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Old 09-08-2014, 02:16 PM   #1 (permalink)
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Arrow Is it ok to brake after coasting towards a stop?

Hello all,

I've been debating this in mind for quite some time now and thought I would ask. I have a few questions...

First off, I drive an automatic. So I know that EOC and P&G is unsafe for my vehicle. I just coast in gear to engage DFCO and DWL on rolling terrain.

I always coast in gear whether to slow myself down or to take advantage of my DFCO. Where I live, it's flat to rolling hill terrain so I never have an opportunity to coast with engine on in neutral.

Question #1:Is it sensible, fuel economy wise, to brake after coasting to a stop? For example: Driving 45-50 MPH then coast down to 25 MPH before coming to a stop sign/stop light then applying the brake to stop.

I know that DWB is the way to drive efficiently but wouldn't the time it takes the vehicle to slow down to a stop and be in a lower gear be wasting more time and thus more fuel versus coasting down to a few MPH then using your brake to stop smoothly???


Question #2: I drive an automatic. Is it more efficient to shift to Neutral at stop lights or just keep it engaged in Drive to reduce wear on the transmission?

Am I taking full advantage of coasting? Am I doing this wrong?

If this has been addressed multiple times, I sincerely apologize.

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Last edited by SilverCrown9701; 09-08-2014 at 02:21 PM..
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Old 09-08-2014, 02:39 PM   #2 (permalink)
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Do you have a scangauge? That would be the best way to test it. I think it would be more efficient to coast to a stop in neutral. Only pressing the gas when needed. If the road goes from 50-20 slow down by coasting in neutral and come to a stop at the line. I would think this is the best way. If you are sitting at a red light you should be in neutral with the engine off. Even with it on it is better to have it in neutral and idle. A obd2 computer like a scangauge ultragauge or torque. Would be able to show you.
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Old 09-08-2014, 02:42 PM   #3 (permalink)
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DWB is an ideal term, not a practical one. The idea is to minimize braking, not to coast to every stop. You're doing great.

I leave the minivan in drive when I'm stopped. I could examine gph while in neutral vs. in drive, but I've never really wondered.
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Transmission type Efficiency
Manual neutral engine off.100% @MPG <----- Fun Fact.
Manual 1:1 gear ratio .......98%
CVT belt ............................88%
Automatic .........................86%

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Old 09-08-2014, 02:47 PM   #4 (permalink)
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edit: fat charlie beat me

Driving without brakes (DWB) isn't completely doable. It should really be called driving using the brakes as little as possible since you can't eliminate using them entirely. Every stop you make you use brakes, you just need to. If you can coast down from 45 to 25 mph before a stop thats pretty good IMO. The slower you coast down the better obviously.

I coast a fair amount in automatic transmission cars. The real test is when you put it back in gear (at speed), does it lurch? If it does, you can try to rev-match to minimize the lurch (I do this). Or, you can coast in gear (least efficient).

Idling in drive always uses a bit more fuel than shifting to neutral. On my Sunfire its about 8% more .
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Old 09-08-2014, 02:50 PM   #5 (permalink)
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If you can come to a complete stop just by dint of gravity then that's one thing, but actually driving without brakes isn't actually practicable in real life. It's an ideal to strive for, that's all. The point is to not unnecessarily throw away any kinetic energy if at all possible.
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Old 09-08-2014, 02:52 PM   #6 (permalink)
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Quote:
Originally Posted by dirtydave View Post
Do you have a scangauge? That would be the best way to test it. I think it would be more efficient to coast to a stop in neutral. Only pressing the gas when needed. If the road goes from 50-20 slow down by coasting in neutral and come to a stop at the line. I would think this is the best way. If you are sitting at a red light you should be in neutral with the engine off. Even with it on it is better to have it in neutral and idle. A obd2 computer like a scangauge ultragauge or torque. Would be able to show you.
I have UltraGauge. I don't slow down fast enough with my engine on in neutral. My car seems to coast for quite a long ways. Shutting off at lights worries me about extra wear on the starter and ignition.

My car has DFCO so that's why I figured leaving it in drive would yield better results.
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Old 09-08-2014, 02:57 PM   #7 (permalink)
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Quote:
Originally Posted by Daox View Post
edit: fat charlie beat me

Driving without brakes (DWB) isn't completely doable. It should really be called driving using the brakes as little as possible since you can't eliminate using them entirely. Every stop you make you use brakes, you just need to. If you can coast down from 45 to 25 mph before a stop thats pretty good IMO. The slower you coast down the better obviously.

I coast a fair amount in automatic transmission cars. The real test is when you put it back in gear (at speed), does it lurch? If it does, you can try to rev-match to minimize the lurch (I do this). Or, you can coast in gear (least efficient).

Idling in drive always uses a bit more fuel than shifting to neutral. On my Sunfire its about 8% more .
Ok, that's good to know! Because I've been pulling my hair out nearly at having to stop every time LOL. I don't like stops but I'd rather not get a ticket or endanger lives either.

If I can safely "coast" through a stop sign at 15-20 MPH with nobody around then I will notice that lurch when I give it a certain amount of throttle but that's when it's in DRIVE, my guess is it's trying to up shift quicker??
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Last edited by SilverCrown9701; 09-08-2014 at 03:02 PM..
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Old 09-08-2014, 03:34 PM   #8 (permalink)
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Say you go from point A to point B the most efficient way would be to only use as much gas as needed to come to a complete stop at point B. We don't want to break any laws either because all that saved gas, would be gone with 1 ticket. I drive the speed limit or near it. If I have a turn I will coast before the turn so I am going a safe speed and don't need to hit the brakes. Go as fast as you want not all of us have all goddamn day to get somewhere. I do tho #!


Every car I have ever driven uses less gas in neutral at a stop Vs drive.
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Old 09-08-2014, 03:45 PM   #9 (permalink)
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My ex-girlfriend insisted that the car used less gas in neutral than park, but I told her that it was not worth wearing out the transmission to go from 0.27 GPH to 0.25 GPH for an average of a minute or less, when the car was rated 25 MPG. If you drive 55 MPH on the freeway (limit 65), you use 2.2 GPH.
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Old 09-08-2014, 04:31 PM   #10 (permalink)
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Quote:
Originally Posted by SilverCrown9701 View Post
I have UltraGauge. I don't slow down fast enough with my engine on in neutral. My car seems to coast for quite a long ways.
That's a good thing! If you have the time, and won't be annoying following drivers (who can't pass you), then start the neutral coast sooner. That'll save more fuel.

Quote:
My car has DFCO so that's why I figured leaving it in drive would yield better results.
If you are *trying* to slow down faster than coasting in N, then using deceleration fuel cut-off in gear is more efficient than using the brakes. But coasting in N is generally more efficient than DFCO because you get off the accelerator (accel. or maintaining speed, burning the most gas) even sooner.

Also, your car only cuts fuel above a certain RPM, and possibly not at all in the lowest gears (your gauge may show you this). I recently drove a brand new Nissan 4-speed automatic that never cut fuel in 1st or 2nd gear.

Quote:
Shutting off at lights worries me about extra wear on the starter and ignition.
I only know of one person who has worn out a starter while trying to save fuel, but he was shutting off at every single opportunity, including pulse & glide (automatic). Driving a Honda.

Stopping the engine when the car is stopped is worth roughly 5-10% better fuel economy in city driving, which is why auto stop/start is now becoming common on new cars (including non-hybrids).

Whether you should do it or not is entirely up to you.

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