Manual transmission driving technique

Contents 1 Cautions 2 Beginning drivers 3 Theory 4 Learning to drive with a manual transmission 4.1 Shift patterns 4.2 Basics 4.2.1 Starting the engine 4.2.2 Moving 4.2.3 Stopping in first gear 4.3 Shifting 4.3.1 Upshifting 4.3.2 Downshifting 4.4 Starting on an upslope 5 Troubleshooting 5.1 Stalling 5.2 Stalling due to loss of traction while braking 5.3 Grinding Gears 6 Advanced techniques 6.1 Power shifting (a.k.a. speed shifting) 6.2 Heel-and-toe 6.3 Double clutching 6.4 Single clutching 6.5 Shifting without the clutch 6.6 Compression braking 7 Fuel efficiency

Cautions

Please note:

This article only applies to cars and trucks equipped with a manual transmission, not to motorcycles or many types of quad bike, which also have manual transmissions but are operated using different techniques.

This article is intended only as a helpful guide, and is no substitute for practice or training by a qualified instructor.

Some countries prohibit driving a manual transmission to people who made their drivers license on an automatic transmission car -- you might have to take extra classes to legally drive a car with a manual transmission.

The extra wear on a vehicle's clutch inevitably caused by a new manual transmission driver is likely to reduce its service life by at least a few hundred kilometres.

Beginning drivers

Driving a car or truck with a manual transmission can be daunting for beginners. In addition to the usual physical and mental skills required to drive any vehicle, a manual transmission beginner must learn to contend with an additional hand control (the gear selector), an additional foot control (the clutch pedal) and a lot more concentration, at first, on what various systems in the vehicle are doing.

Many North Americans would caution new drivers against attempting the additional burden of learning to operate a manual transmission until they have mastered the more basic driving skills involved in driving any vehicle by practicing in a car equipped with an automatic transmission. In Europe, almost all learner drivers start with manual transmission cars, but they may choose to learn to drive with an automatic transmission instead -- for example if they're handicapped, or if they find out they simply don't "get" manual transmission driving. However, such drivers will receive a driving license that is valid for automatic transmission cars only, and must pass a separate test before being licensed to drive a car with a manual transmission.

Theory

Internal combustion engines all share several limitations (compared to electric motors) that necessitate the use of some kind of transmission to make them practical:

They develop little useful power at low engine speeds

Their maximum speed is limited to a few thousand revolutions per minute, above which an engine begins to damage itself.

Due to these limitations, a hypothetical vehicle that had an internal combustion engine but not a multi-speed transmission would have a fixed ratio of engine speed to vehicle speed, and the range of speeds it could attain would be severely limited.

If the vehicle had only a low forward gear, comparable to the first gear of a manual transmission, it would be easy to get it moving, and it would climb steep hills well. It would accelerate well from a standstill, too. However, it would have a very low top speed, making it impractical. Driving at 40 km/h in would waste fuel and wear the engine needlessly. Moreover, the ride would be jerky and uncomfortable, since even small modulations of the pressure on the accelerator would cause the car to speed up and slow down wildly. Such a transmission with a fixed low gear might be acceptable in a special-purpose vehicle which moves slowly, such as perhaps a lawn mower.

A vehicle with only a low gear comparable to second gear would be mildly difficult to start, particularly uphill. It would be good at going up most hills, except at very slow speed or up very steep ones. For general shuttling around a residential neighborhood, this gear would be the best choice if there could be only one. In a typical manual transmission, second gear is the most versatile gear. However, it is too fuel-inefficient for driving on main roads and the severe limitation on top speed would make that vehicle impractical for freeway (highway, motorway) driving.

If the vehicle had only a medium gear, comparable to third, it would be very difficult to start. Getting the vehicle moving would require a lot of clutch slip which would wear out the clutch, yet the acceleration would be poor. Starting against an incline would be impractical. Moreover, the clutch would have to slip or be disengaged for speeds below about 30 km/h, otherwise the engine would lug. It would be difficult to go slowly in bumper-to-bumper traffic, for instance, on level pavement, never mind uphill. Obtaining adequate power to climb steep hills at a slow speed would require clutch slip, in order to allow the engine to spin faster, yet deliver power to the wheels through friction on the clutch disk. And yet, third gear would be too low for fuel-efficient city and highway driving. Going merely 80 km/h in third gear would waste fuel, needlessly wear the engine and make a greater contribution toward air pollution. Between the constant lugging and the excessive RPM's, the engine would not last as long as it should, and the clutch would require frequent service.

