Rauno Aaltonen on Left Foot Braking

reprinted from Goblins Gazette Vol II, No 4, (Dec '68/Jan '69)
(If you know the original source of this article, please contact us) 

Rauno Aaltonen, 1965 Rally champion of Europe, explains this highly
specialised technique to Wilson McComb, BMC Competitions Press Officer.

McC: Every time rally enthusiasts get together nowadays, sooner or later
you will find them talking about left-foot braking. It is a technique
which we associate particularly with Scandinavian and Finnish drivers,
and their use of it is perhaps one of the reasons why they seem to be
unbeatable in international rallies. How did you first hear of it Rauno?

A: About four years ago I heard a rumour that the big boys, like Erik
Carlsson, were using left-foot braking, but it seemed impossible to get
any details. I couldn't find anyone to explain it to me, and Erik himself
said he he was not using it. So I had to learn it for myself. At first it
made me much slower, because although the technique is not easy, it is
certainly convenient. If you panic when you find yourself going too fast
into a corner - and of course, you have a minor panic every time you go
too fast into a corner! - it is very tempting to use the brake too much
and too often if you have learned a convenient way of doing it. But now,
after much practice, I think I have perfected left-foot braking.

McC: Does the technique apply exclusively to front wheel drive cars? Or
is it better or more effective with FWD?

A: No, not at all. It has advantages when driving both types, but the
advantages are different.

McC: Perhaps, then, we should consider them seperately, especially as
they react quite differently when one enters a corner too fast. In
general, I think we can say that a front-drive car will understeer,
whereas a rear-drive car will oversteer; it is the tail which will break
away first when you go over the limit. Let's start with the front-drive
car, since you have achieved most of your rally success with a
front-drive Mini Cooper. And let us emphasise that throughout this
discussion we are considering entering corners far too fast; that is; at
speeds altogether higher than any sane driver would use on public roads.
You are driving your Mini Cooper over a special stage of a rally, a
closed section of mountain pass or forest track where all competitors are
timed and the fastest man wins. How do you approach the corners?

A: Well, some people always throw the car sideways before a corner. (cf.
Roger Clark) It helps to reduce the speed quickly at the last moment, and
of course it looks very impressive for the spectators! But when you are
driving fast over an unknown road, nine corners out of ten look slower
than they really are. So my technique, quite simply, is to go into every
corner a little faster than the speed which appears to be the maximum for
each one. This means in that practice, nine corners go just right but on
the tenth one I find I am going too fast. By the time I have realised
this, it is much too late to throw the car sideways - there is no more
time for that. I am going off the road - straight off with the front end,
you understand. Now I keep the steering wheel position just the same, and
I keep the accelerator still hard down, but very quickly I hit the brake
pedal hard with my left foot - I don't keep it down, I just hit it. This
causes the rear wheels to lock before the front wheels, because the rear
wheels are running free and the front ones are being driven by the
engine. Now, locked wheels have very little grip, so the tail begins to
slide out, the car turns on its axis, and you can continue through the
corner, still on the road instead of using the ditch. I could do exactly
the same thing with the handbrake, but I haven't time to take my hands
off the steering wheel to use it. Also the handbrake is seldom so
efficient.

McC: But all this must happen very, very quickly - the whole thing must
be over in a fraction of a second?

A: Very true. This means you must have your left foot ready all the time,
and then it becomes a great temptation to use it all the time. We used to
say that if you have a close rival who is almost beating you on rallies,
you must teach him left-foot braking - then he will not trouble you again
for one whole season! When it is so easy to slow your speed at any
moment, it happens that you start braking on the straights, too hard
before the corner, on every corner. So you become too slow. Also, I have
known cases where brakes have been burnt out completely in 20 miles by
using them too much in this way. When trying to learn left-foot braking,
many drivers are still accelerating with the right foot as they start
initial braking for the corner with the left foot. This is nonsense - and
besides, it is giving you most braking from the rear wheels at a time
when the weight of the car is being thrown forwards. So at first I think
it is better to use the right foot for initial braking. When you start
accelerating through the corner, move the left foot from the clutch to
the brake, to be ready in case you want to throw the tail out. Later, you
can use the left foot for your straight line braking as I do.

