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  • #16
    This is such a bad idea - even if simply because the person behind you has no signal that you are slowing (hence why you have brake lights). (1)

    The best way to brake is to do so early and gently, reading the road ahead of you and anticipating that the person in front of you is about to pull out is far more effective than having to brake harshly. (1)

    Basically you have two systems - the brakes are to slow and the gears to go; the two systems are designed to be used this way and are most effecient when used as such. Thing is if you're using the gears to change your speed in a rapid reduction in speed you can destabilise your car - exactly when you might then need a rapid change in diretion (bearing in mind you've just destabilised your car already). (2)

    To stop (or slow) safely you have two options.
    1) Releasing or easing off the acecelerator (gas)
    2) Using the brakes (2)

    Remember that if you're fiddling about with gears/OD when you're trying to decelerate severely then you've got one hand off your steering wheel - I'm sure that in that situation you'll want both hands on your wheel so that you can retain control of your vehicle or effect a manouver (2)

    Basically using your gearbox to reduce speed as you've described is really bad priving practice and should be avoided at all cost.

    (1) Source The official highway code, 2007
    (2) Source - Coyne, Mares, MacDonald, Roadcraft the police drivers handbook 2007
    A PSA, if I may, as well as another.

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    • #17
      There are two situations in which I will use the gearbox to reduce speed.

      1. Downhill on a mountain (as stated earlier in the thread).

      2. If my main brakes fail. Then I would use the handbrake and the gearbox to reduce speed, switch my hazards on as soon as practicable, and - well, treat the whole thing as an emergency situation.
      As a last resort if the brakes fail, switch off the engine. This will probably destroy the car, but is better than driving off a cliff/crashing into something at speed. Expect to stop HARD if you do that, so do it only if you're in imminent danger of death or severe injury.

      For standard driving, reducing speed is done with the accelerator (lifting the foot) and the brake.
      Seshat's self-help guide:
      1. Would you rather be right, or get the result you want?
      2. If you're consistently getting results you don't want, change what you do.
      3. Deal with the situation you have now, however it occurred.
      4. Accept the consequences of your decisions.

      "All I want is a pretty girl, a decent meal, and the right to shoot lightning at fools." - Anders, Dragon Age.

      Comment


      • #18
        Quoth Seshat View Post
        There are two situations in which I will use the gearbox to reduce speed.

        1. Downhill on a mountain (as stated earlier in the thread).
        There's a difference between using a brake/gear overlap and using your gears to slow.

        When you're driving you should be using the IPSGA model (Information, Position, Speed, Gear, Acceleration).

        Basically what you're doing is constantly receiving and reviewing all available information available to you - that information allows you to safely review your position which allows you to maintain a speed that is safe for the conditions and then selecting a gear appropriate for that speed. Acceleration is then applied when necessary.

        You should always select the gear for the speed you're travelling at rather than the gear for the speed you want and you should select your gear once you've completed your braking (with a few notable exceptions).

        The times when a brake/gear overlap is needed are generally as follows
        • Going downhill
        • Low speed turns into left & right junctions - with a vehicle behind or approaching
        • Sharp right/left turns - with a vehicle behind or approaching


        What you're doing here is slightly different - let's take the downhill bit.

        Say you're travelling downhill and you're approaching a turn. At your current speed you cannot take the turn safely so you need to slow. Using the above model you would then brake, take your foot off the brake and select your appropriate gear. Problem is that when you're travelling downhill the vehicle won't maintain the speed you're selecting and will begin to pick up speed thus meaning that potentially the gear you're selecting is incorrect.

        What you do is the following
        Brake to the correct speed. Operate the clutch while maintaining your speed with your brake - you are however not performing any further speed loss. Select your gear and then release both the brake and the clutch. If you find that you rev excessively or you have to change gear again then you've got the wrong gear for the speed.

        Please bear in mind that in normal driving engine braking can only be used to produce gradual variations in speed.

        (all information above from Roadcraft, the police drivers handbook)

        Quoth Seshat View Post
        2. If my main brakes fail. Then I would use the handbrake and the gearbox to reduce speed, switch my hazards on as soon as practicable, and - well, treat the whole thing as an emergency situation.
        As a last resort if the brakes fail, switch off the engine. This will probably destroy the car, but is better than driving off a cliff/crashing into something at speed. Expect to stop HARD if you do that, so do it only if you're in imminent danger of death or severe injury.
        For a true braking emergency (in the case of complete and sudden failure) this is absolutely acceptable. If however you're doing it because you already know your brakes are shady then you come under the offence of dangerous driving.
        Last edited by crazylegs; 10-05-2011, 12:39 PM. Reason: removing an extra R...
        A PSA, if I may, as well as another.

        Comment


        • #19
          Quoth crazylegs View Post
          Say you're travelling downhill and you're approaching a turn. At your current speed you cannot take the turn safely so you need to slow. Using the above model you would then brake, take your foot off the brake and select your appropriate gear. Problem is that when you're travelling downhill the vehicle won't maintain the speed you're selecting and will begin to pick up speed thus meaning that potentially the gear you're selecting is incorrect.
          Absolutely agreed. In fact, this (and the parts I cut) is a much clearer description of what I was trying to say.


