Different lines: Every rear-suspension design (and the execution of the design) has a different take on how to give the rider a firm suspension for pedaling while still softening up enough for taking the hits. Knowing how to ride each one can unlock their hidden performance and make you a better rider.
Longer-travel trailbikes have brought a
new level of comfort and control to
riding. With the extra inch or two of
rear-wheel travel, however, there is always
the possibility of too much of a good thing.
Suspension movement due to pedaling
efforts (instead of activation due to the trail
surface) can have many riders questioning the
logic of all that travel.
Luckily, almost every dual-suspension
mountain bike priced over $800 has some
type of technology—be it a shock setting or
a suspension design with a mechanical advantage—that helps to minimize pedal bob.
“Pedal platform” is the blanket term for
any of several strategies, both hydraulic and
mechanical, that are used to prevent a bicycle’s suspension from compressing with each
successive push on the pedals without
restricting the system’s ability to react to
bumps. To get the most performance and
pedaling efficiency from your system of
choice, you need to use a specific riding technique. Don’t be intimidated. Our techniques
are easy to apply, and you are probably using
some of them already.
Many early dual-suspension riders had one choice for
adjusting their compression. They either ran an ultra-stiff
coil spring or pumped air shocks to a seal-blowing psi level.
They quickly found that while this kept the shock from
being affected by pedaling forces, it also kept the shock from
responding to bumps. It was like riding a hardtail, only
heavier.
Shock designers worked around this anti-suspension
option by using hydraulic trickery (usually a valved compression piston) that would resist low-frequency input, but
would flow a large volume of fluid once it was popped open
by a significant impact. Call it ProPedal or CTD (Fox),
Motion-Control (RockShox), Lock Up (Marzocchi), Dual-Range Compression (Manitou) or simply compression
adjustment (X-Fusion), these pedaling-platform shocks were
developed so riders could run a good amount of sag without
feeling like they were pedaling a pogo stick.
How to Tune Them
Most pedaling platforms are fixed at the factory. Some
more expensive shocks allow you to select a level of plat-
form (or compression resistance) with the flick of a lever or
dial. Either way, start by setting the shock sag at 20 percent
of its stroke using spring preload on coil-over shocks and air
pressure on air shocks. If you don’t know how to set sag,
grab your December 2011 issue (you keep all your issues,
don’t you?). Our “Garage Files” explains how to set sag.
Free movement: Trek went to great lengths to design a balanced rear suspension that doesn’t need the mechanical advantage of complex linkages to produce a firm pedaling platform. Properly adjust- ed, this is a great pedaling and descending rear suspension.
Don’t be fooled in the garage. Test ride the shock to verify your sag, because the shock may not settle completely when
it is static. Platform shocks can feel mushy with impossibly
slow rebound, but this is a byproduct of the internal valving
and should only occur when the bike is not moving and the
damping circuits are closed down. Once open, the valving
allows the shock to move freely. Tune the compression
clicker to be soft enough to get full travel on big bumps at
singletrack speeds and with the least amount of rebound
damping that will still prevent bouncing when you land a
jump.
How to Ride on a Platform
Pedal in the saddle as much as possible, and use a smooth
cadence when you are out of the saddle. The compression
valve is only able to resist bobbing when it is shut. Once it
pops open, the high volume of fluid that escapes past the
valve keeps it open until the next compression cycle. Learn
to feel the threshold with your leg muscles and meter your
power to keep from overcoming it.
Read the trail: There are times, like on a rocky ascent, when you should be less concerned with the pedaling platform and more concerned with the bump-absorbing suspension. Many climbs are easier to clear with no platform.
When you jump out of the saddle, try to balance your
weight more over the middle of the bike instead of leaning
over the fork and sawing away at the handlebar like a road
rider. Keeping centered will distribute the downward
thrusts of your pedal stroke between the shock and fork.
Avoid leaning over the fork when you accelerate (an old-school trick that loaded up the fork and unweighted the
shock to make both pedal firmly). You don’t need that trick
if your shock is adjusted properly.
No-brainer: Specialized’s Brain platform allows the rider to just ride. The Brain Fade feature (the blue knob on top of the Brain’s cylinder) adjusts the amount of platform. This is a set-it-and-forget-it adjustment.
