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Art of Changing Gears

Discussion in 'Technical' started by Sat-Chit-ananda, Jul 15, 2013.

  1. <article> Rev matching and down shifting


    Each gear has an effective operating range of speeds which depend on the rev range of the engine. The faster the engine rotates, the quicker you can go – up to the point when you need to change up a gear. Within the operational rotational speeds of the engine, there is a range of optimum efficiency known as the 'power band', and this is where the fastest acceleration can be obtained (see Diagram 1).
    <figure> power-band.png <figcaption>Diagram 1: The power band of an engine in any particular gear </figcaption></figure> Most gearboxes are designed so that when you change up a gear when accelerating, the next gear will be at the start of the engine's power band (see Diagram 2). This design provides maximum acceleration all the way up to the top speed of the car.
    <figure> two-gears.png <figcaption>Diagram 2: Comparing the power bands in two gears</figcaption></figure> At most speeds, a selection of gears can be used (see Diagram 3).
    <figure> gear-overlap.png <figcaption>Diagram 3: Gear choice at different speeds</figcaption></figure> In the illustration above the driver could choose second, third or forth gear. In second gear the engine speed would be at the top of the power band, not leaving room for much useful acceleration until the rev limiter is activated. In forth the revs would be too low, leading to sluggish performance (but perhaps decent fuel economy). In third gear the engine would be at start of the power band providing maximum acceleration – this would be the choice of the performance driver.
    Changing up / up-shifting

    Lower gears provide greater acceleration due to a combination of the gearing and higher engine speeds. Therefore, when accelerating hold on the lower gears for as long as you can, but be careful not to hit the rev limiter (as this slows you down). Only change up when the engine has passed through the upper limits of the power band, not before.
    Changing down / down-shifting

    When approaching a corner, you need to select a gear which will provide maximum acceleration at the exit, and this gear needs to be engaged before entering the corner. This means braking to the speed where you can safely turn into the bend, then shifting before turning in. Gear choice is especially important here – ideally you need to select a gear which will cause the engine speed to increase to a sensible point within the power band so that plenty of power is available when accelerating out of the turn. However if you do select the correct gear and let out the clutch swiftly, three things will happen:

    • Significant levels of engine braking will occur
    • In extreme cases, the wheels can lock up
    • Forward weight transfer will occur
    None of these are good when you're trying to maintain control of a car driving at the limits of grip. Rev matching is the solution.
    Introduction to rev matching

    Rev matching is a technique which should be second nature if you want to be quick on the track.
    When is it used?
    When changing down to create smooth, fast gear changes in a car with synchromesh*.
    * Almost all modern cars have synchromesh, if you don't have it fitted you will need to 'double declutch'
    What rev matching does:

    • Reduces stress on the driveline
    • Prevents forward weight transfers when down shifting
    • Reduces engine braking and chances of wheel lock
    Note: On the track, use the brakes to slow down and the engine to accelerate. Engine braking is not as efficient, and will not slow you down quickly enough for track use. If you have time to use engine braking, you're not going as quickly as you could.
    How to rev match when changing down:

    1. Rev matching is mostly used to change down in anticipation of a corner. Diagram 4 (below) shows a driver accelerating in third gear, approaching the top of the power band.
    Show me what this diagram means<figure> 2.png <figcaption>Diagram 4: Accelerating down a straight in third gear</figcaption></figure> 2. As you approach a corner, brake until you have reached a safe speed to turn into the bend – engine speed will drop as road speed decreases. In Diagram 5 below the driver is in still in third gear, but is planning to select second. Engine speed has now dropped to the point where a change to second would be possible.
    <figure> 3.png <figcaption>Diagram 5: Braking before a corner</figcaption></figure> 3. While still on the straight, press the clutch in order to change down. This disengages the engine from the wheels and thus the engine speed starts to drop. The desired gear is second, but Diagram 6 shows that at the current road speed, the engine revs will need to increase in order to mesh smoothly when releasing the clutch.
    <figure> 4.png <figcaption>Diagram 6: Pressing the clutch in preparation to change down</figcaption></figure> 4. Select a gear which will provide decent acceleration at the exit of the corner, in Diagram 7 the driver has selected second gear. Simultaneously use the throttle to increase the engine speed in order to match the revs in second gear to the road speed.
    <figure> 5.png </figure> 5. Release the clutch smoothly and progressively, then start to accelerate out of the corner. If done well, there should be no jolt as the clutch is released.
    <article><figcaption>Diagram 7: Pressing the clutch, and selecting a lower gear</figcaption> <figure> 6.png <figcaption>Diagram 8: Second gear is selected, engine revs match road speed and the clutch is let out.</figcaption></figure> You don't need to be 100% accurate when raising the engine revs – you'll improve dramatically with practice.

