Question regarding manual transmissions

[myself]

First of all I'm sorry if this topic is a repeat, I'm still a noob, haha...

I've heard here and there that if I were to decelerate when I'm in gear (say slowing down in 4th), and go to neutral once the RPMs are low enough, I'd save more gas than just coasting to a stop in neutral. Is this true?

What I've heard is that there's no fuel supply when you're decelerating and the car is in gear, and it uses the car's momentum...

I'd greatly appreciate it if someone clarified this for me. Thank you.

[flylice13]

that's not true...you're using fuel everytime you decelerate or accelerate in gear. you don't use AS much fuel if you cruise in neutral or in gear with the clutch depressed.

this is the reason some people hesitate to downshift, because it uses more fuel than cruising to a stop in neutral.

[Skarbro]

that's not true...you're using fuel everytime you decelerate or accelerate in gear. you don't use AS much fuel if you cruise in neutral or in gear with the clutch depressed.

this is the reason some people hesitate to downshift, because it uses more fuel than cruising to a stop in neutral.
That's not really true. The only time you use more fuel is when you are actually are pressing the accelerator more. When downshifting, to a stop you only use a very very little amount of gas when blipping into the lower gear - then you stay off the gas while in gear, and this uses NO gas.

You won't SAVE any gas true.

The whole reason for downshifting to a stop is two-fold: control (you want to be in the right gear in emergency situations), and to put less wear on your brakes.

[TheProfessor]

I highly doubt you'd see any significant fuel savings one way or the other. I downshift when I need to slow down and put it into neutral if I need to come to a complete stop.

[Wild Weasel]

That's also not entirely true, and flylice is entirely wrong.

When you let off the accelerator entirely and the engine is still above well above idle rpm, you use NO FUEL AT ALL. The engine will entirely cut fuel until it needs to add some to maintain idle speed.

Thus, if you go down a long hill while in 5th gear with your foot off the gas, you're getting 0L/100km.

So yes, you do save gas by keeping it in gear while decelerating, and you also save a bit of brake wear as the engine is helping to slow down the car.

To take advantage of this, watch for red lights ahead and anticipate when lights are going to turn red. If you let off the gas before you get to the light when you'll be using no gas to get you to the light, and if you don't actually end up having to stop at it, you'll have saved the gas needed to accelerate again.

Just be wary of people behind you getting pissed that you're slowing down too soon. People won't necessarily know what you're doing (and that you're not actually holding them up any since there's a red light ahead) and can get irritable.

[Skarbro]

That's also not entirely true, and flylice is entirely wrong.

When you let off the accelerator entirely and the engine is still above well above idle rpm, you use NO FUEL AT ALL. The engine will entirely cut fuel until it needs to add some to maintain idle speed.

Thus, if you go down a long hill while in 5th gear with your foot off the gas, you're getting 0L/100km.

So yes, you do save gas by keeping it in gear while decelerating, and you also save a bit of brake wear as the engine is helping to slow down the car.

To take advantage of this, watch for red lights ahead and anticipate when lights are going to turn red. If you let off the gas before you get to the light when you'll be using no gas to get you to the light, and if you don't actually end up having to stop at it, you'll have saved the gas needed to accelerate again.

Just be wary of people behind you getting pissed that you're slowing down too soon. People won't necessarily know what you're doing (and that you're not actually holding them up any since there's a red light ahead) and can get irritable.
What are you saying is not entirely true?

Personally, I use a tiny bit of gas when downshifting - that little blip to get the RPMs up for rev-matching. But that's a pretty insignifcant amount of gas.

You've kinda taken the discussion beyond stopping. Sure, there is a technique involved with green-light anticipation. I'm always cautious with this practice because we've all seen idiots running red lights just after it turns red.

[Wild Weasel]

Ah... I think I misread what you said. That's correct.

He didn't ask about downshifting. He just mentioned slowing down while in gear (4th) as opposed to putting in the clutch and going neutral.

You're right in that downshifting doesn't necessarily save gas so much as it saves brakes and leaves you in a proper gear in case you need to accelerate again.

[Soyabean]

i downshift to slow down enough and then put into neutral or just step on clutch to stop. i dunno if i saves gas but i like the sound when i rev match to downshift

[tweak_s]

My first thoughts reflected those of what Skarbro/WW already said.

I do have one question though WW, for example if downshifting into3rd my engine is at say...3000, completely let off gas, will the car be using any gas? (Aside from the initial blip) I know that my dash says it doesn't but I always was wondering how that worked..

[Fuman]

skarbo/WW, you guys are too quick... lol.

[Skarbro]

My first thoughts reflected those of what Skarbro/WW already said.

I do have one question though WW, for example if downshifting into3rd my engine is at say...3000, completely let off gas, will the car be using any gas? (Aside from the initial blip) I know that my dash says it doesn't but I always was wondering how that worked..

The only time the car uses more than idle gas is when you step on the gas pedal yourself. As soon as you remove your foot from the gas pedal, the car is not using any gas - irregardless of what gear you are in or out of. The engine does run very minimum idle gas to keep itself from stalling. This is the same whether you are at a standstill or driving 100 km/h with your foot off the gas I believe. WW will correct me if I'm mistaken.


skarbo/WW, you guys are too quick... lol.