A vehicle with only fourth gear would be close to impossible to start, and useless for normal driving. In some cars, it's possible to drive in fifth gear at a speed as low as 50 km/h, but the engine may already show signs of lugging and won't be fuel efficient. If even a slight incline is encountered, a lower gear is required. About the same observations could be made about 5th gear, substituting 50 km/h for 60 km/h.

A transmission allows a vehicle to employ a variety of gear ratios in transmitting engine power to the drive wheels. Lower gears can be used for applying enough power to start quickly, for climbing hills and for acceleration. Higher gears can be used for cruising in a smooth, fuel-efficient way which prolongs engine life. Thanks to the multiple gear ratios, the clutch only needs to slip for a fraction of a second, when the car is started, and when the gear is changed, so a properly operated clutch can last for a hundred thousand kilometers or more, in spite of being a relatively inexpensive component.

In other words, the transmission with a multiple gear ratio is required for the internal combustion engine to be a practical source of motion for an automobile.

Learning to drive with a manual transmission

Beginning manual transmission drivers should avoid conducting their initial practice sessions on busy streets or in neighbourhoods with many children, pedestrians or cyclists. In fact, it's best to start out in a large, deserted parking lot.

Shift patterns

A car or truck's shift pattern is usually indicated by a small diagram on top of the shift knob. For most five-speed transmissions it looks like this:

Another common five-speed shift pattern (often found in BMWs and Volkswagens) is:

In many BMWs, Volkswagens and all cars with six-speed transmissions, Reverse will appear in a different position, but the positions of the first through fifth gears are the most common used in the automotive industry. (Racing cars with non-sequential transmissions, and some high-performance passenger cars, use a different pattern that is better suited to high performance or race driving.) If you're unfamiliar with a car's shift pattern, study the shift pattern diagram until you're confident you know where first gear and reverse are located.

Neutral is often not indicated on the diagram, but can be selected by moving the shifter to the middle row between the odd- and even-numbered gears. Note that manual transmissions have no "park" setting. To park, the driver engages the parking brake with the transmission in neutral, then turns off the engine.

For extra security, especially when parking on hills, the transmission may be placed into first or reverse gear after the parking brake is engaged. It is customary to select first gear if the vehicle is facing uphill and reverse if downhill (perhaps because these are likely to be the initial gears used in manoeuvering out of the parked position, especially if the tires are turned correctly against the curb), although an argument can be made for always choosing reverse gear, as it usually has the highest gear ratio, which would allow the engine to provide the most resistance to movement of the car.

Some experts argue that the car must never be placed into any gear when parking. In the event of collision while parked, the gearbox may break, and also the car may suffer more damage (because it will not roll).

Basics

Starting the engine

First, the driver must always make sure that the car is in neutral before attempting to start the engine, by either depressing the clutch pedal or moving the shifter to the neutral position. If the engine is started in gear a lot of strain will be put on the starter motor and the vehicle may lunge forward unexpectedly. The clutch is in a disengaged state by depressing it and in an engaged state while no pressure is applied. Many vehicles have a switch that automatically disables the starting circuit until the clutch is fully disengaged. In these vehicles it is necessary to hold the clutch pedal while starting, and in those without the switch it is a good practice, as it disengages the gearbox input shaft from the engine lessening the strain on the starter motor.

Once the engine is running, the transmission is neutral until the driver is ready to move away. Either the parking brake, or the main brake, or both, are engaged until that moment.

Moving

Starting off from a standstill can be one of the more difficult manual-transmission skills to master, but with practice it becomes second nature.

