drivers that the vehicle is coasting/gradually loosing speed? (god knows what kind of disco you would get on a motorway).
I quite often slow down via changing gear (was a major part of my lessons in 2011) however if there is some smart driver who thinks its a 0.2 second rule then i will use my brakes as i don't want them going into the back of me.
I wish more drivers were eco drivers. I need better mpg and prefer reducing speed gradually, but sometimes its just not safe to do so (e.g. duel carriageway roundabout/traffic light junctions.
I've considered in the past it would be good if brake lights also indicated a rate of deceleration. With LEDs now in common use, you could have one or more strips of them. Harder you slow down the more lights in the strip illuminate from the centre to the outside of the car. Would need some rule about not coming on for the general ebb and flow of a human controlling speed. But link it to the speed sensors required for ABS etc anyway, and you're away. Currently we have cars flashing their hazards during hard "panic" braking, so it's not without some form of precedent.I quite often slow down via changing gear (was a major part of my lessons in 2011) however if there is some smart driver who thinks its a 0.2 second rule then i will use my brakes as i don't want them going into the back of me.
I wish more drivers were eco drivers. I need better mpg and prefer reducing speed gradually, but sometimes its just not safe to do so (e.g. duel carriageway roundabout/traffic light junctions.
Wonder how much it'd cost to make it as an "aftermarket" bolt/stick on
timtoo2 said:
I wish more drivers were eco drivers. I need better mpg and prefer reducing speed gradually, but sometimes its just not safe to do so (e.g. duel carriageway roundabout/traffic light junctions.
I remember asking someone once, when conducting 'eco' training what they felt constituted eco driving. Their answer was ‘not to brake’. When I asked them why braking wasted fuel they didn’t know, just heard it somewhere.Our choice of deceleration method should be dependent on various factors, not least what’s going on behind (as you have mentioned), therefore smooth, progressive braking up to roundabouts will not use anymore fuel than taking your foot off the accelerator sooner. The skill (that in my experience) many lack is in judging speed & distance, applying the right amount of pressure to the brakes to get them there linked to forward observation to spot safe opportunities to proceed. Hope that makes sense
7mike said:
I remember asking someone once, when conducting 'eco' training what they felt constituted eco driving. Their answer was ‘not to brake’. When I asked them why braking wasted fuel they didn’t know, just heard it somewhere.
I happen to think that driving slowly and without braking is a fairly bland form of the art, but I do believe that the two factors which affect fuel consumption most are use of the brake pedal and mean squared speed, since these are the places where energy can be dissipated other than usefully. The 40 everywhere brigade do probably get good mileage -- which shows why one should have a job to buy more fuel, IMHO.The reasoning for the brake pedal decreasing mpg is motivated through a thought experiment. Imagine accelerating a car upto 50mph and then running out of fuel (in neutral, as luck would have it). The mpg of the journey is now solely determined by the distance, since there is no more fuel to use. Any use of the brakes will reduce the ultimate stopping point and overall m for the same g. Hence a worse consumption.
Another way to think about it is what the pedals do to mpg. The accelerator, increases the amount of fuel used, but also increases the amount of miles travelled. It is contributing to both numerator and denominator in mpg. The brake doesn't affect the amount of fuel used (so tempting to think it doesn't affect consumption), but it purely reduces the number of miles travelled, so it affects the fuel consumption quotient purely in a worse direction.
Practically, when I've run "not braking" exercises as part of my driving, I've noticed improved mileage. The trick is to get your kicks in the first third.
Edited by 7db on Monday 28th January 22:59
If you rev-match on down shifts in this 'no braking' experiment you are using the throttle to slow yourself down. At least the brakes slow you down, without using any fuel!
But more importantly, if you're not rev-matching, then slowing the car down with the clutch with increase friction disc wear and a set of brake pads will probably cost you £50 on parts and a DIY job in 40 mins. But a clutch could cost upwards of £200 and isn't much fun, laying on your back on a cold drive-way!
Also, for braking, it means you will probably corner slower. The pennies saved per tank full, for the sake of not braking and cornering faster, you'll more than likely have to spend in premature tyre wear.
If you're that conscious about your MPG, buy a diesel. And if you have, ride to work instead...
But more importantly, if you're not rev-matching, then slowing the car down with the clutch with increase friction disc wear and a set of brake pads will probably cost you £50 on parts and a DIY job in 40 mins. But a clutch could cost upwards of £200 and isn't much fun, laying on your back on a cold drive-way!
