[IshaanIan]

Originally Posted by EagleEye

Agree with point no. 1 but point no. 2? For every up & down motion of the pistons some amount of fuel is always pumped into the chamber regardless of the load as long as the engine is on.
The engine maintains the RPMs according to the throttle only and not the motion of the car. This is the whole concept of engine braking and the reason why if you drive downhill in the first (or second) gear without pressing the accelerator, the car's speed will be limited by the engine.
Correct me if I'm wrong??

This is true also if your car's MID shows you an instant fuel bar or something of that sort, you will easily see that it consumes next to nothing. True there is a minimal amount of fuel that is being consumed but it is still comparable to the efficiency when the clutch is depressed.
My question is similar after I go up the flyover and begin the descent, I shift into neutral (yes yes I do not get the optimal amount of braking force blah blah) BUT I do at the same time, have my hand resting on the gear knob so I am ready to engage gear and make use of engine braking if needed or even accelerate as the case may be. So regardless of safety, is coasting in neutral harmful to the car in any way? In the same way depressing the clutch, does it actually cause more clutch wear even if it is fully depressed and one is not accelerating or slipping the clutch in any way?

[bdman]

Originally Posted by bblost

Bdman, this discussion is about coasting.
Should you coast in neutral or not.

Ooops.. Sorry guys, I think I have my threads crossed.

[sgiitk]

You should never be in neutral except when changing gears or static. So coasting is naturally ruled out.

[sushantr5]

Originally Posted by EagleEye

Agree with point no. 1 but point no. 2? For every up & down motion of the pistons some amount of fuel is always pumped into the chamber regardless of the load as long as the engine is on.
The engine maintains the RPMs according to the throttle only and not the motion of the car. This is the whole concept of engine braking and the reason why if you drive downhill in the first (or second) gear without pressing the accelerator, the car's speed will be limited by the engine.
Correct me if I'm wrong??

Car speed will be limited in gear because your downhill rolling force is spending energy on rotating the engine. It all depends on self motion force. If it is sufficient to rotate engine and still continue its motion. Then no need of fuel for engine to keep itself alive. because engine is alive by motion of car. If you are in lower gear and on downhill path then engine has larger resistance because engine rpm will be high. So you move slow. But you have sufficient motion to keep car rolling even after maintaining engine rpm then it means engine is rotating. Then fuel supply will be cutoff totally as there is no need. It all depends on roll motion force, gear, gear ratio and engine resistance.

[JediKnight]

Originally Posted by sgiitk

You should never be in neutral except when changing gears or static. So coasting is naturally ruled out.

Not that simple. It is okay to coast at very low speeds with the car in gear and the clutch full depressed. E.g. in bumper to bumper traffic suppose the car in front of you moves a few feet it is okay to gain some momentum and then coast and bring the car to a smooth halt. This is actually better for your clutch and your are not lugging engine and fighting against the engine's anti-stall.

Coasting can be dangerous in some situations. E.g. You are going downhill at high speed for long distance with the car in neutral. Now you are using only the brake to control the car. This can cause break heating and fade.

[kaushik51094]

WOW. I am overwhelmed by the replies i'm getting here. Never thought 3 pages of replies will come within 12 hours of posting a new thread! No wonder, this is the best automobile forum. . Anyways guys, thanks for all your replies. You people have lit a light in my brain and now, i'm glowing like a 1000 watt bulb (ya. really. see the icon for this post!)

Originally Posted by sushantr5

And what is the whole point of coasting in neutral. To save fuel?

Nope, i never worry about mileage or fuel costs. Just wanted to ensure safety on roads. Never thought coasting will be dangerous. Thanks for your reply.

Originally Posted by dhanushs

Hi kaushik51094,

1. http://www.team-bhp.com/forum/techni...ing-right.html

2. http://www.team-bhp.com/forum/techni...save-fuel.html

When i searched the forums, i wasn't able to get a proper explanation (or maybe that's because i went through only the first page of the search results. LOL). I don't care about saving fuel, but yes, i will read the first thread however. Thanks

Originally Posted by smartcat

Also,

Expect jerky slowdowns/stops because car brakes these days are quite "grabby". Your passengers' heads will be bobbing forwards and backwards like those hip hop stars in music videos.

LOL. Nice explanation there! I can visualize them. Thanks.

Originally Posted by DicKy

The topic has been discussed umpteen times in the forum.
Use the search function.

Sorry, searched for it but the first page of the search results didn't have answers for it, hence started this thread. Sorry if it offends you. And, thanks for the reply.

Originally Posted by RM2488

And trust me, when you're rolling downhill with no brakes, no movie can do justice to the fear that grips you. If you don't have the presence of mind to restart the engine (or faster- just throw it in gear and pop the clutch) then you're looking at a catastrophe. Better to have a habit of keeping it in gear.

