Imagine you are driving along at 60mph on a main road, coming up to a
junction you need to turn down. It is a right angled turn, so you need to
slow down quite a bit. You are currently in 5th gear.
You take your foot off the gas, and hit the brake with your right foot. You
now have engine braking as the revs are coming down and the clutch is still
engaged (engine braking is the reverse effect of engine accelerating - the
engine is trying to drive the wheels slower than they currently are
rotating, so it slows them down), and you also have braking coming from the
brakes themselves.
When the revs come right down, the engine is no longer having much braking
effect on the wheels, and if you don't change gear the wheels will force the
engine to slow down until eventually it will vibrate badly and then stall
when the road speed gets very low. So you need to change down a gear to 4th.
So far, this is nothing to do with heel/toe, this is just what happens every
time you decelerate.
If you have taken your test recently here in the UK, they teach you to hit
the clutch and hold it in while you continue braking, then when you are at
the speed you desire, select the appropriate gear (lets say 2nd), take your
foot off the clutch and drive on. This is the easiest and worst method of
slowing a car down - you might say that it is the slowest method of slowing
down. It takes longest.
An alternative is to hit the clutch, move the gear lever from 5th to 4th,
and release the clutch to engage 4th gear, while still braking. When you hit
the clutch, the engine revs (which were already pretty low), will drop to
idle. The engine revs will be forced up as you engage the gear because the
new gear tries to make the engine run faster, and at the same time the
engine is trying to make the wheels run slower - engine braking again. You
then repeat this for 4th to 3rd and 3rd to 2nd, so you have 4 periods of
engine braking during your slowing down period (5th, 4th, 3rd and 2nd gear),
instead of just one (5th gear). This requires more effort, but no more skill
than the above method and will have a larger braking effect, thus slowing
the car quicker, taking less time to slow down.
The problem with the above method is this: when you change gear, the
synchromesh will not engage the gear until the revs of the input and output
shafts in the gearbox are relatively similar, so when you take your foot off
the clutch, the engine is only partially engaged to the wheels until it has
been forced to gain revs, before the connection is fully made and engine
braking can occur with maximum effect. That's why the engine note increases
as you engage the next gear, before decreasing again as engine braking takes
effect. Surely there is a quicker way of getting the engine revs up,
especially as you want to do it when you have your foot on the clutch? Oh
yes, the throttle! Surely it would be faster still (faster to slow down,
that is) if you didn't have to wait for the synchromesh/clutch combination,
and just blipped the throttle with the clutch in while you were moving the
gear stick from 5th to 4th? Yes it is. The only problem is, you will be
using all three pedals at once, with only two feet. That's why you heel/toe.
Actually you don't have to heel/toe (some people find it quite hard to
rotate their foot sideways so that their toes are on the brake and their
heel is on the throttle), you can do it in a rocking motion, so the left
side of your foot is on the brake and the right side of your foot is on the
throttle.
So the sequence is this:
1) Take your right foot off the throttle, and put it on the brake. Engine
braking and regular braking will slow the car down.
2) When the revs reach almost idle, put your left foot on the clutch and
depress it.
3) At the same time, roll/rotate your right foot to blip the throttle, and
move the gear stick from 5th to 4th.
4) Release the clutch.
Repeat 2/3/4 until you have the gear you need.
Heel/toeing is the fastest way to reduce speed, which is why almost all
rally drivers do it. I remember from the foot cam at Portland this year that
Dario Franchitti does it as well. They don't do it in F1 (because there is
no clutch pedal, although some might say that is because the pay-to-race
drivers can't do it...). The problems are numerous. In a race in a car
without ABS, you are constantly altering the pressure on the brake in order
to maximise their effect. To do this at the same time as rotating your foot
to blip the throttle is quite hard. Also, blipping the throttle the right
amount that the engine revs are almost perfect when you release the clutch
is quite hard also. The idea is you blip the throttle in the time it takes
you to move the gear stick, so there is no time lost, so it can get quite
hectic down there in the footwell. Not to mention the manual dexterity
required to perform the action in itself is pretty tricky to learn.
I use it occasionally on the roads. It has got me out of trouble a couple of
times, when an emergency stop from speed was required whilst still retaining
steering control (no ABS on my car). And thanks to the electronics in the
engine of my car at the moment, there are some temperature ranges when it
can't decide whether to ***or not, resulting in the engine just stalling
the first time you hit the clutch (which is fun because the power steering
gives up at the same time...). The only way to avoid this (without spending
money), is to heel/toe until the engine warms up, simply to keep the revs
well above idle every time I stop. I get some funny looks from the
road-walking folk, and it's kinda ironic that they think it's because I
can't drive properly, when in fact I am doing things most drivers on the
road can't manage ;-)
Hope that helps your understanding. If you don't understand something in
there, just reply in the newsgroup and I'll get back to you.
Cheers,
Nick.
