Driving Lines
Author Jeff Davis
Driving a car takes several skill
sets that have to operate in co-ordination in order to navigate a complex
track, avoid accidents and win races.
These include sight, feel, awareness and knowledge, all of which must be
brought together by your brain.
Therefore thinking ahead is an absolute essential ingredient for
successful driving. This document is
aimed at preparing you to think in advance and use the skills outlined to
maximum effect thus giving you the best chance of winning a race.
Driving a car is not a simple act of
jumping in, pressing the go button and steering round corners. There are 5 main factors which you must take
into consideration before setting off on a journey, whether this is a race or
just a trip down to the shops. These
factors include: -
Ø Road condition – Dry,
Wet, Bumpy, Surface, Dusty, Dirty etc.
Ø Road layout – Straight, Twisty,
Sharp Bends, Width etc.
Ø Capability of the car –
Ø Traffic conditions – No
traffic, Medium traffic,
Ø Your capability –
Experience
Any combination of these will affect
the way you have to approach driving a vehicle, no matter if this is an
electric car or a Formula 1 racer.
Couple these with the skill sets you have to co-ordinate results in
considerable concentration every time you sit in a car.
The above combinations also affect
the driving lines you can take when racing.
One other thing to remember is that
a car will go faster in a straight line.
Turn into a corner and energy is transferred to the tyres, which is
subsequently used to change direction of the vehicle and therefore lost. This will automatically slow the car down
requiring more energy to be taken from the batteries to get the car back up to
speed. This uses up the stored energy
reducing the life of the batteries and hence the distance you can travel on a
single charge. Sounds obvious but
consider a 4 hour race, changing direction such as weaving down a straight or
having to over compensate for incorrect cornering etc will have a devastating
effect on the overall distance you will cover.
The way this is optimised is by using the correct driving lines both on
the straights and the corners, maximising the speed at all times and lowering
the drain of power from the batteries. The other thing to remember is that the
shortest way round a track is not necessarily the fastest.
What is a driving line?
A Driving Line (also know as a
Racing Line) is the imaginary line a car would paint on the road when it goes
around a corner or down a straight. It
is not the shortest distance around a corner but one that minimises the time
spent in a corner whilst maximising the speed through the corner. It is
achieved by fitting in the maximum smooth arc possible into the corner,
starting at the entry point and finishing at the exit point.
Figure 1 shows that there is an
ideal point of turning into the corner [GREEN] and an ideal speed for each
corner encountered. Turning too early is
completely the incorrect way to approach any corner, do this and you will be
off the road [RED] unless you slow down considerably. Turning too late [YELLOW]
and you have to over steer and again loose precious speed. However,
this is from a Greenpower racing point of view, if
you had a powerful combustion engine car, the yellow line may well be the one
for you.
Let’s look at each of these. First the red line, indicating the car has
turned too early into the corner. This
is normally what happens to first time drivers, they see the corner approaching
quickly and over-react by turning early.
The result is that they arrive incorrectly at an early apex of the
corner. With more of the corner to come
the result is either running out of road as they try to exit the corner at
speed or having to turn more violently to keep on the road but transfer copious
amount of energy into the tyres (and potentially brakes) slowing down the car
significantly to avoid an accident. The
car would then be slow out of the corner requiring much more energy from the
battery to get back up to speed.
Next under scrutiny is the yellow
line, indicating that the car has turned into the corner far too late. This happens when the driver turns up at the
corner far too fast and misses the turning point. Unlike the red line where the violent turn is
applied after the apex this scenario requires a violent turn before the
apex. The end result is the same however
with the slight difference that you will either make a late apex or miss the
apex altogether (depending on your speed – again this is from a GreenPower point of view where the fastest cars reach
around 50mph on the straights). The car
will still slow down as before though.
So that brings us to the green line,
the Louis Hamilton approach to driving.
Here the driver will arrive at the corner at the correct speed. This being achieve by: lifting off the power,
using the brakes (whilst in a straight line – Note:
- For GreenPower this should be a “coasting” to
correct speed as we are normally in an endurance race not a speed race, the
brakes should only be used in Sprint racing where the speed of the car is
essential and the distance on a set of batteries is only one lap!)
to slow to the required speed, selecting the correct gear for the exit of the
corner and SMOOTHLY turning the car into the corner to meet the correct
apex. At the apex the driver can apply
the power once again to keep momentum going and hence only loose minimal energy
and smoothly straighten up the car by the exit point of the corner. Simple!
