Threshold braking

Threshold braking or limit braking is a technique wherein the driver adjusts control of the brake system in an attempt to maximise the braking force of the vehicle. Done properly, this reduces the time and travel distance required to stop the vehicle to optimal amounts, or when racing, allows the driver to delay braking when entering a corner. The optimal amount of braking force is developed on a wheel at the point when the wheel just begins to slip. Braking beyond this point, as the tyre begins to slide, the friction force between the tyre and driving surface transitions from the static friction range into the kinetic friction range. The friction force developed between the tyre and driving surface is proportional to the coefficient of friction for the combination of materials involved, namely, the tyre (usually rubber) and the surface (asphalt, dirt, ice).

Cadence braking

Cadence braking is a technique used to stop a car or other vehicle more quickly on a slippery surface. It would normally be used to effect an emergency stop where traction is limited, though for use in an emergency requires a presence of mind that the situation itself might preclude.

Maximum braking force is obtained when there is approximately 11% slippage between the braked wheel's rotational speed and the road surface - at this point rolling resistance is maximised, and there is a small additional contribution from sliding friction - beyond this amount of slippage, rolling resistance diminishes rapidly and sliding friction alone slows the vehicle. Due to local heating and melting of the tyres, the sliding friction can be very low.

Cadence braking involves pumping the brake pedal fairly rapidly but deliberately, to make the wheels lock and unlock. Because a locked wheel creates a smaller braking force than one which is just on the point of locking, this technique may cause the vehicle to stop more quickly, because the point of optimum braking is passed through multiple times. In addition, by avoiding a total lock-up, steering control can be retained, at least in part. While cadence braking is effective on most surfaces, it is less effective than keeping the wheel continually at the optimum braking point. However, this is almost impossible to do manually. Note that the principle of cadence braking is automated in anti-lock brakes (ABS), but done multiple times every second. Because of the fact the human can not modulate the brake pedal that fast, Threshold braking is more effective in keeping the tires close to the optimum slippage. When ABS is present the best emergency stop will be obtained by simply pressing hard on the brakes, forcing the ABS to perform.

Cadence braking (or any other type of braking) will not help much on extremely slippery surfaces such as ice (in theory it would, but in practice the ice can be so slippery that it makes little difference -- a winter tyre would make more difference). Also, on very loose surfaces, a quicker stop can be achieved by simply locking the wheels, forming a wedge of loose material will build up ahead of the wheels and create a substantial braking force. In such conditions, ABS actually increases the stopping distances. On poor surfaces, in the past, rally drivers timed the pulsing of brake application so as to take advantage of the load transfer as the vehicle pitches forwards and backwards in response to the initial braking effort. With modern over damped, stiffly spring, suspensions this is less likely to be effective.

Trail braking

Trail braking is a driving technique where the brakes are used past the entrance to a turn and are gradually released up to the point of apex.  Trail braking helps you rotate the car into a corner by controlling the transfer of weight onto the front tyres, giving them more stick, and thus compensating for any tendency to understeer the car would otherwise have.

To apply this technique, as you approach a turn, apply brakes as necessary to reduce speed. Then, as you enter the turn, partially release the brakes as to keep only partial brakes throughout the turn.  This will give more traction as the front tyres are forced into the track.  How much trail braking you do at a particular corner - (how far into the corner you continue braking braking) depends on the angle of the corner.  For a 60° corner, you'd typically only trail for a few percent of the corner, for a 90° corner, you'd typically trail brake for maybe 25% of the corner, and for a bigger corner, you could do it for up to 50% of the corner.  You are aiming to trail off the brakes until they are released completely at or before the throttle application point (which typically occurs somewhere before the geometric apex).

This technique is commonly used when racing, but motorcyclists can enhance control and add more evasive options for street use making it very worthwhile to learn or at least understand. Be aware that excessive trail braking can result in a loss of grip as the tyre's adhesion is split between braking and cornering forces. It will also noticeably affect the behaviour of the vehicle.

Left-foot braking

Left-foot braking is the technique of using the left foot to operate the brake pedal in a car, leaving the right foot dedicated to the accelerator pedal. It contrasts with the normal practice of the left foot operating the clutch pedal, and the right foot operating the brake and accelerator pedals. It is most commonly used in auto racing, but is also used by some drivers for use with an automatic transmission, as the left foot is not needed to operate a clutch pedal. The most significant consequence is that the driver can operate both the accelerator and brake at once, creating the potential for spins, while not allowing the clutch and brake to be used together.  Critics say that the practice can be dangerous.

At its most basic purpose, left-foot braking can be used to decrease the time spent between the right foot moving between the brake and throttle pedals. It can also be used to control load transfer. 

Karts, many formula cars, and some modern road cars (such as the Enzo Ferrari), have no foot-operated clutch, and so allow the driver to use his left foot to brake.  One common race situation that requires left-foot braking is when a racer is cornering under power. If the driver doesn't want to lift off the throttle, and potentially cause a trailing-throttle oversteer situation, left-foot braking can induce a mild oversteer situation, and help the car "tuck," or turn-in better. Mild left-foot braking can also help cure an understeer situation.