McC: Now let's consider how left foot braking can be applied to a
rear-drive car. Again, you are entering the corner too fast. What
happens?

A: Normally, just before a corner you must get the car to drift slightly
- and I mean slightly; I am very strictly against oversteering cars,
  which are going to much sideways. Let us say this car is perfect in
handling - not oversteering, not understeering - it is neutral. So by
putting full power on before the corner you have it drifting slightly,
with the tail out a little. But now you find you have estimated the speed
wrongly and the tail is going out more. You correct by steering the
opposite way, but soon you will come to the full lock position - you
cannot correct any more. And the car will be starting to spin. Now this
is where you use the left foot instead of the steering wheel. Just before
you reach the full lock position, and still keeping the power on to the
rear wheels, you hit the brake pedal quite hard with your left foot. The
front wheels lock and slide, so the front of the car comes back to the
right direction for the corner.

McC: In fact, this is the exact reverse of the effect achieved with the
FWD car?

A: Yes, but there are other advantages, too. When you are drifting
nicely, with equal grip for all four wheels, it often happens that the
inside rear wheel starts to lift. If you have no limited-slip
differential, this wheel will immediately start to spin - and then you
will lose all driving power to the other wheel. By using the left foot on
the brake you can stop the inside wheel spinning and make more torque go
to the outside wheel. It sounds very strange but it is true. Another
advantage, for all cars, is this. With the brakes on; you cause a certain
twist in the suspension which locks the joints and makes them stiffer.
This makes the car more stable - there is less roll, it does not bounce
and sway too much. That is very important.

McC: What advice would you give to the ordinary motorist who would like
to learn the technique of left-foot braking in corners?

A: I have tried to explain that it is really quite difficult. A friend of
mine in Finland, who tried it when cornering one day, unfortunately
landed in a tree. Another friend in England, who make some experiments
when driving in traffic, drove into the back of a very large bus. Please,
if anyone is doing it, choose a place which is very quiet and far away
from other cars, or there may be some nasty surprises.

...........................................................

>Weight transfer is a dynamic effect. Stabbing the brakes to 
>get the front tires loaded up can be transient. 

Weight transfer is what _all_ the shenanigans we do is all about, we
brake hard to shift weight forwards so that the tires are pushed down
hard, so we can decellerate, and while the weight is forward, and the
back is light, we give it a flick to make the weight shift to the OUTSIDE
FRONT WHEEL so that it bites and we can turn.
It really doesn't matter which foot is used, the Swedes and Finns in
driving 850CC Saabs and tiny Minis against big nasty OHC Healys and crap
wanted to NEVER LIFT the right foot and lose any momentum, so the used to
left foot, and changed gears without the clutch, a brutal but effective
method they went on to advocte as a great thing.
Stuart Turner, Ford rally boss for many years was at BMC in those days
and he said, "Yes they thought it was a great idea, but they weren't buy
the brakes and gearboxes themselves"

Going sideway is just a method about placing weight on the outside front
wheel, any low level skiier can tell you their instructors are constantly
harping on 'weight forward!! weight on the outside ski!!'
And intermediate amature moto/cross rider will confirm: if you want to
turn sharply in low traction, you had better move weight forward, and
like skiing, the bodies palcement is one method we can do skiing and on
bikes which we can't in cars, but the method we can do in both moto-cross
bikes and cars is we can apply the brakes sharp and hard and shift the
weight to the outside
When the weight is one that outside tire, it will carve, and we can drive
around the corner fast.
>
>Left foot braking can be more steady state.
Oh really, for turning, do tell.

You've entered a 
>turn and need to adjust rotation. The front/rear weight 
>bias isn't changing so much as you are overdriving one axle 
>with power to alter the brake balance front/rear. 

huh???
Where did the rotation come from?
>
>The altered brake balance changes the available lateral 
>(sideways) force the tires can create, which alters the 
>rotation rate (understeer/oversteer) 
By locking momentarily the unweighted inside rear wheel and causing it to
skid, the combination of the forwards vector and the outwards vectord
averages out to a vector pointing at the forward, outside wheel, draw a
picture , a curve a car and some arrows.

