Ethical Logistics . com

Heavy combination vehicle stability and dynamics

Sourced from Land Transport New Zealand

An introduction programme for drivers of heavy
motor vehicles

Introduction


New Zealand has a high incidence of rollover and loss-of-control crashes for distance travelled
compared with other countries such as the United States and Canada. Rollovers occurred in 29 percent
of the heavy vehicle crashes attended by the New Zealand Police Commercial Vehicle Investigation Unit
between July 1996 and November 1999.

This high number of rollover and loss-of-control crashes reflects New Zealand’s difficult driving
conditions. The country has more bridges, corners and hills per 100 kilometres of road, and fewer
divided highways, than most other developed countries.

Drivers of large vehicles have an obligation to drive considerately and professionally at all times.
Rollovers in single-vehicle crashes involving trucks often reflect the drivers’ poor appreciation of the
general dynamics and stability issues of the vehicle.

The majority of the factors that influence the stability and dynamics of heavy combination vehicles also
influence the stability and dynamics of heavy rigid vehicles.

The basics


Vehicle dynamics:

This term refers to the motion of a motor vehicle and the various forces that act upon the vehicle when
it is in motion.

An often overlooked aspect of the dynamics of motor vehicles is that in the majority of situations a
vehicle has to be moving before the forces acting on it affect its performance. Thus (with only a few
minor exceptions) a person – the driver – must make the vehicle move. It follows then that if the
person in control of the vehicle is making it move then this person should have total control over
whether the dynamics of the vehicle will be a contributing factor in any crash the vehicle may be
involved with.

The laws of nature


Like everything around us, we are all affected by the laws of nature. These laws ensure that:

injure themselves more out of all proportion to their increase in speed

These same principles apply to our vehicles and, while they cannot be totally eliminated, they can be
controlled and their effects minimised.

Side wind



Vehicles with high flat sides, such as furniture trucks and
trucks transporting containers, are extremely susceptible to
the effects of cross wind (wind blowing onto the side of the
vehicle).

In conditions of extreme crosswind, road controlling
authorities may issue strong wind warnings for some
stretches of road. When these are issued take note and, if
the warning includes advice not to travel over a particular
area of road – don’t.


Remember also that your vehicle will generate its
own wind as it moves along the road. The faster
you go, the greater the wind forces generated will
be. These forces can be sufficient to blow
motorcyclists over and buffet other vehicles to a
point that the driver loses control, so you need to
be considerate of other road users and slow down.

Speed


The effect of speed on the cornering ability, braking distance and impact forces acting on a vehicle
increase as the speed increases. Cornering forces don’t just double when the vehicle speed doubles,
they increase by four times.

This effect is highlighted in the following diagram.

The arrow in the left-most illustration represents the overturning force acting on a truck in a
30 kilometre per hour (km/h) corner. If the same truck is driven through the same corner at 60 km/h,
the overturning forces will be four times higher (2 x 2 = 4, speed-squared effect), represented by the
arrow in the middle illustration. If the truck is now driven through the corner at 90 km/h the
overturning forces will be nine times higher (3 x 3 = 9, speed-squared effect) than at 30 km/h, as in
the third illustration.

This speed-squared effect has a dramatic impact on the vehicle and its controllability.

Gravity


Gravity creates a force that, in simple terms, attracts everything towards the centre of the earth.

This force is measured as weight and means that a person weighing 90 kilograms (kg) and a truck
weighing 15,000 kg are both attracted towards the centre of the earth with the same speed of
acceleration. If both were free to fall they would accelerate at the same rate, called one gravity (1 g).

Centre of gravity

Every object affected by gravity has a centre of gravity (CG),
which is the point around which the object, if placed on a
pointed stick in the ground, would be balanced in all directions.
The higher the CG, the more unstable the object (such as a
truck) will be. The closer to the ground, the more stable the
object.

Thus the stability of a truck is largely dependant on the height
of its CG above the ground. If a load is not centred across its
width; the stability will be reduced when cornering.

If the load is not balanced correctly along its length, wheel lock-up during braking becomes a distinct
possibility. When wheel lock-up occurs, the vehicle loses steering control.

Kinetic energy


Kinetic energy is the energy present in any moving object. The heavier and/or faster the object, the
more energy it will contain.

A bullet, for example, is small but extremely fast and has the potential to do a lot of damage over a
small area owing to its kinetic energy. A truck, on the other hand, is relatively slow but is extremely
heavy and has the potential to do a great deal of damage over a greater area for the same reason.