For reference you can visit the Wikipedia entry at http://en.wikipedia.org/wiki/Apex_(racing).
Not all corners are the
equal.
Life would be simple if
all corners were 90 degrees and had a straight road before and after however,
life is not fair as we all know. You
often come across the notorious hairpin bend, a definite attempt by the track designers
to slow you down and make life difficult.
However the same principles apply when approaching this kind of
bend. Figure 2 gives the correct
example of the required driving line.
Turning in too early or too late will have a dramatic effect, both will
see you off the track or having to slow to such an extent that you loose all
forward momentum.
A hair-pin bend is going to be a
slower corner than a 90 degree one as there is simply more corner to negotiate,
in this case twice as much. It is
therefore obvious that the apex is much deeper into the corner than that of the
first we examined. You can still draw
the smooth arc to find the perfect driving line. It will be might tighter and slower but will
still minimise your time in the corner and maximise the speed of the car.
But again not all hairpins are
equal. The classic for our team is the
one encountered at the Darley Moor race track. Figure 3
shows a similar hair-pin bend which is extended beyond the 180 degree
mark. In this case you need to slightly
change the driving line around the corner.
The red line which was used in the first example is no longer the one to
take as it will now run
out of road. Instead we now look for the
late apex by turning in later. If you
draw a line between the entry point and the exit point you will still see that
the arc is the same smooth line and slightly shallower which means a little
slower into the corner. Not a lot slower
but still slower. The smooth entry into
the corner is all the more essential here as the tightness of the bend means
much more load on the tyres and as such will distort them more giving the
possibility of punctures simply by over-working the tyre to the point of
failure. We have seen this many times at
Darley Moor where the car has to limp down the back straight to the pits on
three wheels, losing considerable time.
Now, to make it more difficult, corners
are not a standalone feature of the race track.
They are not always followed by a long straight; it is quite likely that
one corner will be followed by another corner giving you a series of turns to
negotiate. Let’s take the case shown in Figure 4. Here we have a hairpin bend followed directly
by a left hand 90 degree bend. If taken
in isolation the red line would show the correct driving line 
around each corner. However, if we take the red line around the
hair pin we find ourselves on the wrong side of the track for the entry point
into the next corner. We therefore have
to “think ahead” when driving a
race. The corner “after” the one we are
approaching requires us to be on the other side of the track than the normal
driving line would take us, therefore we have to adjust the initial driving
line to give us the best entry point for the second corner so as to maximise
our speed. We can apply the driving line used in Figure 3 to position the car as
close to the normal entry point for the next corner and still maintain the
smooth (or very close to it) arc required to negotiate the right hand bend. Of course, you may need to adjust even this
line depending on what is coming up next on the track – THINK AHEAD!
Another series of bends you can come
across is the “S” bend. In memory of the
late great Ayrton Senna
many tracks now feature a “Senna S Bend”; a left hand
curve followed by a right hand curve (of varying degrees) or vice-versa. These are often quite fast curves but can
also be known as “chicanes”. The fastest
line through this series of curves will only allow room for 1 car.
To find the driving line does
depend on the aspect of the corner. In Figure
5 we have a typical chicane of 2 very close 90 degree curves. You should clip both apexes to form the
correct driving line. To help you,
imagine a straight line between to two apex points, and then choose an entry
point for the first part of the curve and the eventual exit point. A smooth curve
to the first apex and a smooth curve from the second apex to the exit point will
give the correct driving line for the series of bends. Remember though, the exit point of the last
phase of the bend will determine where you are positioned on the track for the next
bend, so again, THINK AHEAD!
The high speed bend (less
than 90 degrees) does not always require such a strict driving line; however,
you should still apply the same principles as the next section of track could
well demand an exact driving line. Figure
6 shows such a bend.
If you applied the same line (red)
as you would have done for a right angled bend you see that it does not end in
the correct place and will require a series of adjustments to correct. Here you can take a more protracted line,
almost straight, in fact, as straight as possible. The emphasis is on the smooth entry maintaining
speed and energy.
Depending on the next corner or
straight you will need to adjust the line accordingly. You would need to consider if there is an
immediate corner or a long or short straight after the fast bend. Speed could also be a factor in this kind of
bend as it might be fun going flat out around the corner, only to find that you
are standing on the brakes to make the next corner without crashing – not so
much fun!
