Originally posted by Tuschinski
The PSI difference is a bit big here, but my experience is that the suppler you keep your body (is this english?) when you go down a hill, the faster you go. You keep more control, so you can react better and take curves faster. Cramping up because of the high speed results in less control.
The problem with your equation here that it doesn't just involve suspension, but also resistance. I don't think Sheldon's statement can't be tested like that.
Dear Tuschinski,
I agree with you and Sheldon that suspension
improves cornering, braking, and pedal-powered
acceleration, all of which depend on traction,
which is improved by suspension.
Putting your weight on the pedals with your
knees flexed suspends most of your mass
from a long pair of possibly triple hinges
(ankles, knees, hips), which is more supple
than the immobile ischial bones of the pelvis
pressing down on a narrow bicycle seat.
So putting your weight on the pedals and
letting your ankles, knees, and hips absorb
and damp some bumpiness will help keep the
tires on the road for cornering, braking, and
pedal-powered acceleration. (The last not
being likely to matter on pavement except
in our more extreme fantasies--few of us
can hope to break the rear tire loose on
pavement by stomping on the pedals, even
on a bumpy paved road.)
But this is suspension in the sense of two
mechanical actions, first a movement of
two parts of the mass of bicycle and rider
( the bike rising when it hits a bump while
your knees bend to absorb the shock, or
your knees extending when the bike falls
away after a bump) and then some damping
(no complicated hyrdaulics are needed, since
human joints aren't very springy).
But whether your "suspension" involves
a coil spring and a hydraulic damper, your
legs, or just soggier pneumatic tires, the
improved traction always comes at the cost
of increased inefficiency--it takes energy
to work suspension units, energy that
otherwise would increase the rate at
which I hurtle down a long, dull, straight
hill.
This is one reason that bikes with suspension
sometimes come with lock-outs. Going uphill
on pavement, riders stomping on the pedals
notice a pogo-stick or trampoline effect. The
bike moves up and down on the suspension,
wasting some of their effort. Disable the
suspension, move toward rigidity, and the
suspension losses vanish.
So I expect that for a straight downhill roll,
clutching your bicycle as tightly and rigidly
as possible would be faster than any
relaxed, jiggling posture suitable for
cornering and braking.
Let's go the other way. Imagine two
large spheres, both the same size,
each with a thick outer shell and
enough neutral ballast so that they
weigh the same.
One sphere has a rubber coating that
gives as it rolls down the hill, the most
primitive form of suspension possible.
It flexes somewhat and gives a smooth
roll.
The other sphere is steel. It bounces
harshly, compared to the rubber sphere
of the same mass and size.
Which reaches the bottom of the
hill first?
Carl Fogel