bicycle mechanics and repair decal mechanical engineering 98/198 spring 14 lecture 7
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Bicycle Mechanics and Repair Decal Mechanical Engineering 98/198 spring 14 Lecture 7. Components. Nipples. Rims. Hub. Spokes. Types of Wheels. Rims. “Clincher” tire. Tensions spokes uniformly. Provides surface for brake pads. Spoke holes. Braking Surface. Hook. Increases - PowerPoint PPT PresentationTRANSCRIPT
Bicycle Mechanics and Repair DecalMechanical Engineering 98/198
spring 14
Lecture 7
Components
Rims
Hub
Nipples
Spokes
Types of Wheels
Rims
Hook
BrakingSurface
• “Clincher” tire.• Tensions spokes uniformly.• Provides surface for brake pads. Spoke holes
IncreasesWheel StrengthAnd integrity
↔
Tubular(tubie, tubs,
sewups)
Vs
Clincher(hook-rim, wire-bead)
HubsHoles for spoke elbows
Freehub body
• Tensions spokes uniformly.• Provides axis in which wheels rotate.• Rear hubs are threaded for a freewheel or contain a freehub body for a cassette.
Spokes• Tensioned uniformly throughout the wheel.• Connected to the hub and rim.• Supports weight and other forces placed on the rim.• Threaded end connects to rim.• “Elbow” end connects to hub.•Different lengths, gauges, butted
Elbow
Threads
Compression Tension
Good in compressionPoor in tension
Good in tension Poor in compression
Concrete
Rope
Spoke in Tension and Compression
Good in Tension Poor in Compression
Spoke Pretension
Pretension
Applied Compression
Sum
If the spoke is pretensioned, the tension has to be overcome when the spoke is compressed
Pretension
Applied Compression
Sum
+
+
=
=
Pretension > Applied Compression
Pretension < Applied Compression
Spoke Collapses
The greater the pretension, the greater the applied compression can be
Nipples• Connects spokes to the rim.• Allows for tensioning of spokes.
Rim
Spoke
Nipple
Spoke Wrench
A Wheel Stands on its Spokes
http://www.astounding.org.uk/ian/wheel/
Only works because the spokes have been pretensioned
The wheel does not hang from the top part of the rim
High Tension
Lower Tension
Compressive force from road
Advantages of High Spoke Tension
Take bigger hitsCarry greater loads
The greater the spoke tension, the greater the compressive forces the wheel can withstand
A True Wheel
• Wheels with no or very little imperfections such as wobbles or hops.– New, or like-new
An Untrue Wheel
• Wheels with a slight amount of wobbles or hops that prevents even rotation.– This DOES NOT include wheels that have broken
joints, sandwiched, squashed, dinged, broken hubs etc.
Spoke Wrench
• Different shapes but perform same function
• Make sure it is fully on the spoke or you risk stripping it
Spoke and Nipple
As you are looking from the outside of the wheel into the rim, clockwise (righty) to tighten spoke.
As you are looking into the rim, counterclockwise(lefty) to loosen spoke
Loosen
Righty-tighty, Lefty-loosey
Other Common Problems
• Dish
Dish (centering)
• wheel must be centered between dropouts
http://thebiketube.com/wheel-building/how-to-dish-bike-wheelhttp://www.youtube.com/watch?v=N1C2dZnUvuM
Dish (centering)
Truing Basics
• Check the damage• Nut-Bolt
Spoke nipple - nutSpoke – screw/bolt
• Check tension of all spokes
How to Fix a Wobble-Nick
• Find your wobble• Know what is “center”• Spoke adjustment
Tightening pulls rimLoosening pushes rim
Serious Problems
• If wheel has multiple wobbles, fix worst problem areas first and repeat with other problem areas.
• Check the wheel again and make sure all spokes are properly tensioned.
How to Replace Spokes
• Remove broken spoke and rim tape• Replace nipple if needed• Pull spoke through hub• Cross spokes like other spokes• Thread into nipple and tighten• Remove cogs if necessary • Grease the threads!!!
Riding on a Bent or Broken Spoke
• Spokes provide the tension that pushes against the ground. Without spokes, the wheel will be very weak and will easily warp.
• Replace missing/broken spokes ASAP and check spoke tension regularly.