Bicycle Suspension Technology ZACH PIHL PHY-195 SENIOR SEMINAR IN PHYSICS

Introduction to the Bicycle  The bicycle was invented in the early 1800s  It was not until the 1990s that mountain biking became mainstream  It was around this time that bike manufacturers began to produce suspensions on a large scale  Today, the bike is often called “the most efficient machine known to man”  The amount of energy input required to ride a bike is equivalent to around 1000 miles per gallon of petroleum

Mountain Bikes: Hardtail vs. Full Suspension  Hardtail mountain bikes have only front shocks  Lighter  More efficient and responsive  More restrictions on terrain  Requires rider to shift body weight  Full Suspension mountain bikes have front and rear shocks  Typically heavier  Slightly less efficient  Fewer restrictions on terrain  Rider can have a “carefree” attitude

Riding Styles: XC vs. AM. Vs. DH/FR  Cross-Country (XC) – MTB style that involves uphill and downhill riding on a wide variety of terrains including fire roads and smooth single tracks (Hardtails and FS)  All Mountain (AM) - MTB style that involves uphill and downhill riding on a wide variety of terrains that are typically rocky and technically challenging (Mostly FS)  Downhill (XC) and Freeride (FR) – MTB style that involves only downhill riding on extremely steep and rocky terrains and involves jumps and sheer drops (FS Only)

Forks and Rear Shocks: Major Manufactures

Forks and Rear Shocks: Terminology  Travel  Preload  Sag  Solo Air  Dual Air  Rebound  Lockout  Compression  Floodgates

Suspension Travel  Travel is the distance that a shock can move from fully expanded to fully compressed  Typically, forks and rear shocks have a travel distance of anywhere from 80 mm to 200 mm with 100 mm being the most common  Some forks can be rebuilt to change the travel  A few high-end forks have travel adjustment knobs on the upper stanchions

Preload and Sag  Preload sets how much the shock sags under rider weight at a standstill  Shocks have two extreme positions: 1. Fully Extended 2. Fully Contracted  Ideally, the weight of the bike + rider should “sag” the spring by 25%  If “sag” is set too low:  Rider will experience harsh shock rebound  Pogo stick effect  If “sag” is set too high:  Rider risks shock bottom-out  Sag gradients/ zip-tie method

Coil Springs vs. Air Springs vs.

Coil Springs AdvantagesDisadvantages durableheavy Consistent under heatnot very tunable Low maintenance AdvantagesDisadvantages lightweightinconsistent under heat Very tunableRequire more maintenance Air Springs

Coil Springs y = kx

Air Springs y = k 1 *ln(x) + k 2

Solo Air and Dual Air

Rebound Adjustments  Rebound adjustments change how quickly a spring returns to its original position after experiencing a load.  Typically an infinitely variable adjustment  Example:  An Impulse of 100 lb-s will take 0.50 sec to rebound under a “slow” rebound setting  An Impulse of 100 lb-s will take 0.10 sec to rebound under a “fast” rebound setting

Rebound: Graph

Rebound: Internals  Two fluid (oil) chambers  The rebound adjustment knob controls the flow rate between the two chambers  It restricts the fluids flow to control how fast the shock rebounds

Lockout  The uphill rider’s “best friend”  Lockout locks the fork in the fully expanded position and prevents the spring from moving  Cheaper forks use mechanical lockout  Like a dead-bolt on a door  Higher-end forks use hydraulic lockout  Prevents the flow of fluid  Allows for lockout modulation  i.e. the shock can travel 20 mm and then stop  Allow for “blow-off” if a certain force is experienced

Compression Adjustments  Compression adjustments change how quickly a shock moves from its normal state to its compressed state  Speed of compression  the opposite of rebound  Some with compression adjustments also have floodgates with control the magnitude of the compression  Firmness/ softness of shock

Summary Example: Fox 32 F-Series

Ultimate Engineering Goals 1. Comfort  Less impact on the body  More confidence on the trail 2. Efficiency  Less weight  Less pedal-bob  Less brake-dive  Less rider effort 3. Versatility  Ability to go anywhere and do anything

How to Accomplish these Goals 1. Comfort:  Longer travel  Advanced preload and rebound settings 2. Efficiency  Use lightweight materials (carbon, aluminum, etc.)  Use lightweight springs (dual-air springs)  Advanced compression and lockout settings  Incorporated inertial valves 3. Versatility  Adjustable travel  More settings

Proprietary Technologies  Specialized Brain (with Brain fade)  Inertial valves  Fox TerraLogic  Inertial valves  Fox iCD  Electronically and simultaneous shock adjustments  RockShox BlackBox Motion Control  Hydraulic remote compression/ lockout adjustment  Cannondale Lefty  Fork with single stanchion/leg  conical wheel hub  Needle bearings

The “Brain” Explained

The Future  Suspension technology will continue to get…  Lighter  More durable  More efficient  More versatile  More tunable  Less expensive (trickle-down effect)

“While bicycle suspension technology continues to advance, many trail-worn riders miss the good old days of bombing singletracks on rigids—an experience that will always be remembered, yet curiously loved and missed.” -Anonymous Mountain Biker