Twenty-fi rst century casting tech-
niques prevent such entrainment,
producing parts that are strong and
fatigue-resisting even in thin sec-
tions. Count the welds in produc-
tion-cast aluminum chassis on the
fi ngers of one hand.
As rpm of peak power has risen,
better materials for reciprocating parts
have been adopted. The alternative—
thicker parts made of lower-spec ma-
terials—would bring increased bear-
ing loads and friction loss.
Before today’s “upside-down”
forks with their larger tubes on top,
Yamaha stiffened the convention-
al tubes of its Daytona-dominat-
ing TZ750 racer by making them 5
mm thick. Heavy! Tubes gain stiff-
ness much faster from increased di-
ameter than from thicker walls, so
today’s fork tubes are lighter—big-
ger in diameter, thinner in wall. Top
tubes today are aluminum for pro-
duction, carbon fi ber in MotoGP.
Same with axles—in times past,
axles were ineffi cient structures be-
cause they were small in diame-
ter and solid. (Material at the center
makes essentially zero contribution
to stiffness, yet adds weight.) Axles
are now larger in diameter, hollow,
and much stiffer.
The coming of cast or forged
wheels and tubeless tires has made
it possible to chuck 3 pounds of
unsprung weight per wheel—be
gone, ye inner tubes.
When disc brakes arrived in
1969–73, they were over-designed,
but as experience accumulated,
they shed weight. A certain brake
caliper of that era came across the
scale at 4.5 pounds but today’s
all-aluminum MotoGP caliper from
Brembo is just 22 percent of that.
(No more aluminum-lithium 8090
alloy—that’s been banned.) And
in the real world? A Tokico six-pis-
ton caliper at 3 pounds and a Nis-
sin four-piston at 2.5 pounds. Early
steel discs were 7 mm (.276”) thick,
weighing 7 pounds apiece. I just
measured one of a pair from the
Kawasaki ZX-6 family at only half
of that. Everything that spins up
front—tire, wheel, brake discs—in-
creases steering effort, so the light-
er the better.
The 1984 switch from bias tire
construction to semi-radial—followed
15 years later by the fl exible auto-
mation of tire building—has saved
weight there as well. Multi-ply tires of
the bias era generated more heat and
faster wear from the fl exure of their
thicker structure; are you old enough
to remember four-ply and six-ply
auto tires? Twelve-ply truck tires? Ra-
dial construction reduces heating by
requiring less material.Thanks to the widespread adoption
of powerful rare-earth magnet alloys,
electric starters have become tiny—
you can almost hide one in a fi st.
Cylinder castings used to be sepa-
rate from crankcases, and on sport-
bike engines they carried four iron
liners. Today’s engines save 6 or
more pounds by hard-plating—
Nikasil, SCEM, etc.—directly on the
aluminum cylinder casting and de-
leting all that iron. Engine stiff-
ness is increased by casting the
cylinders and upper crankcase in
one self-bracing piece. (Rob Muzzy
said in 1981–82 that Z1-crank-
case fl ex destroyed base gaskets.)
What about the cylinder rebores we
thought were normal every 15,000–
25,000 miles back in the 1970s? Su-
perior oils, liquid-cooling, and elec-
tronic engine controls have all but
stopped cylinder wear.
Even drive chains have lost
weight—before O-ring chains
brought reliable internal lubrication,
giant 3/4” pitch chains were the in-
dustry’s answer—with 1950s-style
drip-feed lubricators. I just weighed
two 5/8” pitch chains at 6 pounds
and 4 pounds
Those big 1970s air-cooled jobs
were heavy—engines of more than
210 pounds and curb weight 540.
Compare the modest 80 or so
claimed horsepower of those days
to the 214 Ducati claim from the
144 pounds of its 1100cc Panigale
V4 engine, with 436 pounds curb
weight. Okay, yes, power and light-
ness have increased in 46 years. Q32
Number of valves in Honda’s
oval-piston, four-cylinder NR1
Weight in pounds of a modern
MotoGP Brembo front caliper.214
Claimed horsepower made by the
Ducati Panigale V/ BY THE NUMBERS/
Everything
that spins up
front increases
steering effort,
so the lighter
the better...
TDC / ISSUE 3 2019 / 19