IF THE OUTSIDE FRONT WHEEL DOES NOT HAVE WEIGHT, IT HAS NO GRIP, AND IF
IT HAS NO GRIP, THE CAR WILL NOT TURN.
>Left foot braking is not (primarily) about altering weight 
>distribution;

Really?? I think you should tell those who are at the WRC level about
your discovery. You can probably find links at the teams website.
THE DIFFERENCE BETWEEN HAPPY AMATURES AND REALLY FAST PROS IS IN BRAKING
CONTROL, have you measured the size of even gravel spec front discs on
real cars? You imagine that they are putting dioscs 290 x 32 on the front
of cars for overdriving axels?
I think they are there to be powerful enough to easily shift a LOT of
weight forward which is needed to prevent locking, (thats where the
control comes in, wanna slow down as hard as you can without locking and
skidding (where? STRAIGHT off)


it's about changing available lateral force 
>during cornering by braking. Normally,this would slow the 
>car, so the power is used against the brakes to not only 
>bias the brakes to the axle desired, but hopefully keep 
>things moving forward. 
>
>I would say things like the pendulum turn are more geared 
>towards catching transient weight transfers and using those 
>to maximize grip and slip. 
>
>I'm a little curious as to why Tim O is calling it weight 
>transfer, although out of context, lots of things get 
>confusing. 

Because he is a rally driver who knows what he is talking about, albeit
somewhat dogmatically when he asserts, or more corrrectly , his students
rreport that he asserts that you absolutley must left foot brake without
exception or the world will come top an end, a silly assertion in light
of many WRC level drivers far faster than Tim ever in his dreams was who
DON'T LFB.
>
>
I think somebody is letting theoretical knowledge run overcook the brakes
on the imagination.
Re-read Altonen.

John Vanlandingham
Seattle, WA. 98168

...........................................................

>I'm not going to disagree with the first statement about braking
>control, but I'm confused as to John's logic (or knowledge of physics)
>on the second one.

You are not the first one to be confused!!!!
somebdy once suggested that the way I write presupposes a fairly high
degree of "broader experience" and the ability to make some possibly not
too intuitive jumps.

But I don't think I am suggesting anything where logic or knowledge of
physics is needed, but rather simple open eyed observation.
And the ability to recall images of things YOU already have seen and
interpert those images while holding in abeyance your previous
ruminations on any given subject.
As always I suggest people to LOOK at what is already established as the
"normal standard stuff" and accept that is what has been chosen by people
who are paid to build World Chapionship Winning capable cars. and then
ponder "why would they do THAT?"
AND IN THIOS VERY SPECIFIC DETAILS SUCH AS DISC DIAMETER AND cCALIPER
PISTON SIZE BECOME CRITICAL as they can show the differences from road
car things and from that certain patterns emerge.

So neither logic or knowledge of physics are needed, and indeed I counter
suggest that even thinking about them wastes an amatures time, he should
be practicing!!!!

>With all due respect, it seems to me that what's stopping you is the
>coefficient of friction between your tires and the road, but that
>involves slowing down the wheel, and your ability to slow down the wheel
>is determined by the coefficient of friction between your pads and the
>rotors - and that's independent of brake size. 

Well sorry but wrongorootie.
Exaggerate the size question, go to brake the size of say MkI
Golf?rabbit....._3"_ diameter aren't they, and a pad the size of a dime.
Normal brake pad coeff say my favorite DS11 .61, and car weight like a
Misterbitchy Gaylant>3400 lbs.

I think in this case you can very obviously see that the ability to slow
the car would be negligible.

The figuring the ability of any pad and piston combo to do work, the
distance from the center is a critical factor as the following simple
illustration shows.
Take a typical bicycle front wheel and while holding the axel, spin it
hard, and give it a couple of more spins then, while it is spinning,
place you caliper (your hand) with its pads (your fingertips) way out at
the rim, and then rapidly grasp the thing at the tire ZZIIIP!
Easy as pie, eh?

Spin it again real fast like before, and now take your caliper,(still
your hand with the same mechanical strength, same ability to exert force,
like hydralic pistons do) with those same pads (your fingertips which
still have the same coeff of friction they did 1 minute ago) and
now........
grab the wheel right by the hub.....
When your broken fingers heal and you can type, tell me what happened.

>Instead, it's dependent on your rotor and brake pad compound. What
>bigger brakes do is shed heat faster, and let you repeat the braking
>over and over without burning them up. 

