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Author Topic: What is the most eco-friendly way to drive up a hill?  (Read 11711 times)

Offline onsk

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Hello

I know that in order to minimize fuel consumption, one should shift to higher gears as much as possible, and maintain a steady speed, but is this true also for driving uphill, when one has to step harder on the accelerator to maintain a steady speed, or is it better, in such cases, to shift to a lower gear, in which the engine can push the car more easily with less pressure on the accelerator?
« Last Edit: 28/04/2009 21:09:06 by chris »


 

Offline Don_1

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Re: What is the most eco-friendly way to drive up a hill?
« Reply #1 on: 27/04/2009 10:38:09 »
If the engine begins to 'labour' it is running inefficiently, not to mention liable to stall.
 

Offline onsk

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Re: What is the most eco-friendly way to drive up a hill?
« Reply #2 on: 27/04/2009 11:23:32 »
Thanks. I am still not sure what to do when I find myself in situations in which the engine does work smoothly, far from stalling, but does not deliver enough power to really accelerate the car, only to maintain the speed it is in if I step relatively hard on the accelerator. If I shift to a lower gear, less pressure is needed on the accelerator to maintain the steady speed (and if pressed harder, the car will even accelerate), but then the RPM is higher.

So, the question is this: when driving uphill, which combination is more fuel-efficient: a high gear and more pressure on the accelerator when, due to gravity, this will just maintain the speed and won't yield enough power to accelerate; or shift to a lower gear, in which the engine will work faster, but will require less pressure on the accelerator to keep the car from decelerating.
 

Offline Karsten

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Re: What is the most eco-friendly way to drive up a hill?
« Reply #3 on: 27/04/2009 17:38:33 »
Most fuel-efficient:
Let the car slow down when it goes uphill.
 

Offline onsk

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Re: What is the most eco-friendly way to drive up a hill?
« Reply #4 on: 27/04/2009 18:01:38 »
Yes, if the car has enough inertia to reach the top. This, however, is not what my question is about. I want to know whether, when driving "against gravity" for any amount of time, and engine power IS necessary to keep the car going, is it more fuel-efficient to use a lower gear, in which a small amount of pressure on the accelerator is enough to keep the car at a steady speed, with the engine working at a medium speed; or use a higher gear, in which one has to press the accelerator more just to keep the car moving at the same speed and prevent it from slowing down. The latter case is a condition in which a normal driver would shift to a lower gear, because the engine output at that RPM is low, and one has to press the accelerator hard just to keep it going at the same speed. The question is whether pressing the accelerator down at such low RPM, (in which the result of pressing it down in just enough power to keep the car moving) wastes more or less fuel than using a lower gear, in which the engine moves faster, but much less pressure on the accelerator is needed to keep it at that speed.
 

Offline Don_1

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Re: What is the most eco-friendly way to drive up a hill?
« Reply #5 on: 27/04/2009 18:13:31 »
Putting the engine under the sort of strain you are talking about can result in fuel not being burned properly. Also the strain can do damage to the engine and transmission. You are better off dropping a gear and increasing the revs.
 

Offline onsk

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Re: What is the most eco-friendly way to drive up a hill?
« Reply #6 on: 27/04/2009 18:22:31 »
Thanks again. You may be right about the fuel not being burned properly, this makes sense. But it is not clear to me why driving at a too-low gear with the accelerator pressed all the way down just to keep the car from slowing down might damage the transmission more. As far as I understand, in both cases it would be under the same amount of pressure, and even under more pressure if the car is not kept at the same speed, but is accelerated.
 

Offline Don_1

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Re: What is the most eco-friendly way to drive up a hill?
« Reply #7 on: 27/04/2009 18:34:14 »
At low speed in a high gear you are putting excessive torque on the whole transmission system, from engine to road wheel. If you need to open the throttle fully to maintain speed, you will certainly be putting the too much pressure on the whole system.
 

lyner

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Re: What is the most eco-friendly way to drive up a hill?
« Reply #8 on: 27/04/2009 19:20:42 »
I have been studying this a lot, lately on my Ford Focus, which has instant fuel consumption information. If the engine does not sound to be labouring, the highest possible gear gives the best figure. Whilst that is an objective measurement, the actual power being delivered is  hard to assess.
If you drive pretending that the car is under-powered and let is slow up on short inclines, the consumption doesn't suffer but it may annoy the guy on your tail!
 

Offline BenV

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Re: What is the most eco-friendly way to drive up a hill?
« Reply #9 on: 27/04/2009 22:31:02 »
I suspect there's far greater energy costs when coming back down - as your momentum is being lost to heat in the brakes.  I expect that the ideal 'eco' solution would be to go up in as high a gear as possible without strain, but timed in such a way as to reach your slowest (practically stopping) at the apex.  This would then mean that rather than dissipating energy all the way down the other side, you use gravity to regain momentum.