Because of their engines' limited torque at low engine speeds, most cars cannot start moving from a standstill by simply releasing the clutch pedal--they will stall. Instead the engine speed must be increased (using the gas pedal) while the clutch is being engaged. The exception here is a diesel powered car, which can provide more power at low revolutions; here, it is possible to move off from a stationary position simply by slowly engaging the clutch.

The amount of throttle required to avoid stalling while starting out varies depending on the vehicle, but in general the engine should be turning between 1200-1500 RPM (indicated on the tachometer) while the clutch is being engaged.

Beginners sometimes find the fine throttle control required to hold the engine speed within this range difficult. It helps to spend a little time practicing with the gas pedal, while the engine is running, the transmission is in neutral and the parking brake is engaged.

To start moving, the driver ensures that the clutch is fully disengaged, by depressing the clutch pedal, and ensures that the engine is turning at the appropriate speed. Then, he gradually engages the clutch by releasing the clutch pedal. If the clutch is engaged too quickly, the car will jolt forward, and likely stall.

By the time the car is moving faster than a brisk walking speed, the clutch should be fully engaged, meaning that the driver's left foot should be completely removed from the clutch pedal. The car is moving in first gear, which is rarely used for speeds greater than about 20 km/h (12.5 mph). It's probably best to practice starting and first gear driving in a large, deserted parking lot where the exercise won't impede other motorists.

Stopping in first gear

Coming to a stop in first gear is achieved by disengaging the clutch by pressing the clutch pedal all the way down with the left foot while applying pressure to the brake pedal with the other foot. The timing isn't important, except that if the clutch is still engaged when the vehicle gets below walking speed, the engine will probably stall.

A beginning driver who is confident starting, driving around and stopping in first gear is ready to explore shifting into the higher gears.

Shifting

For a given speed of travel, the engine speed will vary depending on which gear is selected. So, when you want to change gears, you need to pay attention to the difference between the speed the engine is turning in one gear, and the speed it will be turning in the next.

The difference in engine speeds between one gear and the next varies between vehicles, but in general lower gears will have a greater difference than higher gears. For instance, at 15 km/h (9.3 mph), the engine might be turning at 3000 RPM in first gear or 2000 RPM in second gear, whereas at 100 km/h (62 mph), the engine might be turning at 2800 RPM in fifth gear or 3200 RPM in fourth gear.

With practice, you will become able to time shifts so that you can disengage the clutch, change throttle, shift and then reengage the clutch quickly without any jerkiness. Once again, it starts out difficult but becomes second nature with time.

Upshifting

When accelerating in any gear other than top gear, shift up when the engine is turning at too high a speed for the current gear. The engine speed that constitutes "too high" varies from vehicle to vehicle and according to the driver's taste, but the absolute upper limit is usually marked on most vehicles equipped with a tachometer as a red area called the redline. Running the engine past this speed can cause damage to internal components of the engine (and most modern cars with electronic engine control computers will not permit the engine to be run past the redline). In practice, one usually shifts up well before the engine speed reaches redline. The vehicle's owner's manual should contain a table of recommended upshift speeds, but as a general rule of thumb, consider shifting between 2000 and 3000 rpm - although in some small engines that make power higher in the rev band shifting around 3500rpm can drop you to a better part of the power band in the next gear. (Note that in a diesel you will usualy have to shift at a lower rpm, and the redline is likely to be lower.)

For maximum acceleration, one may shift just before reaching the redline, but for ordinary driving, to conserve fuel, one should shift at as slow an engine speed as possible without "lugging" the engine. With practice, you will be able to tell when to do this by the sound of the engine.

To upshift:

Press and hold the clutch pedal with your left foot.

Decrease throttle to a level appropriate for the higher gear. If you are experienced enough to shift quickly, you may be able to simply release the gas while shifting, and the engine will roughly sync.

Move the gear shift knob, depending on the gear that is currently selected:

To shift from an odd-numbered gear (i.e. 1st or 3rd) into the next highest gear, move the shift knob down, through neutral, to the corresponding position on the bottom row.

To shift from an even-numbered gear (i.e. 2nd or 4th) into the next highest gear, move the shift knob up to neutral, one column to the right, then up to the new position on the top row.

