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How to accelerate for fuel efficiency? (When to shift gears?)

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  • How to accelerate for fuel efficiency? (When to shift gears?)

    Hello people,

    I own a Yamaha Fazer, 150cc, 5-speed. The performance figures are
    Max. torque = 14 Nm at 6000 rpm
    Max. Power = 14 units at 7500 RPM

    So far, I have been able to achieve a FE of 45+ KMPL with simple techniques such as steady speed, coasting, etc. Earlier, I used to get approx. 35 KMPL with inappropriate riding techniques. However, one thing I am not sure is how to accelerate on city roads and the eastern express highway that is more or less like a city road between Sion and CST. The slow moving traffic here eats into my FE figures badly. Therefore this question.

    The basic question is "when" to shift gears? People have suggested me thumb-rules such as 1st gear for 0 - 10, then 2nd gear for 11 - 20, then 3rd gear for 21 - 30, and so on... But after reading a few articles on torque and power, I get the feeling that those above thumb-rules are just incorrect.

    Here is what is going on in my mind:
    Acceleration is a function of torque. FE is maximum when the engine is revving at max. torque RPM value(say 6000 for my Yamaha Fazer). Most of the torque curves suggest that torque will increase along with RPM(but only until the max. torque RPM is attained, after which they will decline). Therefore, the closer we rev to the max. torque RPM figures, the more fuel-efficient we are. But we should also balance it with the throttle. Lower gears have more torque, so we can open the throttle wide and expect more torque.

    So, while shifting up, should we wait for the revs to reach 6000 to experience max. torque and resultant max FE? But the problem with such waiting is that the max. torque is felt by the rider much before the revs reach 6000. That is, the bike will have already picked up enough momentum by 3500K so that the torque at 6000K cannot be felt. Or does this mean that the quicker we rev higher(or simply - if the throttle is opened wider that usual in order to reach higher RPM quickly), more the FE shall be?

    Presently what is happening is that it is difficult to "wait" until the PRM reaches 6000. The sensation of "torque" or "pulling sensation" peaks out when the engine is revving about 3500 - 4000. After that, even as the engine is revving higher(due to widely opened throttle) from 4000 to 6000, the "sensation" diminishes. And this is when I decide to shift up the gears. By this practice, I upshift at the following speeds:

    0 - 14 = 1st gear
    15 - 25 = 2nd gear
    26 - 41 = 3rd gear
    41 to upto 60 = 4th gear
    I usually do not accelerate in the fifth gear because higher gears do not give that much torque. 5th gear is used for steady speed riding. The above shifting speeds are based on my pulling sensations(which are a function of torque) experienced by me.


    Can someone throw some light on this?

  • #2
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    • #3
      Originally posted by rx_rider View Post
      Here is what is going on in my mind:
      Acceleration is a function of torque. FE is maximum when the engine is revving at max. torque RPM value(say 6000 for my Yamaha Fazer). Most of the torque curves suggest that torque will increase along with RPM(but only until the max. torque RPM is attained, after which they will decline). Therefore, the closer we rev to the max. torque RPM figures, the more fuel-efficient we are.
      NO thats not correct, FE is not maximum at the max torque rpm it'll be at lesser rpms. Max torque rpm can be defined as the max speed which can be done at which your efficiency and speed is balanced. i.e, at the max torque rpm you'll be doing the max speed possible without greater loss of efficiency. Post this rpm the vehicle would not be as efficient as it would be at below the max torque rpm. For most of the bikes in indian market, the max efficiency rpm band is 3.5-4k rpm(including your fazer) where it runs stress free and returns max kmpl
      Fun Starts at Redline!!!

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      • #4
        Originally posted by rx_rider View Post
        Hello people,

        I own a Yamaha Fazer, 150cc, 5-speed. The performance figures are
        Max. torque = 14 Nm at 6000 rpm
        Max. Power = 14 units at 7500 RPM

        So far, I have been able to achieve a FE of 45+ KMPL with simple techniques such as steady speed, coasting, etc. Earlier, I used to get approx. 35 KMPL with inappropriate riding techniques. However, one thing I am not sure is how to accelerate on city roads and the eastern express highway that is more or less like a city road between Sion and CST. The slow moving traffic here eats into my FE figures badly. Therefore this question.