While a bullet’s energy is either absorbed by the target or eventually eliminated by friction as it moves
through the air, the energy in a vehicle is converted to heat by the friction that occurs in the brakes
when the driver applies the brakes.

The effects of kinetic energy increase at the square of the speed – and have a major influence on all
motor vehicles in three particular situations, as explained below.

1 Braking

The faster a vehicle goes, the further it takes to stop.

As the table below shows, if a truck’s speed is doubled it will take at least four times the distance to
stop. Longer if the road is wet.

2 Cornering

If a truck enters a corner at 60 km/h, there will be four times more overturning (side) force on the
vehicle than if it had entered the corner at 30 km/h.

3 Impact

The damage to a vehicle (and its driver) at the point of impact in a crash situation will also increase in
proportion to the square of the speed. In other words, double the speed = four times the damage,
triple the speed = nine times the damage. A pedestrian knocked down at 60 km/h will most likely
suffer four times as much damage as one knocked down at 30 km/h.

Friction


Friction is the resistance to motion that occurs when one body or surface moves across another. On a
vehicle the most common points of friction are the brakes, the tyre contact with the road, air
resistance, and engine and transmission components. It is the friction between the tyres and the road
that allows the driving, braking and cornering forces to be transmitted to the road surface.

Friction creates heat. Vehicle braking systems produce large amounts of heat, which has to be
dispersed very quickly. The secret to a good braking system its ability to remove that heat quickly and
efficiently.

The faster a vehicle is travelling, or the heavier it is, the more heat the brakes generate in bringing the
vehicle to a stop.

Centrifugal force (overturning or side force)


Centrifugal force occurs when a moving object, such as a vehicle, changes direction. This is the same
force that causes passengers to slide across the seat and
loose freight to slide across a deck when cornering at higher
speeds.

The weight of a vehicle means that when it is travelling in a
straight line it will try to continue in that direction, even
when the driver turns the steering wheel.

Changing direction causes the vehicle’s weight to move to
the outside of the turn which, unless the driver controls its
speed, can lead to the vehicle rolling over or sliding out.

Centrifugal force is affected by the vehicle speed
and the angle of turn. In other words, the faster
the vehicle is going and/or the tighter the turn,
the more likely the driver is to lose control of the
vehicle and for it to roll over.

Stability


There are many factors influence a vehicle’s tendency to roll over, but the following are the most
crucial:

If all these factors are contained within acceptable levels,
the vehicle will remain stable. If they are not, then the
risk of loss of control and rollover will increase.

Typically rollovers occur during cornering (at either high
or low speed) and sudden evasive steering manoeuvres.

Rollovers at roundabouts


The following is an example of how rollover can occur
at a roundabout even though the truck may be
proceeding straight through.

The driver of a loaded truck intends to proceed
straight through a roundabout. He/she safely
negotiates the left-hand bend at point ‘A’ and the
vehicle rolls to the right. The driver then swings the
steering to the right at ‘B’ to travel around the
roundabout and the vehicle rolls to the left. But this
time it rolls much further than it did at point ‘A’
because the directional changes of the vehicle match
its roll resonance. At this point the load might even
shift, transferring more weight to the left-hand side
of the vehicle, increasing the roll still further and
possibly overturning the vehicle on to its left side at
point ‘C’ as shown. However, if the vehicle is able to
continue past point ‘C’ and the driver then steers to the left, the vehicle will roll back to the right still
more violently and is even more likely to overturn, this time on to its right side at point ‘D.’

This can occur at a surprisingly low speed, speeds which may be quite safe for another type of truck,
even when fully laden. This danger is not restricted to roundabouts; S-bends and violent lane changes
can present a similar hazard.

Evasive manoeuvres


Drivers operating heavy vehicles need to make constant steering corrections, whether to compensate
for simple road undulations and the effects of camber or wind, or when negotiating intersections and
undertaking evasive manoeuvres to avoid other vehicles or obstacles.

These manoeuvres can be at relatively low speed but involve several directional changes (as in a
roundabout) or take place at high speed, as in a steering correction during cornering or changing
lanes. In each of these situations there is transfer of weight from one side of the vehicle to the other.

With a heavy combination vehicle the effect of changing direction at higher speeds raises a number of
additional issues to those normally experienced when driving a rigid vehicle. One of the most
significant of these is rearward amplification or ‘cracking the whip’

Rearward amplification


This only applies to heavy combination vehicles where in the total length of the combination there is
more than one articulation (pivot) point. For example, a truck and trailer combination has a pivot point
in the draw bar coupling; a ‘B’ train has two pivot points, one in each turntable where the kingpin is
locked into the turntable jaws.

