Making Sure You Don t Get Derailed in .NET

Generation QR Code ISO/IEC18004 in .NET Making Sure You Don t Get Derailed

Anyone who has ridden a bike up a windy mountain pass or into a stiff headwind appreciates the ease of shifting into the appropriate gear with a click or twist of a shifter The mechanism that makes shifting a nearly effortless activity is the derailleur To look at a derailleur, you d think that it s the most high-tech part of a bike In reality, derailleurs are simple devices designed to move the chain between the different gears Both the front and rear derailleurs are designed with a

cage through which the chain runs When you change gears with your shifter, the derailleurs force the chain to one side or the other until the chain falls or is lifted onto the chainring or sprocket next to it The front derailleur consists of a cage that, in a side-to-side motion, moves the upper part of the chain the part that transmits power to the rear wheel Because the upper part of the chain is under the force of your pedaling, it wants to stay in place It s more difficult to shift when you re applying a lot of power and moving slowly Its more advanced partner, the rear derailleur, both pushes the chain from side to side and pulls it tight The rear derailleur is designed to serve two main roles: moving the chain between the sprockets and keeping the chain under tension The mechanism controlling the rear derailleur is a hardened spring hidden inside This spring is constantly pushing the derailleur away from the bike and toward the smallest sprocket The cable attached to the bike s shifter opposes the force of the spring When the shifter pulls the cable, the cable overcomes the spring and moves the chain toward the bike and onto the next sprocket When the shifter releases the cable, the derailleur again moves away from the bike Tension of a second spring provides the resistance, which takes up any chain slack Rear derailleurs have a common design (see Figure 2-6) They have a cage that holds two pulleys in the familiar S-shape The top pulley is the jockey pulley (also known as the upper jockey wheel); it guides the chain into what s called the cage The bottom pulley is the tension pulley (or lower jockey wheel); it s designed to keep tension on the chain and take up slack Derailleurs are designed to maintain the appropriate amount of space between the jockey pulley and the rear sprockets as the derailleur moves back and forth The derailleur also move its arm back and forth with each shift to keep its cage centered under the sprocket on which the chain sits Usually, one or more screws are utilized to control the amount of lateral movement and spring tension The rear derailleur cage that connects the jockey pulley and the tension pulley has a length that varies depending on the amount of chain slack needed to be taken up Models with longer cages are designed to support larger, lower-geared cogs and longer chains; they re typically found on bikes with three chainrings Rear derailleurs also have a maximum tooth capacity, which specifies the largest cog onto which it can shift a chain Short cage derailleurs are found on racing bikes; they offer quicker shifting and higher ground clearance, the latter of which is important when cornering in tight curves

On a cold day in the middle of a race in the Italian Alps in 1927, engineer and racer Tullio Campagnolo s hands were so cold that he had trouble removing the wing nuts that held his wheel in place This experience is supposedly what led him to invent the quick-release lever, something that has made lives easier for scores of bikers ever since Anyone who has ever had to remove a wheel on a bike without the benefit of a quick release knows just how much of a convenience Campagnolo s contribution has been Whether you re taking off a wheel to quickly change a flat or to throw your bike into the car, the quick-release mechanism is virtually indispensable to biking The basic design of the modern quick release (shown in Figure 2-7) still resembles the original It s made of a long rod with a lever-based cam mechanism on one end and a serrated edged nut on the other When the nut begins to tighten and the lever is lifted, the cam clamps down on the wheel hub Make sure to clamp the lever as snugly as you can Do not rotate the lever like a wing nut that s what the quick release replaced, and you won t be able to get it tight enough to secure the wheel