Slowing Down To Conserve Fuel

[mdocod]

quote:

---

green band

---

hahahahahhahahahahhahaahahahhah

I live in colorado springs.

Ask anyone what the biggest problem with our city is.


You won't hear "crime, poverty, weather, or taxes." you'll hear "red lights." some genious over in city planning decided, that to save money, we should install cheapo traffic light systems that operate on "sensors" rather than have systems that are linked and timed to create flows of traffic that move throuh many green lights at a time.

The results, are hated- Our comunity would save more on gas than the cost of having a good traffic light system installed.

I can go accross town, and hit nothing but red lights, over and over again. happens all the time.

 

[JHZR2]

quote:

---

Originally posted by NovaMan:
I drive almost 100% city, and my daily driver is an automatic (1990 Ford Taurus). I only get about 19mpg. Would I see much benefit by taking it easy on the go-pedal? I usually go 5mph over, but the last few days I seem to have slowed down for some reason.

---

acceleration in stop and go is the biggest waster of fuel of all.

Drive like there is an egg between your shoe and the gas pedal... Youll likely get 21+ MPG compared to if you drive hard, and if you accelerate to your usual speed or even a tad higher, youll not waste much time at all...

JMH

 

[Al]

quote:

---

Originally posted by JHZR2:

Originally posted by NovaMan:
[qb] Drive like there is an egg between your shoe and the gas pedal... Youll likely get 21+ MPG compared to if you drive hard, and if you accelerate to your usual speed or even a tad higher, youll not waste much time at all...

JMH

---

You are exactly right. If you are in a situation where you won't get rammed..you will get maybe a to 25% increase in gas milage by using less than 20% (15% is better) of the gas pedal range.

I get 28 mpg in my 01 Sentra that is rated as 22 mpg. city.

 

[kenw]

Back when I worked for the Cadillac dealer (1975-76), the battleships had red/yellow/green lamps that used vacuum pressure to give very useful feedback on obtaining maximum mileage. A simple vacuum guage activated the lights, red being low vacuum and low mileage, yellow fair and green good. It was amazing how you could really use these to modify your accelleration habits to keep the green light on as much as possible.

and with a 500+ cubic inch v8 under the hood, you needed all the help you could get.

 

[XS650]

quote:

---

Originally posted by JHZR2:
acceleration in stop and go is the biggest waster of fuel of all.

Drive like there is an egg between your shoe and the gas pedal... Youll likely get 21+ MPG compared to if you drive hard, and if you accelerate to your usual speed or even a tad higher, youll not waste much time at all...

JMH

---

It's the stopping using brakes that wastes the fuel, more than the acceleration does. I takes the same amount of energy to get up to speed, no matter how much throttle you use. The trick is tooperate the engine under efficient load conditions, and real light throttle isn't it.

Moderately brisk acceleration and shifting at low rpm has been shown to use less gas than creeping up to speed. The reason is that gas engines are more efficient at about 80% of full torque for a given rpm than they are at light throttle.

[ September 02, 2005, 10:04 AM: Message edited by: XS650 ]

 

[keith]

Driving habits do count for a lot. I drive with the aim to cruise at a steady speed but with only really really small corrections on the gas pedal. My wife is more herky jerky and when she drives, I can hear the automatic transmission going out and in to lockup, or shifting gears. On the same road with the same traffic, I can drive and the transmission doesn't shift. As well as less wear and tear on the transmission, I use less gas.

As stated prior, braking is the big energy waster (much less so with a regenerative hybrid). Pay attention to how much and how hard you use the brakes. One old tip from a chauffeur is that you should aim to drive so that a nearly full tumbler of water on the dashboard will not spill.

 

[brianl703]

quote:

---

Originally posted by mdocod:
some genious over in city planning decided, that to save money, we should install cheapo traffic light systems that operate on "sensors" rather than have systems that are linked and timed to create flows of traffic that move throuh many green lights at a time.

---

They don't have to link the traffic lights to synchronize them. They can use time-based synchronization, and I believe that most traffic light controllers derive their time clocks from the 60Hz powerline frequency so once the clocks are set they'll stay in sync (till the next power failure, anyway..and then it depends on the accuracy of the battery-backup clock).

Any traffic controller modern enough to operate on sensors can operate on time-based synchronization.

 

[wander2039]

Are people slowing down driving less in your cities? Yesterday while going from Kansas City to Nevada I had the truck set on 65 and I actually passed quite a few cars and not very many passed me, same going home only I passed more people than going down. I know my speedo's aren't off. Traffic today and daily seems to be getting less. I'm almost scared to park my cars on the street nowdays, both get 40+ mpg. I probably have to reason to be since they wouldn't be able to license it without a title.

 

[oilyriser]

I also tested a 1991 Dodge Grand Caravan:
71 mph -- 21 mpg
50 mph -- 29 mpg

using the same calculations as earlier:
$6.70/hr savings rate (lower due to the extreme reduced speed)

 

[NovaMan]

So it seems that while there is disagreement on optimal throttle control on acceleration (egg vs. 80%), everyone pretty much agrees I won't save much by going 40mph instead of 45?

 

[oilyriser]

Yeah, once you're down below around 45, the rolling resistance becomes the biggest factor, and that doesn't change much with speed. You'd have to ditch extra weight to make a difference.

