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

1. Bicycle Mechanics and Repair DecalMechanical Engineering 98/198spring 14Lecture 7

2. Components Nipples Rims Hub Spokes

3. Types of Wheels

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

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

6. Hubs Freehub body Holes for spoke elbows • Tensions spokes uniformly. • Provides axis in which wheels rotate. • Rear hubs are threaded for a freewheel or contain a freehub body for a cassette.

9. 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

10. Compression Tension Concrete Rope Good in compression Poor in tension Good in tension Poor in compression

11. Spoke in Tension and Compression Good in Tension Poor in Compression

12. Spoke Pretension If the spoke is pretensioned, the tension has to be overcome when the spoke is compressed Pretension > Applied Compression Pretension + Applied Compression = Sum Pretension < Applied Compression Pretension + Applied Compression = Sum Spoke Collapses The greater the pretension, the greater the applied compression can be

13. Nipples • Connects spokes to the rim. • Allows for tensioning of spokes. Spoke Nipple Spoke Wrench Rim

14. A Wheel Stands on its Spokes The wheel does not hang from the top part of the rim High Tension Lower Tension Compressive force from road Only works because the spokes have been pretensioned http://www.astounding.org.uk/ian/wheel/

15. Advantages of High Spoke Tension The greater the spoke tension, the greater the compressive forces the wheel can withstand Carry greater loads Take bigger hits

16. A True Wheel • Wheels with no or very little imperfections such as wobbles or hops. • New, or like-new

17. 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.

18. Spoke Wrench • Different shapes but perform same function • Make sure it is fully on the spoke or you risk stripping it

19. Spoke and Nipple Loosen 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

20. Righty-tighty, Lefty-loosey

23. Other Common Problems • Dish

24. Dish (centering)

25. Dish (centering) • wheel must be centered between dropouts http://thebiketube.com/wheel-building/how-to-dish-bike-wheel http://www.youtube.com/watch?v=N1C2dZnUvuM

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

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

28. 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.

29. 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!!!

30. 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.