The Wheel Caitlin Quinn

Front wheel diagram Hub and brake drum assembly Circlip Spoke Bearing Rivets Lining Shoe Plate Nut Nut Nut Lever Spring Shoe Dustcap Bearing Spindle Spoke Nipple Ring Rim Spring Cam

Rear wheel diagram 6) Sprocket Most of the parts of the rear wheel are either identical or very similar to corresponding parts of the front wheel. Highlighted in this diagram are three parts of the rear wheel that are not present in the front. The sprocket (#6 on the diagram) is the gear on the rear wheel that holds the end of the chain. The number of teeth on the sprocket affects acceleration, revolutions per minute (related to fuel economy), and maximum speed. (These are determined by the gear ratio of teeth between front and back sprockets.) The chain adjuster (#25 on the diagram) helps attach the wheel to the frame and control the tightness/slackness of the chain. The speedometer (#28 on the diagram) uses a magnet and the rotation of the speedometer cable to measure speed. 25) Chain adjuster 28) Speedometer

Drum brake Pads Springs Shoes Brake cable is pulled taut (either with the brake pedal or the hand brake), pulling the brake lever (see preceding diagrams) and causing the brake cam to turn. This forces the two brake shoes, connected by the springs, to separate, and the brake pads (also called linings) press against the inside of the hub, creating friction. This causes the wheel to slow and eventually stop. Cam http://www.cyclechaos.com/images/f/f1/Drum1.jpg

Drum brakes Advantages Disadvantages Water-resistant Low-cost and -maintenance Disadvantages Less effective in high-heat/friction conditions (like braking when going downhill with a heavy load) Susceptible to brake fade over a period of time

History of drum brakes First drum breaks premiered in 1900 with asbestos lining. Mid-1930s — fluid-filled cylinder with pistons began to replace cam (though our bike still uses the purely mechanical lever/cam system). 1960s and ’70s — disc brakes began to replace drum brakes. Drum brakes are still common as part of a front- disc/rear-drum brake configuration. Drum brakes premiered in 1900. Early lining was made of asbestos. Starting in the mid-1930s, some drum brakes started to use a little fluid-filled cylinder bookended by pistons to force the brake shoes apart instead of a cam. However, our drum brakes have the original mechanical system of the lever and cam. Disc brakes — calipers straddle two brake pads separated by a rotor (which spins with the wheel). When brake pedal is applied, brake fluid and an internal piston force the pads together, “hugging” the rotor, which creates friction and forces the wheel to slow and eventually stop spinning. Modern drum brakes use a hydraulic cylinder and pistons that forces the brake shoes apart (against the brake drum) instead of a turning cam.

Drum brake with cylinder and pistons This is the type of drum brake that premiered in the 1930s. Our bike does not have this type of drum brake. http://s.hswstatic.com/gif/drum-brake4.jpg

Truing the wheel: Process Start by assembling the hub (brakes, bearings, plate, etc.) and mounting the wheel on a truing stand. The wheel can be laterally and/or concentrically untrue. Both our wheels were concentrically true, so they only needed lateral adjustment. Tightening right-side spokes shifts (that portion of) the rim to the right, allowing for minute corrections of lateral wobbles. Use spoke wrench to tighten/loosen spokes at the nipple. Overtightening will cause spokes to become stripped inside the nipple, which renders them unadjustable. Then they will be much slacker than the others and present difficulties in truing. (The tire must be removed in order to replace spokes. Not worth it for us.) When struck lightly with a metal object, properly tightened spokes sound “right,” like a musical ping, and you can hear the difference between a tightened spoke and one that has been stripped and is now slack.

Truing the wheel: Difficulties Warps and dents in the rim cause wobbling that can’t be corrected by spoke adjustment. The rim of the rear wheel is more susceptible to damage than the front. Stripped spokes cannot be tightened and must be replaced.

Exercise: a single spoke Imagine entire weight of motorcycle is supported by one steel spoke. What is the minimum diameter of the spoke if the breaking point of steel is 100,000 psi? 200 lbs. bike + 200 lbs. rider = 400 lbs. of downward force total, or 200 lbs. per axle σ = F/A 100,000 = 200/A A = 0.002 in2 (We assume spokes with circular faces)

Single spoke with safety factor Introducing a safety factor of 2 would halve the breaking point of steel, so new σ = 50,000 psi. 50,000 = 200/A A = 0.004 in2 (i.e. double what it was originally) Minimum spoke diameter = 0.03568 inches

On our motorcycle Spoke diameter varied between 0.104 inches and 0.130 inches (newer spokes were thicker) For the thinnest spoke: A = πr2 = 0.0085 in2 So the area of the spoke face was more than double the minimum, even with a safety factor of 2.

Sources http://www.cyclechaos.com/images/f/f1/Drum1.jpg http://www.edmunds.com/car-technology/brakes-drum-vs- disc.html http://www.slowtwitch.com/Tech/Wheel_Truing_How-To_3503.html http://en.wikipedia.org/wiki/Drum_brake#History http://s.hswstatic.com/gif/drum-brake4.jpg