Neutral at red lights w/ handbrake up?

illumination on 10/06/2013 - 13:59

I've been driving an automatic, and I've developed a habit of changing to neutral gear and pulling up the handbrake while at a red light. I used to change gears to neutral while going downhill but changed that habit as people told me it's not good to change to N while in motion. The logic is as follows:

  • On drive, the car moves forward (albeit at a slow speed) i.e. it uses up some petrol doing so
  • While at a red light on drive, you are stepping on the brakes to prevent it from moving forward. AFAIK, accelerating AND braking use up petrol
  • Change to neutral and the momentum of the car is determined by the slope
  • Pull the handbrake up and you're not wearing down your brake pads

Sounds like everything is a win-win. Everything makes sense.

Based on some comments from the recent Fiat 500 deal, I decided to try and Google to see if I could get any conclusive answer as to whether it's worth it or not.

Whirlpool forum post from 2006 - first few posts seem to say it's not a problem, while the posts further down talk about wearing down the gearbox
Forum post from 2008 on Gas Savers - they mostly seem to be in support of changing to Neutral while at red light
Forum post from 2003 - seem to be against it.

TLDR: Is it bad to change to neutral gear with handbrake up at a red light?
From reading various forum posts..
Arguments for: Yes it is fine. It saves a bit of petrol (minimal) but it doesn't take much effort.
Arguments against: No don't do it. It wears down the gearbox.

What's your 2 cents?

Automotive

Comments

        • _Bruce_ on 11/06/2013 - 13:03
          +2

          Note that this depends a lot on your car. Most cars take more petrol to start than to keep running, how much more determines how long it needs to be off for to pay off. Additionally most engines are not designed to be turned on/off so frequenty.

          You also run the risk of flattening the battery if you are stopping a lot.

          Even this very green baised source gives 30 seconds:
          http://drivesmarterchallenge.org/money-saving-tips/myths.asp…

          "You should not turn your engine off at a traffic light. However, if you are stuck at a train crossing or bridge opening, and it is likely you are going to be parked for a number of minutes, you should turn off your engine."

          Many other sources say up to 10 minutes.

        • tonyjzx on 11/06/2013 - 16:17
          +2

          realfamilyman,

          you really have no idea how an automatic car works (to be honest, how an automatic WORKS INSIDE largely evades me too)

          a car spins faster in neutral because the car is NOT UNDER LOAD

          ie. if i ask you to pedal a bike that has its back wheel off the ground, how easy do you think it is?

          a car in D but with you on the brake means the engine is still spinning the torque converter but it isnt passing rotating power to the transmission

          it IS passing power, if you take your foot off the brake, the car creeps

          a car not under load will use less petrol than a car under ANY load

          however… i do whats comfortable for me all the time and stuff petrol consumption of mechanical sympathy

          again i dislike that feeling like as if you're on the brake and the motor is OBVIOUSLY trying to force the car forward but you're holding it back on the brake

          to me this feels weird

          i will put up with it for a short length of time but in anything over say a minute, i stick it in the neutral and maybe use the handbrake just the brake

          of course if i'm driving a car with a footbrake or dash mounted brake, forget it

          stuff that for joke, just use the normal brake

        • _Bruce_ on 11/06/2013 - 16:56
          +2

          a car in D but with you on the brake means the engine is still spinning the torque converter but it isnt passing rotating power to the transmission

          it IS passing power, if you take your foot off the brake, the car creeps

          a car not under load will use less petrol than a car under ANY load

          To be pedantic, the power loss in the torque converter does not assume a reduction in petrol consumption, particularly if the RPM does drop. It just moves where the power loss is occuring.

        • Mungulz on 11/06/2013 - 23:59
          +3

          Don't turn your car off at the lights, that's retarded.

          Have fun changing your starter motor and battery on a regular basis.

        • MATTDAMON on 12/06/2013 - 04:26

          Shouldnt effect the battery especially if you drive it some distance, the power used to crank over a hot motor is relatively minor. As for the starter motor yes you are correct, its why these new cars with stop start technology have such beefy starter motors (the one on the VW Diesels with bluemotion is almost the same size as the one in my truck!)

        • jatcave on 13/06/2013 - 20:23
          +2

          Be sure to let us know ow long your starter motor lasts. Thanks

        • Davo1111 on 14/06/2013 - 12:53

          @Munguluz

          My friends car - Mitsubishi lancer? (or something similar) turns off at the lights. I asked him if it saved fuel. He said he didn't know, but it showed the amount of time the vehicle has been turned off for. It was a new car and it showed he had been turned off at the light for 8 hours. Not sure what that amounts to in petrol consumption, but it seems like it's probably saving him some fuel.

        • John Dough on 14/06/2013 - 14:09

          Assuming 1L per hour saved at idle, it would add up over the years if you did the kays in heavy traffic i guess.

          I would be interested to see real world figures compared to the extra cost of specialist stop start battery and starter motor (yes they are quite different and a LOT more expensive than normal ones) hmmm

          I was interested in a subaru XV with this tech, and my brother who is an auto elec by trade said to steer well clear as the specialist parts are very expensive when they wear out or fail. He sees a lot of cars every day and knows his stuff!

        • MATTDAMON on 15/06/2013 - 10:19
          -1

          There should a setting somewhere to turn it off, i know the bluemotion in VW can be switched off via the settings.

          Some of our Auto trucks have the feature of neutralizing when the ECU detects a gain to be had when at idle, its a funny feeling.

        • tonyjzx on 17/06/2013 - 22:54

          very new cars have Stop Start technology

          obviously if its designed to do that, let it do that

        • Medrad on 01/08/2013 - 11:55

          DO NOT TURN YOUR CAR OFF IN ANY CIRCUMSTANCES WHEN IN MOVING (or semimoving) TRAFFIC!

