I was wondering, when going up a hill/incline is it more efficient to leave it in fifth (top gear for me) and give the car a bit more throttle but keep the revs down, or downshift into fourth or even third (I'm not talking about reving it to 5000rpm, but maybe 3000-3500rpm in fourth VS. 2500ish rpm in fifth). I guess the main question: Is it more efficient to use a few more revs with a bit less throttle or a bit more throttle with a few less revs?

Edit: I should probably add that I'm talking about a fuel injected cars.

Do you mean efficient, or economical?

I'm not 100% sure about this but I would say less revs = less fuel being burned. I hope an expert can shed more light on this though, I would like to know as well.

Quote from wheel4hummer :

Do you mean efficient, or economical?

They tend to be used interchangeably. . .

I've been experimenting with this in my own car. The MPG display is almost completely dependant on throttle position from what I've found. It is more economical for fuel to stay in the lowest gear possible, but don't forget you're causing excess wear on the engine, so it's a false economy really. This is why I tend to pop into neutral when going downhill also, it uses a slight bit of fuel to tick over, but it's saving the engine from 3000-4000 revs as opposed to maybe 600 to idle I'm sure it's possible to find a ratio for engine wear:fuel consumed, to find the most economical overall gear and throttle position to have, but I just use my car to get from A to B for now so I'm not too concerned with that

E: I would perceive efficient as meaning getting the most horsepower possible out of the engine for the MPG, and economical as getting the best MPG possible at the expense of power

Quote from dougie-lampkin :

E: I would perceive efficient as meaning getting the most horsepower possible out of the engine for the MPG, and economical as getting the best MPG possible at the expense of power

Really? Well then, I guess I mean economical.

By efficiency, I mean energy in vs. usable energy out. By economy I simply mean MPG.

Quote from dougie-lampkin :

This is why I tend to pop into neutral when going downhill

I would never do this. You lose so much control in the process. The only thing I'd ever do down hill is lift off the gas and let it coast. The engine wear when running at low RPM (2-3k) is marginal at best, so there is no real need to pop it into neutral. If you look after it correctly the engine in a car -more often than not- will out last your interest and ownership.

If you are going up a hill, I would imagine getting to the top as quickly as possible with as little throttle would be more efficient. Low rpm + more gas is asking your engine to try harder than necessary to do a % of work.

I guess it would also depend on the situation.

e.g. If you are travelling at a resonable rate of speed (I.E. the speed limit) before you get to the hill, you can use your momentum to ease the strain on the engine while in higher gears+lower revs+less throttle(gearing down if this hill is steep enough to rapidly reduce your speed of course).

:twocents:

Depends on the car and environment, but as a general rule of thumb: more revs and less throttle. This is both more efficient and economical (in terms of fuel used vs work done).

I used to drive a minibus across the hinterland. With a vehicle like that, you learn to love torque and lower gearing.

More revs and less throttle will be more efficient (and hence give more MPG - ignore what they are saying above).

And don't put the car in neutral on the way down; that's just moronic.

And potentially dangerous, as its like taking away one of the car's main controls, so you're not actually fully in control of the car, as well as engine braking.

I don't know about uphill but downhill I was always taught to keep it in gear. Modern cars don't use fuel when coasting in gear and you can engine brake meaning you don't have to use your brakes which saves them from wearing a little bit.

Quote from P5YcHoM4N :

I would never do this. You lose so much control in the process.

You see people say that, but you can still steer and brake so how do you lose so much control, fair enough you can't accelerate in neutral but why would you need to going down a hill?

because 1st it burns more fuel than coasting downhill and 2nd it's just stupid to corner while in neutral. can't explain it really but you lose the control that the accelerator gives you. weight balance and all that jazz.

Quote from Kalev EST :

I don't know about uphill but downhill I was always taught to keep it in gear. Modern cars don't use fuel when coasting in gear

it depends. i've heard if you go above some predetermined revs it will start injecting some fuel. something about above 3500ish.
but yeah, when coasting with relatively low revs you don't use any fuel.

Quote from Kalev EST :

and you can engine brake meaning you don't have to use your brakes which saves them from wearing a little bit.

your brakes are there to brake. your engine is not there to brake. your brakes are designed to wear out while using them as brakes. your engine is not.

what do you prefer? change your calipers a bit earlier or rebuild your engine a bit earlier?