Gradually release the clutch pedal, allowing the new, lower engine speed to match up with the vehicle's speed.

If you take longer than a second or so to upshift, the engine will probably have slowed down too much for the new gear, and the car will probably jerk backward a bit unless you increase throttle to compensate. Don't increase the throttle too much though, or the engine will be going too fast for the new gear and the car will jerk forward. Once your skill at "matching revs" improves you can release the clutch pedal more quickly without any jerkiness.

Downshifting

When decelerating in any gear above third gear, shift down when the engine is turning at too low a speed for the current gear. The speed that constitutes "too low" varies among vehicles, and you can afford to keep it in a higher gear if little acceleration is needed, but as a rule of thumb, consider downshifting when the engine reaches 1500 RPM. With some practice, you will be able to hear the engine speed and make this judgement.

It is important not to shift into too low a gear for the car's speed. Downshifting increases the speed of the engine. If one shifts into a very low gear (e.g. second gear) at a very high speed (say, highway speeds) it is possible for the car's engine to be driven beyond the redline, conceivably causing severe damage to the engine. (In this case, even the engine control computer's rev-limiting function cannot help, as the engine is being driven by the momentum of the car). It is always safe to downshift to the next lower gear when the engine is turning at too low a speed for the current gear. If you "miss" a downshift and hear the engine revving too fast as you let out the clutch, immediately push the clutch back in and shift into a higher gear.

Due to the larger differences in gear ratio between first and second gear, it's usually best not to downshift into first gear unless you plan to be driving very slowly for some time. Instead, stay in second gear and disengage the clutch when you're about to come to a stop. In some special cases (very steep slopes, crawling traffic) first gear can be useful, however. In some vehicles, it is easier to shift into first gear from a stop than to downshift from second.

To downshift:

Press and hold the clutch pedal with your left foot.

Increase throttle to a level appropriate for the current speed of travel in the lower gear. This is (somewhat) optional, since gradually releasing the clutch will adjust for a slight mismatch, however if you completely release the accelerator while shifting you are likely to have the car jerk somewhat.

Move the gear shift knob, depending on the gear that is currently selected:

To shift from an even-numbered gear (i.e. 2nd or 4th) into the next lowest gear, move the shift knob up, through neutral, to the corresponding position on the top row.

To shift from an odd-numbered gear (i.e. 3rd or 5th) into the next lowest gear, move the shift knob down to neutral, one column to the left, then down to the new position on the bottom row.

Gradually release the clutch pedal, allowing the new, higher engine speed to match up with the vehicle's speed.

If you don't match the engine's speed properly for the lower gear, the car will probably jerk a bit. Once your skill at "matching revs" improves you can release the clutch pedal more quickly without any jerkiness.

Starting on an upslope

Decades ago, Studebaker invented and used a clutch-brake interlock mechanism called Hill-Holder, which is currently (2004) available only on Subaru Foresters. Most Mercedes-Benz vehicles, and some Volkswagens, also hold the brake automatically until the clutch is at the friction point (sometimes called the biting point). Even without these aids, starting on a hill should be no more difficult than starting normally if proper starting technique is used.

The correct way to do this is to use the parking brake. This is sometimes referred to as a hand brake, but some parking brakes are foot operated. Firstly, when stopped on a hill, the parking brake should always be engaged. The driver must not rely on the main brake alone, for safety reasons. If that braking system fails, or the driver's foot comes off the pedal for whatever reason, the car will start rolling backward. The parking brake and regular brake are distinct, redundant systems. If one fails, the other can still stop the car. For this reason, the parking brake is also called an "emergency brake", particularly in North America where most drivers own cars with automatic transmissions which have a parking system built into the transmission itself.

To start, these steps are performed in rapid succession:

Initial conditions:

the car is in neutral gear, stopped, and facing upslope.

The parking brake is engaged and latched with its ratchet mechanism.

The engine is running.

The driver's left foot is off the clutch, and the other foot is on the brake.

Press the clutch all the way down, and select first gear.