Rearward amplification, or cracking the whip, occurs during a rapid lane change where a relatively
small steering input of the towing vehicle is amplified (increased), through each pivot point. The result
being that the end trailer in a combination can react very violently to the lane change.

Overseas research has demonstrated that cracking the whip becomes a significant stability factor at
road speeds above 60 km/h.

Manoeuvring


Manoeuvring a combination vehicle, particularly at lower speeds, introduces a number of factors of
greater significance than those encountered when manoeuvring a rigid vehicle.

As a general rule, the more manoeuvrable a combination vehicle is, the less stable it is likely to be in
open road driving situations.

Low-speed off-tracking


When a long vehicle makes a low-speed turn,
at an intersection for example, the rear of the
vehicle may off-track (take a different path)
around the corner than the towing vehicle. In
some situations there can be several metres
difference.

This is shown in the picture below.

Drivers of heavy combination vehicles must
be aware of this whenever they manoeuvre a
vehicle, particularly when the result of off-
tracking could be for the vehicle to come into
contact with another vehicle or a building.

Swept path


When a heavy combination makes a turn, especially
a sharp turn to the left or right, the trailer or trailers
do not necessarily follow in the same path (track) of
the towing vehicle. This is similar to off-tracking.
Swept path is illustrated in the drawing below.

Swing out


Associated with swept path is swing out. This is the effect
that is caused by the rear of the trailer (its rear overhang)
taking a path outside that of the rest of the vehicle. This is
illustrated in the drawing below.

Drivers of combination vehicles must also be aware of this
effect and make allowances for it when manoeuvring, again
particularly at lower speeds.

Trailer yaw


Any vehicle that is being towed by another vehicle will
experience some degree of sway from side to side (yaw). The amount of yaw experienced by the
towing vehicle is influenced by a number of factors, but speed and loading conditions are the most
crucial factors. Yaw is generally explained as the way in which the trailer trails the towing vehicle.

Once a trailer has started to yaw (sway from side to side) it can quickly develop into an uncontrollable
situation and can easily result in the vehicle overturning. A safe method of reducing trailer yaw is to
slow down but do not use the brake as this could easily develop into a jack knife situation.

Trailer yaw should not be confused with rearward amplification. Trailer yaw is a swaying motion that
can be encountered on straight roads and can develop without any steering input from the driver.
Rearward amplification on the other hand is a result of a lane change or similar manoeuvre where the
driver alters the path of the vehicle through the steering.

Rating different types of combination vehicles


There are two common types of combination vehicle in use on New Zealand roads: truck and trailer;
and semi-trailer including ‘B’ trains. A third type common some years ago was the ‘A’ train, but many
of these had an inherent stability problem, which has resulted in them being progressively withdrawn
from service.

The drawings below show typical examples of common types of heavy vehicle combinations that can
be found in New Zealand, together with their relevant maximum dimensions


Truck and trailer unit


Semi-trailer


‘B’ train (two semi-trailers)


‘A’ train (one semi-trailer with a full trailer behind)

On a stability rating chart, and taking all relevant factors into consideration, the above combination
vehicles can be rated against each other as follows:

Notwithstanding the above, each type of combination has some inherent characteristics that drivers
need to be aware of when they are operating a vehicle of the particular type.

Vehicle and load factors


Vehicle inspections


A number of the items that must be checked during a daily inspection of a vehicle can directly affect
the stability of that vehicle. Some of these are outlined below.

Tyres


Tyres transmit all the driving, braking, steering and cornering forces from the vehicle to the road. They
also play a crucial role in maintaining stability. Tyres that are not inflated to the correct pressure will
wear out much more quickly. Research has shown that the life of a tyre that is consistently operated at
a pressure 20 percent below what it should be can be reduced by at least 25 percent.

Tyres must be checked for compatibility, tread, inflation and damage at the commencement of the day
or driving shift and spot checks of the tyres condition should be carried out during the shift. Tyre
pressures should be checked with a gauge at least weekly.

Suspension


The suspension supports the entire vehicle’s weight and isolates the vehicle and the load from road
shocks.

While air suspension can provide superior stability and handling to traditional leaf springs, all
suspension components must be checked for damage or distortion regularly.

