Gear Changing

Following on from the Under Use Of Brakes thread and the arguments about not changing gear while braking I've copied the relevant paragraphs from my (admittedly old - 1979) copy of Roadcraft.

I don't see anything that say one shouldn't drop down the box as the vehicle decelerates, merely that the most efficient way to *stop* (my emphasis) is to use the brakes. It does say however (para 18c) that one should select a lower gear approaching a hazard so as to be able to accelerate away if required.

Has the teaching changed since 1979?

Comments invited.

Gear Changing

11 Effective acceleration is possible only when a useful and economical increase in engine revolutions is obtainable. The use of the gearbox must therefore be considered in conjunction with the capabilities of the vehicle.

12 One of the hallmarks of a good driver is the ability to change gear smoothly and make the best use of the gear ratios of the vehicle he is driving. To this end the use of the double de-clutch method of changing gear may be beneficial.

13 The driver's judgment of the correct use of the gears available to him will improve if he has a good knowledge of the main components of the gearbox and their functions.

14 No matter how well a driver may handle a vehicle, his use of the gearbox will do much to make or mar his driving. The essential ingredients are the ability to accurately match engine revolutions to road speed together with precise operation of clutch, accelerator and gears. The first clbutt driver should aim always:

(a) To be in the correct gear for every road speed and traffic situation.

(b) To make all gear changes quietly and smoothly.

(c) To be capable of engaging a particular gear without first using an intermediate gear.

(d) To know the approximate maximum road speed in each gear of the vehicle he is driving.

Moving from Stationary

15 If the gearbox and clutch are skilfully used a vehicle will be put into motion smoothly and its speed increased progressively by the use of higher gear ratios. Maximum acceleration through the gears will be necessary only on rare occasions of pressing need. Care must be taken not to 'over rev' in the lower gears nor to remain in a gear beyond the limits of its optimum performance.

Changing Down

16 When the speed of a vehicle is reduced by a gradient, for traffic conditions or other hazards, a lower gear may be needed. A driver must develop his judgment of when to change to a lower gear.

17 A lower gear will be selected for one of two reasons:

(a) loss of road speed to within the range of the next lower gear despite continued pressure on the accelerator pedal, and

(b) on the approach to a hazard when a more responsive gear is required.

18 The selection of a suitable lower gear at the correct time will provide advantages in the following circumstances:

(a) On an up gradient; to maintain the power to climb the hill.

(b) On a steep down gradient; to control speed with engine compression, thereby avoiding long periods of hard braking.

(c) At the approach to a hazard; to enable the driver to accelerate out of the hazard, if this is safe, or to stop more readily if necessary.

(d) When travelling at low speeds or when in doubt about traffic conditions ahead, to provide the reserve of power and flexibility to accelerate or decelerate by control through the accelerator pedal.

(e) On a slippery road; when the use of engine compression to lose speed is safer than braking, since the latter would be liable to cause skidding.

Faults

19 Common faults relating to the use of gears are:

(a) Poor co-ordination between foot and hand to effect a clean, smooth gear change.

(b) Inability to recognise by the sound of the engine when a gear change is required.

fc) Failure to select the correct gear for the existing road speed.

Id) Changing to a lower gear on a "closing gap", e.g. inadequate braking followed by a gear change and hurried re-application of brakes.

(e) Changing down instead of braking (other than in the circumstances shown in paragraph 18e).

(f) Failure to take a proper grip on the gear lever when moving it from one position to another. This is the root of many gear changing difficulties.

(g) Late gear changing, or entire failure to change down, at the approach to a hazard when the road speed and conditions demand a lower gear.

(h) Failure to match engine revolutions to road speed when changing down.

(i) Timidity and reluctance to attempt necessary changes down to low gears.

20 Some common faults when driving vehicles fitted with automatic transmission are:

(a) Failure to ensure brakes are 'ON' before engaging 'D' or 'R' from stationary.

(b) Engaging 'D' or 'R' with a high revving engine (often buttociated with use of choke).

(c) Engaging lower gear 'hold' at too high a road speed.

(d) Moving the selector to 'N' when making temporary stops in traffic.

(e) Braking with the left foot (except when manoeuvring at low speed).

21 Car sympathy is a quality to be developed in many ways, not the least of which is gear changing. The driver who demonstrates delicacy and smoothness in his gear changing will be on the way to acquiring that polished style which is the ultimate aim.

Braking

22 More important than being able to accelerate and change gear is the ability to slow down or stop the vehicle when required. There are two ways in which this may be done:

(a) by deceleration as the pressure on the accelerator pedal is relaxed, or

(b) by the application of the brakes.

23 When pressure on the accelerator pedal is relaxed, the engine will slow down due to the compression in the cylinders and this slowing down will be transmitted to the wheels. Thus the engine is acting as a brake and the reduction of speed will be smooth and gradual with little wear to the vehicle.

24 The loss of road speed by engine deceleration will be more pronounced when a low gear is engaged, including an automatic gearbox. This will be valuable when driving on slippery roads when normal braking could lock the wheels or where making long descents in hilly country but for normal driving requirements it is inefficient other than for minor variations in speed.

25 For normal driving a more efficient method of slowing down than relying on engine deceleration is to applv the brakes. Pressure on the footbrake pedal can be varied at the discretion of the driver from a barely perceptible effect to such force that all wheels will lock. For all normal braking the initial free movement of the pedal should be taken up gently and pressure progressively increased as necessary until it can be relaxed as the unwanted road speed is lost. When braking to a standstill the final effort should be so judged that the vehicle is brought to a gliding halt without jerking or settling down suddenly at the rear end.

26 Apart from other considerations the speed of a vehicle at any time must not exceed the speed at which it can be stopped within the distance the driver can see to be clear. The driver must know the distance he needs to slow down appreciably or stop from all road speeds. Not only must he know the distances he must be able to relate them to the road on which he is travelling. On a good dry road the average vehicle should be capable of stopping in the following distances:

(table removed)

These distances will, of course, increase considerably in wet or slippery conditions. (A guide to the braking distance of a vehicle in feet may be found by squaring the speed in m.p.h. and dividing by 20.)

27 To the braking distance must be added the distance-travelled in the driver's reaction time to arrive at an overall stopping distance. Reaction time may be defined as the time that pbuttes between the moment the driver observes the need for action and the moment he takes that action. The average driver takes 0-7 seconds from seeing an emergency situation to placing his foot on the brake pedal. The distance covered in that time is known as the "thinking distance" and will be the same figure in feet as the speed in m.p.h., e.g. 30 m.p.h. = 30 feet. Thinking distance + braking distance = stopping distance.

28 The thinking distance will vary' in three ways:

(a) With the speed of the vehicle.

(b) With the physical and mental condition of the driver.

(c) With the degree of concentration being applied.

29 Controlled, progressive braking is preferable to a sudden hard application. Figure 5 illustrates the behaviour of a moving car under the influence of braking. The weight is thrown forward and downward on to the front wheels and the rear tends to lift. The resulting unequal distribution of weight makes the steering heavier and reduces the general stability of the car, especially at the rear wheels. This effect can be dangerous, particularly when the vehicle is travelling on a curved path.

30 To reduce these disadvantages as much as possible the following rules for braking should be applied:

(1) Brake firmly only when travelling in a straight line.

(2) Brake in plenty of time.

(3) Vary brake pressure according to the condition of the road surface.

(4) When descending a steep winding hill brake firmly on the straight stretches and ease off in the bends. Remember the value of engaging a low gear at an early stage in the descent.