Shifting Technique

This article covers the fundamentals of advanced shifting techniques relevant to performance driving. All of the techniques described are in constant use in race and performance driving.

Many people use the term “heel and toe” to refer to rev-matching while shifting and double-clutching under braking, but it is actually just one component of these processes.

Rev-Matching

Rev-matching refers to matching the engine speed to the transmission input speed before re-engaging the clutch. This is particularly desirable when downshifting for a corner.

In a hard corner, the suspension needs to be stable and the tyres need to be loaded so that all of their traction is being used to generate cornering force. If the engine is at a different speed than the transmission input when the clutch is re-engaged, the resulting force on the driveline will upset the stability of the suspension (weight transfer) and may cause the tyres to exceed their traction capability if the corner is being taken near the limit.

Rev-matching is necessary when cornering near the limit. It is not strictly required for slower corners, but it makes them smoother.

Another benefit is that heel-and-toe rev-matching allows the driver to downshift at the last moment before entering the turn, after braking has begun and the car has slowed, so the engine speed when the lower gear is engaged will not be too high.

As the power band of most rally cars is high in the rev range, this technique also ensures that engine RPM does not drop below the power band under braking. If this happened, there would be a delay between the driver pressing the throttle after the corner and the car responding — especially true in turbocharged cars. Rev-matching ensures that maximum power is available the instant the brake pedal is released and the throttle is fully applied. This can also be achieved with left-foot braking.

Double Clutching

Double clutching is a technique for rev-matching the transmission’s intermediate shaft to the output gear that is to be selected. This function is normally handled automatically by the transmission’s synchromesh gears. Double clutching is useful for extreme gear changes, for older transmissions with worn synchros, or simply to reduce wear on the synchromesh rings.

Most drivers, when downshifting, merely press the clutch after lifting off the throttle, move the lever into a lower gear, and release the clutch. In modern vehicles with synchromesh transmissions this works, but it is usually accompanied by a sudden rearward weight transfer and sometimes less-than-harmonious noises from the drivetrain. This sudden weight transfer can have an adverse effect on handling. Perhaps more importantly, the lifespan of the synchromesh may be shortened. The solution is to double-clutch.

How the Clutch and Transmission Work

Before I get into the specifics of rev-matching and double clutching, it would probably be good to review the inner workings of the clutch and transmission.

A petrol engine has a limited output bandwidth of approximately 1,000 to 6,000 RPM. It cannot operate from 0 RPM (as an electric motor can), so it needs a device — the clutch — to disconnect it from the drivetrain so that it can idle while the car is stationary. The power output is not constant across the RPM range, so different gear ratios in the transmission are necessary to extend the car’s useful operating speed range and maximise available acceleration.

The clutch is integrated with the engine’s flywheel. A disc with friction material, similar to a brake pad, is connected to the transmission input shaft on a sliding spline. This disc sits between the flywheel surface on one side and the pressure plate surface on the other. The pressure plate is spring-loaded to squeeze the clutch disc against the flywheel, effectively creating a solid connection. Pressing the clutch pedal moves the pressure plate, releasing the coupling between the flywheel and the clutch disc so that they can rotate independently.

The Three Clutch States

Clutch disengaged (pedal pressed down): The engine flywheel and the clutch disc rotate independently. No power is transferred.

Clutch slipping (pedal brought up to the point where the clutch starts to grab): The flywheel and the clutch disc are still rotating at different speeds, but power is being transferred. If the pedal continues to be brought up properly, the speeds will equalise. This is the state in which clutch wear occurs.

BTW, just for training, with your car parked and with engine off (or running in neutral gear), SLOWLY push your clutch pedal all the way down. Try to feel the difference in force needed to push. Somewhere in the middle of the way (usually 1/3 of the way), you should feel something like a small “step”, like a small change in force needed. After this point, force is again the same as before. Now, try slowly to release the pedal all the way up. You have to feel the same “step” at more or less the same position. This position is the point where the clutch starts to grab. It’s good to remember this position because in a fast gear change you don’t need to push the clutch pedal all the way down to release the clutch, but only a bit more than the point you found in the steps explained above. One more thing: the clutch slipping point is easier to feel in “sportier” cars, cars made for faster driving, and of course in sport and high-performance cars with a classic clutch pedal. Family cars for slow cruising from A to B can have the clutch pedal smoothed down with hydraulic actuators, and this slipping point can be unrecognizable.

Clutch engaged (pedal up): The flywheel and the clutch disc are locked together. Full power is transferred, and no clutch wear occurs.

