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Left Foot Braking.

There have been a couple of questions regarding left foot braking (LFB)
recently, and not being shy about revealing the limits of my knowledge, the
following is my contribution.  There are three reasons, that I can think of, why
one would engage in LFB:

One; Normal driving with an automatic transmission.  I've been doing this for
many years and find it an excellent technique for transitioning from accel to
decel, and back by having both feet working the pedals.  I drive with the left
foot _off_ the pedal but positioned to swivel to the "brake alert" position in
anticipation of any situation where decel may be needed.  The rapidity with
which the brakes can be applied has saved my relationship with State Farm on
many occasions.  When in a "high performance mode," (good curvey road, minimum
traffic and high testosterone levels), the left foot is planted hard in the
footwell and stays there.  To me the demands of these two types of driving
require the two styles.  Interestingly, I've never had an instance of, "...now
which foot is it that has brake duty?"  I know, I know... using both feet is, to
my knowledge, not taught by anyone!  Is it not for everyone.  Being on this list
indicates that you are not part of the herd and are likely to be able to seek
and develop driving/thinking skills that, like your automobile, are high
performance.  One size does not fit all, decide for yourself.

Two;To let the turbo spool up.  In 1980 I bought a Saab Turbo.  Fun, but turbo
lag could have been measured by sticks and relative sun positions.  I was keenly
interested in ways to overcome/avoid this problem when I came upon an article
about a Swedish rally driver, name escapes me, that essentially drove a turbo
rally car with right foot flat on floor and adjusted speed with left foot
applying brake.  (That writer observed an instance where during a rally they
changed pads during a pit stop.  This was a scheduled evolution given the abuse
this driver was known to inflict on the brakes.  After the car resumed the race
the writer glanced at the discarded pads... they were still glowing red hot
several minuted after being changed!)  Shall we say that this is rather
stressful on the equipment and the pocketbook.  I did try going into corners,
having previously selected the exit gear, while LFB and using the right foot to
spool up the turbo... and was greeted with immediate and large accel just where
I needed it!  Then there was the instance when the green Z-28 took exception to
being left behind coming out of the corners, entered the next one too hot and
exited with a series of great slewing oscillations and a could of blue smoke as
I streaked away.  Gratifying.  

Recall the Rover-BRM turbine car of, I think, 1964 where the turbine had such a
lengthy spool-up time that the normal cornering technique was to get out of the
throttle only briefly (actually it's a foot-actuated power lever as turbine
engines are not 'throttled'), brake with left foot and apply power with
sufficient anticipation so it was available when needed.  Reports were that it
launched from corners in a magnificant fashion.  Finished, I think, in the top
five at Le Mans that year.  

Three; To influence handling.  In a FWD car there are instances where one can
adjust the under/oversteer characteristics through judicious application of
brakes while under power.  As FWD cars tend to understeer while under power, a
bit of braking can make that corner 'easier' as the car rotates more easily and
even reduces front slip angles.  (Easy does it, though, as a spin with both feet
planted is difficult to explain except in terms of your helment having been too
tight.)  My understanding is that the subtle forward weight transfer reduces the
normal force on the rear tires giving them slightly reduced traction.  Recall
that traction is a function of the coefficient of friction and normal force

 I recall seeing a video of both the feet and out the windscreen of a quattro
rally driver at work.  (Anyone have a copy of this?)  His footwork was amazing! 
Left foot operated clutch, right foot operated throttle, both feet operated
brake... which one depended on what the other foot was doing at the time.  Fred
Astair would have envied the footwork.

How does this pertain to a quattro?  I suspect that it all applies but in more
subtle amounts than in less well developed automobiles.  My assessment is that
our cars are sufficiently capable of high performance such that the skill of the
driver will usually be the limiting factor, and that high performance LFB is a
rather high-order technique that most of us will never need to perfect.  How
about some drivers' reports from the field?

Comments?  Corrections?

Regards,  Gross Scruggs