Unlatch the parking brake without disengaging it. If it's a hand-brake, this means lifting it and pressing the button that releases it from the ratcheting mechanism, allowing for free play. Maintain adequate tension (or pressure, as the case may be) on the parking brake to keep it engaged and prevent the car from moving backwards, and remove your foot from the main brake.

Now, for a brief moment, the vehicle is held in position by the parking brake alone. If it rolls backward at all, stomp on the main brake and increase the force you are applying to the parking brake.

While continuing to apply force to the hand brake, follow the ordinary procedure for starting the car: increase the engine RPM, while slowly releasing the clutch. But of course, the car cannot move because of the brake.

as you sense that the clutch is engaging and the car wants to move, release the parking brake, while maintaining engine RPM and finish the starting manoeuver as usual.

expect that slightly more clutch slip will be required than when starting on a horizontal surface, and somewhat more engine throttle.

the car may move anyway as the clutch starts to grab, because the engine power may overcome the force of the parking brake. This can be used to advantage. The parking brake has a force range of its own which, with practice, can be incorporated into the technique.

Thus, essentially, starting on an upslope is much like the ordinary starting technique, with a correctly-timed release of the parking brake blended into the procedure.

Some manual-transmission drivers start on hills without using the parking brake, in spite of being experienced. This is wrong and shouldn't be done or recommended to others.

In fact, in some localities it is necessary to demonstrate mastery of the handbrake technique to pass a driving test.

It is possible to maintain your vehicle's position on an upslope without using the brakes by "riding the clutch" for short periods, namely using some throttle and modulating the clutch's engagement. In spite of being possible, this is damaging to the clutch and should never be done. A related technique which should also never be practiced is driving up steep hills at such a slow speed that, even in the lowest gear, the clutch is required to slip in order to maintain adequate engine RPM. If such a driving situation is expected to occur regularly, and cannot be avoided, the driver should consider owning a vehicle whose power train design supports that use.

Troubleshooting

Stalling

When a vehicle's engine is turning at low speeds it is unable to provide much torque, and placing excessive demand on the engine will cause it to stop running suddenly, an event known as a stall. Stalling usually causes sudden jerking movements of the vehicle.

The following behaviours are likely to cause stalls:

At a standstill, engaging the clutch too quickly, while the engine is turning too slowly.

Coming to a stop with the clutch engaged and the transmission in gear.

If you stall the engine, don't panic. It happens to all beginners and even occasionally to experienced drivers, and it's nothing to be ashamed of. Just step on the clutch, start the engine up, and try again. If you feel like the engine is about to stall, step on the clutch. If you get scared or need to come to a stop, don't forget to step on the clutch while you're instinctively hitting the brakes, otherwise you'll probably stall.

The clutches in different vehicles vary in their sensitivity and range of movement, so even a very experienced driver in an unfamiliar vehicle can stall its engine a few times until he or she becomes familiar with its clutch.

Stalling due to loss of traction while braking

When decelerating, a driver will apply brakes and then disengage the clutch shortly before stopping (around 1000 RPM in 1st gear or somewhere above "walking speed" as above). In normal conditions with good traction, this is fine. However, on some surfaces, and depending on the severity of the braking, without an Antilock Braking System, the wheels can lock up. This can happen easily on slippery surfaces like snow, ice and loose gravel. The poor traction on such surfaces can prevent the momentum of the car from turning the wheels. The only real force for the brakes to oppose is the engine's.

When this happens, if you don't disengage the clutch, you will stall the engine. Thus a manual transmission driver, without ABS, should take to disengage the clutch if braking hard, or even if braking lightly on slippery surfaces. See also cadence braking, an important skill for winter drivers without ABS equipped vehicles.

Grinding Gears

A grinding sound coming from a synchronized manual transmission during a shift is a usually sign of improper technique. Some hobbyist drivers blame the machinery: they claim that the synchro mechanism is worn, or there is some issue with the manual transmission lubricant. This comes up again and again in online automotive forums. In fact, the synchro mechanism would have to be completely gone for this to be true, and it's almost certainly not an issue with the lubricant.