More detail on clutch operation can be found in the clutch article.

Transmission Internals

The transmission has an input and an output. There are typically five or six forward gear ratios (the highest is most often a straight 1:1 ratio) and one reverse. The forward gears are all constant-mesh, meaning the gear teeth for all ratios are always engaged with each other. Rather than sliding a gear out of engagement, each gear is disengaged by disconnecting it from the shaft. Only one gear ratio pair can be connected at a time. The reverse gear is the only sliding gear whose teeth actually disengage when not in use.

Each forward gear can be coupled to its shaft by a sliding locking coupler. This coupler connects splines on the shaft to splines on the gear. The coupler needs to match the speed of the gear splines to avoid grinding. (When people refer to “grinding the gears”, it is actually the splines that are grinding, not the gear teeth.) To synchronise the coupler with the gear splines, an intermediate device called a synchromesh is used.

The synchromesh is a lightweight ring with spline teeth on one side and a conical friction surface on the other. It sits between the sliding coupler and the gear splines. The gear also has a conical friction surface that mates with the synchromesh.

When a gear is to be engaged, the shift linkage selects a sliding coupler to connect to a gear. At this point, the coupler and the gear are usually spinning at different speeds. As the coupler starts to slide, it first engages the spline teeth of the synchromesh ring. Because the synchromesh is lightweight, it can almost instantly match speed with the coupler. As the coupler continues to slide toward the gear splines, the friction surfaces are pressed together, accelerating or decelerating the transmission’s input shaft (which should be disconnected from the engine by the clutch) until the coupler and gear are spinning at the same speed. A synchromesh is limited in how much mass it can accelerate and how quickly.

The Double-Clutch Process

There are three separate spinning entities that need to be coordinated when shifting: the engine, the transmission input (I’m going to refer to this as the intermediate shaft), and the transmission output (which is directly related to the vehicle speed through the differential).

When the clutch is disengaged and the transmission is in neutral, the intermediate shaft is essentially free-spinning. In normal shifting, the synchros control the intermediate shaft speed as it engages with the gears.

Decades ago, transmissions did not have synchromesh (and many large trucks still do not). On these transmissions, the driver had to manually control the intermediate shaft speed to match the speed of the gear to be engaged. The process when shifting is:

1. Power is removed and the clutch is disengaged (pedal down).
2. The transmission is shifted from the original gear to neutral.
3. The clutch is re-engaged (pedal up) — the driver now has control of the intermediate shaft speed by controlling engine speed.
4. The driver blips the throttle to match the intermediate shaft speed to the speed of the new gear (this takes practice).
5. The clutch is disengaged (pedal down).
6. The transmission is shifted from neutral into the new gear.
7. The clutch is re-engaged (pedal up) and power is applied.

Steps 1–3 can be done casually or quickly. Steps 4–6 must be done quickly so that the intermediate shaft does not slow down before engagement. If step 7 is also done quickly, the engine will be rev-matched to the rest of the driveline for a smoother engagement.

If braking is required at the same time as downshifting, the heel-and-toe technique is necessary throughout the process, particularly during step 4.

It is worth noting that shifting to neutral may not always be necessary. The driver can blip the throttle with the clutch pedal depressed, then shift to the lower gear and release the clutch. While a modern synchromesh transmission does not require double-clutch shifting, a driver may choose to do so to reduce wear on the synchronisers.

Rev-Matching in Practice

When pulling away from a stop and shifting up through the gears, the normal process (steps 1, 2, 6, 7) is sufficient. The synchromesh easily controls the intermediate shaft speed, and the engine naturally slows down, which is appropriate when upshifting.

When downshifting, the engine needs to spin faster to match the new gear. This is achieved by blipping the throttle as the transmission passes through neutral. If the engine is not manually sped up, it will be forced up to speed by the driveline when the clutch is re-engaged. This is acceptable for normal driving, but when cornering near the limit it can upset the suspension and tyre adhesion. If braking simultaneously, heel-and-toe technique is necessary.

The synchromesh is usually adequate for downshifts of one or two gears. Aggressive downshifts (such as fifth to second from high speed) benefit from double-clutching to assist the synchros. Shifting into first gear in a tight hairpin is nearly impossible without double-clutching and heel-and-toe technique, especially if the exit is uphill.

Learning the Techniques

The most common difficulty in learning these techniques is attempting to incorporate everything at once. The recommended approach is to learn each element progressively, one at a time.

