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Old 12th April 2012, 22:59   #136
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Default Re: Does coasting save fuel?

Even in gear(the one in which you can climb up) the vehicle seems to be accelerating more than needed and one needs to keep the thumb on the brake.

Neutral when downhill is only the shortest way to the valley.
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Old 20th June 2013, 17:47   #137
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Red face No coasting in Neutral! Why?

First up, Hi everyone!

I am a novice driver (18y old and just got my driver's license) and a newbie here in Team-Bhp. I was reading the article that discusses about safe driving in the highway. It says "Never, ever coast in neutral or with the clutch depressed." and i was wondering why . Suppose that while driving in highways, i don't want the car to decelerate through engine braking, why shouldn't i coast in neutral or with the clutch depressed? help me and share your knowledge/experiences regarding this.

Mods: I think i have posted it in the right section. If not, please move the thread accordingly! Thanks in advance.
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Old 20th June 2013, 18:31   #138
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Default Re: No coasting in Neutral! Why?

There are two reasons for this....

1) Engine assisted braking is very important for effective braking. If Engine is in decoupled state by putting neutral or pressing clutch then brakes need to work hard. If you are in gear then engine helps in great extent while braking.

2) And what is the whole point of coasting in neutral. To save fuel? Right. Then you are wrong. Modern engines are smart engines. Your ECU calculates load on engine and based on that fuel is pumped in. It means if you are coasting in neutral then engine still needs power to idle and still some amount of fuel is pumped in. Ok fuel is saved as requirement is very low. But if you are in gear and your or on downhill. So engine has negative load you can say. in that case engine keeps rotating by rolling motion of car. So fuel supply is totally cut off from engine. Only when we have positive load then only fuel is pumped in.

Though we save fuel in coasting with neutral but advantage is really really small with today's engines. But coasting in gear gives you far more advantage in case of braking.

Last edited by sushantr5 : 20th June 2013 at 18:37.
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Old 20th June 2013, 19:24   #139
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Default Re: No coasting in Neutral! Why?

Hi kaushik51094,

There are two very detailed threads on this topic. You will get all the info in there..

1. http://www.team-bhp.com/forum/techni...ing-right.html (Shifting to Neutral or Pressing the Clutch when Braking - Is this right?)

2. http://www.team-bhp.com/forum/techni...save-fuel.html (Does coasting save fuel?)

Thanks,

Dhanush
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Old 20th June 2013, 19:25   #140
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Default Re: No coasting in Neutral! Why?

Also,

You will also notice that it is quite difficult to modulate your braking when the car is in neutral gear. 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.
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Old 20th June 2013, 19:28   #141
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Default Re: No coasting in Neutral! Why?

Quote:
Originally Posted by sushantr5 View Post
There are two reasons for this....

1) Engine assisted braking is very important for effective braking. If Engine is in decoupled state by putting neutral or pressing clutch then brakes need to work hard. If you are in gear then engine helps in great extent while braking.

2) And what is the whole point of coasting in neutral. To save fuel? Right. Then you are wrong. Modern engines are smart engines. Your ECU calculates load on engine and based on that fuel is pumped in. It means if you are coasting in neutral then engine still needs power to idle and still some amount of fuel is pumped in. Ok fuel is saved as requirement is very low. But if you are in gear and your or on downhill. So engine has negative load you can say. in that case engine keeps rotating by rolling motion of car. So fuel supply is totally cut off from engine. Only when we have positive load then only fuel is pumped in.

Though we save fuel in coasting with neutral but advantage is really really small with today's engines. But coasting in gear gives you far more advantage in case of braking.
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??

Last edited by EagleEye : 20th June 2013 at 19:30.
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Old 20th June 2013, 19:37   #142
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Default Re: No coasting in Neutral! Why?

Quote:
Originally Posted by EagleEye View Post
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??
Sir, again, let me please point you to this thread. http://www.team-bhp.com/forum/techni...save-fuel.html (Does coasting save fuel?)

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Old 20th June 2013, 19:39   #143
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Default Re: No coasting in Neutral! Why?

The topic has been discussed umpteen times in the forum.
Use the search function.
My friend and his dad has this habit of coasting in neutral for saving fuel. Earlier in their Accent CRDi and now in their Fluence.
Well, i was also guilty of coasting in neutral before stops during my initial driving years.(just hated the engine braking, thought it was a unnecessary load on the engine) but now driving the proper way.
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Old 20th June 2013, 20:17   #144
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Default Re: No coasting in Neutral! Why?

Quote:
Originally Posted by sushantr5 View Post
Engine assisted braking is very important for effective braking. If Engine is in decoupled state by putting neutral or pressing clutch then brakes need to work hard.
If engine is running then brakes would be normal irrespective of in gear or neutral. But the effects of engine braking will be missed.
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Old 20th June 2013, 20:51   #145
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Default Re: No coasting in Neutral! Why?