Bigger brake are, for a given piston size, either stroner, or conversely
able to do the same work easier. (somebody is after all pushing on a
pedal, this is not physics it is DRIVING a car we are talking about,
remember the bigger picture.)
I believe I said "to shift lots of weight forwards easily".

So with regards disc diameter think ease
disc width think repated ability, but mass is important too
and Pad VOLUME for durability of the pad itself.
and that leaves out the hydraulic end of the equation, the actual power
the master cyldiners will make, and the 'weight' of the pedal, or how
much leg is needed to generate the power.


>As for the technique of LFB, do you drag the brakes through the whole
>turn, or just rest your foot above the pedal and give it a smooth pulse
>to get the car to rotate onto the line you want? That Aaltonen article
>would indicate the latter,

Yes Rauno is always talking about a momentary locking of the rears, and
to accomplish that his Minis would use a rear wheel cylinder with a 3/4"
bore vs the road cars 5/8" bore, curiously enough the same exact wheel
cylinders which Saab homologated for use in the SAAB 96 for use even in
Gp1 (which corresponded to our current GpN, and as such all changes to
standard road cars had to be homologated).

If you watch many tapes of WRC even on asphalt you will see tarmac
specialist doing very momentary little erk! erk! lockups espeially
noticable on the INSIDE rear wheel, diagonally opposite of where they are
shifting weight.

> but when I drive I generally ride 'em a little and try to modulate them
> as I turn. I keep wondering if this just slows me down too much, but I
> don't want to unsettle the car with a quick shot either. 

Yes you do. If you are really going to drive fast.

> Also, assuming you have a car with adjustable bias, do you adjust the
> bias more rearward for tight twisty stages to give you better rotation
> with LFB?

Since 1984 I have seen only one tight twisty stage, EVERY other is medium
to fast to insane fast.

Additionally we seem to have much less tight 60-90 degree junctions, and
as such I set my car up a bit more rear than a road car, not quite a 2:1
ratio in terms of piston area (same disc F&R)

> Or do you just leave it balanced with the fronts locking up slightly
> before the rears? 

Well leaving road cars alone will get you approx 3.5:1 hydraulic ratio
and usually micrscopic pads, and fronts will tend to lock long before
rears, especiall if the road car rear limiters are present.
I aim for the ability to modulate the lock up of the rear, even induce it
with the little flick so that while it is unweighter, I can flick, take
the last littl;e bit of weight off and cause it to lock and begin to
rotate the back of the car.

I use my right foot, but then I am a dinosaur.

Now was there any need for phyisics or logic here???

John Vanlandingham
Seattle, WA. 98168

...........................................................

>Spin it again real fast like before, and now take your 
>caliper,(still your hand with the same mechanical strength, 
>same ability to exert force, like hydralic pistons do) with 
>those same pads (your fingertips which still have the same 
>coeff of friction they did 1 minute ago) and now........ 
>grab the wheel right by the hub..... 
>When your broken fingers heal and you can type, tell me what 
>happened. 

Actually, I think you're confusing the mechanical ability of
the system to exert force with the actual stopping power. I.e.,
you're confusing clamping force with frictional energy transfer.
Clamping force has nothing to do with stopping power, and everything
to do with driver feedback.

To take your bike wheel example to an extreme, consider that
there are three main kinds of brakes available on modern bikes.
Nearly every kid's bike made when I grew up had "coaster brakes",
which where a tiny drum brake mounted in the rear hub that was
activated by stomping on the pedals in the "reverse" direction.
If you recall, these brakes had *plenty* of stopping ability -
indeed they were all to easy to lock up. The problem wasn't that
the brake was ineffective, the problem was that it was very
difficult to modulate the amount of pressure required to activate
them, especially when you were standing up.

The alternative, available on "grownup" bikes, was a center-pull
caliper, which clamped two pads against the rim, activated by
a cable pulled by hand levers mounted on the handlebars. Again,
these provided plenty of stopping power, and it was easy to lock
up the wheels, but required a fair amount of muscle strength to
activate them. If you were racing on long downhills, your hands
quickly got tired. This could be offset by either having longer
levers or a mechanical cam within the lever mechanism, but the
former just made it so you had to pull the lever a farther distance.
The latter gained some popularity for awhile, but that coupled with
the inherent slop within the system made it really hard to "feel"
what your brakes were doing...and hard to modulate them to just
below the lockup point.

