bicycle mechanics and repair decal mechanical engineering 98/198 spring 14 lecture 7

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.