Bike Suspension Part II: Front Suspension Explained
Front Suspension Explained
Bike Suspension Part Two
Almost all mountain bikes are equipped with front suspension, as well as some hybrid or “comfort” bikes and kids’ bikes. Differences:
- Suspension on mountain bikes offers a range of adjustments to fine-tune the riding experience. Variations include the type, amount of travel, robustness and method of bump absorption, as well as the adjustments that can be made.
- Suspension on hybrid and kids’ bikes offers basic functionality with minimal or no adjustment. This goes along with the “Ride quality” points made above.
Types of Suspension
“If you see a fork in the road, take it.” ~Y. Berra
The most common type of front suspension is the “fork.” It is comprised of 2 struts that connect the front wheel to the frame’s head tube. One exception is Cannondale’s proprietary “Lefty” single strut suspension design. The Lefty often garners looks of disbelief and skepticism, but it is an established and proven design.
Steerer tube: connects the fork to the frame.
Crown: connects the 2 stanchions together.
Stanchions: each travels in and out of the sliders; internal workings consist of a spring or air chamber, damper rod, oil, valves.
Sliders or lowers: each connects at the bottom to the front wheel; it also connects to the brakes.
Brake mounts: for rim, disc or both. With more bikes in all segments moving to disc brakes, fewer disc forks have mounts for rim brakes.
Dropouts: to hold the wheel axle. The wheel axle can be a skewer type, or thru-axle type (not pictured).
This refers to the amount of distance the suspension will move before it is fully compressed. Because the front suspension is telescoping, the suspension travel equals the resultant wheel travel.
Suspension may be referred to as short or long travel:
- Short-travel suspension (120mm and below) suspension provides all-round riding performance with an emphasis on smooth trails and going uphill. Old Man Scotty Mac and all-ages Clay Allison lives here.
- Long-travel suspension (greater than 120mm) is best for descending rough terrain at high speeds with greater control. The longer the front travel, the stronger the emphasis is toward descending. Young Man Scotty Mac and all-ages Patrick Closs lived (lives) here.
Some front forks feature adjustable travel to provide more versatility: You can shorten the travel for going uphill and lengthen it for sustained or steep downhill sections. Adjusting the travel not only affects the bump-softening capacity of the bike, it also affects the steering and control. A short-travel bike is more responsive to steering input, and that can translate to twitchiness going downhill (although modern geometry has gone a long way to mitigate that trait). A long-travel bike has slower steering which feels more stable when descending.
Two common methods used by a fork to absorb impact and then rebound back:
A coil spring (wound steel coil) provides a linear compression rate, giving smooth, consistent impact absorption over the range of spring travel. Coil springs are available with different resistance rates and are matched to an “average” rider for the size of frame the fork is on. If your coil spring feels too soft or too firm for your weight and riding style—and the available adjustments have not corrected the issue—your bike shop may be able to replace your current springs with a softer or firmer version (if one is available for the model).
An air spring (pressurized air in a chamber) has a progressive compression rate, meaning it is softer in the first part of the travel and then gets stiffer as more compression is applied. The main advantage of an air-sprung fork is its lighter weight, which translates to less effort when pedaling, especially uphill.
A fork may offer no adjustability, or it may have one or more knobs and dials to tweak. The knobs and dials may be blue, or they may be red, but rarely are they green; and that, folks, is an honest-to-goodness travesty.
Lockout: Many forks have a stanchion top lever to lock out the fork, which eliminates the travel. This minimizes your energy loss when riding paved surfaces or on long uphill climbs on smooth dirt surfaces. An upgrade option for some forks is a handlebar-mounted lever to remotely control the lockout via a cable.
Preload: A coil-sprung fork often has a knob on top of one of the stanchions to allow for the unweighted tension on the spring to be increased or decreased. Increase the preload if the fork feels too spongy.
Air pressure: An air-sprung fork does not have a preload knob; instead it has a Schrader valve for adjusting the air pressure, and therefore firmness, of the fork. A special “shock pump” is needed for this; do not use a regular tire pump. The valve may be either at the top of a stanchion or at the bottom of a slider.
Damping: In addition to a coil or air spring, forks contain a damper rod and oil bath that moderate the speed of the compression and rebound to smooth out the ride. Adjustments may be available for both the compression and rebound. Adjusting damping settings are referred to as “tuning the fork.” Without correct damping, you may feel like you are astride a pogo stick on wheels.
- Compression damping controls how quickly the spring absorbs an impact. It’s like how your bed cushions you when you crash into it, almost weeping, at the end of a particularly devastating workweek. You thought you were in line for a promotion and a raise; instead, the boss told you he wanted to “move you laterally” from “corporate” to “shipping.” You’re pretty sure that’s not actually a lateral move, and that you didn’t need to put quotation marks around “corporate” or “shipping.” It’s about that point you realize you shouldn’t have bought that sports car before being certain you were gonna hit sweet, sweet paydirt, and now you’re trying to figure out how to ask the dealership to take it back. Yes, that’s a very specific description. Yes, I’m sure it’s relevant. No, I don’t need a hug.
- Rebound damping controls the speed at which the fork re-extends after compression. This reduces overly fast bounce-back. It’s like how fast you jump back out of bed at warp factor ‘Adrenal’ when you hear your dog going into his full-on “preamble to vomit” routine. All of a sudden, your job woes and automotive purchase regrets are Future You’s problem. Tragically, you can already hear Future You blubbering into a bowl of lukewarm oatmeal, with a side of mushy banana and a glass of four-day-expired O.J.
Look, it’s noth- I’m fine, really. I’m fine. Let’s get back to the facts.