The uphill thing really depends on throttle position more than revs.
A modern engine only injects the amount of fuel it can really use, but accelleration/keeping speeds at a hill is never economical. Drive in a gear high enough so you don't have to press the loud pedal through the floor, and low enough so your engine doesn't sound like Iron Maiden (haha, Runnn toooo thääää hiiiiiiiiilllllls). This will keep your engine powerful enough to get up without burning fuel by high revving or full throttle motor stutter.
For coasting it depends on where you are. if you roll up to a red light and there's a long distance to go, then neutral. If you have to break ou you are on the way downhill then the engine can brake without any problems.
During engine braking no fuel will be burnt (theoretically, in reality you burn 0.000whatever litres per 100kms) but oil will still flow through the system.
The engine IS there to brake as well and it can withstand a lot of it. No motor has ever broken down from engine braking that hasn't been already broken in some way. Especially here in the Alps you ruin your brake pads in no time if you try to go down a pass just on your wheel brakes!

The chatter about having more control when not in neutral is a bit off... If you are a hoodie with a Civic driving like a nutcase yes, you want to have more control :-) Same for Tristan e.g., he's constantly just under the limit, he needs to balance his car with everything he's got.
But in normal life, at reasonable speeds there is no need for a gear when you approach a corner or so. Except for when you have to brake, then again use the engine together with the pads.

Maaan, 's been two euros again

greetz

der butz

I am just amazed at how you folks over there even survive. What, with all the perfect control you must have when driving, how do you guys not crash everywhere...

I'm glad driving physics are different over here because its nearly impossible to find a vehicle that isn't automatic. Thus, the engine sits at idle while going downhill off the throttle all the time because of the lack of direct mechanical linkage between the drivetrain and the engine.

Seriously people, operating a car is not that difficult to do. People lose control because they are flat out complete morons, not because they coasted down a hill in neutral.

Quote from george_tsiros :

your brakes are there to brake. your engine is not there to brake. your brakes are designed to wear out while using them as brakes. your engine is not.

Utter nonsense. Using engine braking doesn't increase engine wear. On a long downhill stretch, what would YOU prefer? Boiled brakes and falling over the edge of the mountain, or a tiny, tiny, tiny, immeasurable amount of additional wear to the other side of your gear train?

Anyone, and I do mean anyone, who says that engines are not for slowing down with is a bit thick.

For starters, whilst you're in neutral (just using the brakes to slow [plus, of course, wheel bearing friction and the like]) does your engine and gearbox somehow magically not suffer any wear, or even repair itself? Of course it doesn't. You just end up putting more heat and wear into your braking system that might see you end up dead.

Definition of loss of control:

When one or more control option is not available or will take longer than prudent to become available.

ie. the inabilility to do one or more of the following instantaneously at any given point in time is deemed to be loss of control:

1. Steer
2. Brake
3. Accelerate.

Putting the car in to neutral at any time looses you the ability to accelerate. So by definition you have loss of control of your vehicle.

the amount of braking the engine can give is inexistant compared to the braking that your brakes can give. you can increase the engine braking if you downshift to twice the redline, asking the engine to rev to 12K and back, ok that way you will have a bit more braking.

also, going out of gear when going downhill is completely stupid. i can not for the life of me understand why would someone willingly do unnecessary motions to remove a method of controlling their car... for what? having the engine burn fuel idling? this brings to mind drivers who do stupid things like rev the engine while turning it off, use the starter motor for far longer than necessary, redline their engine to go faster etc

seriously

is it stupid day today? did i miss something?

Quote :

(theoretically, in reality you burn 0.000whatever litres per 100kms)

how would it do that?

what if i turn the engine off, but keep it in gear. does it still use even a drop?

Quote from tristancliffe :

Utter nonsense. Using engine braking doesn't increase engine wear. On a long downhill stretch, what would YOU prefer? Boiled brakes and falling over the edge of the mountain, or a tiny, tiny, tiny, immeasurable amount of additional wear to the other side of your gear train?

