A common problem for new drivers in a manual car is pressing the clutch down at the wrong
time and allowing the car to freewheel. This is known as ‘coasting’ and will not only
reduce the driver’s control over their car, but also increase fuel consumption and brake
wear. Since many drivers don’t even know that they are coasting, in this video we will
explain what coasting is, show the problems it can cause, and finally how we can avoid
it. As always, if you would like to be notified of our next video please subscribe to our
channel, and if you have any questions about this video then please leave a comment below.
The most common situation where we see coasting is when the driver pushes the clutch down
unnecessarily, resulting in the car rolling along without any gear engaged. This can happen
when approaching a junction on a main road, when coming to a stop, or after a gear change.
Another form of coasting is when a driver selects neutral while the car is still moving
- this has similar disadvantages and should also be avoided.
Let’s have a look at the three biggest problems that coasting can cause.
Coasting is potentially dangerous, as it reduces the control we have over our car. When a car
is driven with a gear selected and the clutch engaged this mechanical link gives us a way
to control our speed. When we lift off the accelerator, drag from the engine will slow
the car gently and reduce the need to use our brakes. If the clutch is pushed down unnecessarily
the car is allowed to roll at whatever speed it wants to - and this can be dangerous, especially
when driving downhill. Coasting would not normally fail a driving test by itself, but
if it is done excessively or leads to a more serious fault such as poor observation at
a junction then it could result in a fail.
When slowing down in a modern car with a gear engaged, the momentum of the car will keep
the engine turning over and the fuel injection will not need to use any fuel. In contrast,
coasting will actually waste fuel, as whenever the clutch is pushed down the engine has to
use a little fuel to keep the engine running at idle speed. In addition, because coasting
uses the clutch and brakes of the car more often they will also wear out faster than
normal.
Coasting can prevent us from reacting promptly to a changing situation on the road. If approaching
a red traffic light in gear with the clutch engaged, should the lights change we are able
to accelerate away without delay. If we approach with the clutch depressed and neutral selected
then we are unable to react promptly, as we will have to engage a gear again before being
able to accelerate. In an emergency this delay might even put us in danger, so we should
never select neutral until the car has fully stopped.
Next, let’s look at 4 simple ways we can avoid coasting.
Coasting can be dangerous when driving downhill - as when we hold the clutch down the engine
is disconnected from the wheels and the car is able to freewheel at whatever speed it
wants to. We are going to coast down this hill to see what happens. As the hill gets
steeper, the car speeds up on its own so much that it actually reaches the speed limit.
Notice that as we engage the clutch again, this reconnects the engine to the wheels and
brings the car speed under control without the need to use the brakes. On a longer or
steeper hill we would be forced to use the brakes much more, and this could overheat
the brakes to the point that they fade or fail altogether.
If we drive down the same hill again with the clutch engaged, the engine braking effect
keeps the cars speed in control. The car speed only rises a few MPH and there is no need
to brake. So whenever driving down hills, select a suitable gear and keep the clutch
pedal up. On very steep hills we may need to brake a little as well, but we will still
have far more control than before.
Holding the clutch down as we approach junctions will reduce control over our speed. On a downhill
junction it allows the car to enter the junction too fast. This will reduce the time we have
to judge other traffic and we might be forced to brake suddenly or swerve around the corner.
On a driving test the fault might be recorded as poor observation or steering control, but
the coasting on approach would certainly have contributed to the situation. On uphill junctions
the opposite could happen - if we approach with the clutch pressed down there is nothing
to drive the car forward up the hill, so it could stop anywhere it wants to - or even
roll back! To lose control like this on a test would certainly be recorded as a serious
fault.
Lets repeat these junctions, and see how much difference approaching them with a gear engaged
makes. On the downhill junction second gear controls the car speed, and we don’t need
to brake as hard to stop the car - giving us more time to stop smoothly and look for
traffic on the main road. Once up to speed we look ahead for the uphill junction, and
ensure we slow the car early enough to allow us to select and engage the best gear for
the junction - normally this is second. When we lift the clutch pedal the wheels are linked
to the engine again and this will help the car slow down smoothly. We can then drive
around the junction in full control and at the correct speed. Second gear is able to
drive at very low speeds in most cars, and if we let the engine idle without pressing
the accelerator the car will roll along at under 10mph normally - which is slow enough
for almost any junction.
When stopping the car at the side of the road we should try to avoid pushing the clutch
down earlier than necessary, as we will have less control over where the car stops. If
there is an uphill gradient or we misjudge the car’s momentum it might stop earlier
than we need - forcing us to engage the clutch again to keep the car rolling. If we forget
to select 1st gear in this situation it will probably result in an unnecessary stall.
To stop the car precisely where we want to and avoid any coasting, all we have to do
is keep an eye on the car’s rev-counter as it will show us when to push the clutch
down. The idle, or minimum speed for a car engine is just under 1000rpm, so if we make
sure that we disengage the clutch before the rev counter needle drops under 1000 then we
will minimise coasting, without any fear of stalling the engine. It doesn’t matter what
gear we are using, pushing the clutch down at 1000rpm will prevent the car from stalling.
When driving at higher speeds keeping the car in balance is essential to maintain control
around bends. If a driver always presses the clutch down every time they brake, this can
unbalance the car. This is because every time the car’s clutch pedal is lifted to engage
the gear it has to bring the engine up to speed. The drag from this happening will slow
the car, and is similar to braking on a corner, this can unbalance the car and potentially
lead to a loss of control.
Let’s drive that section of road again. Expert drivers will always corner at a constant
speed with a gear engaged as this maintains the car’s balance. In addition, it is possible
to control the car’s speed purely by varying the amount of accelerator used, as the engine
braking effect when lifting off the accelerator will gently decelerate the car without the
need to constantly use the brakes. For more information please watch our other video called
‘Balanced Cornering’.
The basic principle to remember is that we should keep the clutch engaged for as much
time as possible, as this will give us better control over our speed and also reduce wear
to the clutch and brake systems.
So, remember to: Always keep a gear selected when moving
Stay in control on hills Approach junctions in gear
Push the clutch down at idle speed when stopping
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