          By turning your car off you lose control of your brakes, steering and some emergency functions.

          If you need to move your car in a hurry or have full need of brakes, you won't have this ability and safety is a major concern.

          Just leave your car in drive, realise that they're designed for this, suck up the extra drop in the tank that you might or might not be using, operate a car safely.

          edit this comment didn't post below the post I hit reply to. Sorry team!

  • robbie613 on 11/06/2013 - 12:58

    Not sure about other cars, but when I pull the hand brake on my car, I get brake lights out the back. Kinds of makes sense, no? So the rear lights argument isn't valid. It's more a question of petrol use /engine wear.

    For me, it's more if I want to shuffle around in the car (kids want a toy, need to turn my head). If I put it in park and put on the hand-brake, my right foot can relax.

    • _Bruce_ on 11/06/2013 - 13:05

      What car is this? It is certainly far more common for the hand brake not to trigger the rear lights.

      • robbie613 on 11/06/2013 - 13:07

        Jeep Grand Cherokee. Can't say i've tested other cars extensively for this though. BTW I obviously meant left foot not right foot in previous post :)

        • jatcave on 13/06/2013 - 20:30

          I sure hope you did mean your right foot. In an auto, your left foot should not be used. I see numerous people drive with their left foot resting on the brake pedal. The brake lights come on early in the piece, so they are constantly on, thus eliminating their usefulness entirely.

  • grechy on 11/06/2013 - 16:54
    +2

    Buy a hybrid.. Otherwise it simply isn't worth it even if it saved you $2 a week. The risk of accidentally going into reverse and forgetting your not in drive ect isn't worth it.

    • onlyletters on 12/06/2013 - 16:48

      and when your out of warranty, which mechanic will even touch your car?

  • bargdebarg on 11/06/2013 - 18:05
    +3

    best option is not to drive, save on wear and tear!

  • Cheapo333 on 11/06/2013 - 20:02
    +1

    In the AU Falcon, applying and releasing the handbrake repeatedly loosens the handbrake shoe. Gradually, the handbrake clicks become too high and pulling the handbrake all the way up fails to fully lock the rear wheels.

    I usually tighten the handbrake shoe up myself once a year.
    Last time I brought the handbrake down from 18 clicks to 5 clicks.

    Yes, I like it tight.

    • [Deactivated] on 12/06/2013 - 07:44

      Agree somewhat. Excessive use of your handbrake will stretch the handbrake cable which causes the handbrake shoe to loosen. Neglecting to tighten the cable regularly will cause the handbrake to fail over an extended period of time and will cause to vehicle roll when parked and left in neutral. Learnt this during advanced driver training.

  • deviant on 11/06/2013 - 22:31

    how about when you are going 60km/h and instead of going to neutral and letting it slide, you downshift the gears? say from 4th gear to 2nd gear? of course this wastes more petrol but does it wear the gears?

    • _Bruce_ on 12/06/2013 - 07:32
      +1

      how about when you are going 60km/h and instead of going to neutral and letting it slide, you downshift the gears? say from 4th gear to 2nd gear? of course this wastes more petrol but does it wear the gears?

      It uses less petrol. I don't understand why people keep getting this so wrong.

      As long as you are not letting your engine rev up too much you are saving your brakes and petrol. Just be careful about the driver behind you not paying attention.

      • John Dough on 12/06/2013 - 13:28

        If your foot is 0% on the accelerator you are using next to no fuel when decelerating. At idle you use a little more to keep the motor running.

    • onlyletters on 12/06/2013 - 16:47

      why would you develop a silly habit, are you aware that this will kill your transmission? its not made to be driven this way.

      • Mungulz on 13/06/2013 - 10:38

        Well then buy a real car, I have a Volvo 240 and still smash through gears sometimes when having fun, it will chirp a rear tyre from compression lockup when I hit first.

        300,000km on it.

  • SydBargainer on 12/06/2013 - 13:14
    +1

    Sell Automatic. Buy manual. Problem solved.

    • [Deactivated] on 12/06/2013 - 14:53
      +3

      Get a push bike. No manual or automatic to worry about. No registration. No insurance and 100% NO fuel bills.

      • onlyletters on 12/06/2013 - 16:46
        +1

        yes but you get to work late and your more likely to die crashing into a car coming out of a drive way.

        • [Deactivated] on 12/06/2013 - 20:21

          Leave home an hour earlier. The cars coming out of driveways is a problem. Not much that can be done about that.

        • Oofy Doofy on 13/06/2013 - 11:05
          +1

          I have to say a bike is a good idea, but in Brisbane 1/3rd of all emergency admissions are from bicycle riders. (the stat is out there, was in the newspapers recently).

          If not for the fact our roads and walkways are not designed for bikes, I would say peddling to and fro most places would be a good idea much of the time.

        • RefusdClassification on 15/06/2013 - 02:35
          -1

          I don't understand why people espouse bicycles so much. They are fine for just travelling around your own suburb (down to the library, video rental store, doctor, etc), but useless for shopping, and if you have to travel a long distance you arrive sweating, panting and totally unpresentable. And don't even think about riding when it's raining.

          All of my friends love their automobiles and never uses public transport or bicycles unless absolutely necessary. Bicycles and communal transport are for students and people on welfare that are too poor or sick to own and operate automobiles. I am sorry to say this, but people who think riding a bike makes them hip and superior are deluded omega-male losers. How impressed would a date be if you arrived at her house on a rusty old $250 mountain bike? You could get away with it in India or China, but not in a wealthy nation like Oz.