Also, for braking, it means you will probably corner slower. The pennies saved per tank full, for the sake of not braking and cornering faster, you'll more than likely have to spend in premature tyre wear.
If you're that conscious about your MPG, buy a diesel. And if you have, ride to work instead...
7mike said:
otolith said:
7mike said:
smooth, progressive braking up to roundabouts will not use anymore fuel than taking your foot off the accelerator sooner.
Can you expand on your reasoning for this?otolith said:
We're not talking about safety here - if you had said "smooth, progressive braking up to roundabouts will use more fuel than taking your foot off the accelerator sooner but will be safer" that would be a different statement.
Depends whether you want to factor in an additional trip to the body shop 
I also said
7mike said:
Our choice of deceleration method should be dependent on various factors, not least what’s going on behind
So I suspect we adopt similar methods; with good judgement of deceleration & distance to cover the brakes can be applied lightly, sufficient to light up the brake lights whilst achieving the same benefits of being off the accelerator longer. I accept what you're saying though, I did say brake rather than off the gas sooner (my mistake).7mike said:
Our choice of deceleration method should be dependent on various factors, not least what’s going on behind
That is the ultimate answer, for any given situation. I'm trying to find out if engine braking uses more fuel as it raises RPM when you change down (even though you are not using the gas pedal?) all I know is that modern Mini engines don't use any fuel until when you lift your foot off the gas - therefore I would infer you will get better MPG by lifting and costing to a stop that keeping on the gas and braking. I'm not aware if this is commonplace for all manufacturers yet? (and also, surely it must use some fuel as a tick over of the engine?) I'm sure there would be some impact on engine life etc, but if your engine is still using fuel when engine braking and higher RPMs (even if for a short few seconds) would you end up with worst MPG?
if anyone understands my point well done!
timtoo2 said:
That is the ultimate answer, for any given situation.
I'm trying to find out if engine braking uses more fuel as it raises RPM when you change down (even though you are not using the gas pedal?) all I know is that modern Mini engines don't use any fuel until when you lift your foot off the gas - therefore I would infer you will get better MPG by lifting and costing to a stop that keeping on the gas and braking. I'm not aware if this is commonplace for all manufacturers yet? (and also, surely it must use some fuel as a tick over of the engine?) I'm sure there would be some impact on engine life etc, but if your engine is still using fuel when engine braking and higher RPMs (even if for a short few seconds) would you end up with worst MPG?
if anyone understands my point well done!
As I understand it (happy to be corrected): on an ECU controlled car, when you are off the throttle, and the forward momentum of the car turns the engine at a speed [perhaps some way] above idle, I would expect no fuel to be injected. If it didn't then you'd have unburnt fuel which is a problem for cats etc.I'm trying to find out if engine braking uses more fuel as it raises RPM when you change down (even though you are not using the gas pedal?) all I know is that modern Mini engines don't use any fuel until when you lift your foot off the gas - therefore I would infer you will get better MPG by lifting and costing to a stop that keeping on the gas and braking. I'm not aware if this is commonplace for all manufacturers yet? (and also, surely it must use some fuel as a tick over of the engine?) I'm sure there would be some impact on engine life etc, but if your engine is still using fuel when engine braking and higher RPMs (even if for a short few seconds) would you end up with worst MPG?
if anyone understands my point well done!
Regarding changedown, you appear to be talking about unmatched shifts, i.e. not blipping the throttle to raise the revs for the new gear. The same principle as before stands, unless you let it fall to idle, but you are adding wear to the drivetrain as a previous poster describes.
Edit, so that you are clear about this: when you change down and the revs go up, what actually happens is you are turning some of the energy in the car's forward motion into accelerating the engine up to the required RPM (which for a given speed is of course higher in the lower gear). This has to happen in the time window between clutch down and clutch up, which is brief, and the sudden energy transfer can cause undue wear.
A better changedown involves a blip of the throttle. However, at least if you do this in a manual car, the clutch is depressed and the fuel required to freely rev the engine must be fairly small in the grand scheme of things.[/footnote]
Edited by trashbat on Tuesday 29th January 13:19
7mike said:
So I suspect we adopt similar methods; with good judgement of deceleration & distance to cover the brakes can be applied lightly, sufficient to light up the brake lights whilst achieving the same benefits of being off the accelerator longer. I accept what you're saying though, I did say brake rather than off the gas sooner (my mistake).
Similar to the IAM/RoSPA stance on using lower gears in urban limits, sacrificing some fuel economy for better control - although I do remember seeing one of those organisations being quoted as saying that there was no economy cost, which isn't the case in any car I've measured it in!
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