Brakes and steering


These must be checked prior to moving off. Any problems that are found must be reported and
immediately rectified.

Excessive ‘freeplay’ in the steering will result in difficulty maintaining a correct and proper driving line.
As a general rule, any free movement at the rim of the steering wheel must not exceed 1/5 of the
steering wheel’s diameter. For example, for a steering wheel that has a diameter of 380 mm, the free
play must not be more than 76 mm. If it has more than that, you should have it investigated
immediately.

Hub temperatures can be checked as a way to identify whether individual brakes are binding or,
alternatively, not operating at all. One brake out of adjustment can add metres to the stopping
distance.

Load placement


Load placement and load security are key factors in
vehicle handling and dynamics. Drivers must make
sure there is enough weight over all axles to provide
adequate brake balance, directional stability and to
ensure individual axles are not overloaded.

The load must be distributed evenly across the vehicle
as shown below. When offloading freight, it’s
important to consider redistributing the remaining
cargo to maintain the loads balance across the vehicle
deck.

Heavy items should be placed to the bottom of the load so that the CG remains as low as possible.

Load transfer


When a vehicle is braking, the weight of the load is moved towards the front of the vehicle. This can
increase the weight on the front axle, at the same time reducing the load on the rear axle(s). In severe
braking applications, the load on the rear axle may be removed almost completely and the vehicle will
skid sideways, making the vehicle out of control. This may be particularly pronounced on wet or
slippery roads or roads where the surface is not stable, such as on gravel.

It is for this reason that braking should always be smooth and steady and not aggressive.

Trailer loadings


The government has imposed maximum loadings that can be placed on heavy combination vehicles.
Generally speaking, the gross mass (weight) of the rearmost trailer in a combination vehicle set must
not exceed 1.5 times the gross mass of the towing vehicle. For more detailed information on this you
should consult Land Transport Rule: Vehicle Dimensions and Mass 2002.

Dealing with specific types of load


There are a number of types of loads that require special consideration in regard to their stability.
Some examples of these are listed below.

Tankers


Although there have been many improvements to tanker
design over the years to improve their on-road stability,
such as lowering the height of the tank, these types of
vehicle still require special skills because of the nature of
the freight they are transporting.

A liquid in a tank will
surge (that is move back and forward as the vehicle
accelerates and slows down) so drivers of tankers must
be constantly on their guard to ensure that this
movement does not override their actions in controlling
the vehicle. To overcome this problem ,some tankers
(those that carry only a single product at a time) may
be fitted with baffle plates to reduce the amount of
surge, while tankers that carry a range of products in one load will have a series of self-contained
compartments, effectively mini tanks inside a common shell.

Bulk dry goods


These types of vehicles often have an inherent high CG. The load can shift and, because of the nature
of the load, once it has shifted it may not flow back to its original level.

Hanging meat


Meat hanging in a chiller body can be a very unstable load. Not only will the load have a high CG, but
the load can act like a pendulum and swing from side to side. This pendulum effect can be very
noticeable on winding roads or when executing sharp turns at speed.

Livestock


Livestock can move around, even in approved stock crates. The effect of this can be reduced by
keeping animals bunched together, but even then the animals may lean over when the vehicle is going
around a corner, altering the CG.

Tip trucks


Particular attention must be paid to tip trucks, especially
when they are being moved with the hoist up, such as
when spreading road metal.

It is not uncommon for loads in tip trucks to stick to the
sides of the dump body, causing a weight transfer to one
side, and when this happens the vehicle may tip over.

Load security


The Truck loading code sets minimum standards for load restraint and operators must familiarise
themselves with it. These standards are designed to prevent load shift under normal operating
conditions, including braking, acceleration, cornering and movement over uneven ground.

Any load that shifts will decrease vehicle stability dramatically, particularly during braking and
cornering. Any loads positioned more than 100 millimetres away from the curtains or sides of a vehicle
must be restrained in accordance with the Truck loading code, to prevent load shift during cornering.

Loads carried on a vehicle must be restrained according to
the following basic rules. Restraints must:

forward direction, and

sideways direction, and

rearwards direction, and


The responsibility for loading the vehicle correctly, including making sure it is secured to the minimum
requirements, as shown in the Truck loading code, rests with the driver. The responsibility starts at the
time of loading. Placing loads that increase the height of the vehicle’s CG or shift it off-centre (closer to
one side) will reduce the vehicle’s stability and dramatically affect its handling.

Drivers of vehicles with loads that have a high CG must drive more carefully, especially around curves.

