Bicycle Suspension TechnologyZACH PIHL

PHY-195 SENIOR SEMINAR IN PHYSICS

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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

Advantages Disadvantages

durable heavy

Consistent under heat

not very tunable

Low maintenance

Advantages Disadvantages

lightweight inconsistent under heat

Very tunable Require more maintenance

Air Springs

Coil Springs

y = kx

Air Springs

y = k1*ln(x) + k2

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 Goals1. 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