          The higher the rate of automobile ownership per capita, the more prosperous a country - Australia has about 800 per 1000 people! Quite a few households in the middle class suburb where I live have 4 cars and a garage or carport added after the house was built (we only have 1 car).

          And you are correct about bicycles being unsafe. My brother has hit by a car while riding 6 months back and needed surgery to fix his broken body. He was taking narcotic analgesic for several months afterwards.

        • illumination on 16/06/2013 - 01:56

          @Thaal
          I agree with your first paragraph about bicycles.

          Your second paragraph though.. too judgmental for my liking.
          People who take public transport/bicycles are people that are too poor or sick to own/operate automobiles.. it's probably complicating it a little bit, but what about people that just don't have a licence, or don't know how to drive?
          Or what about simply, people that want to read books/sleep/play games on their phone while getting around? These are things you can't do as an operator of an automobile.
          Tourists?

          By the way, do you drive around thinking that buses are full of poor/sick people?

          Why must you relate it to how impressed a date would be? Automobiles, public transport are a means of getting around and not just for a date. In your defence, I agree with you but it'll be tough to find someone who thinks they'd impress a girl on their $250 mountain bike.

          I personally don't believe the travel by private car is the way of the future. It just isn't quite sustainable. Driving is basically a necessity of life in this day and age, which I don't have a problem with. Public transport is the way of the future. If we continue to consistently drive vehicles everyday to everywhere we need to get to, roads just become more and more congested and it's bad enough as it is (in Sydney). No doubt, public transport just isn't an option for a large proportion of the population but it's a vicious cycle.

  • onlyletters on 12/06/2013 - 16:46
    +1

    you might save you a little money on fuel but be prepared to have your transmission rebuilt, it kills the gear selector mechanism really early.

    • cloudy on 13/06/2013 - 12:11

      i think your comment is slightly extremist, excuse the pun.

  • Medrad on 13/06/2013 - 07:59
    +1

    Everyone, including the OP needs to watch the Top Gear episode where Jeremy Clarkson "Hyper-miles" his V8 Audi from London to Glasglow and back on one tank. You never take the car out of gear, you never apply undue acceleration, you apply braking force gently and evenly.

    I can't find the video, but it's out there, somewhere.

    • Davo1111 on 14/06/2013 - 12:59

      You never take the car out of gear,

      Not sure that was a factor. I'll re-watch that episode though.

      Our vehicle manual mentions fuel economy for different speed, with the optimum speed of 80km/hr due to the way the transmission is set up. Once you get over that speed, fuel economy decreases with wind resistance and revs (in top gear).

  • roguescholar on 13/06/2013 - 08:36
    +1

    Here you go.

    http://www.flixxy.com/audi-a8-diesel.htm

    And related to the original post.
    As mentioned previously, maybe just buy a car with engine start stop tech?

  • Duff5000 on 13/06/2013 - 11:14
    +1

    BTW. shifting to N down a hill is a bad idea. Make a mistake and hit R instead of D can cost you big $$$

    My wife made that mistake once, luckily there was no other card around on the highway as the car screeched to a stop from 80kmh. Gearbox on the 81 Datsun must have been well made as it survived luckily.

    • Shwayne on 13/06/2013 - 12:01
      +1

      Shifting it to N down a hill is a bad idea because your engine is no longer connected to the cars wheels, and your disk brakes have to contribute 100% of the stopping power required to slow down the car.

      It's also dangerous.

      • Mungulz on 13/06/2013 - 22:58
        -1

        WOW the brakes have to contribute 100%!?!?!

        I've never known an auto sitting in drive to offer much in the way of compression braking.

        How about diesels? They can't really compression brake at all, are diesels dangerous? (aside from causing cancer and shit)

        why post at all if you have no idea what you're talking about, disk brakes are actually pretty awesome and over engineered to the extreme, it takes extremely spirited driving to create fade, thrashing down a mountain for 10 minutes will generally do it, but you have warning, smell, and noticeable fade before you lose braking.

        • _Bruce_ on 14/06/2013 - 07:07

          Mungulz: This is not helpful. Sure compression braking is a small factor, but we are talking about efficiency here, a 1% saving can add up. No need to just throw insults around for no good reason.

        • Duff5000 on 14/06/2013 - 11:02

          What would make you think a diesel cant compression brake?

          All those signs telling truck drivers to avoid engine braking in built up areas must be pretty redundant.

        • Davo1111 on 14/06/2013 - 13:02
          +1

          engine braking and compression brakes are different.

          Compression braking is trapping air between the pistons (it makes that machine gun noise) http://en.wikipedia.org/wiki/Compression_release_engine_brak…

          Engine braking is gearing down http://en.wikipedia.org/wiki/Engine_braking

        • Duff5000 on 14/06/2013 - 16:07

          Ah never thought of that.

          Reading that 2nd link though does imply that while the mechanics are different most modern diesels or (or any with a turbo) do have a very similar effect due to restriction in the exhaust. So while the naming and reasons may be different diesels do decelerate while rolling in gear.

        • Medrad on 15/06/2013 - 11:35

          Diesel engine trucks that use engine braking is a much more complex system than just using the resistance of an engine to slow the truck down. There are systems in place where the compression vacuum helps boost the brake cylinder compression and also uses compression braking at the same time. You don't even have to change down gear.

          It's to do with exhaust air pathways, not just compression.

        • MATTDAMON on 15/06/2013 - 12:45

          Thats because there is no 'vaccum' on a diesel like their is in a petrol car.

          What your talking about is comp braking/jake braking or using of a retarder.