Load security legislation


The Land Transport Act 1998 contains the load security legislation that is administered by Land
Transport New Zealand and enforced by the NZ Police. It provides strict liability for offences involving
insecure loads and loads falling from vehicles. Offences attract fines for an individual of up to $2,000
and a licence may be disqualified for a period as the court thinks fit. The maximum fine for a body
corporate is $10,000.

Load distribution and arrangement on vehicles


dimensions. The load should be placed against the headboard if this can be done, provided the
handling of the vehicle is not impaired. If the load cannot be placed against the headboard,
baulking should be used or twice the strength of lashings are required.

stacked, larger and heavier items should be placed at the bottom. The vehicle should be loaded
to give correct axle distribution and an even weight distribution over its floor area.

possible to, the centre line of the vehicle. It is better for heavier items to be carried on the
centre line of the vehicle than at the sides.

for security and the lashings tested. Weather conditions can affect the tension of ropes and this
may lead to damage of the load or loss of security

Rated strength of vertical securing devices for rigid loads on heavy motor


vehicles


A Combined rated strength = 2W

Securing devices (lashings) have a combined rated strength of at least twice the weight of the load,
where not loaded against a headboard.

B Combined rated strength = W

Securing devices (lashings) have a combined rated strength of at least the weight of the load, where
packets are loaded against a headboard, such that the top packets have at least 150 mm supported.

C Combined rated strength = 11⁄2W

Securing devices (lashings) have a combined rated strength of at least one and a half times the weight
of the load, where lower packets are supported by a headboard but upper packets are not supported
by at least 150 mm.

Failure of the load restraint could result in the load developing sufficient momentum, if allowed to
slide, to demolish the headboard or other abutment with potentially serious consequences.

Anchor points


Traditional rope hooks or rings, and the method by which they are attached to the vehicle structure,
cannot be relied upon for the restraint of other than light loads. For this reason, platform vehicles in
particular should be equipped with load anchorage points, so designed and integrated into the
structure that the maximum forces likely to be imposed on them are transmitted to the main chassis
frame of the vehicle. It is common practice to utilise the coaming tie rails and, in this case, it is
necessary to tie in the vicinity of the cross member and tie rail junctions to prevent distortion of the tie
rail.

Each anchor point must have strength at least equal to the rated strength of the lashings secured.

Loose bulk loads


Loose bulk loads can generally be described as having a nature which does not readily lend itself to
any form of packaging or containerisation, eg sand, aggregate, shingle, rubble, rubbish, asphalt and
other similar materials.

Clearly, the loading and securing of such loads do not pose the many problems associated with general
freight, but nevertheless they do have security problems peculiar to themselves.

Basic safety principles


should at no time be higher than 100 mm below any side of the body in which the load is being
transported. If the load is heaped to its own natural ‘angle of repose’, this could result in load
shedding due to the vehicle’s movement.

ensure all body-to-chassis attachment points, eg, ‘U’ bolts, hinge pins, hinge pin brackets, are
always secure and that these and the body are in sound condition.

there is a risk of load shedding due to wind action or movement

Driver factors


Steering


It is important to have two hands on the steering
wheel whenever it is possible. This applies not only
during turns and cornering but also when travelling on
straight roads. A driver who adopts a relaxed, two-
handed steering style responds more readily to normal
vehicle movement than one who consistently leaves
one hand off the wheel.

The effects on vehicle handling that occur as a result of
the steering actions of the driver must not be
underestimated, particularly by those who operate
vehicles carrying high-CG loads.

The system of vehicle control


When negotiating intersections, roundabouts and other
potential hazards, such as road works, railway crossings and crash sites, it’s important to control the
vehicle’s speed and side-cornering forces before entering the site.

Drivers who use the system of vehicle control will be concentrating on potential trouble spots, not on
the brakes and gear lever.

While the system of vehicle control does take some getting used to, once perfected it produces an
unrushed, deliberate and safe driving style that reduces the risks, particularly at intersections and even
more so at roundabouts, where these changes in direction can occur, and vehicles carrying high-CG or
‘live’ loads often come to grief. In these situations the combination of road camber and running trailer
wheels onto kerbs can make the stability problems even worse. The system of vehicle control is
explained below.

1 Course

the road.

2 Mirrors

3 Signal

out any manoeuvre.

4 Brake

5 Gears

the right gear before you manoeuvre.

6 Mirrors

7 Execute

8 Accelerate


A very cautious and planned approach to corners is always necessary.