Why does grinding happen in a synchronized transmission? It's because the overly zealous driver engages the clutch too fast, in parallel with moving the gearshift, in an attempt to minimize the overall shift time. Or, perhaps the driver is doing everything in the correct sequence, but failing to press the clutch far enough! Either way, the gear selector has already "passed through" the synchronizer, but not gone far enough for the teeth to actually engage. At this point, if the clutch is engaged, even slightly, the speed of the input shaft will change, and the synchronization will be lost. Since the selector has already been pushed through the ring, it's too late: the stick can be moved so that the teeth make contact. The result is grinding.

Quite possibly, there could be a problem with the clutch: perhaps it is not disengaging all the way when the pedal is being pressed to the floor. The pedal might need adjustment, or there is some problem with the hydraulics or mechanical linkage, or other problem with the clutch mechanism itself. But here we are assuming that there is no mechanical problem.

To avoid grinding, do the waltz: think 1-2-3. On the count of 1, press the clutch all the way down to the floor. On the count of 2, move the stick to the desired gear. On 3, release the clutch. To speed up the gear change, you must speed up these motions individually, and not "cheat" by trying to overlap steps 2 and 3. There is little room for that. In particular, the lever must be in the final position before the clutch moves off the floor. Where you can save time is by tightly combining 1 and 2. Push or pull on the stick while pressing the clutch, to get it moving as soon as possible. Practice the waltz: count 1-2-3 in your head. Try doing it very slowly, and then speed up the tempo.

To do a fast gear change without grinding, push the clutch pedal to the floor as fast as possible, in advance of moving the stick, but start moving the stick even before the clutch hits the floor. The clutch should be all the way down as the stick passes through the neutral position to the other gear, and should remain floored. Move the stick as fast as possible from one gear to the other, using speed and force. You should feel a resistance followed by a click; that's the resistance of the synchro, which needs time to do its job before allowing the selector to proceed. Finally, release the clutch. This is the slowest part of the transaction, but with practice, it can be sped up significantly.

The common mistake that causes grinding is not moving the stick fast enough before releasing the clutch; failing to coordinate the two motions. Sometimes drivers complain about grinding during steep gear changes, when the engine is revved to a high RPM in the lower gear. The synchro has to do more work to slow down the input shaft of the transmission to match up the next gear! This takes more time, but the driver is not adjusting for it. He or she is not waiting for the lever to pop through the synchro, and is releasing the clutch using a rehearsed timing, independently of what is going on in the gearbox. The foot doesn't know what the hand is doing and vice versa! The foot must be trained to wait for the hand to complete the gear selection.

Follow these steps, and you will enjoy grind-free shifting in any situation, whether you are red-lining the engine in every gear at a track race, or lugging casually around town.

Another situation in which grinding can be heard is when placing the transmission into reverse from a stopped position, e.g., when leaving a parking space. Grinding occurs here in part because reverse is often not a synchromesh gear. If one does not leave the transmission in reverse or a forward gear when parked, it is likely that s/he will hear grinding in the transmission when shifting into reverse no matter how far the clutch pedal is held in when shifting. To avoid grinding in reverse, one must "clear the gate": first place the gear shift into a forward gear, then shift into reverse. This will eliminate any grinding that is heard. On most 5-speed synchromesh transmissions, the gates will lock out a shift from 5th gear down into reverse as a safety feature; therefore, place the shifter into another forward gear before shifting into reverse.

One last note: the transmission oil can make a difference if the shift is being done improperly. A lubricant that doesn't have the proper friction additives will cause the synchro to take more time, giving rise to more opportunity for premature clutch release. This is why some technically inclined drivers report experiences like "I switched my manual transmission fluid from brand X to brand Y and now I get more (or less) grinding". Some cars also shift more easily when the transmission oil has warmed up; Mazda Miatas are particularly known for this.

Advanced techniques

This section discusses performance driving techniques, which may be detrimental to the life of the power train and other components of the vehicle.

Power shifting (a.k.a. speed shifting)

This is an advanced technique that gives a speed boost to the car when upshifting. This should only be used in racing applications, as it is very hard on drivetrain components, especially if done improperly. Even done properly, it generally puts undue stress on the drivetrain, and shortens the lifespan of the driveline components.