You could coast down the other side, but a driving instructor would tell you off...
 

Offline turnipsock

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Re: What is the most eco-friendly way to drive up a hill?
« Reply #10 on: 28/04/2009 00:40:52 »
is a higher gear a low ratio gear...its a bit of an ambiguous term?

for climbing hills, imagine you are a cyclist, their legs spin away at a high rate of knots (well, the ones that are good a climbing do) so I guess high revs is more efficient.
 

Offline BenV

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Re: What is the most eco-friendly way to drive up a hill?
« Reply #11 on: 28/04/2009 01:11:22 »
for climbing hills, imagine you are a cyclist, their legs spin away at a high rate of knots (well, the ones that are good a climbing do) so I guess high revs is more efficient.
I may be exposing a terrible misunderstanding of this, so feel free to correct me, But with a car, doesn't each rev use the same amount of fuel? Whereas with cycling the faster movements in lower gears require less force, so the two are not really analogous.
 

Offline Karsten

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Re: What is the most eco-friendly way to drive up a hill?
« Reply #12 on: 28/04/2009 03:01:59 »
If you are driving a manual transmission car (and I will assume you are), I would suggest you let your car slow down a bit when you reach an uphill section. If your car slows down so far that the engine seems to labor, shift into a lower gear and keep the speed you have. No reason to accelerate going uphill. If you have an tachometer (rpm gauge) that tells you the rpm of your engine you can see what downshifting does. If your engine runs rpms that are around what it usually does, you should be OK.

Once you have reached the top, shift up as soon as possible and slowly let the car gain speed again. Best to wait until it goes downhill again before you accelerate. Some people let the car accelerate in neutral on the downhills to save on gas. Some even turn off the engine when it goes downhill. Dangerous though since you loose power brakes and power steering and if you really don't pay attention could lock your steering.

Just let her coast. If coasting is not an option/not desired, help as little as possible with the engine.
 

Offline Don_1

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Re: What is the most eco-friendly way to drive up a hill?
« Reply #13 on: 28/04/2009 08:35:13 »

I may be exposing a terrible misunderstanding of this, so feel free to correct me, But with a car, doesn't each rev use the same amount of fuel?

Yes, but the burning of that fuel can be effected by the load. If the engine is under strain (labouring) the fuel in the cylinder may not all burn. This is when you get that smell of petrol (gas) or diesel in the exhaust.

.... Some even turn off the engine when it goes downhill. Dangerous though since you loose power brakes and power steering and if you really don't pay attention could lock your steering.

Just let her coast. If coasting is not an option/not desired, help as little as possible with the engine.

While this may seem to be the best option as far as fuel consumption is concerned, coasting can be dangerous, especially in less than ideal conditions and/or on a less than ideal road surface. You should always maintain traction. There are good reasons for this, not least of which is the fact that it is illegal to allow a vehicle to coast, in the UK & Europe. I suspect the same is true in the US and most other countries.
 

Offline chris

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What is the most eco-friendly way to drive up a hill?
« Reply #14 on: 28/04/2009 21:15:35 »
Ben - the engine load affects the revs and hence how hard you need to press the accelerator to achieve that rate of rpm. In other words, with the engine in neutral a light touch to the accelerator is sufficient to rev the engine up to almost red line. But in a high gear the same accelerator depression would not have the same effect. Under load the engine could be running very low revs with the accelerator wide open.

Chris
 

Offline techmind

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What is the most eco-friendly way to drive up a hill?
« Reply #15 on: 28/04/2009 22:31:08 »
At low speed in a high gear you are putting excessive torque on the whole transmission system, from engine to road wheel. If you need to open the throttle fully to maintain speed, you will certainly be putting the too much pressure on the whole system.

No - the torque in the transmission system between the gearbox and the wheels will depend only on the gradient of the hill and whether or not you are accelerating. Going uphill in too high a gear increases the torque on the between the gearbox and the engine (including the clutch).

On the other hand if you're in a low gear going uphill and jab the accelerator abruptly you could put an especially high torque into the mechanics from the gearbox to the wheels!


And these days you don't need to coast to save fuel - modern fuel injection systems will not put any fuel into the engine if you're going downhill and using engine-braking (so you might even use less fuel than if it were idling!).
 

lyner

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What is the most eco-friendly way to drive up a hill?
« Reply #16 on: 02/05/2009 13:03:37 »
Use you brakes a little as possible. If you can see a hold-up in the distance, ease up immediately. At times, you may need to issue passengers with brown trousers but you will save money. You may also offend the vehicles following you, as you slow down prematurely but stuff them.

I think that modern engine management does a lot to optimise the consumption - detecting unburnt fuel, for instance, and cutting down accordingly, when the engine is labouring (unlike a carburettor, which will pour fuel into the engine willi nilli).