          Retarders tend to be fairly quiet, unlike a Jake which is where you will get that loud BRRRRRR sound on deacceleration

          http://en.wikipedia.org/wiki/Retarder_%28mechanical_engineer…
          http://en.wikipedia.org/wiki/Compression_release_engine_brak…

          http://www.youtube.com/watch?v=z3bLqjPBlx8

          Also compression braking is completely legal anywhere in Aus, regardless of what the signs say since its a braking aid.

        • coin saver on 16/06/2013 - 07:29

          i drove a cruise diesel until recently and never had to brake going down hill simply changed back to the right gear did no harm to the car at all

    • cloudy on 13/06/2013 - 12:09

      most new cars wont let that happen, u can engage in R unless u are travelling at like 1km or less, i accidently did this and my car just beeps at me, lol

      • Duff5000 on 13/06/2013 - 15:40

        I will not try in my 4x4 as i think it probably will engage in that. :)

    • OZBer on 13/06/2013 - 14:25

      "Make a mistake and hit R instead of D can cost you big $$$"
      The newer cars won't let it happen. Mythbusters did a similar test on a not-so-new vehicle to see if it stops a car more quickly than using the brake pedal. The car just wouldn't allow shifting to R while in forward motion.

      • Duff5000 on 13/06/2013 - 15:40

        Well it was a 1981 datsun so it wasnt new. I havent tried it in anything else, i imagine anything without a direct link to the gearbox would just beep. Most cars now the whole gear shift assembly is just an oversized switch that tells the computer you want to put it into X gear.

    • [Deactivated] on 14/06/2013 - 12:28

      Um… In a manual or auto? If you go to reverse in an auto while moving forward, the engine just grabs and stalls, then free wheels. In a manual, unless you grab the stick and jam it in HARD on purpose, the gearbox teeth mesh (grind) and it refuses to go in. (I know, because a nitwit driving a Mitre 10 delivery truck that I was a passenger in, did it three times at 40-60km before he was successful.)

      • Duff5000 on 15/06/2013 - 20:25

        Auto, I can assure you it didnt just grab, stall then free wheel.

        How did the van go after he managed to get it into reverse?

        • [Deactivated] on 18/06/2013 - 11:17

          Hm… I wonder why… I did it a few months ago by mistake at 60km/hr - engine stalled, car kept going forward - shifted into neutral, restarted engine, back into drive while still rolling.

          The Mitre 10 truck was on a gravel road. Rear wheels locked, truck shook like an earthquake as it skidded through the gravel.

    • Davo1111 on 14/06/2013 - 13:03

      It's also illegal because you're not in proper control of the vehicle.

  • Shwayne on 13/06/2013 - 11:57

    It's not any more fuel efficient than leaving the car in Drive.

    It however does incur minor wear on the transmission. (Normal day to day wear, but if you stop a lot, you are wearing it out (2 * times_stopped) * 100% more than you normally would.)

  • CMI on 13/06/2013 - 13:14

    Pull the handbrake up and you're not wearing down your brake pads

    You're not wearing down your brake pads when you're stopped. They wear when you're moving along and you use your brakes, because they're rubbing on the moving wheel. When you're stopped, there's no friction to cause wear.

    • johnno07 on 18/06/2013 - 15:13

      If there was no friction… you wouldn't be stopped.

      • emibel19 on 18/06/2013 - 15:25

        You don't need brake friction once you're stopped, unless you're on a slope or leave the car in gear.

        • _Bruce_ on 18/06/2013 - 15:32

          … or leave the car in gear.

          Like all Autos. johnno07 is right, there is definitely friction, but no energy transfer as the applied force from the slope/gear does not exceed the braking friction.

        • emibel19 on 18/06/2013 - 15:42

          What if you put an automatic in neutral, or switch the engine off on a horizontal surface? Why do you need brake friction to keep it stopped? Johnno07's statement is not correct as it stands. For a start, he never said anything about the type of transmission.

        • _Bruce_ on 18/06/2013 - 17:46

          If we are going to be picky it is correct as he did not specifically say no braking friction, and there needs to be some kind of friction. I get your point though.

        • emibel19 on 18/06/2013 - 17:56

          Fair enough, I just assumed he was talking about brakes because of the post he replied to :)

  • lameturd on 13/06/2013 - 16:03
    +4

    In terms of transmission damage, shifting to N while moving is fine on the transmission.. presuming you want to go back to D when you've reached the bottom of the hill, you'll need to come to a complete stop to shift to D as shifting from N to D while moving is going to apply years worth of transmission damage.

    pretty surprised no one brought this up yet.

  • Pratty on 13/06/2013 - 16:17
    +4

    Haven't read all the comments, but as far as I've always known you shouldn't leave an auto idling in neutral. I remember seeing it on an NRMA/RACQ website, but this is all I could find on the matter.

    http://www.popularmechanics.com/_mobile/cars/alternative-fue…

    I know it does put extra stress on the tranny also.

    • _Bruce_ on 13/06/2013 - 19:06

      That article is about going downhill, which has been discussed at length. Nothing damaging about idling in Neutral, just pointless.

  • Harold Halfprice on 13/06/2013 - 19:16

    i have a 6spd manual with a an aftermarket heavy duty clutch
    and damn is the clutch pedal heavy, most people are unable to drive my car because of it. i will 95% of the time keep the clutch pressed in at the lights in 1st gear, with the brakes on. occasionally i might put it in neutral with the brakes as the clutch can get tiresome and annoying at long stops.

  • Ether on 13/06/2013 - 19:20
    +1

    No it doesn't hurt to shift to N + handbrake while you stop at lights.

    But no one would do that. Why? Because it goes against the very existence of automatic gear box: let it do the gear shifting for you.

