bicycle suspension technology zach pihl phy-195 senior seminar in physics
TRANSCRIPT
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Bicycle Suspension TechnologyZACH PIHL
PHY-195 SENIOR SEMINAR IN PHYSICS
http://www.wallsave.com/wallpaper/1024x768/mountain-bike-fever-125949.html
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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
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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
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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)
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Forks and Rear Shocks: Major Manufactures
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Forks and Rear Shocks:Terminology
Travel
Preload
Sag
Solo Air
Dual Air
Rebound
Lockout
Compression
Floodgates
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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
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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
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Coil Springs vs. Air Springs
vs.
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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
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Coil Springs
y = kx
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Air Springs
y = k1*ln(x) + k2
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Solo Air and Dual Air
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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
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Rebound: Graph
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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
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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
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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
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Summary Example:
Fox 32 F-Series
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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
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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
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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
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The “Brain” Explained
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The Future
Suspension technology will continue to get… Lighter
More durable
More efficient
More versatile
More tunable
Less expensive (trickle-down effect)
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“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