Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/125810
PART I:
TH-E THEORY
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FOR CAFE ROAD RACERS
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by Lane Campbell
Going fast and staying legal has
always been a bugaboo to the aggressive
spirited rider or driver. I ~ow that
Stoplight Grand Prix and 100·plus mph
record runs across ·the flat may turn
some people on;.however both pastimes
,are grossly illegal, they are super rough
on machinery and they make little real
demand on the rider's skill. Rather, as
an exercise in unmItigated gall, they
rank somewhere along with running
toilet paper up flagpoles on dark and
windy nights.
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To me the corneTS will always be
where it's at; and on a motorcycle
there's a tremendous amount of fun to
be had withou t doing violence to the
law. This assumes that you live in a state
that does not take those little "safe
speed" placards that hang on each curve
sign too seriously. On a motorcycle you
have a tremendous advantage over a car
when playing fun and games on wiggly
bits of road. A car, when it's on the
limit, usually advertises the fact by
running at a considerable angle of drift
(if not an ou trigh t broadslide)
accompanied by audible protest from
the tires. Even though the driver may
deem himself in complete control, the
gendarmes will take his cornering
attitude as prima facie evidence that he
is NOT and issue a reckless driving
citation forthwith. With a cycle the
major evidence of on the limit cornering
is a low side toe brushing pavement. To
eVidence loss of control in the legal
sense you have to fall off or leave the
road, in which case a ticket is the least
of your worries.
Another advantage with a bike is that
you can use a considerable amount of
road in a corner without leaving your
legal lane. A question immediately arises
to the novice: Why should you want to
use a considerable amount of road?
Well, kiddies, this has to do with taking
the racing line through a corner; and
leads us directly into all the theories
that lie behind this whole business of
high performance cornering.
First, let's agree on one thing: For
every curve there is a limit, one that no
supcrrider can violate without falling off
no matter how ROod he is. How you
approach that limit without exceeding it
is the whole' nitty-gritty of fast
cornering without bqdily injury. Three
things determine what this limit is going
to be, in general order of importance:
a)
the maximum. performance
9PabiJ,ities 9f yo,!Jl' tires;
.
b)' the radius ot the curve;
c) the chassis/suspension
characteristics of your motorcycle
and h6W you nde it.
Taking it from the top, no
motorcycle or rider can be any better
than the tires you put on the road. The
contact patch between tire and road is
all that stands between you and instant
disaster. So, let's get a working idea of
how much force this patch will
withstand before breaking loose. The
simplest way I've found of rating
cornering capabilities is in terms of
"g's" (Le., multiples of one gravity) the
same way we rate acceleration and
braking capability. If a set of tires can
generate a cornering force equal to the
weight of the machine, you've got a
"one g" capability. If a force equal to
3/4 the weight of the machine will
break it loose, you've got 3"14 g
capability and so on.
The, best there is, around 1.4 to 1.5
g's, is generated by the topline racing
cars with appropriate tires. A factory
prepared road racing bike on Goodyear
racing tires or equivalent rubber hangs
in there also, maybe slightly less. On a
good well prepared street bike with the
best available rubber you can approach
(or momentarily exceed) one g. So let's
use one g as a typical figure. Note:
We're talking about running on good
high traction DRY pavement. Wet,
rough or ,oily surfaces can cut you to
less than 0.2 g. This is where the fun
comes in.
OK, let's asSUl1lt you got the rubber
and you got the good pavement. Where
do we go from here? I have a little
formula; see Fig. 1. It works as long as
you plug in the right numbers: Radius
in feet and speed in feet per second.
You then have to convert back to miles
per hour (60 mph is 88 fL/sec.). If
you're an algebra freak you can use it
several ways. You can figure the g's you
need to pull to enter a given curve at a
given speed. Or, if you know the g limit
of your tires, you can figure how fast
you can take a given curve. If you're
speed you can make through there is
limited by the radius of the curve at
that point. Anything you can do to
increase the radius (or decrease the
curvature) of your own path will get
you more speed. Under racing
condi tions this means entering the
corner at the extreme outside edge of
the road, coming in a smooth arc to clip
the inside verge near the middle of the
corner, then drift toward the outside as
you exit. On the open road, you with
your motorcycle can play this game
mentally lazy use the graph in Fig. 1.
Pick the line that comes closest to your
g limit and for any given speed you can
pick off the graph the tightest radius
you can handle at that speed. Or vice
versa. For a given radius you can pick
qff the maximum speed you can hang it
with.
We'II use the chart when we get to
this business of racing line. If you go
through a corner in one steady curve,
right in the middle of your lane (as a car
must due to its width), the maximum
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