When upshifting, both the engine and intermediate shaft naturally slow down, bringing them near the speed of the higher gear. Active rev-matching or double-clutching is rarely required for upshifts.

Three indicators determine how good a gearshift is: Was only light pressure required on the lever? Was the shift smooth? Was the shift fast?

There is one exception regarding forcing the shift lever. To extract the very last fraction of acceleration, it can help to rush the shift sequence by forcing the lever into the next gear and re-engaging the clutch with the engine already on power. This slightly reduces shift time and throws some extra inertia from the engine into the drivetrain. However, this technique adds wear to the synchros, the clutch, and the rest of the drivetrain. If the car is not being pushed to the point of lighting up the tyres, the technique offers little benefit.

Three Downshifting Scenarios

There are three basic scenarios involving downshifting that I can think of:

1. Downshifting without braking from an established speed (such as when overtaking another car).
2. Downshifting while braking, then re-accelerating in a straight line (no corner involved, such as when braking for a car turning ahead).
3. Downshifting while braking to enter a corner.

There may also be occasion to downshift for a corner without braking, such as when turning off a road with a low speed limit.

Many drivers learning a manual transmission deal with downshifting for a corner first, without active rev-matching or double-clutching. By approaching the corner at a casual pace, there is no significant speed difference between the engine, intermediate shaft, and the rest of the driveline. The synchros handle the engagement, and it is possible to smoothly re-engage the clutch while exiting the corner.

Cornering at the Limit

The tyres have a fixed amount of traction on any given road surface. This traction can be used for braking, cornering, accelerating, or a combination. If the car is cornering near the limit, there is no traction available for braking or accelerating. It’s that simple! Everything about traction limits is explained in my article about the traction circle. Great stuff to read.

The suspension needs to remain stable and steering inputs need to be as smooth as possible.

A good high-performance corner consists of braking in a straight line, smoothly transitioning into the corner while releasing the brakes, holding the car through the tightest section at the apex, transitioning out of the corner onto the throttle, and accelerating through the exit.

The two transitions are the most important parts. The goal is to keep the tyres near their maximum traction while braking, then smoothly change the direction of traction to sideways for the corner. The same principle applies when exiting — the direction of traction changes from sideways to forward as the car accelerates.

The key point is to hold the level of tyre traction constant while changing only its direction.

If there is a gap between releasing the brakes and steering into a corner, the suspension becomes unsettled (reducing cornering ability) and time during which the tyres could have been working is lost.

How Shifting Affects Cornering

If there is any jerking of the driveline when cornering near the limit, the additional load imposed on the tyres — even momentarily — will cause the limit to be exceeded. The driver must interpret the corner, monitor the car’s response, and operate a steering wheel, shift lever, and three pedals with just two hands and two feet.

Most performance corners require a reduction in speed, implying a downshift of one or more gears so that the car is in the correct gear to accelerate out of the corner. A fifth-to-second downshift is a significant change.

The downshift cannot be done before braking because the car’s initial speed would cause the engine to over-rev. On a rear-wheel-drive car, light power needs to be applied to the wheels during the corner so that the suspension is neutral or slightly oversteering. This means the downshift must be completed before entering the corner.

This leaves one place to downshift: towards the end of the braking phase. The shift must be done while braking, and the engine must be sped up to rev-match the new gear so that the tyres are not jerked past their limit. All three pedals must be operated at once — this is where heel-and-toe operation of the brake and throttle is required. Depending on how many gears the shift covers and the condition of the synchros, double-clutching may also be necessary to get the lever into gear.

Progressive Learning Approach

Many drivers trying to learn rev-matching and double-clutching attempt it while cornering first. This is the most difficult scenario. It is much easier to practise without braking or cornering. Braking can be added second, and finally cornering.

Brake timing does not have to be an issue initially if practising at reduced speeds with moderate deceleration. The main focus should be on timing the downshift so that it is completed just before the steering wheel begins to turn. As the clutch is re-engaged, the throttle should be held at the level appropriate for maximum cornering force.

The whole process of learning to shift well takes lots of practice and determination, but it’s well worth the effort. Everyone that I know who’s learned to do this really ENJOYS shifting. I believe all of them have a really strong preference for manual transmissions. I know that I do.

Related Articles

For a complete picture of performance driving, see: Corners, Setup, Traction circle, Using tyres, Left-foot braking, Braking, Advanced braking, WRC braking technique, Slipstreaming, Drifting, Cornering, Heel-and-toe driving, and Steering technique.