Know Your Suspension

A look at what makes your bike bounce and what keeps it from bouncing
By: Jason Giacchino


    Although many facets of bicycling (road mostly) still offer performance through rigid bike (suspension-less) frames, it is becoming more and more common in the realm of Mountain Biking to ride with dual suspension set-ups.  Aside from the obvious soaking of bumps on the trail noticed by your back muscles, not many riders give much attention to the physics and technology behind the performance.

   The Basics:

   Both front and rear suspension systems contain two essential pieces of hardware working in conjunction: A damper and a spring.  It is the spring that offers 'give' along the suspension travel, giving the wheel a place to go (generally upward) as it passes over an obstruction of terrain.  It is also the spring that pushes the wheel back down to the ground immediately after passing over the terrain.  However if suspension relied only on the spring, the system would be terribly unstable, as the entire wheel would continue to bounce on its own force.  The damper is how suspension disperses the stored energy within the spring, acting as a stabilizer to the suspension.

   Inside The Damper:

   Most mountain bikes rely upon oil-filled damping systems to supply the energy absorption process.  This literally means the inside chamber of the shock is filled with oil that becomes compressed (by a piston) on wheel impact- forcing the oil to pass through a tiny hole.  The energy required to push the oil through the hole (being supplied by the push or pull of the wheel) instantly transfers to heat (from friction).  Once the spring begins to recoil, the process takes place in reverse due to the vacuum in the chamber and the damping takes place again, this time battling the spring so as to keep the wheel grounded.

 Big hits vs. Trail Junk:

   As the shock is compressed faster, naturally a greater volume of oil attempts to squeeze through the hole within the chamber thus more pressure is then required to give the oil the needed push.  Because of this relationship the shock becomes stiffer and more energy can be dissipated into heat.  What this means is that as you put more compression on your suspension, the more energy it can resist.  This is what makes modern suspension supple enough to track over uneven terrain and ruts but firm enough to absorb big hits without adjustment.

   When Winter Comes:

   As temperatures begin to drop to slightly above the freezing point of water, the oil within the chamber will thicken and noticeably slow the rate of damping.  Most modern suspension offers a variety of settings to compensate however if your setup does not: Simply switch to a lighter weight oil, which will remedy the situation by flowing more freely within the chamber.