Most car these days (all?) have brakes that do not function well (the assist is gone) when the engine is off. So in addition to the advantages mentioned above, if you are driving someone else's car (with questionable maintenance- possibility of engine dying in idle), the brakes will still perform well since the engine is turning over. Same with power steering. 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.
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Old 20th June 2013, 21:18   #146
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Default Re: No coasting in Neutral! Why?

Neutral/Clutch braking: I beg to be differ.. In the old days, car brakes were not powerful enough to stop the car quickly enough. So everynew driver was though to use engine braking and keep downshifting as the vehicle speed reduced. These days, depending on the vehicle you drive, the brakes are powerful enough to stop the car. So in an emergency, I press the brake and the clutch. 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.
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Old 20th June 2013, 22:07   #147
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Default Re: No coasting in Neutral! Why?

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

The examiner will tell you you don't have proper car control. Apart from the various items mentioned by other members why you shouldn't do this, shifting into neutral also unsettles the balance of the car.

So don't.

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Old 20th June 2013, 22:08   #148
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Default Re: No coasting in Neutral! Why?

Quote:
Originally Posted by kaushik51094 View Post
First up, Hi everyone!

I am a novice driver (18y old and just got my driver's license) and a newbie here in Team-Bhp. I was reading the article that discusses about safe driving in the highway. It says "Never, ever coast in neutral or with the clutch depressed." and i was wondering why .
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.

There were 3 main reasons why you shouldn't coast in neutral.

(1) Possibility of brake failure. Even 30 years ago, brakes were not what they are now. Vacuum booster assist, disc brakes, DOT4 brake fluid, tandem master cylinders, high quality rubber parts, etc. didn't exist. You used the brakes too much, and you got brake fade. You used them too frequently, and the hydraulic fluid could leak out from a wheel cylinder. At the back of your mind was the worry that the next time you applied the brakes, they might not work. The next best way to slow down the car was to use engine braking - so, in preference over using the brakes to slow down and keep control over your car, you used engine braking, minimizing use of the wheel brakes. Today, engine braking in fancy cars helps to extend the life of those 50,000-rupees-a-pair brake pads.

(2) Engine braking as additional brake force. Braking the car in an emergency meant you had to apply a LOT of force on the B-pedal - actually standing on the pedal if required (no, I'm not joking - remember, no vacuum assist - and in older days, no hydraulics either), as well as pulling up the handbrake, plus some more effort - which came from engine braking. But gears were not slick and synchromesh, and took some arm-wrestling tactics to slot in. So in shifting from neutral to a gear, you lost precious seconds. To avoid losing those seconds, you left your car in gear at all times when cruising/coasting/decelerating. This also helped make for a comfortable, stress-free, no-pain-in-the-knees-from-standing-on-the-brake-pedal-at-all-times journey. Brakes have evolved, are effortless to apply, and gears slot in at the touch of your little finger today (automatics don't even stay in gear when coasting) - so this reason may not apply today for keeping a car in gear while coasting.

(3) Being ready to pull out. Dogs, cows, horses and men (and women) used to run across roads, other newbies learning to drive equally unmanageable cars as yours used to pull out at junctions, and following traffic rules had not evolved into a fine art in most parts of the world (and we all know that that is still the case in India). And it wasn't easy to slot into gear, remember? So, even today, when a truck comes charging at your B-pillar from that side road, or even when that bullock cart (or the guy driving with the mobile phone stuck to his ear) gradually wanders into your lane and is about to cut you off, while the state transport bus is trying to take up residence inside your boot, you need to floor that throttle to get you out of harm's way. And when you are happily coasting in neutral, you WILL forget to shift into gear (or get into the wrong gear) before hitting the A-pedal. In the process, you lose precious seconds and the window of opportunity closes down.

My belief is, reason (3) is the most vital reason to stay in gear and not coast in neutral. Not only do you need to brake to stay out of trouble, as a good driver you ought to remember that sometimes you need to ACCELERATE to get out of trouble. The fine judgment about when to hit the B-pedal and when the A-pedal, is what makes a superlative driver.

Hope this helps. Happy driving, and stay safe (and in gear!).
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Old 20th June 2013, 22:13   #149
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Default Re: No coasting in Neutral! Why?

Quote:
Originally Posted by Jeroen View Post
Apart from the various items mentioned by other members why you shouldn't do this, shifting into neutral also unsettles the balance of the car.
For front wheel drive or rear wheel drive car?And how is the "balance" affected whether the brakes are used or the engine braking used?

In motorcycles where balance is much more important, slipper clutches are now being fitted to reduce the effect of engine braking which riders found affects the balance when they are leaned over and braking through a corner.
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Old 20th June 2013, 22:24   #150
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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!
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