Specialized Brain Shock
Fox and Specialized developed an inertia
valve that separates downward force generated
by the rider from upward accelerations caused
by bumps in the trail. The “Brain” shock is
exclusive to Specialized bikes. The inertia valve
is a spring-loaded weight that closes off the
compression circuit. When the tire rolls over a
bump, the motion slides open the weight, and
the suspension is set free. A downward thrust
from the rider, like a pedal stroke, slides the
weight closed and makes the bike pedal as if it
were a hardtail. A delay retards the speed of the
inertia valve, so the suspension can compress
over a bump while you are pushing down on a
pedal. In this mode, the inertia valve damper
still feels rigid, because the downward push
on the pedal is countered by the upward
acceleration from the bump.
How to Tune It
The Brain shock will not compress when the
bicycle is stationary, so you must ride around to
activate the suspension. Then, make incremental adjustments to set the proper spring rate
and damping adjustments. As with all stable-platform suspension, set the shock or fork to
ride as supple as possible, just stiff enough so
the suspension sags between 20 and 25 percent
into its travel.
Some Brain shocks have a “Trail Tune”
adjustment that allows you to dial in the
sensitivity of the inertia valve. This is a rider
preference, and the wrecking crew is all over
the board on this adjustment. Some feel that
you should run the Brain at the firmest setting,
while others want a more traditional rear
suspension and dial in more movement.
It is an easy adjustment that encourages
experimentation.
The inertia valve tends to make the rear
suspension ride high. Try to increase the fork’s
ride height with additional preload or spring
pressure to compensate for the tall-riding
shock. Use an O-ring or a zip-tie to gauge your
sag measurement and to ensure that you are
achieving full travel. Avoid running the
suspension too stiff to hedge against bobbing;
the inertia valves do that job so well that even a
moderately stiff spring setup may prevent full
travel.
How to Use Your Brain
Just get on and pedal. The Brain shock rides
hardtail-firm in any pedaling mode—from
dainty spinning to big-gear mashing.
Mechanical Advantage - Designed for Resistance
While the two previous examples rely solely on the
shock to control suspension bobbing, many suspension
designers have come up with mechanical solutions to
keep bobbing in check. Brands who follow this route on
some of their models include Niner, Giant, Pivot, Ibis,
Intense, Turner and Santa Cruz.
Damage control: Staying in the saddle and spinning smoothly is great advice that no rider can follow all the time. When you do need to leave the saddle, stay centered (like Cody here) with your torso low.
While each design is unique enough to carry patents,
they generally work with a pair of links instead of a
normal swingarm pivot to move the rear wheel in an
S-shaped path that angles backwards, away from the
cranks. Chain tension created by pedaling counteracts
suspension bob by opposing the rearward movement of
the swingarm. Hitting a bump momentarily overwhelms
the chain tension’s effect on the swingarm and
compresses it past the center of the “S” path where the
suspension is free to move through the remainder of its stroke.
The drawback to many mechanical platforms is that you don’t always have a way to tune around it if, for
example, you are looking for a softer beginning or
middle travel. Riders may also detect chain growth
(a slight pushback from the pedals) on certain
mechanical-advantage designs.
How to Tune It
Read the instructions. To properly set up a mechanical-advantage suspension, you must set the sag spot-on.
Every linkage has a slightly different wheel path, so the
sweet spot—where the suspension rides right where
pedaling pressure will resist bobbing, but not completely
freeze up the suspension over bumps—varies between
models and brands. Pivot takes this so seriously that
every bike is delivered with a sag tool to help measure
the perfect setting.
Start where the bike company recommends in their
manual, and experiment with softer and stiffer preload
settings to determine which provides the least amount
of movement when you are pedaling. Outside of sag
guidelines, tune the shock the same as you would any
conventional shock. That means you need to set the
clickers to minimize compression and with enough
rebound to keep the seat from pushing up after you
smack a big low-speed bump.
Be Mechanical
The small amount that a mechanical-advantage design bobs at low-power outputs doesn’t amount to a
measurable waste of power, but it can feel a tad sluggish.
Use the linkage to your advantage. Maintain your
momentum by standing up to power over short hills.
When you are soft-pedaling, concentrate on a smooth
cadence. Stay away from using the firm settings of
pedaling-platform shocks. In many cases, you won’t need
any type of platform shock to make this rear suspension
work properly.
Again, read the owner’s manual. Companies that
employ a mechanical-advantage rear suspension have
spent a great deal of time testing the shock’s valving to
work with their design. You have to set the shock to
their recommendations to get the best performance out
of the system.
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