To perform a power shift, keep the gas pedal on the floor (instead of lifting) while pushing in the clutch. At the same time, quickly shift to the next gear. Quickly re-engage ("pop") the clutch as soon as the new gear is selected. If done properly, the car will receive a "bump" in acceleration (due to the jerk of the decelerating engine) as the clutch is re-engaged. If done improperly, it can result in engine or transmission damage, sometimes catastrophic.

Heel-and-toe

While decelerating, the technique of heel-and-toe shifting allows advanced drivers to maintain pressure on the brake pedal while simultaneously "blipping" the throttle to aid downshifts.

Double clutching

"Double-clutching" (also known as "double-declutching" in Europe) is an old technique that dates from before the days of synchromesh gear boxes. It can make downshifting (and arguably upshifting) smoother and can reduce transmission wear. It involves depressing the clutch and dropping into neutral, releasing the clutch, using throttle to match revs for the gear to be selected, depressing the clutch again and selecting the new gear. The action (which sounds more complicated than it really is) ensures that the output shaft is running at the right revs before a gear is selected hence creating smoother shifts and reducing wear on synchromesh systems. Some types of unsynchronized manual transmissions require double-clutching. These transmissions may be found in some older vehicles and race cars, as well as on large trucks, especially tractor-trailers.

Double-clutching on a synchronized gearbox is unnecessary in most driving situations. However, it is possible that an unskilled driver may second-guess something that the machine is designed to do automatically, and can cause more harm than prevent it. A true unsynchronized transmission is unforgiving to mismatched speeds, requiring a great deal of precision from the driver. A synchronized transmission will allow the driver to get away with sloppy double-clutching, and an unskilled driver may end up causing more harm by not matching the engine speed properly.

However, even with a synchronized gearbox, double-clutching under skilled hands is desirable when shifting down to the lowest gears. The synchronizer, particularly the one for the second gear, receives much abuse, as the speed differential it has to manage is usually the greatest. It is indeed usually the second gear synchronizer that fails first. Some recent Honda manual transmissions incorporate a triple-cone synchronizer in the lowest gears for extra durability.

Many transmissions until recently did not have a synchronizer on the first gear. It is therefore necessary to double-clutch when downshifting into the first gear, though such instances are rare. Some transmissions today still do not have a synchronizer for the reverse gear, requiring that you come to a complete halt before shifting into reverse (see the "Grinding gears" section above for futher implications of this). Double-clutching is of course impossible, as you cannot reverse the direction of the engine rotation. You must simply wait for the car to come to a halt and engine revs to drop to idling.

Single clutching

A downshifting technique similar to a cross between double clutching and shifting without the clutch. The transmission is taken out of gear whilst the clutch is still engaged. The accelerator is then 'blipped' to bring the output shaft to the correct speed, the clutch is disengaged, the lower gear is selected and the clutch is engaged again. This is a fairly common racing technique.

Shifting without the clutch

It is possible to shift gears without using the clutch at all, by careful throttle manipulation. When transmissions were unsynchronized this was usually the easiest method, and still works in modern cars, although it requires a lot more practice than the usual methods described above.

Although the technique works in synchronized gearboxes, it is inappropriate in nearly all circumstances. A synchronized gearbox has a small clutch called a synchronizer (or "synchro") in every forward gear which brings the input and output rotation to the same speed before allowing them to engage. Like the main clutch, these synchronizing clutches use friction. These synchronizing clutches will allow for a margin of error when engaging without the main clutch. If the engine speed is somewhat too high or too low, the synchro will essentially take on the job that the fully engaged main clutch isn't doing. However, a synchro ring is not intended to do the job of a main clutch. Its job is to spin up or spin down just the input part of the transmission that is assumed to be disconnected from the engine. It is not intended to speed up or slow down the entire engine. Such experimentation done on a regular basis will prematurely wear out the synchro rings, which will have to be replaced.

On cars with a freewheel, such as the older SAAB with a two-stroke engine, shifting without the clutch is standard procedure. But actually, the freewheel is a form of clutch: one that is disengaged whenever the input rotation is slower than then output rotation. One must disengage the freewheel by allowing the engine revolutions to drop, which is analogous to pressing the clutch pedal.