        The basic question is "when" to shift gears? People have suggested me thumb-rules such as 1st gear for 0 - 10, then 2nd gear for 11 - 20, then 3rd gear for 21 - 30, and so on... But after reading a few articles on torque and power, I get the feeling that those above thumb-rules are just incorrect.

        Here is what is going on in my mind:
        Acceleration is a function of torque. FE is maximum when the engine is revving at max. torque RPM value(say 6000 for my Yamaha Fazer). Most of the torque curves suggest that torque will increase along with RPM(but only until the max. torque RPM is attained, after which they will decline). Therefore, the closer we rev to the max. torque RPM figures, the more fuel-efficient we are. But we should also balance it with the throttle. Lower gears have more torque, so we can open the throttle wide and expect more torque.

        So, while shifting up, should we wait for the revs to reach 6000 to experience max. torque and resultant max FE? But the problem with such waiting is that the max. torque is felt by the rider much before the revs reach 6000. That is, the bike will have already picked up enough momentum by 3500K so that the torque at 6000K cannot be felt. Or does this mean that the quicker we rev higher(or simply - if the throttle is opened wider that usual in order to reach higher RPM quickly), more the FE shall be?

        Presently what is happening is that it is difficult to "wait" until the PRM reaches 6000. The sensation of "torque" or "pulling sensation" peaks out when the engine is revving about 3500 - 4000. After that, even as the engine is revving higher(due to widely opened throttle) from 4000 to 6000, the "sensation" diminishes. And this is when I decide to shift up the gears. By this practice, I upshift at the following speeds:

        0 - 14 = 1st gear
        15 - 25 = 2nd gear
        26 - 41 = 3rd gear
        41 to upto 60 = 4th gear
        I usually do not accelerate in the fifth gear because higher gears do not give that much torque. 5th gear is used for steady speed riding. The above shifting speeds are based on my pulling sensations(which are a function of torque) experienced by me.


        Can someone throw some light on this?
        Wow! That's some research. But your logic is a bit wrong. You are mixing up power and torque here which is unnecessary.
        Simply put,

        1. At maximum RPM (rotations per minute) your piston would make more revolutions (more fuel intake & more output of gases).
        Say you are cruising at 2nd gear 6000RPM, the top speed your vehicle would be doing is 40kmph.
        Same, in 5th gear 3000RPM you will still be doing same speed of 40kmph.
        But in this case there was almost 3000 less rotations of cam head saving 50% fuel consumed. Thus higher gear and lower RPM saved you on fuel spent.

        2. Every bike has its own torque and power curve RPM. So what exactly are these?
        Torque: (Intial pickup) More torque means more load pulling. This has got nothing to do with speed. Thus trucks and mining lorries have tremendous amount of torque which is required to pull the vehicle through. Similarly in your bike too the maximum toruque is attained around 4500RPM. So if you were to overload your bike and it was pulling slow then changing gears and keeping RPM around 4500 will give you the ability to easily pull through.
        Peak Power RPM: Maximum RPM at which your bike gives you the highest power. When your bike RPM reaches around 7500 you get peak RPM, at this point your bike engine is doing its most efficient work in transferring power to your wheel, [More power = more work done], here the work done is in travelling from point A to point B in a given time that is nothing but top speed.

        3. This goes way above the head, tell me how to get more mileage!
        a. Keep your bike well maintained, engine oil changed, air filter cleaned and maintain good quality of fuel and proper tyre preassure.
        b. Ride from 2000-5000RPM range.
        c. Shift gear to higher one when you are about to cross 3500RPM.
        There are no short-cuts to any place worth going. So ride safe when you are treading uncharted roads.

        Comment


        • #5
          Originally posted by prajnyan View Post
          1. At maximum RPM (rotations per minute) your piston would make more revolutions (more fuel intake & more output of gases).
          Say you are cruising at 2nd gear 6000RPM, the top speed your vehicle would be doing is 40kmph.
          Same, in 5th gear 3000RPM you will still be doing same speed of 40kmph.
          But in this case there was almost 3000 less rotations of cam head saving 50% fuel consumed. Thus higher gear and lower RPM saved you on fuel spent.
          1. In the case of fuel injected bikes, doesn't the ECU make changes to the ratio when accelerating quickly at low RPM's of each gear to reach the 40 kph or higher speed?
          2. In stop and go traffic, how is it better to accelerate? slow and steady in each gear or to quickly try to reach the final gear without lugging the engine?
          3. While braking, is it more fuel efficient to clutch in and keep the RPM's at idle, or decelerate through the gears?...