Vehicle dimensions and dynamics


Track


The distance between the centres of each tyre on an axle is known as the
track. The wider the track, the better the stability of the vehicle will be. In
other words the wider the vehicle (within the maximum permitted vehicle
dimensions), the more stable it will be. This results in better handling and
improves the overall dynamics of the vehicle.


|Track|


Wheelbase


The wheelbase of a rigid motor vehicle is the distance between
the centre of the rear axle(s) and the centre of the front axle.
In a twin-steer vehicle the wheelbase is measured between the
centre of front (foremost) steering axle and the centre of the
rear axle(s).

The length of a vehicle’s wheelbase is major factor in the manoeuvrability of the
vehicle. The longer the wheelbase, the less manoeuvrable the vehicle is likely to be.
All motor vehicles in New Zealand must be able to complete a 360-degree turn,
both to the left and to the right, within a circle with a wall-to-wall diameter of
25 metres. The only projections which can be outside this circle are collapsible
mirrors. It is for this reason, to improve manoeuvrability, that vehicles used in
areas where manoeuvrability is important, such as rubbish collection, often have
their front, steering axles moved backwards. This is called an offset front axle.

However, moving the front axle backwards can place an additional load on the front axle and upset the
balance of the load between the front and rear axles, thus affecting brake balance and load transfer.

Overhang


Overhang in either the front or rear will also affect the
manoeuvrability of the vehicle. In New Zealand front overhang is
measured from the front edge of the driver’s seat (in its rearmost
position) to the foremost point of the vehicle or its load. The
maximum permitted front overhang is three metres.

When front overhang is excessive, the part of the load that is
overhanging the vehicle will travel in a wider arc than that taken by
the rest of the vehicle and may come into contact
with a vehicle in the other driving lane or even a
building on the other side of the road.
Rear overhang means the distance from the rear
axis to the rear of the vehicle or its load, whichever
is greater. For a heavy rigid vehicle, in which the
rearmost axle is a non-steering axle, the maximum
rear overhang is either 4 metres or 70 percent of
wheelbase (A in the diagram), whichever is lesser.

The affect on the manoeuvrability of a vehicle with excessive rear overhang is similar to that with
excessive front overhang, that is, the extra length of the load will swing wide and may come into
contact with an object on the other side of the road or a vehicle travelling in the another lane.

Cornering


No two corners are exactly the same, so road controlling authorities
sometimes provide an indication of a corner’s severity by using advisory
signs.

These signs often include a recommended speed and a diagram of the
corner’s line. The recommended speed is set for cars and not trucks, so in
most circumstances the posted speed will be too high for a truck to safely
negotiate the curve. To safely go around the bend in a truck the speed of the
truck should be at least 10 km/h lower than what the sign indicates.

For example, the signs on the right indicate that the curve ahead has an
advisory speed limit of 65 km/h. For a truck to safely go around this curve it
should be going no faster than 55 km/h.

Feeling the uncertainty


Drivers of vehicles who have been in rollover or had severe loss of control situations will often not have
had any sense that the vehicle is about to go out of control until it happens. By this time it is often too
late to take any corrective action. Some drivers however may recall sensing a load shift immediately
before loosing control of the vehicle and will often blame this as the cause of the crash. However,
investigations have found that often the shifting load was a result of excessive vehicle tilting, resulting
from the driver losing control of the vehicle, and not the cause of it.

By far the most important aspect of dynamics control is the driver’s response to corners. While every
corner is different, each has three definite points.

1 Entry. This is where the driver begins to turn the
steering wheel to enter the corner. At this point the
driver must have completed all deceleration, braking
and downshifting. They should be at, and
maintaining, the desired speed as they enter the
bend.
2 Apex. This is the point where the vehicle is closest
to the inside of the turn. The driver should maintain
the entry speed to this point and now start to slowly
accelerate. The steering line should now be
completed.
3 Exit. The driver should have accelerated from the
apex to this point, which is where the vehicle returns
to a straight line.

Vehicle rollovers normally occur between the apex
and the exit of a corner as a result of excessive speed or braking. When towing a trailer, the prime
mover must pull the trailer through the bend, not be pushed by it. This can only be achieved with the
cornering technique. Cornering stability will be improved, and the effects of centrifugal force reduced,
if the correct cornering line is also applied.

Summary


It is a driver’s responsibility to understand how the dynamics of a vehicle affects the way the vehicle
handles on the road.
Drivers need to:


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