Years of practice on other car forums. :chuckle

[Wild Weasel]

That's right. When the readout says 0, it means 0. When you're in gear and decelerating with your foot off the accelerator, you are using no gas at all. The ECU will take a brief moment to know what's going on before cutting fuel entirely, and when your RPM's come down to near idle, it'll start putting gas back in to keep it at idle speed. You'll usually see that reflected on the readout. The readout tends to be pretty inaccurate a lot of the time, but when it says 0, it's 0.

[Fuman]

faster than tech support.

[Wild Weasel]

heh. Really depends on how much I know about the subject, and how busy I am at work. :chuckle

[myself]

Thanks for the elaborate responses.

Yea I didn't mean down shifting. I meant staying in a gear (for argument's sake 4th, in city driving) when you're approaching a red light and slowing down, instead of just slowing down in neutral.

Now I have another question, why does this not apply to automatic transmissions? I hear that because of the way the torque converter works.

[Skarbro]

Thanks for the elaborate responses.

Yea I didn't mean down shifting. I meant staying in a gear (for argument's sake 4th, in city driving) when you're approaching a red light and slowing down, instead of just slowing down in neutral.

Now I have another question, why does this not apply to automatic transmissions? I hear that because of the way the torque converter works.
Well first of all, it's stupid to put an auto into neutral while rolling to a stop. There's no advantage whatsoever. In fact, you'll only succeed in making your brakes wear faster.
Secondly, I'm fairly certain that in autos it's the exact same principle as a manual - if you foot is off the gas pedal, then it doesn't use any gas.

[myself]

Well first of all, it's stupid to put an auto into neutral while rolling to a stop. There's no advantage whatsoever. In fact, you'll only succeed in making your brakes wear faster.
Secondly, I'm fairly certain that in autos it's the exact same principle as a manual - if you foot is off the gas pedal, then it doesn't use any gas.

I don't mean putting an auto in neutral. I'm talking about when you're just coming to a stop while you're in drive.

[Fuman]

I don't mean putting an auto in neutral. I'm talking about when you're just coming to a stop while you're in drive.
works the same way.
If your foot is off the pedal and the car isn't idling you are not using any gas.

[Skarbro]

I don't mean putting an auto in neutral. I'm talking about when you're just coming to a stop while you're in drive.
Actually the second part of my post I was speaking about when the auto is in Drive. ;) I thought you were still comparing the two situations.

[alhope34]

I don't know what the regular 3's have, but my MS3 has DFCO, or deceleration fuel cut-off. This is a VERY useful tool for decelerating. I first read all about it on the Yaris forums. When decelerating in any gear, the ECU cuts fuel COMPLETELY to the engine, you are essentially driving for free. With my dad's auto Yaris I started to gear down to 3-2-1 down to every light and saw gains of about 6-8 MPG without changing any other habits, I still drove her as hard as ever, I would just gear it down to a stop at lights. If you want to read more on how to use DFCO to get the best MPG out of your car, this guy really knows his stuff. http://www.yarisworld.com/forums/showthread.php?t=4248&highlight=dfco





lol... fuel efficiency tips from someone driving a turbocharged car...how ironic...

[Noisy Crow]

With my dad's auto Yaris I started to gear down to 3-2-1 down to every light and saw gains of about 6-8 MPG without changing any other habits, I still drove her as hard as ever, I would just gear it down to a stop at lights.

Yep... by forcing the ECU to turn the fuel off you use less gas than you do when idling.

The thing to keep in mind with this is that you are trading clutch & syncro life for fuel economy.

[alhope34]

Yep... by forcing the ECU to turn the fuel off you use less gas than you do when idling.

The thing to keep in mind with this is that you are trading clutch & syncro life for fuel economy.

Not if you rev-match properly. Which I do. Maybe one out of 20 down shifts it will jerk a tiny bit. But then I normally just throw it in neutral when slowing for a light. I'm boosting everywhere I drive anyway, so the little bit of gas saved by taking advantage of the DFCO doesn't really matter to me. And yes, when decelerating in gear you of course use less gas than at idle, it uses NO gas!

[Mike]

I actually try to avoid downshifting when slowing down and instead I try to use my brakes. I assume that wearing down my brakes is cheaper and easier to fix then wearing down and fixing my clutch.
Is there any truth to that or am I missing something?

[Skarbro]

I actually try to avoid downshifting when slowing down and instead I try to use my brakes. I assume that wearing down my brakes is cheaper and easier to fix then wearing down and fixing my clutch.
Is there any truth to that or am I missing something?
There are definitely 2 prevailing schools of thought. It's true that you will save the clutch some wear in the long run. But the better you are at rev-matching, the less wear you will put on the clutch. But it's safer to downshift. You want to be in the right gear if you ever need to step on the gas quickly in an emergency situation.

And one more fact: It's illegal to coast in neutral in many States.