The fastest line between
two points is a straight line. What an
obvious statement but one which is not always observed. When entering a long straight you know that
at the end is some sort of bend and due to the fact that you are going down a
straight (hopefully in a straight line) means that you will arrive at that bend
going very quickly. It is therefore
extremely important to be in the correct position so as to enter the corner on
the right driving line. You know that
you want to be heading into the breaking zone in a straight line so that you
are ready to turn smoothly into the corner.
To get to that point as quickly as possible you imagine a straight line
from the exit point of the previous corner to the breaking zone of the next and
drive straight down that line. Figure
7 shows both the correct line (green) and the wrong line (red), the latter
requiring some form of serious correction to get to the entry point of the
corner (leading to swerving, lowering of speed, loss of energy – in fact about
all the wrong things you 
want to happen). Smoothness, straight lines, neat curves all
adds up to faster laps, further distance and winning races.
Let’s put some of this together into
a series of bends which is not too dissimilar to a track we use. Applying the knowledge given above, slightly
modify it to fit the track and we should get something approaching Figure 8. Here we have the approach to a hair-pin bend
which required an adjusted exit point from the previous corner to arrive at the
correct entry point. A late apex in the
hairpin as it was greater than 180 degrees.
Following this a slight left hand bend is encountered which naturally
takes you across to the right hand side of the track. In front is a long straight which we can
drive diagonally across to reach the breaking point for the next right hand 90
degree bend and then off for the rest of the lap.
Speed is not everything.
To be fast around a circuit does not
mean you have to be flat out at all stages.
If you watch any racing on the television, especially Formula 1, you
will notice the many different driving styles that people have. The ones who throw the car around the track
quite often do not win the race. It
looks exciting but unless they have exceptional power and fantastic tyres
sooner or later they will fail. The
smooth driver, such as Jenson Button, is one who maximises the potential of
their car by going up to, but never beyond, the limits outlined in the first
paragraph of this paper. Smooth entry into
a corner maintains speed and energy, it also minimises the stress placed on the
car and tyres. Maintaining speed gets
you to the next turning point quicker, maintaining energy allows you to go a
greater distance. Over a 4 hour race,
every ounce of energy needs to be used to go forward – not sideways. Where you do need to deviate from the
straight then the correct speed is essential.
Try not to use the brakes in a 4 hour endurance race (unless you do end
up in a corner too fast or safety becomes the priority – you are just about to
hit someone!).
As we do not have a variable speed
control on the cars (only a simple on/off switch) balancing the power around a
corner is not much of an option. It is
therefore important that the correct speed is attained at the entry point to
the corner. This may require a period of
braking (in a straight line) just before the entry point followed by a smooth
turn into the corner. When you see the
apex you can apply the power to pull you around the corner and smoothly to the
exit point.
Any sudden turns will not only loose
energy and speed but could also cause an accident. If the driver behind you does not expect a
sudden change in direction they could begin an overtaking manoeuvre which may
result in you both being at the same point on the track at the same time (the
scene of the accident).
As we have fast cars you will find
yourself in many overtaking positions.
If someone moves suddenly and unexpectedly in front of you the outcome
could be the same. To avoid this “thinking ahead” is again required. In this case “anticipation” on your behalf is the answer. Giving another driver space is good practice
as is sounding the horn well in advance of overtaking. However, when overtaking “do not forget” you
still need to make your driving lines.
It is no good hammering down the straight and overtaking on the wrong
side of the car in front only to find that you have arrived at the next corner
either too fast or on the wrong part of the track and having to hit the brakes
even harder to make the next corner.
THINK AHEAD; when coming up to
overtake another car think:-
Ø Where do you need to be
after overtaking?
Ø Left or right side of the
track?
Ø Fast or slow?
Ø Can I complete the
overtaking manoeuvre before the entry point to the next corner?
In most cases, due to the speed we
race at and the width of the track a certain amount of margin exists but when
approaching certain corners such as a hairpin this margin narrows considerably,
so think ahead and be safe on the
track.
What to do when going racing?
First thing, you need a track
diagram, one big enough to show all the corners and straights with a scale to
give you an idea of distances. From the
track layout get a rough idea of your initial driving lines, where you think
they are and where likely entry and exit points will be. At the track, either walk the circuit or get
some practice laps in to test out your theory.
Look at the track surface to see where the bumps are; maybe you can
avoid them with a slightly different line.
Maybe there are gradients which will affect your race. All in all, plan your race in advance – THINK AHEAD, do not just simply turn up and sit in
the car.