Compression braking

This is also called "engine braking"; the use of the engine's internal resistance to slow down the vehicle, or keep it from accelerating down a hill. This is done by shifting the car into a lower gear and releasing the clutch, with the foot off the throttle.

Some feel that you abuse your manual transmission and engine by "engine braking". They feel that you should downshift only when you anticipate that the car will be in a lower speed for some time, not when coming to a full stop. Some feel that the reason why you must keep the car in gear while slowing down or stopped but with the clutch disengaged is for emergency manuevers, for it will give you the extra time to escape a pending accident. In this case, downshift late, allowing the car to slow to pretty a low engine RPM's before shifting down.

Using the manual transmission to stop the car is inappropriate under normal driving conditions. Simply put, when using the engine to slow the speed of the transmission, the clutch and synchronizers are unnecessarily being worn out for what the car brakes are designed to do. In comparison, the clutch typically costs around US$1000 to fix as opposed to US$300 for new brake pads and installation. The method is provided only because one may find it occasionally necessary or useful to use engine braking (when one needs to decelerate more quickly than usual, for instance).

If decelerating towards a full stop while in an upper gear, such as 4th, a downshift to a lower gear should be made, as this increases the time that a gear is engaged, therefore keeping the brake and power steering servos engaged and so power is supplied. Coasting time should be kept to a minimum using effective and well-timed downshifts.

On the other side of the coin, some feel that engine braking is relatively harmless to the engine and transmission. The idea is that during decceleration the engine creates a vacuum in the cylinders which pull a very small amount of oil past the rings, increasing protection. This, combined with the fact that the forces involved are typically less than those normally seen during acceleration lead some to conclude that it will make no real difference in the lifetime of the engine and transmission.

There is a situation when engine braking is truly called for: going down steep hills which are also very long, and for whatever reason, it is undesirable to pull over and stop the car. Braking downhill for a long time can overheat the brakes leading to failure. A combination of gearing down and using the brakes is safer. But heat can be dissipated from brakes also by pulling the car over and letting it stop for a while, effectively dividing the long hill into a sequence of shorter ones.

In fact, drivers find that most of the time, the best manual transmission driving practices closely mimic the actions of an automatic transmission, except in cases when the automatic transmission lacks anticipation of changing conditions. To be a good manual transmission driver, drive an automatic and observe what it does. Modern engine and automatic transmission control (such as that found in the 2005 Toyota Tundra) incorporate downshifting the automatic transmission out of overdrive during braking.

See compression braking for more information.

Fuel efficiency

Manual transmissions have an inherent fuel efficiency advantage compared to conventional automatic transmissions (the type that have a torque converter coupled to a planetary gearbox) because the torque converter, a kind of fluid-coupled clutch, wastes a percentage of the engine power. Many automatic transmissions have a locking mechanism which bypasses the fluid coupling by mechanically engaging the moving parts of the torque converter together; but this only happens when cruising in the overdrive gear.

To make the most out of the fuel efficiency advantage, a manual transmission car has to be driven in certain ways. Some things that manual transmission drivers do can waste fuel in ways that wouldn't happen under an automatic transmission.

The first general guideline is to shift earlier rather than later. Shift at the lowest possible RPMs in the current gear that will allow the engine to run without lugging in the next higher gear. Shoot for a target of about 1500 to 2000 RPM in the next gear. This is especially true for diesels where the torque band peaks at lower RPM than petrol engines.

Second, accelerate gently. Fuel consumption is directly related to how hard the gas pedal is pressed.

Third, look for and anticipate stops and red lights up ahead. Whenever you have to bring the vehicle to a full stop, you are turning all of its kinetic energy into heat in the brakes. That energy has to be regenerated from the car's fuel in order to get moving again. Don't race toward red lights. In most modern, fuel-injected cars, if the car is in gear and coasting, no fuel is used. In this case it is best to leave the car in gear while it slows, and then change to the correct gear when accelerating again.

When approaching a hill, slowly speed up the vehicle to build momentum before reaching the hill.