In the mid-90s or so, V-brakes were invented. These worked basically
in the same way as the center-pull brakes, but the calipers were
designed such that they were more efficient at transfering cable-pull
forces to the pads. Again, you could lock the brakes up just fine,
but now, because you were more closely coupled to the brake, you
had a better "feel" for what the brake was doing, and it was easier
to modulate it. Now you neither needed a longer lever, nor (much) of
a lever cam, and you could pretty much lock 'em up with just one
finger on a short lever.

Note that none of these increased the stopping power of any
particular brake system. Instead, what the various improvements
did was give the rider more control over modulating the stop, i.e.
more control over the clamping.

>
>Bigger brake are, for a given piston size, either stroner, 
>or conversely able to do the same work easier. (somebody is 
>after all pushing on a pedal, this is not physics it is 
>DRIVING a car we are talking about, remember the bigger 
>picture.)

Ah, yes. Agreement. 100%. They may be stronger (depending
on how they're manufactured of course). With larger pistons,
they require less brake fluid pressure to exert the same
amount of clamping force as a smaller brake. When you work
this all the way back to the brake pedal, what this means
is that for the same brake pedal movement *distance*, bigger
brakes will require less pedal *pressure* to generate the same
clamping force. This translates to faster speeds simply
by allowing better driver feedback and less driver tiredness.

Note that you can achieve the effect of having bigger brakes
by having some third party boost your brake-pedal efforts -
say a hydraulic system run off the engine. Hey, look, gee,
that's what "power-assisted brakes" are. In racing, however,
this isn't really a desirable line of pursuit because 1)
it's another thing that can break, 2) it decouples the driver
from the braking feel somewhat, and 3) it still leaves the
heat-dissipation issues mentioned in my previous post.

>So with regards disc diameter think ease 
>disc width think repated ability, but mass is important too 
>and Pad VOLUME for durability of the pad itself. 
>and that leaves out the hydraulic end of the equation, the 
>actual power the master cyldiners will make, and the 
>'weight' of the pedal, or how much leg is needed to generate 
>the power.

Yup, yup, no arguments here - although it should be noted
that bigger brakes and calipers result in larger unsprung
mass. However, I think it's been proven that the benefits
outweigh that.

By the way, I'm not arguing *against* bigger brakes, I'm 
just arguing against the notion that they help you stop
faster.


>>As for the technique of LFB, do you drag the brakes through 
>>the whole turn, or just rest your foot above the pedal and 
>>give 
>>it a smooth pulse to get the car to rotate onto the line you 
>>want? That Aaltonen article would indicate the latter,
>
>Yes Rauno is always talking about a momentary locking of the 
>rears, and to accomplish that his Minis would use a rear 
>wheel cylinder with a 3/4" bore vs the road cars 5/8" bore, 
>curiously enough the same exact wheel cylinders which Saab 
>homologated for use in the SAAB 96 for use even in Gp1 
>(which corresponded to our current GpN, and as such all 
>changes to standard road cars had to be homologated). 
>if you watch mant tapes of WRC even on asphalt you will see 
>tarmac specialist doing very momentary little erk! erk! 
>lockups espeially noticable on the INSIDE rear wheel, 
>diagonally opposite of where they are shifting weight.

Ah...good intel. I will recheck my WRC rally tapes and look
for that.

>>when I drive I generally ride 'em a little and try to modulate them as
>>I turn. I keep wondering if this just slows me down too much, but I
>>don't want to unsettle the car with a quick shot either. 
>
>Yes you do. If you are really going to drive fast.

Ok, so you're intentionally upsetting the car in order to
get a shot of "weight transfer" to the front wheels, particularly
the outside one, and break the back end loose a little - enough
to get it rotating (again).

>I use my right foot, but then I am a dinosaur. 
>
>Now was there any need for phyisics or logic here??? 
>

Well, arguing without physics or logic leaves me at a distinct
handicap, I must admit. My apologies if I've invoked them more
than you'd like in formulating this response.

hoche

...........................................................

