Julian Daley asks >
>Could someone enlighten me as to the meaning of 'trail braking'
>(I thought it was what the leader of a jungle expedition did :> )
No, that's "trail breaking".
Here are a couple of definitions:
Left-foot Braking = Using your left foot on the brake instead of your
right. Sometimes this is done in conjunction with clutch-less shifting.
It is not the same as trail braking. I used to left-foot brake (in a
straight line) autocrossing the Midget, as long as I did not have to
shift. In the Sonett, I often found that I could adjust the attitude in
sweepers by stabbing the brake with my left foot while on the power with
the right. Such strategies are probably not in the cards for the Europa
due to the steering column running between the clutch and brake pedals.
Trail Braking = Braking while turning. Done to unload the rears and
transfer weight to the fronts to minimize understeer or cause oversteer.
It can be done with either foot. Generally done in front-wheel-drive cars
while entering a turn. Also can be done to delay braking as long as
possible at the end of an important straight, in conjunction with an early
apex. Be sure you have runoff room if you do this. If you screw up, you
will buy some cones. Just make sure there is nothing harder to hit.
Left-foot braking and trail braking are not synonymous, but are often done
concurrently.
Trail braking is worthless, according to Jackie Stewart. When informed
that Bob Bondurant teaches it at his schools, he replies, "Oh? And just
how many Formula 1 championships has Bob Bondurant won?"
Stewart believes in threshold braking in a straight line before starting
turn-in. Very late turn-in, getting most of the turning done early,very
late apex, accelerating all through the corner, with his radius increasing
the whole time. His tires remain on the edge of the traction circle,
making the transition from "all cornering" at the beginning of the curve
to "all acceleration" at the end of the curve very smoothly. He says that
trail braking will never give you the exit speeds that his method will.
He is indisputably right about this. (To quote another Scot: "I kinna
change the laws of physics!") The point of argument would be how much you
lose at the END of each straight. Stewart says it is better overall to
straight-line brake.
"Car & Driver" (a USA magazine) had a track session in 1991 with Jackie
Stewart and several good race drivers (although none of them F1 champs!)
at the Ford test track. They all drove a special Taurus wired to sensors
in the track to record car positions. This allowed them analyze the
speeds, lines and techniques. Stewart was faster than everyone else. No
surprise there, eh? The surprise is that he was slower in the sections
immediately before and in the first part of each corner. His exit speeds
were so much higher that his overall lap times were better. One of the
racers commented about the Slow In, Fast Out theory: "We all believed in
SIFO, but Stewart showed us that we did not believe in it enough."
In my advice to autocrossers, I have written: If your car does not
require trail braking to force oversteer, stay away from it, as it is less
efficient than straight-line braking. If your car is a hopeless
understeerer without it, then you have to use it anyway. Only in stock
class should it be used, as proper chassis tuning will eliminate the need
for it. I expect some disagreement from trail braking proponents.
Trail braking would also seem to imply a diminishing-radius line. Using
Alan Johnson's method of classifying corners according to importance by
their relation to a significant straight, the corner before a straight
would require a late-apex (increasing-radius line with heavy acceleration)
and the corner after a straight would require an early-apex
(decreasing-radius line with heavy trail braking). But in practice, I
think the late-apex approach is the answer in nearly every corner.
Phil Ethier, THE RIGHT LINE, 672 Orleans St, Saint Paul, MN 55107-2676 USA
h (612) 224-3105 w (612) 266-6244 phile@stpaul.gov
"That's why I'm here." - James Taylor
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