Bicycles and Bicycling - Introduction
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Assignments:
- Tuesday, 9/20: Ch 12 Kreighbaum & Smith.
Sports & Fitness Equipment Design. Also, website:
History and evolution of bicycles
- Thursday, 9/22:
• Go to one of the bicycle manufacturer’s websites (slide
23) and select a bicycle to suit your purposes
• Read PDF bicycle review article posted on courses
website. Submit 2 questions from article or other
readings on bicycle design.
Bicyces & Bicycling Introduction
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History and evolution of the bicycle
- History and evolution of bicycles
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Cycling as a sport and as an exercise
- Reference: Faria and Cavanagh. The
physiology and biomechanics of cycling
- Muscles and movements
- Physiological demands
Bicycle Frame Design Objectives
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Distribute rider’s weight appropriately
Performance - ensure transfer of power from
rider to machine
Comfort – management of forces from
machine to rider
Fit - points of contact must fit the rider:
- handlebars
- seat
- pedals
Anatomy of Diamond Frame
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Important parts: Front triangle (tubes), rear triangle
(stays), fork, lugs, bottom bracket, head tube
Types of bicycles: (1) Road bike (10-speed) touring, racing, and sport; (2) mountain, or all-terrain;
and (3) hybrid
Other Frame Types; :Ladie’s
Frame
Top tube is sloped considerably
Design Features - Height
 Height
of bottom bracket (bike’s center of
gravity)
- Lower for more stability
- Higher for more pedal clearance
 Height measurements determine size of
rider
 Frame size - length of seat tube and top
tube
Design Features - Bike Length
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Wheelbase length - (Fig 12.6)
- Shorter for quicker response, longer for more stability
(varies from 38 to 44 in)
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Chainstay length
- Shorter chainstays are used on racing bikes for more
Design Features: Frame Angles
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Head tube - steeper for rougher ride, more efficient
power transfer; shallower for handling ease and
shock absorbing, but less responsive
Rake (amount of bend in fork blades) and trail affect
steering stability. More trail equals more stability
Design Features on Different Types of
Bicycles
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Road bicycles (10-speeds)
- Touring, or comfort - long wheelbase, shallow
angles, fair amount of trail (21 speeds)
- Racing - short wheelbase, steep angles, little trail
(18 gears)
- Sport/triathlon and cross bikes - in between (100
or more miles at high speed)
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Mountain, or all-terrain
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- Fat, knobby tires, upright, sturdy frame,
suspension systems
Hybrid - Cross between road and mountain
Bicycles - Frame Materials
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Important characteristics are elasticity, stiffness, and strength
(esp st/wt ratio)
Butted and splined tubing - thicker at ends than in the middle,
with ribs inside
Steel - most widely used on cheaper bikes. Reliable,
inexpensive, durable, predictable in handling - but is relatively
heavy
Aluminum alloys - light, shock absorbent, comfortable. Newer
alloys have improved properties of stiffness and strength (e.g.,
zirconium on trek bikes (trekbikes.com)
Titanium alloys - stiff, strong, lighter, more shock absorbent but is expensive hard to weld and hard to machine
Composites - greatest strength/wt & stiffness/wt ratio - but
expensive, bonding problems. Used mainly in front fork and
stays. May fail catastrophically in other areas of frame.
Frame Materials used by Trek
Schwinn Frame Technology
Trek
Racing
Frame
Schwinn Suspension Frame
Trek Mountain Suspension
Bike
Fisher Suspension Bike
Recumbent
Bikes
Tubing design and Construction
Methods
•Lugs no longer used:
•Laser mitering
•Butted tubes – varying
wall thickness
•Splined tubes
•Diameter and shape
changes
Suspension systems
Shock absorption, or suspension
system consists of one or two elements:
spring and dampener, both may be
adjustable for both travel and stiffness.
 A suspension system may be on front
fork (FS), seat, or rear chainstay (DS)
 Review article on courses website on
suspension systems
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Sports Med Article on Shock
Absorption Systems
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Introduction
- Designed to improve bicycle comfort and handling by
dissipating terrain-induced energy
- May also dissipate cyclist’s energy through small oscillatory
movements called “bobbing”
- Three basic approaches to examine efficacy of these
systems
• Engineer’s perspective – measuring or modeling estimates of power
output loss of cyclist
• Exercise physiologist/biomechanist perspective – measuring energy
consumption/expenditure (VO2)of cylist
• Behavioralist perspective
– Ratings of comfort and perceived exertion to estimate stress
Suspension systems review
article (cont’d)
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Common suspension designs (Figure 2)
Engineer’s perspective (Figure 3 and 4)
- DS resulted in 1.3% power loss, reduced to .7% when rear
pivot location optimized (Figure 4) to same vertical height as
top of chainring
- When standing, power loss increased to 5%
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Physiologist/biomechanist perspective
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No sig diff in VO2 in smooth treadmill
DS better than FS and NS on bumpy treadmill
In time trials, FS performed better on level smooth track
On uphill courses, suspension systems seem to work better,
although results of studies don’t also demonstrate this
Behavioral perspective
- Suspension systems reduce RPE and comfort ratings
Bicycle Accessories
Drive Train -Crank, chainrings (front
driving cogs), freewheel, derailleurs
(indexed and automatic shifting are
recent innovations)
 Shoes and pedals - clipless or with
clips?
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Accessories (cont’d)
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Rims, tires, brakes
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Saddles
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Stems & handlebars
Accessories (cont’d)
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Helmets
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Gloves, shorts
Websites on Bicycles
How to select a bicycle
http://www.primusweb.com/fitnesspartn
er/library/equipment/equip.htm
 Manufacturer’s websites
- Trek
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- Schwinn
- Specialized