    The way I see it, is that the neutral gear is used in manual cars for the driver to take his/her foot off the clutch without stalling (and also just before turning off the engine). In an automatic, there is nothing the P gear can do that the N gear can't do apart from going down hill and still moving. And on that topic… it is never a good idea to leave a moving vehicle in neutral gear. I reckon it is similar to turning a fast corner with clutch down in a manual - very dangerous (I dare not try it).

    In some very old cars, the neutral gear will help lessen the terrible shaking (and noise) of the engine while idling at traffic. But if you do happen to come across a situation where you need to stay idle for a long time, then I would do P + handbrake.

  • maddy86 on 13/06/2013 - 22:53
    +1

    Don't want to sound like an ass but am a mechanical engineer.

    When you hold your foot to the brake the viscous fluid inside your torque converter is heated due to the sheer forces at play. This is essentially loss of enery which means that you must be burning more fuel to generate it. However the differences in fuel consumption by doing this at a couple of traffic lights for 30 seconds at a time on the way to and from work would be so insignificant its not funny.

    There are something called air/fuel ratios in combustion cycle engines and if you know anything about it then you know that the amount of fuel your engine burns at idles is stupidly low, thats why you can leave the engine running for hours but the fuel gauge wont move and yet you put your foot down in traffic and accelerate a couple of times and it drops like a rock.

    By increasing the number of shifts per drive you are wearing out the bands in your automatic transmission which allow that smooth shift between gears. All in all it makes negligible difference to your fuel consumption, accelerates drive-train wear and causes delays in stop-start traffic.

    • Mungulz on 13/06/2013 - 23:00

      To put some numbers to it, 1-2L per hour idling.

      Personally I even think stop start tech is a waste of time, might save 0.2L/100KM in peak hour conditions.

    • [Deactivated] on 14/06/2013 - 12:31

      the differences in fuel consumption by doing this at a couple of traffic lights for 30 seconds at a time on the way to and from work would be so insignificant its not funny.

      the amount of fuel your engine burns at idles is stupidly low

      Genuine question… Don't these two statements contradict?

      • maddy86 on 14/06/2013 - 14:05

        No they actually don't. Idle rpm,less than 800rpm in most vehicles, is about what the car will also sit at when the brake is applied. In fact due to the load generated by the torque converter, the engine will sit at a lower rpm than at idle.

        What I meant is that at such low rpm the fuel consumption is very low. So minutely small variances in consumption between braking whilst in D and sitting at idle in Neutral would be negligible.

        btw when a vehicle is idle it can either be in D with brake applied or in neutral with handbrake. Idle just means that the vehicle is stationary.

  • The Gent on 14/06/2013 - 14:46

    Learn how to drive a big-boy car where you change the gears and this crap doesn't matter.

  • [Deactivated] on 14/06/2013 - 15:59
    +1

    Many mechanics will tell you it makes little difference to modern auto gearboxes whether you go to N at lights or sit with your foot on the brake in gear for short periods. If you go the neutral route just remember to keep a watch in your rear vision mirror or flash your brakelights - especially at night. Anyone who consistently stays in gear and depresses the clutch at lights in a MANUAL is asking for trouble over the longer term. It's not the clutch plates at risk but the thrust/throwout bearings and spring. Neutral/brake/handbrake 99% of the time if you care about your car and wallet.

    • The Gent on 15/06/2013 - 01:03

      Why is compressing the clutch in gear bad for the car?

  • cbpeh1 on 14/06/2013 - 18:50

    I actually suspect putting the car into N instead of D might actually increase fuel consumption (slightly) because the absence of load from the torque converter would cause the engine to idle at a slightly higher rpm.
    With regards to reductions in brake pad wear, when the car is not moving, there is no wear even when you apply the brake pedal!

    • _Bruce_ on 14/06/2013 - 21:45

      I actually suspect putting the car into N instead of D might actually increase fuel consumption (slightly) because the absence of load from the torque converter would cause the engine to idle at a slightly higher rpm.

      Again with this idea that higher RPM means more fuel. Why do people think this?

      • maddy86 on 15/06/2013 - 11:24

        Correct, higher idle doesnt mean more fuel consumption. Fuel consumption is dependent on rpm and injector duty cycle (idc). Mainly dependent on IDC though, this is the time that the injector is open allowing the fuel into the cylinder. The IDC is based on load, therefor contrary to how the person a few posts above mentioned, the torque converter putting load onto the engine slightly (however negligibly) increases the IDC, thus more fuel consumption.

  • ronnknee on 14/06/2013 - 21:45
    +1

    While we are discussing habits that reduce fuel consumption, be gentle with the acceleration and braking.

  • jasef on 15/06/2013 - 08:20
    +2

    By gosh whats wrong with you all! Clearly the MAIN reason to put the car into neutral, ESPECIALLY when going down a (twisty, reverse camber, inappropriately steep) hill is for FUN! It's called angel gear because there's nothing quite like the feeling of praying dear god will I make it!???!

    • maddy86 on 15/06/2013 - 11:25

      hahah so true

    • [Deactivated] on 15/06/2013 - 19:03

      You'll make it alright. All the way to the morgue.

  • illumination on 16/06/2013 - 02:27
    +1

    This post has become quite techincal indeed.