In rallying it applies primarily to front wheel drive vehicles. It is closely related to the handbrake turn, but involves locking the rear wheels using the foot brake, which is set up to apply a significant pressure bias to the rear brakes. The vehicle is balanced using engine power by use of the accelerator pedal, operated by the right foot. The left foot is thus brought into play to operate the brake. Rear wheel drive rally vehicles do not use this technique because they can be much more easily turned rapidly by using excess power to the wheels and the use of opposite lock steering.

Swedish rally legend Stig Blomqvist is considered to be the inventor of left-foot braking, developing it while driving for the SAAB works team in the 60's and 70's.  This technique should not be confused with Heel-and-Toe, another driving technique.

Many modern vehicles use a "Drive By Wire" or Electronic throttle control system instead of the traditional mechanical throttle linkage. These systems often do not allow for left foot braking. As the throttle is connected to the car's ECU, it can detect when both pedals are pressed simultaneously and will immediately cut the engine power. This is in case of a malfunction in the throttle body or a stuck pedal.

Double declutch

A double declutch (also called a double clutch) is a driving procedure used for vehicles with an unsynchronised manual transmission.

Before the introduction of synchromesh (1920s) and helical cut gears, double declutching was technique required to prevent damage to an automobile's gear system. Due to the difficulty involved in learning the technique, and because of the advent of synchronised gearing systems it has largely fallen into disuse. However, drivers of large trucks still use double clutching, as those vehicles are usually equipped with the older, more efficient, and more durable unsynchronised gearboxes.

The purpose of the double clutch is to match the speed of the rotating parts of the gearbox for the gear you wish to select to the speed of the input shaft being driven by the engine. Once the speeds are matched, the gear will engage smoothly. If the speeds are not matched, the dog teeth on the collar will "crash" or grate as they attempt to fit into the holes on the desired gear. A modern synchromesh gearbox accomplishes this synchronisation automatically.

When shifting up on a double-clutched vehicle, the clutch pedal is pressed, the throttle is released, and gearbox shifted into neutral. The clutch pedal is then released. As the engine idles with no load, the engine speed (rpm) will decrease until they are at a level suitable for shifting into the next gear. The driver then depresses the clutch again and shifts into the next gear. The whole manoeuvre can, with practice, take no more than a fraction of a second, and the result is a very smooth gear change.

However, in order to downshift, engine revs must be increased while the gearbox is in neutral and the clutch is engaged. This requires the driver to shift into neutral, release the clutch pedal, apply throttle to bring the revs up to a suitable speed, depress the clutch again, and finally shift into gear. This operation can be very difficult to master, as it requires the driver to gauge the speed of the vehicle accurately and is often conducted as cars in front slow down.

A related technique is called Heel-and-Toe, during which the brake and accelerator pedal are pressed by the right foot while the clutch pedal is pressed by the left foot. Note that Heel-and-Toe can be used with any downshift clutch operation, not just with double-clutching. Though difficult, mastering Heel-and-Toe in conjunction with double clutching is essential for high performance driving (e.g., rallying) because non-synchronised transmissions are frequently used.

Heel-and-toe

Heel-and-toe is a driving technique used in performance driving. It involves operating the accelerator and brake pedals simultaneously with the right foot, while facilitating normal activation of the clutch with the left foot. It is used when braking and downshifting simultaneously (like when going around a turn), and allows the driver to "blip" the throttle to raise the engine speed and smoothly engage the lower gear.

Heel and toe braking has the following steps:

       Brake with the ball (left edge) of your right foot while the car is in gear

       Disengage (press) the clutch once the car has slowed down significantly (if double clutching, shift to the neutral position and engage the clutch)

       Blip the throttle to match the engine rpm to the rpm needed for the selected gear using either the heel or the right edge of your right foot

       Shift the gear lever to correct gear (disengage the clutch first if double clutching)

       Engage the clutch, release the brake and roll your foot onto the accelerator

Heel-and-toe is used before entry into a turn while a vehicle is under braking, preparing the transmission to be in the optimal gear to accelerate out of the turn.  One benefit of downshifting before entering a turn is a jolt to the drive train, or any other unwanted dynamics, will not upset the vehicle as badly when going in a straight line; the same jolt while turning may upset the vehicle enough to cause loss of control if it occurs after the turn is begun. Another benefit is "heel-and-toeing" allows you to downshift at the last moment before entering the turn, after you have started braking and the car has slowed, so the engine speed when the lower gear is engaged will not be too high.

Performance vehicles are usually modified (if necessary) so that the heights of the brake and accelerator pedals are closely matched to permit easy use of heel-and-toe, and that the pedals are not too far apart.

The name, stemming from earlier automotive designs where the accelerator pedal was on the left and could be actuated with the heel while the brake pedal was actuated with the toe, is misleading regarding how the technique is carried out in modern cars, i.e., operating the brake with the left edge of the foot, while rocking it down and to the right to operate the throttle. With practice, it becomes possible to smoothly and independently operate both pedals with one foot. The technique is common in all forms of motor sport, especially rallying.

