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Author Topic: Anyone shifting to neutral on downhill to save gas ? Back to Topics
Vibe03

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Toronto

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Message Posted: Jul 21, 2010 9:12:55 AM

When it is not steep downhill and you don't need to brake the car to slow it down, coasting down around 55 mph at idling gives the engine a rest also save gas. Just not sure if the vacuum and other stuff are operating at normal level
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FocusSVT
Champion Author Toronto

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Message Posted: Apr 26, 2015 11:54:20 AM

dontuknowOH
Great thoughts - hats off to you
Had been practicing it for quite some time, less wear and tear on the car and saved a lot of gas. Just changed my set of Goodyear TripleTread to Pirelli P7 All Season Plus, Goodyear gave me 70,000 miles still has good tread left but starting to have bit more road noise ( after 9 Summers ! )
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b899
Champion Author Connecticut

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Message Posted: Apr 26, 2015 8:49:47 AM

no
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GustheCat2
Champion Author San Antonio

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Message Posted: Apr 26, 2015 8:32:39 AM

No
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dontuknowOH
Champion Author Ohio

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Message Posted: Apr 26, 2015 8:07:18 AM

drydem; I'm having a bit of doubt relating to the findings of >>>> A non aerodynamic vehicle <<<< Wouldn't benefit energy wise, by releasing some of the resisting forces to motion. >>> would not help an aerodynamic vehicle <<<. ? ?

The doubt comes from knowing that heavier vehicles on down grades have more sustained ability to continue momentum, mainly by the increased weight factor, hence, the use of larger brakes necessary where increased weight is present. Saying/agreed that the bulk of non aerodynamics of vehicles does hamper any savings but the extra weight continues by gravity to balance the fuel energy use even on down grades.

It depends then on weight in motion and the % of incline, length of travel at those specs, along with the other forces, like wind, rolling friction, draft currants of traffic by traffic motion, air density, tire inflation, really many other forces.

One can tell that at times with using the cruise control, when in use it doesn't always back off Totally on certain down-grades, back off of the vehicles fuel faucet/fuel energy which is the economy part.

I just find that any vehicle can benefit from a down-grade where the level of energy gets used, regardless of it's bulk, granted the savings to be less, but not totally out of the picture, Hills have a downside, often must have an upside, that is the "Berries". or buries energy greatly! at times. I enjoy your posts, Thanks!
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KLR56
Sophomore Author Illinois

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Message Posted: Apr 25, 2015 1:10:50 PM

Yes I have. But it is illegal to do so.
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bmwred
Rookie Author Oakland

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Message Posted: Apr 25, 2015 9:34:43 AM

No
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b899
Champion Author Connecticut

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Message Posted: Apr 25, 2015 9:30:01 AM

no
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windrider17
Sophomore Author Virginia Beach

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Message Posted: Apr 25, 2015 7:41:28 AM

Yes
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drydem
Veteran Author Maryland

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Message Posted: Apr 25, 2015 7:29:28 AM

Warning: Many local jurisdictions in the USA have outlawed this practice. doing this. Barring the legality of this practice, this driving technique is called Nice in hypermiling (put in Neutral the Internal Combustion Engine) and the science-engineering has already been tested and validated via the Shell fuel efficiency marathon runs from many decades ago. Shifting into neutral on a downhill to save gas is premised on the ideal that a vehicle has enough initial momentum/speed to continue forward without additional force from the engine, by disconnecting the power plant - engine from the transmission-wheels also prevents the internal drag from the engine from slowing down the transmission-wheel, and that the force of gravity going downhill will help counteract any aerodynamic drag. On a regular car with motor running in idle the vacuum and other stuff is working at idle/no load speed. If a vehicle's initial speed is 55 mph about 50% of the energy expended is to counteract aerodynamic drag. With non aerodynamic vehicles like a Ford F-150 pickup or a hummer E3 - aerodynamic drag at 55 mph is over 66% of the energy needed to sustain a 55 mph speed and you would need a steep downhill to maintain your speed - putting your transmission in neutral would not help a non aerodynamic vehicle and your Ford F-150 pickup would quickly slow down to 40 mph unless the downhill grade was very steep, there was a +15 mph tail wind (a wind blowing from the rear to the front of your vehicle's direction) or the vehicle was drafting behind another vehicle's slipstream. All these scenarios would be risky. You probably could sustain a 50 mph coast going downhill on a slightly downhill grade road with the engines turned off or disconnected from the transmission if the vehicle was a aerodynamic 2001 Honda Insight or a GM EV1 - a tailwind, slipstream, or very steep downhill would not be needed. Disconnecting the power plant from the transmission gives you about a 5% boost in energy efficiency (which is about the same boost in MPG as from using low rolling resistant tires).

[Edited by: drydem at 4/25/2015 7:38:11 AM EST]
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StArrow68
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Message Posted: Apr 25, 2015 6:10:49 AM

herbie......, your observations seem counterintuitive to the real world. Try driving on cruise control, maintains a constant speed, folks going up hill mostly slow since they don't add gas to compensate for the hill and many pick up too much speed going down hill and don't use the brakes. Probably a good reason lots of speed traps are at the base of the hills driving back to the Bay Area from the Sierra's.
As for coasting in neutral in a manual shift car down a modest slope where the car would lose speed from engine braking, it is neither difficult nor dangerous for someone that knows what they are doing. But, it is probably stupid for most folks. Enjoy what you drive.
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gus8441
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Message Posted: Apr 25, 2015 2:11:39 AM

no
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BCNU
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Message Posted: Apr 25, 2015 1:54:32 AM

Nope
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herbiepopnecker
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Message Posted: Apr 24, 2015 11:20:51 PM