    Conclusions drawn so far:

    • Shifting to N and/or using handbrake at a traffic light is stupid/unnecessary/impractical - some arguing that switching to N could even increase petrol consumption
    • Turning off the engine at a traffic light could be a better way to save you petrol, but could potentially damage the motor of the car/reduce the lifespan of the battery
    • If you ever do shift from N to D, make sure you are at a complete stop to prevent potential transmission damage(what about low speed? e.g. 10km/h)
    • Higher RPM does NOT directly correlate to higher petrol consumption
    • Rear-ending a car is almost always your responsibility - even if you were stationary (because you are expected to maintain a safe gap between the car in front). On this point though, I've wondered:
      What if you are driving along a 3-lane road in the right lane, and a car in the middle lane cuts you off by changing into your lane and you subsequently rear-end them because you were in their blindspot? Whose responsibility is that, and how do you prove your case?
    • Angel Gear = Neutral Gear
    • Braking only consumes petrol when you apply brakes while moving (i.e. slowing you down). When you are stopped there is no wear on the brakes as there is no friction. Petrol consumed while stationary is simply the petrol consumed to keep the engine running (which is minimal)
    • Excessive use of the handbrake can loosen the handbrake shoe (don't even know what handbrake shoe is to be honest) which could result in the car rolling in park/neutral
    • Foot brake > hand brake (effectiveness)

    Other questions I've been curious about:

    • What is the difference in terms of fuel efficiency between E10, the old regular Unleaded (don't know the Octane), Unleaded 95 Octane, Unleaded 98 Octane?
      I know there are supposed to be some differences in power delivery to the engine, and that Unleaded 98 Octane supposedly cleans the engine, but these are not fuel-efficiency related. I also know that the effectiveness or the difference between these petrol types could depend on your car model. (i.e. comparing driving a Toyota Corolla with E10 vs Unleaded 98 Octane would have an insignificant difference)
    • What is the optimal speed of travel? I've read that it's 50km/h, 60km/h, 80km/h and 100km/h. From my limited experience, I would imagine it would be somewhere between 60-80km/h. Surely a car would consume more petrol maintaining 100km/h than 60km/h? I don't understand how maintaining it at 60km/h is more efficient than 40km/h though.
    • Are maintenance costs for hybrid cars really absurd? To the point that getting a hybrid with "fuel saving" as one of the main factors just isn't worth it?
    • _Bruce_ on 16/06/2013 - 09:17
      +2

      What if you are driving along a 3-lane road in the right lane, and a car in the middle lane cuts you off by changing into your lane and you subsequently rear-end them because you were in their blindspot? Whose responsibility is that, and how do you prove your case?

      This is absolutely their fault (better example is they cut you off while doing half your speed: see also: merging). Can be hard to prove though.

      What is the difference in terms of fuel efficiency between E10, the old regular Unleaded (don't know the Octane), Unleaded 95 Octane, Unleaded 98 Octane?

      Regular is 91. Older engines designed for 95 or 98 will 'knock' causing damage at lower octane. Newer engine will run on lower octane than designed for, but will lose efficiency so it isn't a great idea (no damage if that is all you can get though). Putting in higher than your car is designed for is near useless, 'cleaning' is pretty much rubbish. E10 is a special case and again is mostly about if your engine design accounts for it.

      What is the optimal speed of travel? I've read that it's 50km/h, 60km/h, 80km/h and 100km/h. From my limited experience, I would imagine it would be somewhere between 60-80km/h. Surely a car would consume more petrol maintaining 100km/h than 60km/h? I don't understand how maintaining it at 60km/h is more efficient than 40km/h though.

      Depends on the car but almost all are targeted at 80 (under powered cars are probably more like 60). The point you are missing is that petrol consumption is measured per km, not over time. So half an hour of driving at 80 will use more petrol than half an hour of driving at 60, but you will have traveled further.

      Are maintenance costs for hybrid cars really absurd? To the point that getting a hybrid with "fuel saving" as one of the main factors just isn't worth it?

      Actually they aren't that terrible, the main difference being just that there are less of them, so you are always going to pay more (anyone got a rotary engine?). What is terrible is the asking price. You will never get ahead and need to consider the extra cash you are paying as a donation to the industry to develop hybrids (maybe buy a diesel and donate the money somewhere else).

    • WT on 16/06/2013 - 11:20

      *Turning off the engine at a traffic light could be a better way to save you petrol, but could potentially damage the motor of the car/reduce the lifespan of the battery

      Every time you start your engine, there is ring gear and starter wear. You would need to weigh up the petrol savings vs. replacement cost of ring gear/flywheel and starter. From a cost stand point, its not worth doing. From an enviroment point of view, its worth while

      *Higher RPM does NOT directly correlate to higher petrol consumption

      It does, but its not much in normal road use or if done every now and then. It makes a massive difference if your on the track though. Engines require more fuel at high rpm, zero load conditions to give a smother off/on throttle transition. If it used the excact injector duty cycle as idle, it will have an abrupt surge as you crack open the throttle, no matter how smoothly you do it. Its a drivability thing. Back to the track though, its not always viable in race conditions to save the fuel though as the loss in engine braking could hinder lap/race elapsed time.

      • _Bruce_ on 16/06/2013 - 11:30

        Higher RPM does NOT directly correlate to higher petrol consumption

        It does, but its not much in normal road use or if done every now and then.

        It does NOT. It indirectly correlates. Higher RPM does NOT mean higher fuel consumption. Lower RPM does NOT mean lower fuel consumption. Why not do all your driving in fifth gear?

        • [Deactivated] on 16/06/2013 - 17:21

          For any given gear there is a direct correlation between revs and fuel burning. Higher revs = more fuel burnt. Anyone who believes otherwise should write a thesis on how it can be otherwise and patent the process involved. The aim of smooth (fuel saving) driving is to accelerate slowly and in the case of manuals, keep the revs relatively low by using the gearbox appropriately. Every car is different but broadly speaking to achieve optimal fuel consumption there is a rev sweetspot for every gear before you change up. Obviously you don't want to labour the motor and gearbox by driving in high gears at low speeds.

        • _Bruce_ on 16/06/2013 - 19:56

          For any given gear there is a direct correlation between revs and fuel burning. Higher revs = more fuel burnt.

