Bicycle Mechanics and Repair Decal Mechanical Engineering 98/198 spring 14 Lecture 7

Components Rims Hub Nipples Spokes

Types of Wheels

Rims Hook Braking Surface “Clincher” tire. Tensions spokes uniformly. Provides surface for brake pads. Spoke holes

Increases Wheel Strength And integrity ↔ Tubular (tubie, tubs, sewups) Vs Clincher (hook-rim, wire-bead)

Hubs Holes 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

CompressionTension Good in compression Poor in tension Good in tension Poor in compression Concrete Rope

Spoke in Tension and Compression Good in TensionPoor 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 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 Dish (centering)

Truing Basics Check the damage Nut-Bolt Spoke nipple - nut Spoke – screw/bolt Check tension of all spokes

How to Fix a Wobble-Nick Find your wobble Know what is “center” Spoke adjustment Tightening pulls rim Loosening 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.