Other than being a stupid, dangerous idea most people are too chicken to even think about it. They DO rife their brakes downhill all the time. They actually go faster (over the limit) uphill, then on come the brakes and they're under the limit going down.
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jl1rp
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Message Posted: Apr 24, 2015 4:49:41 AM

no
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twt
Champion Author Virginia Beach

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Message Posted: Apr 23, 2015 5:27:42 AM

Hard, on the transmission.
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8_Ball2014
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Message Posted: Apr 23, 2015 2:01:07 AM

Time to take public transit if I'm that desperate.
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redfish67
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Message Posted: Apr 22, 2015 1:30:18 PM

no
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DAG2015
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Message Posted: Apr 22, 2015 9:00:11 AM

No.
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the1roadhog
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Message Posted: Apr 22, 2015 8:20:43 AM

nope
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hoopitup2000
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Message Posted: Apr 22, 2015 6:38:54 AM

Sure, it's a manual. No wimpy manual transmission for me.
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RalphHightower
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Message Posted: Apr 22, 2015 6:08:48 AM

No
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andy616
Rookie Author Seattle

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Message Posted: Apr 22, 2015 4:46:35 AM

never
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FocusSVT
Champion Author Toronto

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Message Posted: Apr 21, 2015 10:21:04 PM

Great topic - learnt a lot
Also getting Low Rolling Resistance tires also get better mileage and inflate tires 2+ PSI
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nickless
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Message Posted: Apr 21, 2015 4:13:29 AM

hahaha
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Kingair2013
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Message Posted: Apr 21, 2015 12:33:42 AM

Never
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JohnCur
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Message Posted: Apr 21, 2015 12:25:38 AM

no
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b899
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Message Posted: Apr 20, 2015 7:44:35 AM

no
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b899
Champion Author Connecticut

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Message Posted: Apr 20, 2015 7:43:44 AM

no
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twt
Champion Author Virginia Beach

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Message Posted: Apr 18, 2015 6:41:37 AM

Good way to mess up a transmission.
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dannidb
Rookie Author Michigan

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Message Posted: Apr 18, 2015 6:11:30 AM

haha I thought I was alone in doing this, I shift it into neutral when going downhill to those pesky four way stop signs & I seem to think it saves on my brakes also as I am not in drive when I hit that dead stop, must be used to it from driving truck all them years past,hmmmn
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PaylessKY
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Message Posted: Apr 18, 2015 5:38:18 AM

Not me
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jonjax14
Champion Author Jacksonville

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Message Posted: Apr 18, 2015 12:11:35 AM

no hills around here
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PaylessKY
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Message Posted: Apr 17, 2015 3:29:25 PM

No
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b899
Champion Author Connecticut

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Message Posted: Apr 17, 2015 6:51:29 AM

no
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poetdog73
Champion Author Toledo

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Message Posted: Apr 16, 2015 9:38:28 AM

not on this flatland
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Vin63
Champion Author San Bernardino

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Message Posted: Apr 16, 2015 9:33:20 AM

Nope, my vehicles have common rail fuel injection that shuts off when going down hill in gear.
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hyeglenn
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Message Posted: Apr 15, 2015 7:27:06 AM

Dangerous to do!
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hoopitup2000
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Message Posted: Apr 15, 2015 6:24:57 AM

Yes, at times
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dontuknowOH
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Message Posted: Apr 15, 2015 5:48:55 AM

I haven't driven many hills lately, where a fuel savings would be realized only to just let off the Go Pedal then break even on the speed/gravity balance.

I do benefit if the wind flow is with Me on the down-grades using N.. mode, by extending then the distance of ground coverage greatly at times before clicking back into drive.

No doubt My econo has DEFCO used as a fuel extender when off the pedal, still I can avoid about 3:1 ratio engine (favored) comp. braking which kills off momentum rather quickly. My idle partial consumption is very slight when engine is operating with normal temps. Summer. Often depends on the tach./Engine RPM speed in relation to gravity force/% decline.

Sometimes even slight down-grades offer a steady momentum retained speed for extended travel distance, when no braking is necessary. As far as dangerous, any driver can't throw good logic out the window for any reason.

MPG indicators do pretty well on training drivers to know if they are driving economical, many Drivers don't care, or want to be bothered about it still. Keep logical good safe following distance and you will save fuel, by less pedal braking/resuming.
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Sun_Man
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Message Posted: Apr 15, 2015 12:26:53 AM

No and I think it's dangerous
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bluebird1
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Message Posted: Apr 14, 2015 11:29:38 PM

NO...doesn't save fuel on modern cars. Most cars from early 2000 onward turn off injectors when coasting (ie. car speed exceeds engine revs), so this coasting you say is actually using more gas!!! PS: my 2002 doesn't have this but the likes of Hondas, Toyotas did!!
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b899
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Message Posted: Apr 14, 2015 6:40:45 AM

no
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juniperus98
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Message Posted: Apr 12, 2015 1:36:52 PM

No
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twt
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Message Posted: Apr 11, 2015 6:21:08 AM

Good way to blow an automatic transmission.
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andy616
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Message Posted: Apr 10, 2015 2:18:40 PM

yes
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silvereb
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Message Posted: Apr 10, 2015 1:25:30 PM

Do not try this with an automatic transmission.
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car54BC
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Message Posted: Apr 10, 2015 9:39:35 AM

No run away needed
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b899
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Message Posted: Apr 10, 2015 8:35:40 AM

no
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Skyjunky
All-Star Author Portland

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Message Posted: Apr 8, 2015 12:52:37 AM

If I need the gears to help slow me down NO if I do not and there is no traffic sometimes
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krazkar
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Message Posted: Apr 8, 2015 12:02:09 AM

Nope
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b899
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Message Posted: Apr 7, 2015 8:14:26 AM

no
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