          Still wrong. Particularly in Autos with a torque converter which is where most of the mistakes in this thread come in. Also the incline of the vehicle and many other engine factors influence this.

          Anyone who believes otherwise should write a thesis on how it can be otherwise and patent the process involved.

          Or actually pass high school physics.

          The aim of smooth (fuel saving) driving is to accelerate slowly and in the case of manuals, keep the revs relatively low by using the gearbox appropriately.

          No, the aim is to keep the RPM at the most efficient point for your motor and load conditions. Often around 3000 RPM for cruising, but if you are accelerating it is generally better to go significant higher.

        • [Deactivated] on 16/06/2013 - 22:22

          Still wrong. Particularly in Autos with a torque converter which is where most of the mistakes in this thread come in. Also the incline of the vehicle and many other engine factors influence this.

          Unlike you we are talking about the actuality of driving. A driver has next to no control over what the gearbox does but he/she does have control over the accelerator. By depressing the accelerator he (indirectly) introduces more fuel into the engine which causes higher revs and increased power - until the gearbox reacts. In MOST real-world situations higher revs certainly does equate with higher fuel use. It's the basis of how a motor works.

          No, the aim is to keep the RPM at the most efficient point for your motor and load conditions.

          That is essentially what I said in the next two lines, but you can't (well most of us can't) magically reach the efficiency span on the power/rev/energy input graph without using your accelerator and gearbox, which is the obvious point I was making. What I also didn't say, and what any good pedant will know, is that depending on your vehicle you don't have to sequentially change gears either. There are many situations where it is far more efficient to skip change. I shouldn't need to say it, but for your benefit - it depends on your vehicle and a range of other things such as whether you are going up or downhill or along the flat.

          Often around 3000 RPM for cruising, but if you are accelerating it is generally better to go significant higher.

          Wrong, since you're obviously a stickler for precision over generalisation. The ideal rev range can and does differ markedly depending on motor capacity, gearbox, and differential, and is obviously dependent on the speed you "cruise" at, and whether your vehicle has overdrive.

        • _Bruce_ on 17/06/2013 - 07:27

          Rather than reasoning you are just getting defensive now so I'll just make some brief statements. The bulk of this thread is about driving in the sense of stopping and rolling down hills. You are now also almost making the same point that I was in the first place while claiming to disagree with me. I also fail to see what overdrive has do to with anything.

        • WT on 17/06/2013 - 10:33

          Going down a hill in 5th gear at say 60klms at 2000rpm

          Go down the same hill, same speed in 4th or 3rd will use more fuel. Read the rest of my post for an explanation why. The RPM the engine is at is DIRECTLY causing the engine to use more fuel.

          I will, shift into 5th gear at 50klm around suburbia when power is not required

          Lower RPM does NOT mean lower fuel consumption. Why not do all your driving in fifth gear
          I made no such claim…

          No, the aim is to keep the RPM at the most efficient point for your motor and load conditions. Often around 3000 RPM for cruising, but if you are accelerating it is generally better to go significant higher.

          For the majority of cars, 3000 is high for "cruise" conditions. It takes very little power to keep a car maintaining its speed on a flat road. 3000 is generally where you would want to be if you were approaching a hill or wanting to overtake since its just before the point of peak torque on most passenger cars. You are mistaking the engines power effieciency. That being it is more effiecient at making power (at the expence of fuel consumption). This is not to be confused with fuel effeicency.

          Before you reply this post, how about a little test. Since it souds like you cruise around at 3000rpm, try using 4th or 5th while cruising for a tank this week. Come back and tell us how much extra you got out of your tank! If its a small engine, it might only be an extra 20klms, if its a big engine, it might be 100klms.

        • _Bruce_ on 17/06/2013 - 11:36

          Go down the same hill, same speed in 4th or 3rd will use more fuel. Read the rest of my post for an explanation why. The RPM the engine is at is DIRECTLY causing the engine to use more fuel.

          Hmm, you still don't get it. The engine is being turned by the potential energy transfered from the mass of the car dropping to a lower point. Changing to a lower gear will increase the RPM which can have an effect on engine braking but will NOT use fuel.

          I didn't want to have to spell it all out but here we go:

          RPM is determined by the power into the engine, minus the power lost/delivered from the engine. The RPM will then be at a point where the internal loss at that rate equals the excess power.

          Power in can be:

          • From going down a hill depending on

            • Mass of vehicle
            • Slope of hill
            • State of clutch/torque converter
            • Gear

          • From deceleration depending on

            • Mass of vehicle
            • Rate of deceleration
            • State of clutch/torque converter
            • Gear

          • From Fuel depending on

            • Air fuel mix
            • Compustion efficiency

          Power loss can be from:

          • Wind resistance depending on

            • Wind conditions
            • Speed
            • Aerodynamics

          • Travelling up hill depending on

            • Mass of vehicle
            • Slope of hill
            • State of clutch/torque converter
            • Gear

          • Acceleration depending on

            • Mass of vehicle
            • Rate of acceleration
            • State of clutch/torque converter
            • Gear

          • Drive chain loss depending on

            • Current speed
            • Rate of Turning
            • Driving surface/tires

          ANY of the above factors will affect RPM. Yes if you change the air/fuel mix without changing anything else then RPM is affected, but you can also change any of the other factors (like changing gear/chaning slope) and change RPM WITHOUT using more fuel (unlike in the example you gave). Furthermore even if you are just increasing fuel to increase RPM it will inturn change other attributes here (unless you are in neutral (mostly)) which confirms that THEY. ARE. NOT. DIRECTLY. CORRELATED.