[Wild Weasel]

Yeah... people can argue over whether or not downshifting is a good idea, and the answer is generally dependant on the skill of the driver... but there's never any excuse for just coasting in neutral.

The options are to either stay in gear or downshift. You don't go to neutral until your RPM's are down to near idle speed so you're nearly stopped.

[Skarbro]

Ah good point. I assumed that Mike was talking about going into N, but he could very well have meant just leaving it in the high gear without downshifting. That's ok in my books.

[Mike]

I guess I kinda meant to say put it in neutral and brake to come to full stop. Anyway, maybe I just need to work on my skills.
Any good tips on getting better at rev-matching? Is there any good threads talking about it?

[Skarbro]

I guess I kinda meant to say put it in neutral and brake to come to full stop. Anyway, maybe I just need to work on my skills.
Any good tips on getting better at rev-matching? Is there any good threads talking about it?
The only thing I can say is practice. It will come.

Blip the revs up
Clutch in
Shift down
Clutch out

The hard part is letting the clutch out when the revs are matched. If you are revving too high or too low, then the wheels will react accordingly.

[Wild Weasel]

The only thing I can say is practice. It will come.

Blip the revs up
Clutch in
Shift down
Clutch out

The hard part is letting the clutch out when the revs are matched. If you are revving too high or too low, then the wheels will react accordingly.

Umm... not quite...

Clutch in
Blip the revs up while shifting down
Clutch out

If you've got the revs right, then the RPM shouldn't change as you let the clutch out. It'll go nice and smoothly and then you continue declerating as though you were already in the lower gear.

[Skarbro]

Umm... not quite...

Clutch in
Blip the revs up while shifting down
Clutch out

If you've got the revs right, then the RPM shouldn't change as you let the clutch out. It'll go nice and smoothly and then you continue declerating as though you were already in the lower gear.

LOL I can't believe I mixed up those steps. :chuckle

[Wild Weasel]

heh. Blipping the revs before putting the clutch in will not help you slow down... :chuckle

[Flagrum_3]

HaHa I'd love to hear a conversation between WW and Skarbro after a couple of drinks, you guys are hilarious :) (I mean that in a good way)....I think the main point and the thing to practice is you must blip the throttle at the precise moment as you let the clutch out and with the precise amount of blip to match revs.


_3


.

[Mike]

I'll try that on my way home tonight. I have a feeling there's gonna be some grinding noise happening!

[Wild Weasel]

I think you're making it sounds more complicated than it really is. It's not that precise. You put the clutch in, then give it a little stab of gas to bring the revs up. It doesn't have to happen in the same instant. It just has to happen before you let the clutch back out. Obviously with practice you can do it quicker and smoother, but there's no point in scaring the noobs.

And really... we all say "blip the throttle" simple because that's how quickly we do it.

For the slow motion version...

1. Put clutch in.
2. While moving the shifter down to the next gear, use throttle to bring the revs up to where they need to be in that next gear, and hold them there.
3. Let the clutch back out.
4. Let off the gas.

If you're wondering where the RPM's need to be for the next gear... that comes from experience. If you want to find out, and then remember, here's the basics:

If you're doing 70 km/h in 4th gear and want to downshift to 3rd...

Drive your car. When you're in 3rd gear, get up to 70 km/h. Look at your tach. That's what the RPM needs to be in 3rd gear at 70 km/h.

When you're in 4th gear at 70 km/h, they'll be lower than that. When you're downshifting, you need to bring them up to that.

When doing it quickly, only the pros would be practiced enough, and care enough, to get it dead on. When you're just driving casually, you can just give the throttle a stab to bring them up to a little higher than they need to be and then let out the clutch. If you've got it right, you won't even feel it when you let out the clutch. The rpm's will instantly snap down a little to where they need to be and you're on your way.

Conversely, if you don't give 'er enough and bring it up to a little BELOW where it needs to be, you WILL feel it when you let out the clutch. The car will lurch a little as the RPM's are forced up by the transmission. You don't want this. It's not nice and smooth, and this is when your clutch may see a little more wear than usual.

So err on the side of a little high, and then practice.

[Wild Weasel]

I'll try that on my way home tonight. I have a feeling there's gonna be some grinding noise happening!

At no point in any of this should there be any grinding of gears.

You're still only moving the gear shift while the clutch is in.

Also... don't try to downshift from 2nd to 1st. 4th to 3rd should become automatic. 3rd to 2nd will be a matter of choice, when you're in the mood. 2nd to 1st should be left for later once you're already very comfortable with the process.

The reason is that there is a large enough difference in the gear ratios that shifting to 1st can sometimes be difficult as the synchros have to get the input shaft spinning quite a bit more in the tranny. That's where double-clutching comes into play, and is far too advanced to be taught to beginners.

Of course, if you've got a speed 3 with more synchros than the chinese olympic team, it's not a big deal... but that's not the point here. :D

[Mike]

Great advices. I think I was picturing changing gear without the clutch for some reason. I had a bad a experience with my old 78 VW bus when the clutch cable snapped and I had to drive it home without a clutch. There was lots of grinding then! :chuckle