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Clutch manoeuvre

Know your way around the clutch for some smoother driving

india Updated: Aug 28, 2009 11:32 IST
Grease Monkey

You now know what your clutch is (at least, you do if you’ve read last week’s column) and what it does. You know that you should use it only while changing gears or while rolling to a stop. There is something called ‘clutchless shifting’ which, if mastered, will allow you to change gears without using the clutch. Please note: I am not recommending you do this because it isn’t necessary and you can cause serious damage to your gearbox if you don’t do it right. Here’s how it works.

Multiplying your car’s power
Gears are a way to multiply the engine’s power to the wheels. What this means is that the first gear makes the wheels turn for, say, every ten times the engine turns, while fifth is an overdrive gear, which means that the wheels spin faster than the engine does. This is why you can accelerate faster in first gear, but will get better speed and fuel economy out of fifth. If you pay attention to your tachometer, you’ll notice that a particular road speed will equate to different engine speeds in different gears. For example, if 30 kph in second gear has the engine spinning at 5,000 rpm, the same speed in third will have the engine humming away at 4,000 rpm, and fourth will have it going at a comfortable 3,000 rpm. When you change gears, the engine goes to neutral for a split second while it passes through the gate. It then engages the next gear when you push the gear lever into that gear.

Avoiding jerks while shifting gears
You may have experienced a momentary jerk sometimes, especially while downshifting to overtake a vehicle. This is due to the engine having to rev itself to match the wheels’ speed once the lower gear is engaged and the clutch is let out. You can eliminate such jerks by ‘blipping’ the throttle in that moment when the gear lever goes through neutral, and then engaging the next gear. To use the example above, if you were going to shift from fourth to third yet maintain 30 kph, you’d have to get into neutral, depress the accelerator just enough to rev the engine from 3,000 rpm to 4,000 rpm, and then engage third.

Racing drivers use this technique because they need to be smooth while driving. Know the engine noise you hear from Formula One cars while they brake for a corner? That’s the car’s computer blipping the throttle to match the wheels’ speed. The average Joe doesn’t need to know how to do this because of ‘synchromesh’ gearboxes, which are designed to engage smoothly. If you’ve heard a strange noise from an old car or truck, especially while getting into first gear, it’s the non-synchromesh gears grinding together.

Perfecting cluthless shifting
Clutchless shifting is possible if you match the engine speeds and wheel speeds — if we reverse that fourth-to-third example, you can get out of third to neutral (works in any gear — it’s the getting into another gear that’s the hard part). Then you have to let the revs drop to the speed matching the wheels — 3,000 rpm for our example. If you shift it exactly at 3,000 rpm, it’ll slot neatly into gear without you touching the clutch pedal at all!

Do it wrong, though, and your gears will make a horrible grinding noise that can result in some very expensive repairs.

Now that you know to blip the throttle for downshifts, the only jerks you’ll now have to worry about are the ones in other cars.