Yup, will sure do it hereafter. haven't been driving a lot (I'm a newbie driver). Looks like these driving tips will save me even during a brake failure. Thanks

Originally Posted by bdman

I would also argue (that if your brakes are powerful enough) that this approach will reduce your stopping distance as your brakes do not have to fight with the engine once the wheel speed gets below what the engine is trying to keep it at.

Exactly my point. as i have done this numerous times with bikes, i thought it would be safe to continue it with cars too. Looks like it's ok at speeds below 50kmph (let's say) and anything above it, one will have to settle for engine braking. thanks for your reply.

Originally Posted by Jeroen

In many (Western) countries shifting in neutral to soon during coasting and or braking will be a 100% fail during your driving test.
Jeroen

Will keep in mind if i ever apply for a driver's license abroad. Thanks for the knowledge.

Originally Posted by SS-Traveller

Hi Kaushik, first of all, welcome aboard Team-BHP.

Next up, I am going to congratulate you on the healthy curiosity you have about the safe driving (and any other) rules - you don't follow them blindly, but question the reason(s) why. You'll make a great petrolhead yet!

Then I am going to tell you why you need to leave your car in gear when coasting or decelerating - you don't really want to trawl though dozens upon dozens of pages on those other threads, do you? But as I do that, I am going to give you a history lesson on the evolution of motorcars.


Hope this helps. Happy driving, and stay safe (and in gear!).

Thanks for the welcome and this lesson. You have put in a lot of knowledge into my brain. And yes, i now understand why no coasting in neutral. The 3rd point is vital, i see. Will remember this always. Thanks a ton for your reply. and yes, will remember to stay safe (and in gear!).

Originally Posted by abirnale

Wow! The way SS-Traveller explained the issue and reason number three, I think it's great. Although you can train yourself to act on these situations without wasting those precious seconds, I wonder if its worth doing all this ... and for what? Saving fuel or just for the sake of doing so?

I myself have faced problems at signals in Bangalore when the timing of someone honking behind you at traffic light is the fastest reaction you sometimes have to respond to green light. And if you are in neutral, due to the sheer honking pressure or sometimes being in some thoughts probably, I seldom forget to put first gear and simply rev the engine Some time that has attracted my co-passenger doubt if I know driving!

Yup, SS-Traveller has indeed given a beautiful and satisfying explanation. And, about the thing in signals, You really do that? LOL. Even if i was a passenger at such a time, i'll have the same doubt. LOL. no offence. Thanks for your reply.

Originally Posted by Ricci

I don't recommend coasting purely from a safety point of view Say, you see a traffic light about to go red - you put the car in neutral, coast slowing and let speed decay, and then brake to a halt - depending on your initial speed and distance, you will either end up braking a little to stop completely, or time it so perfectly that you coast to a near zero speed and only need a light tap on the brake to halt. At idle, this distance should be covered burning the least fuel , as compared to using the engine , since you'll be doing higher RPM, and thus have more combustion cycles even if your ECU is programmed to reduce fuel injection quantity to a minimum.

From this, i get it that coasting is ok at slow speeds (10-20kmph) but not so at high speeds. Will remember that. Thanks for your reply.

Originally Posted by bblost

My first automatic experience in the hill I forgot to shift out of D mode when going downhill.

When I finally stopped the car the smell of burning brake pads was a stark reminder of why we need engine braking.

LOL, Have never driven an automatic yet. I don't like automatic for one simple reason - what fun? But fate makes me own a scooter rather than a bike (ya ya, it was thrusted upon me by my mom, who else?). Ok, so if in an automatic, it shouldn't be in D mode while going downhill, what else should the gear be in? A noob at this, please help. and, thanks for your reply.

Originally Posted by Gansan

There is only one vehicle in which this is permitted - trains, and their drivers practice it all the time!

In a road vehicle, you want motive power and traction all the time. Disengaging power train = loss of traction and motive power. Very very dangerous. So never ever do it.

I don't get it. What does traction have to do with disengaging power train? You mean the traction b/w the tyres and the road? or b/w the powertrain and the wheels?

Originally Posted by Octane_Power

Suppose one is coasting with the clutch pressed and the gear slotted in 1st.
Due to the downhill, there is only going to be an increase in the momentum of the car; it may so happen that the car crosses 35-45 kmph without one realizing it and by mistake(or wrong reflexes in emergency situations) if the foot is lifted off the clutch one can imagine what kind of jerk the passengers and the car will suffer from.
Maybe causing some serious damage to the engine too in the process.