    </article>Heel and toe shifting

    Heel and toe is the art of changing down a gear and rev matching while braking. By combining the braking and gear change when approaching a corner instead of performing them as two separate actions you'll be faster in any driving discipline - an essential skill to master.

    What does heel and toe shifting achieve?

    • Reduces stress on the driveline
    • Prevents forward weight transfers when down shifting
    • Reduces the chances of wheel lock in extreme cases
    • Allows rapid, smooth down changes before entering a corner
    How do I do it?

    This technique is possible by turning your right foot inwards, using your toes to operate the brakes and your heel to increase the throttle. Although this sounds complicated, it's actually a relatively easy technique to master with a bit of practice. The technique is vital on the track, but will also make you a much smoother driver on the road.

    Here's a video showing the technique, the article below shows how to do it step by step.

    Heel and toe – step by step:

    1. Heel and toe is mostly used to change down in anticipation of a corner. Diagram 1 (below) shows a driver accelerating in third gear, approaching the top of the power band.
    Diagram 1: Accelerating in third gear.
    Show me what this diagram means
    As you approach the braking point of a corner, cover the brake pedal with the ball of your right foot. The brake is the priority of the two pedals, so ensure good contact and no risk of your foot slipping off. In some cars it is very difficult to heel and toe due to the pedal position. It's useful to wear racing boots or thin soled shoes to increase your pedal feel and decrease chances of your foot sliding off the brake.
    2. Apply the brake and reduce your road speed to a point where it's possible to change down without over-revving the engine (see Diagram 2 below). In this example, the driver is in third gear, reducing speed.
    Diagram 2: Braking hard before a corner, engine speed decreases as road speed drops
    3. When it's possible to change down, while still braking rotate your right foot and prepare to press the accelerator with your heel. Alternatively if your pedals are close together it may be possible to use the side of your foot.
    At the same time, press the clutch with your left foot to disengage the wheels from the engine.
    Diagram 3: Rotating the right foot in preparation to press the throttle, pressing clutch
    4. Once the clutch has been pressed, engine speed will start to drop further. Increase the engine speed using the throttle with the heel of your right foot in order to match the revs in second gear to the road speed.
    Diagram 4: Pressing the throttle to raise engine speed
    5. When the road speed and the engine speed match, select the gear which will allow you to exit the corner quickly, in this case second (shown in Diagram 5).
    Diagram 5: Changing to second gear
    6. Smoothly and progressively release the clutch.
    Diagram 6: Release the clutch, and accelerate out of the turn
    7. Take the corner, accelerate smoothly and prepare for the next bend.
    Diagram 7: Acceleration
    Congratulations, you've just successfully shifted using heel and toe. But practice makes perfect.

    Article and pictures are courtesy of http://www.drivingfast.net/car-control/rev-matching.htm</article>
    Last edited: Jul 15, 2013
    Rituraj, kirenh, bharath and 3 others like this.
  2. rsinfo

    rsinfo Regolare

    New Delhi
    Can't see the diagrams !
  3. I am able to see them perfectly fine.Not sure what is the problem
  4. shams

    shams Esperto

    yes, only text is visible in place of diagrams!
  5. It is looking similar in the parent site, it should be back to normal after some time.
  6. naveen2cool

    naveen2cool Superiore

    The pictures say, visit drivingfast.net
  7. Linear

    Linear Amatore

    ^^Same here.
  8. fiatlover

    fiatlover Esperto

    Grande Punto 1.4
    No images visible here too.
    I use the clutch-acceleration combination like the action in a See-Saw. Nothing new, maybe you all follow the same technique. Clutch release and acceleration happens progressively. You get better acceleration especially in the first three gears - where you release the clutch slower- compared to fourth and fifth gears.

    Image courtesy: Google Images
    Last edited: Jul 15, 2013
    1 person likes this.
  9. gurjinder

    gurjinder Staff Member Janitor

    It's possible that the website does not allow any hotlinking to its pics.

    1 person likes this.
  10. ENKI

    ENKI Esperto

    Ok.. Although i know where i should select the next gear (2200 RPM - 3200 RPM) but developed very strange habit of skipping gears.

    I accelerate till 2nd gear @ 5000 RPM @ 70 km/hr and slot it directly into 4th or 5th (depending upon how occupied the road is). In corners, if i am slowed down to less than 30 km/hr, slot it in 2nd again, catch 65-70 km/hr and put it in 4th-5th again. If it is more than 30 km/hr, slot it in 3rd and accelerate to where 5th can take over. I can drive other way too where FE takes a little hit and engines note is consistent but that has to be intentional rather than spontaneous.

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