 

[oilyriser]

1992 Subaru Legacy, FWD sedan: 75 mph -- 29 mpg; 63 mph -- 40 mpg.

300 miles at 75 takes 4 hrs, and 10.34 gal.
300 miles at 63 takes 4.76 hrs and 7.5 gal.
difference: 0.76 hrs, 2.84 gal

savings rate = 3.74 gallons per extra hour.
At $3/gal that's over $11/hour.

You'd have to earn about $15/hr before taxes to match this.

 

[Audi Junkie]

I've slowed. I keep it under 70 hwy and stay at the 45-50 sweet spot as much as possible on secondary roads. Coasting helps. I had to teach it to my nephews, they drove like playing a video game...strait from gas to brake. Two techniqiues come into play. It's hilly here, so I get off the gas before the crest and slow, just to regain speed on decent. Generally, slower on uphills and faster on downhills, I figure downhill you have some "free" (spare?) potential energy and can "waste" drag w/some extra speed and uphill you should reduce drag to help overcome the physics of ascent. I figure the optimum is not one speed, but one throttle position, and this mocks what would occur at a single position (that is hard to maintain). I simply wait until the flat or downhill section to accelerate to speed too. Another technique I use in-town is braking for redlights way before the intersection. I can maintain some velocity approaching the light so I can do a start from a roll, if it's possible to time it right. Another one...I should not say...you know those "No Turn on Red" signs? Some are pretty stupid when there is a clear mile with no traffic. VERY few tickets are written for that, BTW. Something like 40 in the whole City of Phila in a year, iirc.

 

[XS650]

quote:

---

Originally posted by oilyriser:
Yeah, once you're down below around 45, the rolling resistance becomes the biggest factor, and that doesn't change much with speed. You'd have to ditch extra weight to make a difference.

---

There is something else working against you as you slow down. At the low level of power the engine is putting out, it has just about fallen to the bottem end of the fuel efficency curve.

I can't find reference right now but remember seeing along time ago that the average car got optimum mpg someplace between about 38 and 45 mph.

If you have car that burns 0.4 gpm at idle it is getting 0 mpg at idle.

If the car is an automatic and you leave it in drive, it might roll at 5 mph at idle. That's 12.5 mpg at 5 mph. The mpg will keep improving up to some speed, then start dropping.

It would be interesting to see some mpg vs speed curves for a few cars.

 

[oilyriser]

A car with engine cutoff would be great on hilly terrain. The engine would be very efficient climbing the hill, then you'd coast down the other side with the engine stopped.

I'd like to see a car with one small engine, and one large one, connected in the middle with a clutch. The small one would be just enough to go 75 on the highway, while the large one could be started up for climbing hills. The computer would synchronize everything during the transisition. This would be more efficient than the 8-6-4 cylinder cutoff idea.

 

[Al]

quote:

---

Originally posted by oilyriser:
I'd like to see a car with one small engine, and one large one, connected in the middle with a clutch. The small one would be just enough to go 75 on the highway, while the large one could be started up for climbing hills. The computer would synchronize everything during the transisition. This would be more efficient than the 8-6-4 cylinder cutoff idea.

---

Doubt that would be a viable solution. An engine that woujld b e able to power a vehicle at 75 would be large enough that the extra complexity and weight fort both engines would't be viable. Also the expense would be out of control. A better more efficient concept (which is already available) is a low displacement (less than 2 liters) in a smaller light frame vehicle.

Engine efficiency in smaller engines is where its at. For instance..I had a 1980 Datsun with 4 speed , 1.2 liter engine. Its best milage was agout 34 mpg. I now have a heavier 01 Sentra with an automatic. Its a 2.0 Liter engine and makes 145 HP (over twice that of the 1.2) Yet I have gotten 39 mpg with it. And this engine is now one generation behind the more fuel efficient engines.

I would guess that the new Honda Si coming out witha 2.0 L engine-200Hp

will do better than that. I like to see a 1.5L with about 125 HP. It would get 50 mpg with conservative driving.

 

[XS650]

quote:

---

Originally posted by Al:
It would get 50 mpg with conservative driving.

---

Conservatives don't drive rice, they drive Merkin cars.

 

[Al]

quote:

---

Originally posted by XS650:

quote:

---

Originally posted by Al:
It would get 50 mpg with conservative driving.

---

Conservatives don't drive rice, they drive Merkin cars.

---

OK..I meant Democratic Driving

 

[oilyriser]

Honda should make the special 1.3L motor they use in the hybrid available in the non hybrid car. Subcompacts used to come with 75 hp motors, and people survived.

I'm still hoping to find data on BSFC vs engine load at different speeds for a modern engine. How badly does efficiency suffer when you take a 150 hp motor and throttle it back to 15 hp?

 

[brianl703]

I tried to get the highest possible fuel economy out of my 1996 Ford Contour on the 50-mile trip to Fredericksburg today.

According to the scangauge, I got 38.5MPG..normally I'd get 31-33MPG...with the highest till now being 35MPG. I tried to keep the gas pedal in one position as much as possible..this is all on back roads with 55MPH or slower speed limit (and very little traffic).