Finally, how much fuel would one save by doing all this coasting and stuff?
20 rs ? 25 rs? Definitely not more than that.
Come on, You own a 6 lac rupee car which as it saves you alot of money by giving excellent fuel-consumption figures, how much more do you need?
Just drive the car in gear and stay in complete control of it.That's it!
Don't waste so much of your energy in saving a couple of 10-bucks of fuel!

-Bhargav

Oh ya. Now i get it, slotting in the wrong gear at the wrong speeds does induce pretty bad jerks. But, no, i didn't ask this question with regards to saving fuel. Safety is most important. Thanks for your reply.

Originally Posted by bdman

For example what help will engine braking be on a a car braked like this?

LOL, never knew gallardo had such osm brakes!

Originally Posted by IshaanIan

This is true also if your car's MID shows you an instant fuel bar or something of that sort, you will easily see that it consumes next to nothing. True there is a minimal amount of fuel that is being consumed but it is still comparable to the efficiency when the clutch is depressed.
My question is similar after I go up the flyover and begin the descent, I shift into neutral (yes yes I do not get the optimal amount of braking force blah blah) BUT I do at the same time, have my hand resting on the gear knob so I am ready to engage gear and make use of engine braking if needed or even accelerate as the case may be. So regardless of safety, is coasting in neutral harmful to the car in any way? In the same way depressing the clutch, does it actually cause more clutch wear even if it is fully depressed and one is not accelerating or slipping the clutch in any way?

Exactly my driving style (and many others' too, i guess). Not the part about coasting (haven't done that much, knew it was dangerous, only now got to know about the reasons for it being dangerous) but the part about one hand on the steering and the other on the gear lever. And, that's a pretty good question since i think brake pads are cheaper than clutch parts. And answers for this question guys? IshaanIan, thanks for your reply.

Originally Posted by bdman

Ooops.. Sorry guys, I think I have my threads crossed.

LOL. You hijacked my thread. LOL. Just kidding.

[SS-Traveller]

Originally Posted by sgiitk

You should never be in neutral except when changing gears or static. So coasting is naturally ruled out.

Originally Posted by JediKnight

Not that simple. It is okay to coast at very low speeds with the car in gear and the clutch full depressed.

In most automatics, every time one lifts the foot off the throttle when in 'D', one coasts. Only when going downhill does one select a gear to get engine braking assist - and that's something not commonly done when going down a flyover, so coasting happens anyway!

But then again, in an automatic, this reason...

Originally Posted by SS-Traveller

(3) Being ready to pull out.

...is always a given. While coasting in 'D', flooring the throttle always selects the best ratio for acceleration, and safety isn't compromised.

[manim]

Coasting in 'N' in an AT may mean breaking the law and is very dangerous, but sometimes when I hypermile I do it on 4-lane roads with nearly no traffic to slow down.

I never do it when I climb down-hill on ghat-roads which is extremely dangerous, but I do it sometimes when I (hypermile) have to climb a flyover and come down again, I try to start the climb at the correct speed in 'N' so that I use gravity to do the work (the car slows in the climb and gains speed downhill).

I have achieved up-to 17 kmpl on the Civic-AT using these and other techniques!

[kaushik51094]

Originally Posted by SS-Traveller

While coasting in 'D', flooring the throttle always selects the best ratio for acceleration, and safety isn't compromised.

Originally Posted by manim

I never do it when I climb down-hill on ghat-roads which is extremely dangerous, but I do it sometimes when I (hypermile) have to climb a flyover and come down again, I try to start the climb at the correct speed in 'N' so that I use gravity to do the work (the car slows in the climb and gains speed downhill).

I have achieved up-to 17 kmpl on the Civic-AT using these and other techniques!

But guys, what if the auto gearbox doesn't have a selected gear ratio. Like say, it has only D-N-P-R. Then, how do you prevent coasting? I just googled "automatic transmission" and saw some gear boxes which had only these four.

[abirnale]

Originally Posted by kaushik51094

Yup, SS-Traveller has indeed given a beautiful and satisfying explanation. And, about the thing in signals, You really do that? LOL. Even if i was a passenger at such a time, i'll have the same doubt. LOL. no offence. Thanks for your reply.

Yes, you read it right, and that feeling of yours will make me more nervous

I unfortunately still have that stigma in my mind. I just get panic when many people start honking all at once without realizing that its still red. Trust me, even after lakhs of kms driving, i still get afraid of this new type of road rage if i am not myself (like bad start, tense day at work) behind the wheel - people behind you honking like mad.

And long story short - as you said fuel saving is not your intention, for pure safety reasons of acting fast, its not recommended to coast in neutral.

Happy and safe driving.

[DerAlte]

Originally Posted by manim

Coasting in 'N' in an AT may mean breaking the law and is very dangerous, but sometimes when I hypermile I do it on 4-lane roads with nearly no traffic to slow down. ...

Err... what is 'hypermile'?

