The ceramic parts of ceramic bearings
are the perfectly round balls.
THE BEARING OF KINGS
What is the deal with ceramic ball
bearings? Wouldn’t they be perfect
for motocross bikes?
Ceramic bearings are actually
hybrid bearings because only the
balls are made from the nonferrous
ceramic material (although there are
ceramic races, but only for special
uses). Everything else on the bearing
is identical to a standard bearing.
The ceramic bearing ball is formed
through the action of heat, just like
making a ceramic coffee cup. A
ceramic ball begins as a fine silicon
nitride Si3N4 powder. Under heat
and extreme pressure, the Si3N4
powder is formed into a bearing
ball. The key to its toughness is the
spherical shape; it perfectly contains
the high-pressure innards. A ceramic
bearing ball has twice the Rockwell
hardness of steel. Once shaped into
a ball, it is the third-hardest material
known to man, following diamond
and cubic boron nitride.
A ceramic bearing ball is two-thirds
the weight of a steel ball. The surface
of the ceramic ball is nonporous and
mirror-like. In comparison, a magnified steel ball looks like the surface
of the moon. Ceramic is not an oxide
and thus cannot rust. The synthesized ball is very resistant to wear
and abrasion. It also has very low
deformation under load and very low
thermal expansion. By themselves,
the ceramic balls are so smooth and
glass-surface perfect that they do not
need lubrication. But, the steel races
they ride in do.
A Si3N4 ceramic ball is 1000 times
more precise than a steel ball and
is preferred in high-precision CNC
machinery. Ceramic bearings are the
choice where excess bearing heat,
due to high shaft speed, is an issue.
The spin rating of some ceramic
bearings is as high as 300,000 rpm
and easily 10 times faster than the
best steel ball bearings.
As far as motocross use goes, some
factory and privateer teams do use
ceramic ball bearings. As a rule, they
use them in places where the light,
ultra-smooth and perfectly round
balls make it easier for the bearing
to accelerate. The light and smooth
balls spin without hesitation or drag.
By reducing bearing drag, you create
horsepower. A ceramic bearing here
and there, like on the crank, won’t
make much of difference. But, the
cumulative effect of ceramic bearings
on every turning spindle, axle and
shaft in the drivetrain, as well as in
the wheels, can make a noticeable
difference. Used in unison, they could
reduce friction by 1 to 2 percent,
which may not sound like much, but
that could equal a half-horsepower
gain on a 250 four-stroke. That is an
easy horsepower gain.
It is, however, not a cheap horsepower gain, because ceramic bearings cost three times more than the
most expensive steel bearings. For
example, a steel crank bearing will
cost $20, while a ceramic bearing
will run $85. For a factory team, the
cost of ceramic would spread across
four race bikes and eight engines (at
least). And since those race bikes are
typically torn down every two hours,
the cost could run to several thousand dollars in a 29-race season.
Cutting a spring does more than just
make it shorter.
FOR SHORT PEOPLE
I am on the short side—very
short —and want to make my bike
lower. I tried cutting the
seat foam, but that was very
uncomfortable. Now I am thinking
of cutting the shock spring. How
much do I cut off to lower the
bike by 2 inches?
Whatever you do, do not cut
your shock spring in an attempt
to lower your bike. Cutting the
spring might well let the shock
sag down further, but the spring
rate will get so stiff that you
will hate it more than your
uncomfortable seat. If you cut a
250 psi spring in half, you turn
it into a 500 psi spring. We are
pretty sure that you will not be
happy with a very stiff spring.
Your cheapest option is to slide
the forks up in the clamps
15mm and run the shock’s race
sag at 110mm. If you are willing
to spend money, any suspension
company can shorten your shock
(with an internal spacer).
Your Suzuki RM250 does not need a
$30 spark plug.
THE 430 SPARK PLUG
I have a 1996 RM250, and
the stock spark plug is an NGK
R6918B- 7. My dealer wants over $30
for this plug. What should I do?
Suzuki spec’ed this special
R6918B- 7 plug from 1996 to 2001,
but very few racers ever used the
ultra-expensive plug. Instead, they all
ran a BR8EG. You should be able to
find this plug for around $6.