Anyone, and I do mean anyone, who says that engines are not for slowing down with is a bit thick.

you're getting on my nerves tristan. i surely hope you are not referring to me because if it were someone else i would ignore it, but i listen to your opinion and it would hurt me if you refered to me.

you think we don't have ridiculous inclinations here in greece? remember where one of the toughest rallies in the world was held. one was 1000 lakes... the other was?

of course in a steep long downhill road i would use a combination of braking, engine braking and relatively low speed. i would not either use only my brakes (which would demand my engine being near the idling speed which is not optimal for anyone) not only my engine (which would leave the brakes without work) and not go fast.

i can go sometime in a mountain road nearby and i can show how you i drive. then you can tell me if i am thick or not.

Well, in most of the cars I've driven, which is more than a couple, using the gears mean I can maintain a speed - say 40kmph - without having to use the brakes. If I was in neutral, I'd need to be applying a reasonable amount of braking effort.

Engine braking isn't insignificant when heading back down the Alps (or even a hill in your town/village).

Edit, since George posted: Yes, I was referring to you. It's just drivel I'm afraid, especially the bit about wearing the engine being the main reason not to use engine braking.

Quote from tristancliffe :

Well, in most of the cars I've driven, which is more than a couple, using the gears mean I can maintain a speed - say 40kmph - without having to use the brakes.
.

... and that's the ideal way. Same gear for downhills as the hill upwards. Easy.

did you notice what was said, that i replied to?

Quote from Kalev EST :

and you can engine brake meaning you don't have to use your brakes which saves them from wearing a little bit.

he said DON'T HAVE TO USE YOUR BRAKES.

can you now understand what i am saying that your engine is not there to brake? he says that you don't have to use the brakes! does that not imply that he is only using the engine to brake? is that good? he didn't say "don't have to only use your brakes" or "don't have to use the brakes a lot".

you are not paying enough attention i'm afraid.

How does it remove control? The idea of going downhill is to control your speed. I have a big square pedal in the middle of the floor that does that very job for me, far better then the one on the right actually. It does burn slightly more fuel, either in neutral or coasting in gear my MPG display shows 99.9 MPG though, so it's not very significant. And it does save the engine slightly, if you're coasting you're going to be revving at around 2-3k, which is 4 or 5 times more wear than caused by idling. Nothing you'll notice in the short term, but it all adds up. My car (which is VVT-i) has an idle cam, a "cruising" cam, and a fast cam position, meaning the saving is even better when the idle cam position is in operation

It takes a whole second to put in the clutch and engage a gear anyway, so I don't see what the safety issue is? If it's a large enough hill that I'm going into neutral, I'm not going to be absolutely flying it. And why would you want to sharply accelerate all of a sudden when going downhill, so much that you couldn't take a second or two to re-engage a gear?...I never said anything about staying in neutral while going around corners either? If there's a downhill road with a significant corner, it's probably a disused B-road (they've all been bypased here, the only people that use them are the locals, who beat around them anyway), in which case I won't be in neutral, I'll probably have my foot flat to the floor

Our driving instructors have a saying here: "Gears are to go, brakes are to slow". Makes sense really, you have brakes to slow you down when going downhill, engine braking won't add much of an effect unless you're revving the bejases out of the car in the first place Or you could fashion an air brake out of plywood or something, apparently the one on the Veyron has more braking power itself than the brakes on your average shopping trolley

That's not being out of control gezmoor. Being out of control is when you're struggling to stop yourself crashing. So you're saying if I'm stopped in a car park (in which I wouldn't be able to steer or accelerate suddenly, as I'm stopped obviously), I'm in immediate peril?

Tristan, if you're going down a hill long and steep enough to cause your brakes to boil and fail, engine braking (unless you're in 1st gear doing 100km/h) will have next to no effect. Even using engine braking alone (with wind resistance too), my car takes about 10 seconds to fall from 160 to 150km/h, on a flat straight motorway. Add into this a mountain road (since you're threatening falling over the edge of a mountain, it's safe to assume the road is fairly steep), and engine braking is useless. Although if I was going down a hill that steep, I would of course leave it in gear. The hills I'm talking about coasting in neutral would be a long hill just steep enough to keep your speed constant. Coasting down 1 in 5 roads is obviously fairly ridiculous