          Comment


          • #6
            Found a related link when I google'd "Calculate best RPM for gear shifting" When to shift But perhaps, the page is not specifically oriented towards gear shifting to maximize fuel efficiency. Atleast, it does not claim so anywhere! The bottom-line is you must change the gears such that it feels "smooth". Changing the gears should not give you a jolt or thrust feeling. However, how to adapt such behavior with fuel efficiency in mind, that is my question.

            After reading a few articles, I seems to me as if most of our "Indian" commute bikes are not designed for "stop and go" traffic because the engine must be revved higher to reach peak torque RPM where FE is best. Our commuter bike engines produce very less low-end torque.
            Last edited by rx_rider; 01-21-2013, 12:33 AM.

            Comment


            • #7
              Originally posted by rx_rider View Post
              After reading a few articles, I seems to me as if most of our "Indian" commute bikes are not designed for "stop and go" traffic because the engine must be revved higher to reach peak torque RPM where FE is best. Our commuter bike engines produce very less low-end torque.
              This is completely wrong Buddy.. Our Commuter bike's engine are rather designed with great low end torque..

              If u want to feel the difference , just ride any commuter bike, viz Fazer, P150, ..... anything in this segment, and then ride a ninja 250. U will get it. even my bike Pulsar 200NS doesn't Have such good low end torque as of Any other commuter bikes..
              sigpic
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              Only thing I can say - "The storm is coming"

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              • #8
                For gear changes listen to the engine it gives a cue when gears need to be changed
                It will give stress signal or vibrations or grunt then up shift
                Sticking to numbers quoted by people is surely not the way everybody's bike behaves differently due to the way they drive.

                if overtaking be in the power band where you feel more torque is available

                Keeping the engine sounding smoother while riding will ensure efficiency
                Also some bikes have that fuel efficiency band noted in speedo i doubt yours has it. if it does follow it.

                sion to cst you would be probably driving only in power band not much can be saved then.
                ASHWIN NARVEKAR

                My Blog - http://driftwiththeclouds.blogspot.com/
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                • #9
                  Yes, partly correct.

                  1. In fuel injected(FI) bikes, the ECU adjusts the amount of air+fuel based on the throttle position, RPM etc . So if you are in higher RPM, ECU fills in more petrol. In normal bikes your carburettor has small needles or pins in which fuel sprays into carburettor and mixes within the air present, generally there is one thin needle pin for low throttle, one mid and one bigger pin for open or full throttle. This varies.
                  But the basic fact remains same in any kind of vehicle, opening more throttle, riding in higher rpm will result in more petrol being consumed.
                  2. In stop and go traffic, stick to lower gears. If you see the needle drop below 2 to 2.2K RPM, then to prevent lugging, down shift to a lower gear. Don't change gears frequently, or until you gain enough torque, say above 3k-4k RPM for higher gear to save on fuel.
                  3. Never use clutch while slowing down. It will wear the brakes fast and can also result in loosing control of bike as tyres get locked/skid when you press clutch and brake. The best way to come to a stop is press brakes, and when speed reduces gradually down shift gears. Always stay in gear while slowing down.
                  Note: If its suddent braking too, apply same logic, dont clutch down, keep vehicle in power band. Make sure to put more braking power to front wheel and less to rear. Press clutch in end when you will sense bike may stall or jerk. Its all an instinct.
                  Last edited by prajnyan; 01-22-2013, 11:09 AM.
                  There are no short-cuts to any place worth going. So ride safe when you are treading uncharted roads.

