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Old 09-06-2012, 07:23 AM   #31
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The question is what if you're going to have to stop anyway, why would you hold the higher speed longer before coasting in gear vs coasting in neutral to try and maintain a higher speed at the end of the coast?
Is that a question for me? Again, my assumption is that you want to reach the stop at the same speed either way, so you can coast longer in neutral because your rate of deceleration will be less without the drag of the engine.
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Old 09-06-2012, 07:34 AM   #32
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Is that a question for me? Again, my assumption is that you want to reach the stop at the same speed either way, so you can coast longer in neutral because your rate of deceleration will be less without the drag of the engine.
The rate of deceleration would be less due to the fact that you've de-clutched the transmission from the engine in neutral sure, but if you're going to have to stop, unless the point is much further away where you can use more of your momentum over a longer period of time to slow down you'll use a lot more fuel in the short run if you pop it into neutral a the same starting speed and end up going a lot quicker before a shortly approaching stop. So its a trade off.

For stop light to stop light stuff in town its probably better to adfso down in gear and not worry about putting it into neutral. On a rural road perhaps where you can coast a good long time without interfering with traffic and end up doing better over the distance in neutral then sure. Or coasting down from the end of a 70 mi/hr freeway becoming a 50 mi/hr highway in town with traffic lights before the city bit.

I used to coast down in neutral over longer distances in my manual car, but over the shorter ones its likely better to stay in gear and be able to more quickly change acceleration rates if need be. Of course with a manual you're always in charge of gear selection no matter what, and its not really that much more effort than popping it in and out of neutral.
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Old 09-06-2012, 07:42 AM   #33
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Originally Posted by suss6052 View Post
The rate of deceleration would be less due to the fact that you've de-clutched the transmission from the engine in neutral sure, but if you're going to have to stop, unless the point is much further away where you can use more of your momentum over a longer period of time to slow down you'll use a lot more fuel in the short run if you pop it into neutral a the same starting speed and end up going a lot quicker before a shortly approaching stop. So its a trade off.

For stop light to stop light stuff in town its probably better to adfso down in gear and not worry about putting it into neutral. On a rural road perhaps where you can coast a good long time without interfering with traffic and end up doing better over the distance in neutral then sure. Or coasting down from the end of a 70 mi/hr freeway becoming a 50 mi/hr highway in town with traffic lights before the city bit.

I used to coast down in neutral over longer distances in my manual car, but over the shorter ones its likely better to stay in gear and be able to more quickly change acceleration rates if need be. Of course with a manual you're always in charge of gear selection no matter what, and its not really that much more effort than popping it in and out of neutral.
I think you're kinda stating the obvious with the first 2 paragraphs. This was just an idealistic scenario comparison to give folks food for thought and make their own conclusions. If you KNOW you're going to have to stop a half mile ahead and traffic is light ahead of you, you should be better off coasting in neutral.

As for popping it into and out of N, the consensus on this thread seems to be it should be no problem. The computer will protect the tranny if you gotta go from N to D at speed.

http://www.focusfanatics.com/forum/showthread.php?t=296990
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Old 09-06-2012, 08:58 AM   #34
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Quote:
Originally Posted by suss6052 View Post
The question is what if you're going to have to stop anyway, why would you hold the higher speed longer before coasting in gear vs coasting in neutral to try and maintain a higher speed at the end of the coast?
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Is that a question for me? Again, my assumption is that you want to reach the stop at the same speed either way, so you can coast longer in neutral because your rate of deceleration will be less without the drag of the engine.
I am thinking along the same lines as suss6052 ... If you know you have to slow down, why not take your foot off the gas at the start of the "test stretch", slow down in gear (faster than in N due to engine braking) and then just creep along for the rest of the stretch? ... Maybe this would use even less fuel than slowing down in neutral? (i.e. in actual driving I wouldn't wait to slow down like in your nifty test! :) ...
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Old 09-06-2012, 09:08 AM   #35
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I am thinking along the same lines as suss6052 ... If you know you have to slow down, why not take your foot off the gas at the start of the "test stretch", slow down in gear (faster than in N due to engine braking) and then just creep along for the rest of the stretch? ... Maybe this would use even less fuel than slowing down in neutral? (i.e. in actual driving I wouldn't wait to slow down like in your nifty test! :) ...
Technically I can imagine that might burn even less fuel, sure. But I guess it seems to me that scenario is less practical in an everyday sense than the two I considered. Who wants to slow way down in the beginning and then creep along at 10mph or so that final 1 or 2 tenths of a mile to the stop? True "creeping" is thought to be hard on the DCT clutches, plus you're going to royally piss off anyone behind you. That might be delving into "hypermiling" territory, whereas all I want to do is do some "easy" stuff in the hopes of increasing MPG by a modest 1 or so.
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Old 09-06-2012, 09:21 AM   #36
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Technically I can imagine that might burn even less fuel, sure. But I guess it seems to me that scenario is less practical in an everyday sense than the two I considered. Who wants to slow way down in the beginning and then creep along at 10mph or so that final 1 or 2 tenths of a mile to the stop? True "creeping" is thought to be hard on the DCT clutches, plus you're going to royally piss off anyone behind you. That might be delving into "hypermiling" territory, whereas all I want to do is do some "easy" stuff in the hopes of increasing MPG by a modest 1 or so.
I see what you're saying. I was thinking of the scenario where you're on a very quiet road, and you see a red light far ahead (the kind that can stay red 'forever'). In that kind of case, I would just coast in D until the light changed ... then BOOT IT cuz of the gas I had just saved!
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Old 09-06-2012, 09:49 AM   #37
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I see what you're saying. I was thinking of the scenario where you're on a very quiet road, and you see a red light far ahead (the kind that can stay red 'forever'). In that kind of case, I would just coast in D until the light changed ... then BOOT IT cuz of the gas I had just saved!
Yes, that's what I would do too. Whatever you can do to avoid having to accelerate from 0 back up to cruising speed is paramount and trumps any of the decel scenarios. I'm just talking about when you know you'll have to stop no matter what, like a stop sign or a train crossing.
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Old 09-06-2012, 10:12 AM   #38
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Yes, that's what I would do too. Whatever you can do to avoid having to accelerate from 0 back up to cruising speed is paramount and trumps any of the decel scenarios.
Yes, I always find it entertaining to see drivers rush up to the red light as if they have the devil on their backs, or that they somehow think they can intimidate the light into changing green faster just for them!
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Old 09-06-2012, 10:15 AM   #39
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Yes, I always find it entertaining to see drivers rush up to the red light as if they have the devil on their backs, or that they somehow think they can intimidate the light into changing green faster just for them!
I cheer for those guys. They race ahead and trigger the light so I don't have to stop.
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Old 09-06-2012, 10:19 AM   #40
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I cheer for those guys. They race ahead and trigger the light so I don't have to stop.
Good Point!
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