          For a true braking emergency (in the case of complete and sudden failure) this is absolutely acceptable. If however you're doing it because you already know your brakes are shady then you come under the offence of dangerous driving.
          If my brakes are becoming shady, the car goes to the mechanic.

          No, what I described is an emergency measure ONLY. Sudden and catastrophic loss of brake fluid, for instance.

          In fact, presuming that my mechanic is competent and my car is checked every (X) months or (Y) kms, the only reason I can think of to need to use such measures is a genuine accident - running over something that looks innocent but severs a brake line, for example. (Causing sudden and catastrophic loss of brake fluid - thus, no brakes!)

          Using the handbrake/gearbox method means the car will then need to be towed to the mechanic, and potentially will mean needing to replace parts of both. EXPENSIVE.
          (Basically, you use the handbrake to slow the car - it's not meant to do that, so you're overloading it - then change into a lower gear as soon as possible. This will probably 'crunch' the gear, damaging the teeth. Also out of its design parameters. Handbrake to slow to the next gear down, change down. Repeat until you're in first gear, then handbrake to stop. By this point, both handbrake and gearbox are damaged, possibly beyond repair. But you're alive.)

          Using the 'stop the engine' method .. well, assume the car is a writeoff. Better to destroy the car than kill the people, but it's much cheaper (and safer) to have well maintained brakes.

          In other words: I believe we agree, here.
          Last edited by Seshat; 10-05-2011, 01:59 PM.
          Seshat's self-help guide:
          1. Would you rather be right, or get the result you want?
          2. If you're consistently getting results you don't want, change what you do.
          3. Deal with the situation you have now, however it occurred.
          4. Accept the consequences of your decisions.

          "All I want is a pretty girl, a decent meal, and the right to shoot lightning at fools." - Anders, Dragon Age.

          Comment


          • #20
            Quoth Seshat View Post
            In other words: I believe we agree, here.
            I think we are
            A PSA, if I may, as well as another.

            Comment


            • #21
              Quoth Seshat View Post
              As a last resort if the brakes fail, switch off the engine. This will probably destroy the car, but is better than driving off a cliff/crashing into something at speed. Expect to stop HARD if you do that, so do it only if you're in imminent danger of death or severe injury.
              I'd be careful doing that. Many cars have power steering and brakes. Both are actually operated (via pulleys) by the engine. If you kill power to the engine, you can find yourself with a locked steering wheel, or one that takes a *lot* more effort to turn. Plus, you have to consider that traffic *behind* you might not be able to stop as quickly or take steps to avoid hitting a suddenly-dead car car in their path.
              Aerodynamics are for people who can't build engines. --Enzo Ferrari

              Comment


              • #22
                It's an absolute-last-resort manouver, one to be done only if the alternative is death or severe, life-threatening injury.
                Seshat's self-help guide:
                1. Would you rather be right, or get the result you want?
                2. If you're consistently getting results you don't want, change what you do.
                3. Deal with the situation you have now, however it occurred.
                4. Accept the consequences of your decisions.

                "All I want is a pretty girl, a decent meal, and the right to shoot lightning at fools." - Anders, Dragon Age.

                Comment


                • #23
                  *raises hand* Car noob here. How does shutting off the engine help to stop the car quickly?

                  Wouldn't the car just coast with the engine off?

                  Comment


                  • #24
                    If the car is in gear, not in neutral (or for a manual, the clutch is engaged), then the wheels and the engine are directly connected. (oversimplification - there's the differential and some other bits and pieces, but it's close enough.)

                    Shutting the engine off will pretty much stop it from turning. If it can't turn, the wheels can't.... you'll skid for a bit, then stop. HARD.
                    Seshat's self-help guide:
                    1. Would you rather be right, or get the result you want?
                    2. If you're consistently getting results you don't want, change what you do.
                    3. Deal with the situation you have now, however it occurred.
                    4. Accept the consequences of your decisions.

                    "All I want is a pretty girl, a decent meal, and the right to shoot lightning at fools." - Anders, Dragon Age.

                    Comment


                    • #25
                      Quoth Seshat View Post
                      As a last resort if the brakes fail, switch off the engine. This will probably destroy the car, but is better than driving off a cliff/crashing into something at speed. Expect to stop HARD if you do that, so do it only if you're in imminent danger of death or severe injury.
                      Quoth protege View Post
                      I'd be careful doing that. Many cars have power steering and brakes. Both are actually operated (via pulleys) by the engine. If you kill power to the engine, you can find yourself with a locked steering wheel, or one that takes a *lot* more effort to turn. Plus, you have to consider that traffic *behind* you might not be able to stop as quickly or take steps to avoid hitting a suddenly-dead car car in their path.
                      What happens if you shut off the car? Assuming gasoline engine and manual transmission, the wheels will be turning the engine (same as if you were using engine braking - the closed throttle valve resisting airflow is what provides most of the braking force). Of itself, this is not going to destroy the car. You will still have power brakes (boost is from manifold vacuum, which is still being generated because the engine is turning - you also have a reservoir which is good for one or two pedal applications after the engine stops turning), and power steering if your car has hydraulic power steering (driven by a pump off the engine, which is still turning - up until a few years ago, this was the only system).