                  Comment


                  • #10
                    Originally posted by prajnyan View Post
                    3. Never use clutch while slowing down. It will wear the brakes fast and can also result in loosing control of bike as tyres get locked/skid when you press clutch and brake. The best way to come to a stop is press brakes, and when speed reduces gradually down shift gears. Always stay in gear while slowing down.
                    Note: If its suddent braking too, apply same logic, dont clutch down, keep vehicle in power band. Make sure to put more braking power to front wheel and less to rear. Press clutch in end when you will sense bike may stall or jerk. Its all an instinct.
                    Thanks for that tip man. I am a new rider and always break after pulling in clutch. That's how I thought we are suppose to do.

                    Comment


                    • #11
                      Anybody has the torque curve and/or power curve for Yamaha Fazer or FZ or FZ-S. I emailed Yamaha India but they have forwarded me to their Yamaha Dealership in Thane (AIMS Yamaha). Yet to visit them.

                      Comment


                      • #12
                        Originally posted by prajnyan View Post
                        3. Never use clutch while slowing down. It will wear the brakes fast and can also result in loosing control of bike as tyres get locked/skid when you press clutch and brake. The best way to come to a stop is press brakes, and when speed reduces gradually down shift gears. Always stay in gear while slowing down.
                        Note: If its suddent braking too, apply same logic, dont clutch down, keep vehicle in power band. Make sure to put more braking power to front wheel and less to rear. Press clutch in end when you will sense bike may stall or jerk. Its all an instinct.
                        I get this. The reason im looking for ultimate fuel efficiency is because i fill 7 ltrs on my duke every 5-6 days, and i faked a bill the last time(Girl reasons) so i gotta last for 5-6 days with 3 ltrs. And today is the 2nd day.

                        Normally, while braking i decelerate-clutch in-blip throttle-change gear-clutch out all gears. Redline often and generally keep it in the power curve. It's difficult to alter one's riding style to a fuel efficient style i realize. For the moment im looking for maximum fuel efficiency and i'm not sure how to do that in stop n go traffic, as my commute is generally in the city...

                        Comment


                        • #13
                          Originally posted by prajnyan View Post
                          3. Never use clutch while slowing down. It will wear the brakes fast and can also result in loosing control of bike as tyres get locked/skid when you press clutch and brake. The best way to come to a stop is press brakes, and when speed reduces gradually down shift gears. Always stay in gear while slowing down.
                          Note: If its suddent braking too, apply same logic, dont clutch down, keep vehicle in power band. Make sure to put more braking power to front wheel and less to rear. Press clutch in end when you will sense bike may stall or jerk. Its all an instinct.
                          Sorry, but I am not clear what this means. I, while slowing down, always keep the clutch level pulled in. Otherwise the speeds drops quickly. Actually such coasting forms a major part of my daily commute to work. I frequently let the bike go ahead by its momentum rather then burning fuel, esp. while downhill on flyovers, approaching traffic jams or red lights, etc. Is such "coasting" that harmful?

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                          • #14
                            Originally posted by rx_rider View Post
                            Is such "coasting" that harmful?
                            AFAIK, coasting is not harmful in itself, but it is always recommended to be in appropriate gear so that the engine braking process will work. Also, if a vehicle is in gear, it will have more control when going downhill.

                            Having said that, coasting and engine braking is not recommended for 2-stroke engines. This is what I understand from reading stuff on other forums. Members here can throw some light on it, please?
                            So with my RX what I do is, keep the bike in correct gear and also keep the throttle to stabilize speed. Never let it just coast off with clutch pulled or keeping the vehicle in neutral.

                            For the fuel efficiency part, especially for smaller engines (those in smaller cars and bikes), the lower it revs, the better the FE. But do not lug the engine. Having said that, it DOES NOT mean that the engine is working in it's most efficient band - i.e power v/s FE. This is true of most smaller engines.

                            Guys, please let me know if my above understanding is incorrect. Thanks.

                            <<<< If you stand for nothing, you'll fall for anything! >>>>

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                            • #15
                              How to accelerate for fuel efficiency? (When to shift gears?)

                              @ rx_rider. Reving the engine to the max rpm in every gear gives the bike the max power and it usually done in racing where pick up and top speed matters. So for normal riding I don't think you have to rev the bike to that rpm.
                              In 2 stroke the coasting can be harmful due to the lubrication problem. But i am not sure about the engine braking part. I think this has been discussed many times though I don't remember the thread title. If somebody knows the thread please put up a link.
                              A lot more expert discussion is needed in this matter.


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