Years ago I was advised to drive in bare feet with a drawing pin sticking up from the accelerator pedal. I think the principle still applies.
« Last Edit: 02/05/2009 13:08:13 by sophiecentaur »
 

Offline onsk

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What is the most eco-friendly way to drive up a hill?
« Reply #17 on: 02/05/2009 14:04:36 »
Thanks for the enlightening information. The last reply raised in passing a different problem a that has to be taken into account as well: the response of other drivers. If one's efforts to minimize fuel consumption raise the level of anger in others, make pass them speed up and pass more violently, the overall result may be the burning of more fuel.
 

lyner

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What is the most eco-friendly way to drive up a hill?
« Reply #18 on: 02/05/2009 22:50:20 »
That's up to them. They need to learn a bit of patience and self control.
Smug answer.
 

Offline Don_1

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What is the most eco-friendly way to drive up a hill?
« Reply #19 on: 03/05/2009 13:04:30 »
Thanks for the enlightening information. The last reply raised in passing a different problem a that has to be taken into account as well: the response of other drivers. If one's efforts to minimize fuel consumption raise the level of anger in others, make pass them speed up and pass more violently, the overall result may be the burning of more fuel.

This is, unfortunately a very valid point. When perfectly ordinary, nice people get behind the wheel of a car, they can turn into monsters. Its a Jekyll & Hyde thing.

High performance cars have brought great benefits to the modern auto. Without them, we would not have high performance ABS, suspension, tyres, crumple zones, aerodynamics etc. But I think we have gleaned all we need from high performance, now we should look toward high efficiency and reduce the acceleration and speed capabilities of ALL cars.

Now that will upset an awful lot of people with Porsche's, Lambo's and even Ford RS Turbo's.
 

Offline Karsten

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What is the most eco-friendly way to drive up a hill?
« Reply #20 on: 06/05/2009 21:57:46 »
Thanks for the enlightening information. The last reply raised in passing a different problem a that has to be taken into account as well: the response of other drivers. If one's efforts to minimize fuel consumption raise the level of anger in others, make pass them speed up and pass more violently, the overall result may be the burning of more fuel.

That is difficult to measure or estimate. There is not way telling whether me pushing my car harder than I like reduces overall gasoline consumption or me driving slower and other people feeling the need to drive more aggressively results in an increase. All I know is how to do it best in my situation (or think I know). I might imagine that me driving my car slowly and efficiently will be be witnessed by an engineer who works for a big car company and finally creates the efficiency control I would like to see invented and it is made available to all and reduces gas consumption even more. This is just fiction. Anything goes in fiction.

Should I not build a small house because some people will build an extra big one once they see me doing the right thing? Should I consume huge amounts of meat because vegetarians make meat eaters angry who eat more just in spite? Should I worry about other people's nasty habits taking over because they cannot handle a little slow-down? If someone is in a hurry I pull over or make it easy for them to pass me without stress. But I live in a huge place with little traffic and this is easily possible.
 

Offline nicephotog

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What is the most eco-friendly way to drive up a hill?
« Reply #21 on: 08/05/2009 02:06:17 »
Quote
Onsk:
 If I shift to a lower gear, less pressure is needed on the accelerator to maintain the steady speed (and if pressed harder, the car will even accelerate), but then the RPM is higher.

Quote
Karsten:
Most fuel-efficient:
Let the car slow down when it goes uphill.

Near right. But you need to be a motor mechenaic to know that, or unfortunately an Engineer with chemistry and a major in combustion chamber physics.

There are two, fuel metering systems(regardless the gear you are using).
1. Is with a carburetor.
With a carburetor it is best to use high RPM to go up the hill and also with some loss of speed only because the engine must not over-rev.
Carburetor types should never have the accelerator pedal down to or near the floor on a hill or massive loss of fuel occurs from a special set of holes called ports for supplying fuel under vacum(or in this case that is left of it) in the throat of the carburetor.
The two ports that cause that are called the "compemsation port", and the other is a special port that only is exposed and used under low vacum condition called the "acceleration port". The acceleration port is more plain neat whiskey than port swhen supplied to the engine. It is inclusively designed as being air to fuel ratio at the bar or table uneconomic deliberately. It simply gets roaring straight.

2. With fuel injection there is a huge improvement, but the effect can be the same as the problem of deciding what the trouble is to supply more power for the conditions the engine has to cope does not really change in that a vehicle or a driver is in. Its simply the metering is not as simple and "bravo" with the juice as the accelerator port system.

Depending having a hill behind you and the speed limit you can take a run-up by using a quantity of allowance for your vehicle to slow down before changing gear and not pushing the accelerator pedal too close to the floor.

Or just pay for more fuel.

« Last Edit: 08/05/2009 02:20:05 by nicephotog »
 

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What is the most eco-friendly way to drive up a hill?
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