Coasting in N is not breaking any law, but as @jeroen explained it is contrary to safe driving, and definitely deserving of points on / cancellation of license.

Why would one at all want to do it? Not fuel saving - since the injection controller anyhow doesn't send any fuel to the cylinder on 'no load' (flat road or downhill). Not saving the wear and tear of components (the difficult-to-understand penchance in India) - whatever is supposed to rotate or go up and down while the car is moving, will continue to do so as long as it is moving, *even if* you are in Neutral.

However, the major factor mentioned by @SS_T would be disabled / prevented from working: the ability to accelerate out of trouble. "with nearly no traffic to slow down" highlights the fact that you have not even considered what can go wrong that would require that the wheels are powered / connected to engine at all times. With Tyre problems (puncture), skids and other road surface disturbances, acceleration is the best safety move. Since you are in Neutral, you will neither have the time nor the means to make the necessary correction.

What can be a worse paradox than "... is very dangerous, but sometimes when ..."? Is there any sense to be disciplined, and then willfully let the discipline slip sometimes? If you observe, only children indulge in that for the sake of experimentation, oblivious of the risks associated. The obvious and most usual result of that is a mishap! That is not adult behaviour.

[DicKy]

Originally Posted by kaushik51094

WOW. I am overwhelmed by the replies i'm getting here. Never thought 3 pages of replies will come within 12 hours of posting a new thread! No wonder, this is the best automobile forum. . Anyways guys, thanks for all your replies. You people have lit a light in my brain and now, i'm glowing like a 1000 watt bulb (ya. really. see the icon for this post!)

Thats what makes TeamBHP....... well TeamBHP This is an auto enthusiasts virtual home!!!!

Originally Posted by kaushik51094

Sorry, searched for it but the first page of the search results didn't have answers for it, hence started this thread. Sorry if it offends you. And, thanks for the reply.

oye.. now i am really offended...
Sorry if the tone of my post made you feel i was arrogant. Now it feels like a Moderatorish post. You are free to ask any questions about cars here, thats why this community exists.
Saw others post like this in other threads where already discussed topics are brought up, so me too wrote like that

[kaushik51094]

Originally Posted by abirnale

Yes, you read it right, and that feeling of yours will make me more nervous

I unfortunately still have that stigma in my mind. I just get panic when many people start honking all at once without realizing that its still red. Trust me, even after lakhs of kms driving, i still get afraid of this new type of road rage if i am not myself (like bad start, tense day at work) behind the wheel - people behind you honking like mad.

And long story short - as you said fuel saving is not your intention, for pure safety reasons of acting fast, its not recommended to coast in neutral.

Happy and safe driving.

Yup, hate the same thing at all signals here. But, i don't panic for that, rather, i'll just stay put right there with my brakes held firmly and won't budge till the signal turns green. There have been people who have shouted at me for this, but i just tell them "you go if you are in such a hurry. I'll move only when the light turns green."

Originally Posted by DicKy

Thats what makes TeamBHP....... well TeamBHP This is an auto enthusiasts virtual home!!!!


oye.. now i am really offended...
Sorry if the tone of my post made you feel i was arrogant. Now it feels like a Moderatorish post. You are free to ask any questions about cars here, thats why this community exists.
Saw others post like this in other threads where already discussed topics are brought up, so me too wrote like that

That's ok. I for once thought you got mad at seeing this topic again. Hence apologized. I shouldn't have started this thread in the first place w/o searching for more results, my bad! Thanks to moderator GTO, he moved the thread to the correct place now.

Cheers

[SS-Traveller]

Originally Posted by kaushik51094

But guys, what if the auto gearbox doesn't have a selected gear ratio. Like say, it has only D-N-P-R. Then, how do you prevent coasting? I just googled "automatic transmission" and saw some gear boxes which had only these four.

'D' or 'Drive' automatically selects the best ratio for road speed and engine rpm combination when the engine is revved. And it's actually P-R-N-D, not D-N-P-R.

[sagarpadaki]

Originally Posted by Ricci

If fuel flow completely shuts off, won't the engine stall and quickly stop the vehicle? No, I don't agree that fuel flow is completely shut off, there will always be some fuel metered through to maintain combustion to keep the engine running, but the amount of air-fuel mixture combusted is too low to provide enough net force to maintain current speed (total opposing force greater than motive force), so the vehicle decelerates. As for stress, yes , the inertia of the vehicle and it's rotating powertrain will load the transmission and engine, won' it ? I'm not saying it will very soon require an engine rebuild, but I doubt an engine that's been heavily used with engine braking will be healthier than one with more judicious use of engine braking, other running duties/cycle being equal.

Just to confirm you that fuel supply is totally cut off while coasting in gear. Have verified it using torque android app and a obd on my I20 diesel