User Guide

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Larger wheels provide stability
This last statement depends somewhat on
the bike design. As an example, the high
wheeler had a well-deserved reputation for
being easy to pitch forward. The reason for
this lies in the location of the rider’s center
of gravity relative to the pivot point when
they pitch forward (Fig. A4). Pitching over
the bars is not limited to downhills, but can
occur any time the forces holding the rider
behind the axle are less than the forces push-
ing them forward. So a sudden deceleration
on the flats can make a rider pitch, much
like flipping over the bars on a steep descent.
Unless the front brake is locked up, the pivot
point for the flip is the front axle.
In the case of the highwheeler, the rider sat
quite high and well forward. Their center of
mass was only just barely behind the front
axle. With this position, it took little force to
push them forward over the axle.
However, for this discussion we’re talking
about two modern mountain bikes that have
only a slight change; a different wheel diam-
eter. The bottom bracket is the same height
from the ground on a 29er as on a bike
with 26” wheels, so the rider’s center of mass
hasn’t changed location. The only real differ-
ence is the larger front wheel has a higher
pivot. It takes more force to push the rider
forward over this higher pivot (Fig. A5). The
larger front wheel makes the bike more sta-
ble as it runs over small obstacles that cause
a deceleration of the bike, and this makes it
easier to descend. On the Fisher 29ers you’ll
notice this effect mostly on steeper downhills.
You won’t have to slide back in the saddle
as much to feel stable. This also means you
can stay in the ‘power position’ for effective
pedaling, so it even helps on the uphills!
Longer forks make a bike more stable
Trail is the distance from the tire contact
patch to the center of the steering axis where
it meets the ground. If the head angle and
fork offset remain constant, a larger wheel
diameter increases trail (Fig A5).
Trail is what allows a bike to run in what
we perceive as a ‘straight’ line. Its actually
not straight at all, but instead a constant
series of wiggles. These wiggles occur as the
bike tries to maintain a state of equilibrium.
Here’s how it works. As a bike is tipped to
the side, the front tire contact is moved to
the side. You can try this; simply lean your
bike to the side and watch what happens.
The front wheel turns in the direction of the
lean. With forward propulsion, the bike turns
toward the lean and lifts the bike back into
an upright state of equilibrium (not really
balanced, but trying to balance).
The reason the bike steers into a lean is
trail. As a bike is leaned, the contact patch
is no longer in line with the steering axis,
but to the side. This puts a torque about the
steering axis, which turns the handlebars.
The more trail there is, the further the con-
tact patch is from the steering axis, and the
stronger the steering effect as the bike is
leaned. Consequently, the more trail there is,
the more forceful the centering of the bike
when its leaned, so the more stable it is.
On the Fisher 29ers you’ll notice this effect
mostly as a ‘steady’ feel as you head down
the trail. The handlebars seem quiet, and as
a result your hands and forearms can relax.
Want to make the bike turn quickly? Just lean
it over, engage some of the front tire’s massive
side knobs, and rail it through the turn!
Larger wheels are faster
For every 35% increase in wheel diameter,
there is a 20% decrease in rolling resistance
Fig. A4
Fig. A5