It's true.
The ability to play with the effects of those two concepts is what is
needed and indeed what is a lot of the fun of this sport and of say
moto-cross and skiing.
Ever notice ACPs siggy thing.
He's not only a lawyer, he's a Canajian Lawyer and he drives some
Misterbithy thing, but he has the right isea what he's really doing, even
if he does also get a bit theoretical at times.
"Flirtin with the laws of physics"

I have known well a number of World Champions in moto-cross, and I would
never associate the words logical or knowledge of physics with any.
(OK, OK, the Swede Åke Jonsson was actually a trained engineer and he
knew his stuff, but he was never World Champion, just second a couple of
times)
They did apply the principles however.

>Oh yes. Practicing is great. It's a little hard to practice 
>when I'm stuck here in front of a computer, but I don't 
>disagree with that. 

For example, none of those Swedes or even the 3-4 belians I knew who were
World Champions ever suggested "go study logic and Physics"
They said "RunRunRun!!! Practice ! Practice! Practice! Give yourself 10
years!"

>Actually, I think you're confusing the mechanical ability of the system
>to exert force with the actual stopping power.  I.e., you're confusing
>clamping force with frictional energy transfer.  Clamping force has
>nothing to do with stopping power, and everything to do with driver
>feedback. 

Maybe you should write AP racing and Willwood and tell them the above,
all I will say is OI!!! and

Wrong again, driver feedback is a function of the mounting of the various
components and how much rigidity and parrellelism there is in the
disc/pad combined with the master cylinder size vis a vis the caliper
pison sizes. 

I have to say I have a feeling you are discussing this from a point of
view of never having done some or any of these things regarding modifying
brakes on a car, and an assumption that all that mountain bike stuff was
news when we went through a whole bunch of the exact same issues on bikes
a long time ago.

The specifics of the hardware differs sometimes but the needs and desires
are the same.

Want to talk about the radius of the cam which operated the shose on Euro
motocrossers vs the production small lightswith crap sold on all Jap bike
until the 79 model Honda 250 Elsinore??(when they finall sold the larger
stuff they had been using on their factory bike for years, and made
efforts to give a decent shape to the cam in the drums.)

>Yup, yup, no arguments here - although it should be noted that bigger
>brakes and calipers result in larger unsprung mass.

Not a fact, the huge OEM calipers on many street cars weigh 15-18 lbs per
side, the all iron OEM discs are also quite heavy.  A Willwood Superlite
IIa weight 4.2 lbs, an aluminum hat weights approx 1.25 lbs, leaves a lot
of room for increasing the disc size without penalty.

>By the way, I'm not arguing *against* bigger brakes, I'm just arguing
>against the notion that they help you stop faster. 

I suggest you continue to exaggerate the dimensions in the example until
it becomes obvious.

>Well, arguing without physics or logic leaves me at a distinct handicap,
>I must admit. My apologies if I've invoked them more than you'd like in
>formulating this response. 

No probs, but driving on gravel is not an intellectual excercise or a
discussion, and less a debate.
For 99.5% of us, including me in this sport, it is a fun playing with
cars and a emotional experience as well as a social activity.

The problem with writing as a social thing is you can't come here and be
shown actual parts and setups and so the discussion becomes one seeming
awfully close to a debate, and I can't just say "shut up and LOOK!" (like
those taciturn Swedes who taught me about the _approach_ to the sport,
who usually preceeded with a conk or slap upside the head, I should point
out, and a few choice word like "What the hell are you thick in the head
or WHAT!!!?? CAN"T YOU SEE???!!" they were harsh.)

But I learned that there were different modes of speech, and altho these
guys may have talked like tough guy "hårdingar", that was just the way
that class of person spoke, and that so much of their person went into
the riding and training, and less into social intercourse and language
development.

But the mere fact that they were talking shows that they were trying to
share, and that they cared.

I listened, they were afterall on the way to or becoming professional in
the sense of making a living from their racing, and their help enabled me
to do the same a few years later.

But I stress, I listened, I accorded them some authority because I knew
that their results (and not just on the track, in the garage as well)
showed the were applting their knowledge even if they struggled sometimes
with the exact descriptions.

and called me "tjockskallen" and "Colombo" 

John Vanlandingham
Seattle, WA. 98168

...........................................................