Before entry to the bend, the car is turned towards the bend slightly, but quickly, so as to cause a rotating motion that induces the rear of the car to slide outwards. Power is applied which applies further sideways movement. At the same time, opposite lock steering is applied to keep the car on the desired course. As the car reaches the bend it will have already turned through most of the needed angle, travelling sideways and losing some speed as a result. A smooth application of power at this point will accelerate the car into the bend and then through it, gradually removing the sideways component of travel. Overall, the bend will have been negotiated much faster than driving through it in a normal manner. In skilled hands, the result is a dramatic and fluid motion which looks incredibly natural. When executed poorly, the result is often the complete opposite.

For front-wheel drive vehicles, there is much less natural tendency for the rear wheels to break traction because they are not transmitting power, so often such vehicles are set up with a strong bias to the rear brakes, allowing the driver to control traction using the brake pedal. The brake bias (front/rear) may be continually controllable by the driver using a hand lever. Left-foot braking is the favoured technique for using opposite lock in a front drive vehicle.

A related technique is the handbrake turn, in which the rear wheels are deliberately locked in order to break the friction between the tires and road surface.

Handbrake turn

The handbrake turn is a driving technique used to deliberately slide a car sideways, either for the purpose of negotiating a very tight bend quickly, or for turning around well within the vehicle's own turning circle.

The driver starts by using steering input to transfer weight to the outside tires; the handbrake is then used to lock the rear wheels, thus upsetting the adhesion between the tires and the road surface. With practice, the car can be placed accurately by releasing the handbrake and accelerating the vehicle. The technique is used in some forms of motor sport, for example rallying, auto testing and motorkhana.  A related technique is left-foot braking.

The technique employed to start a handbrake turn:

       Find a smooth open space without any obstacles for safety

       Come at a speed more than 15mph

       Start making the turn by turning the steering wheel in one direction with one hand

       Immediately after starting the turn, pull the handbrake with the other hand while keeping the button on the handbrake pressed

       The rear part of the car will start the skid

       Release the handbrake and start pushing the accelerator when the desired direction is achieved.

In a rear-wheel drive manual transmission vehicle, it is also necessary to operate the clutch to prevent the handbrake from stalling the engine.

Drifting (motor sport)

The basic driving techniques used in drifting are constant, though each car and driver will employ some subset of these techniques. They include:

       Hand-brake or Emergency brake drift - The hand-brake is pulled to induce rear traction loss. This is generally the main technique to attempt to drift a FWD car. Also, this technique is used heavily in drift competitions to drift large corners.

       Power oversteer or Power slide - This drift is performed when entering a corner at full throttle to produce heavy oversteer through the turn. The excess power causes the drive wheels to lose traction in a RWD or AWD car. This is the most typical drifting technique for all-wheel drive cars.

       Kansei, Lift off, or Taking In - By letting off the accelerator while cornering at very high speeds, cars with relatively neutral handling will begin to slide, simply from the weight transfer resulting from engine braking. The drift is controlled afterwards by steering inputs from the driver and light pedal work, similar to the Braking drift.

       Shift lock - Initiated by downshifting (usually from third to second or fourth to third, and using a very fast shift) instead of braking, without rev-matching, causing the drive wheels to lock momentarily. Helpful for very tight corners, allowing the driver to approach the corner at a slower speed and lower revs, while allowing quick acceleration when exiting the corner. This technique can be very damaging to the engine if misused as the ECU is unable to rev limit when the engine is over speed by the rear wheels. Premature down shifters are called "Rod Stretchers".

       Braking Drift - This drift is performed by braking into a corner, so that the car can transfer weight to the front. This is immediately followed by throttle in a RWD car causes the rear wheels to lose traction. FWD cars can also use this technique as it does not depend on the rear wheels being driven.

       Clutch kick - This is done by "kicking" the clutch (pushing in, then out, usually more than one time in a drift for adjustment in a very fast manner) to send a shock through the powertrain, upsetting the car's balance. This causes the rear wheels to slip.

       Inertia (Feint) drift, or Scandinavian flick - This is done by transferring the weight of car towards the outside of a turn by first turning away from the turn and then quickly turning back using the inertia of the rear of the car to swing into to the desired drifting line. Sometimes the hand-brake will be applied while transferring the weight of the car towards the outside to lock the rear wheels and help the rear swing outwards. This type of drifting causes the car to accelerate faster afterwards, because of momentum built up while drifting.

       Dirt drop - This is done by dropping the rear tires off the sealed road onto dirt, or whatever low-grip surface borders the road, to maintain or gain drift angle. Also colloquially called "Dirt Turbo".

       Choku-Dori - This is done by swaying the car's weight back and forth on straightaways, using opposite lock and throttle to maintain a large angle. This is a show manoeuvre that usually involves many cars following the same line.