                      Downside to shutting off the car - if you have electric power steering (some newer cars have it), this gets turned off. With automatic transmission (which provides less engine braking than manual anyway), virtually anything made in the past 10 years has an electronically controlled (rather than mechanically controlled based on engine speed and either manifold vacuum or throttle position) transmission, so the transmission controller will shut down, with results that will vary from model to model. It might stay in the gear it's in now, might drop into neutral (NO engine braking, and you lose power brakes and power steering because the engine stops turning because it's shut off and isn't being driven by the wheels), or might drop into park (instant wheel lockup and destroyed transmission). The parking pawl is not designed to take the load of stopping a moving vehicle, so you could get a brief lockup, followed by no braking effort when the pawl breaks off.

                      Worst of all is that you might accidentally turn the key past "off" and into "lock", which will lock your steering (anti-theft measure introduced in the '60s or '70s - if the car is hotwired rather than using the key to start it, the thief can't steer it).

                      Summary: the best case situation of shutting off the engine is equivalent to using engine braking with your foot off the accelerator. Don't risk it.
                      Any fool can piss on the floor. It takes a talented SC to shit on the ceiling.

                      Comment


                      • #26
                        (Seshat goes into thinking mode)

                        You're right. In pre-1990, possibly pre-1980 cars, I'm right. In modern cars, you are.

                        Damn. I'm sooooo dated.
                        Seshat's self-help guide:
                        1. Would you rather be right, or get the result you want?
                        2. If you're consistently getting results you don't want, change what you do.
                        3. Deal with the situation you have now, however it occurred.
                        4. Accept the consequences of your decisions.

                        "All I want is a pretty girl, a decent meal, and the right to shoot lightning at fools." - Anders, Dragon Age.

                        Comment


                        • #27
                          Quoth Seshat View Post
                          (Seshat goes into thinking mode)

                          You're right. In pre-1990, possibly pre-1980 cars, I'm right. In modern cars, you are.

                          Damn. I'm sooooo dated.
                          Sorry, but all cars work this way. There was no period in time when if the engine was cut off you screached to a halt and destroyed the car. On a manual transmission car the transmission will continue to spin the engine until the car comes to a stop though depending on what gear you are in it might get a bit jerky as the speed comes down to the single digits. In an automatic transmission the tansmission will continue to spin the engine until it drops out (which would vary by different technologies and eras) but the car continues to roll.

                          On an automatic the last thing you would want to do in a brake failure situation is turn off the engine as the power steering is gone when the engine stops. You can still steer but the time to learn how to handle your car with no power steering isn't when you're heading toward a fiat full of pregnant nuns and have no brakes.

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                          • #28
                            Let's simplify this a bit:

                            1) If your foot brake fails but nothing else does, leave the engine on and use the handbrake instead. In America it's usually called the emergency brake, for a reason.

                            2) If your engine won't stop revving, turn off the engine. This prevents it from making power to make you go faster. Then use the foot and/or handbrake to stop. Try not to engage the steering lock, but there should be no other noticeable side-effects. Modern power steering has deliberately no effect at highway speeds anyway - it only provides assistance at low speeds, when large steering inputs are needed.

                            3) If the engine won't turn off, put the transmission into *neutral*. This prevents the engine power from reaching the wheels and thus making you go faster. It might damage the engine, but not if the rev-limiter is still working.

                            4) If you are going down a steep hill, you can select a low gear so that engine-braking means you need your normal brakes less. This probably won't work on automatic transmissions though. With manual transmissions, engine braking can also sometimes be useful for gentle deceleration - learn clutch control properly and it should come naturally.

                            Comment


                            • #29
                              This is such a bad idea - even if simply because the person behind you has no signal that you are slowing (hence why you have brake lights). (1)
                              I never said anything about someone being behind me.

                              Comment


                              • #30
                                Quoth PepperElf View Post
                                I never said anything about someone being behind me.

                                Quoth PepperElf View Post

                                However I've found that on the highway it really works well for slowing down my momentum before I put on the brakes. I mean normally if you just take your foot off the gas and coast it will eventually slow down. My car's a bit heavy so it does slow down well this way... but it does it very well - about 5mph slower instantly - with the Overdrive off.

                                So if I need to stop for road hazards I find I can get it slower a little bit faster using that first and then the brakes. In fact sometimes just turning it off give me exactly what I need without touching the brakes. (especially since i've been finding myself around cars that only want to do 60-65 or so in the 70 zone. seriously, i normally do 80 but i haven't felt like it lately and .. .have found myself having to pass people still when i'm just doing 70 or 75). so sometimes that OD off comes in hand when approaching slower traffic...
                                I would suggest that unless you have the entire highway to yourself there will be someone behind you within visual range, no matter how far away they are.

                                If you're slowing for slower traffic it's only right that you give warning everyone that you're slowing...
                                A PSA, if I may, as well as another.

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