        • rhino015 on 17/06/2013 - 11:54
          +1

          Yeah, if you are engine braking down hill at high RPM with 0 throttle, the ecu in a modern electronic fuel injected car will cut the fuel injectors so that it's using no fuel because the momentum of the car is keeping the engine running. Whereas if you are in neutral, fuel will be used to keep it idling.

        • [Deactivated] on 17/06/2013 - 20:31

          You are surely NOT suggesting that driving down a hill in second (with commensurately higher revs) will return the same fuel consumption as doing the same in say 5th gear - assuming the same throttle position (or no throttle at all where possible)? Absolutely clueless.

          In regard to overdrive: the reference was simple enough to understand even if the mechanics aren't. Presumably you know why overdrive was introduced? Basically when a gear ratio is better than 1:1 vehicle speed can be maintained but engine revs reduced. This results - in the real world - in lower fuel consumption (all other things being equal). In your odd world presumably OD never results in lower fuel consumption.

    • ronnknee on 16/06/2013 - 13:32

      Angel Gear = Neutral Gear

      So glad you included that.

    • ronnknee on 16/06/2013 - 14:57

      What is the optimal speed of travel? I've read that it's 50km/h, 60km/h, 80km/h and 100km/h. From my limited experience, I would imagine it would be somewhere between 60-80km/h. Surely a car would consume more petrol maintaining 100km/h than 60km/h? I don't understand how maintaining it at 60km/h is more efficient than 40km/h though.

      I'll try to explain this using physics in Layman's terms and in a logical thought sequence at my best.

      "Optimal speed" okay so we're trying to find a speed such that your car travels the most distance while using the least petrol. What increases petrol consumption? Acceleration. Every time you increase the speed of your car (either from stationary or already moving), you are accelerating which causes your car to burn more petrol. So why do you want to accelerate?

      The obvious are:
      1. You stopped at the traffic light and now it has turned green.
      2. You want to go faster and faster.

      The less obvious is:
      3. You are being slowed down.

      How are you being slowed down? Drag and friction [1]. I'll talk about drag only as it is the largest contributor for deceleration. When your car is moving, it is actually going against the air. The air pushes your car back causing it to slow down. How hard does the air push your car? It is quadratically proportional eg. you go twice as fast, you get pushed back four times as hard; three times as fast, nine times as hard; or mathematically it can be represented as D = kv^2 for D is the drag, k is some number [2] and v is the speed. This mean the faster you travel, the more you are being pushed back. Consequently, you slow down. What is your natural reaction? You accelerate.

      So back to the original question. How do you determine the optimal speed? You minimise acceleration. Unfortunately there is no optimal speed on suburban roads simply due to the traffic lights. You have to accelerate and stop frequently which causes more petrol burn. However on a highway where there is no traffic lights and can travel at a higher speed, you can find your optimal speed.

      Try this next time when you're on the highway with little traffic. Accelerate your car to the limit (eg. 90 km/h) and let it slow down due to the drag/friction. You'll notice that the speed drops very quickly initially but over time, the decrease becomes less and less until the difference is very little. This is your optimal speed as you can travel for a very long time without having to accelerate. For me, this number falls around 60 km/h but can be different for your car.

      Now this poses the next question. Do you want to travel at a speed that is two-thirds of the limit just to save petrol? Some considerations include taking a longer time to reach your destination and slowing down the lane which can cause inconvenience to other motorists.

      TLDR: Read the whole thing.

      [1] For completeness, friction is due to the rough surface of the road.
      [2] This number depends on other factors such as the density of air, and the size and shape of the car.

      • rhino015 on 17/06/2013 - 11:52

        This is all true. I guess the only part not discussed in this post is the rpm that the engine is most efficient. In your highest gear, you may find that 60kph requires 80% throttle position whereas 90kph might require 2%.

        Also, I'm not sure about your example saying that it stops slowing down at 60kph. Are you still in gear at this point? if so, that would be because the engine is sitting at idle and the car will not allow it to drop lower and so it is opening the idle air control valve, effectively accelerating for you. If you wanted to test this effect of the rate of deceleration, you would do it in neutral to remove the factor of the engine accelerating.

        • ronnknee on 20/06/2013 - 23:46

          Yes, the optimal RPM for the engine definitely plays a part, and so do many other factors. I kept the model as simple as possible so that the OP (and others) can understand since he did mention his physics is not his forte.

          You are correct in changing to neutral gear so that the effects of drag/friction can purely be observed. However, the engine is running at all times anyway and it's practical to keep it that way so it doesn't change the way of finding the optimum speed.

        • rhino015 on 31/07/2013 - 11:16

          Well in terms of finding the optimal speed for wind resistance, you would have to factor in optimal engine RPM and wind resistance. The test you mentioned, if still in gear, would not give you any indication of wind resistance if you were sitting at minimum RPM. In the end, the optimal speed for efficiency is always at the highest gear that you have, so 60kph is unlikely to be that optimal speed because in your highest gear your car would probably be using the IACV to a large degree to attempt to stop the engine from stalling at such a low speed. This would be equivalent to standing on the accelerator, but you may not realise it is happening.

    • Davo1111 on 16/06/2013 - 16:37

      (what about low speed? e.g. 10km/h)

      I wouldn't. There really isn't any need too anyway?

      rear-end them because you were in their blindspot?

      Not really a rear end, there would probably be scrapes down the side of their car.

      What is the difference in terms of fuel efficiency

      NRMA did an efficiency test regarding that a few years back. Turns out the engine running e10 used more fuel, removing any cost savings

      What is the optimal speed of travel?

      My car says it in the handbook, and is 80km/hr.

      It's all to do with the efficiency of the gears + wind resistance

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