Why did my derailleur go into the spokes?
When your derailleur goes into your spokes, it may not only destroy your frame, but it may end up destroying your wheel, derailleur, and derailleur cable and housing. In really bad cases, it will destroy your chain as well.
So why does it happen and what causes it? There are two possible reasons: 1) improper adjustment, or 2) a bent frame (derailleur hanger).
If the limit screws were not set properly during assembly or someone has been fooling around with the high or low adjustment screws, the derailleur is vulnerable to "over-shifting" or chain derailment which can allow the derailleur cage to contact the rear wheel. If this happens when the wheel is in motion, the derailleur cage can get trapped between the spokes and cause irreparable damage. This type of occurrence would be considered improper assembly/adjustment and would not be covered by the limited warranty.
A second likely cause is a bent derailleur hanger. The derailleur hanger is the piece of the frame that the derailleur screws into. Sometimes the hanger is removable and replaceable, but not on all bicycles. When the derailleur hanger gets bent, it misaligns the whole derailleur system. This is usually exhibited by sudden poor shifting behavior. In most cases, the derailleur hanger and the derailleur will be bent towards the wheel.
The problem may not seem serious until you shift into your lowest gears with the rear derailleur. If the derailleur hanger is bent in, this shift will drive the lower pulley of the rear derailleur cage right into the spokes of the rear wheel. Hangers or frames can become bent if you crash or lay your bike down roughly on the drive side, or run over a foreign object (like a stick) that pushes the rear derailleur into the wheel.
If your hanger is bent, you will need to go to a shop to get it re-aligned or replaced. For bicycles that do not have a replaceable hanger, you may need to replace your entire frame or bicycle. Since a bent frame is usually the result of force caused by an impact, this would not be considered a manufacturing defect (a deficiency in materials or workmanship) so take care to inspect and perform scheduled maintenance routinely.
My bicycle doesn't shift gears
Most bicycles these days have multiple gears that can vary between 15 to 27 speeds. Different gearing is achieved by mounting 1 to 3 sprockets at the crank and 5 to 9 cogs on the rear wheel. To determine the number of speeds your bicycle is equipped with, multiply the number of sprockets on the crank by the number of cogs on the rear wheel (3 x 8 = 24 speeds).
Shifting between all these gears is controlled by levers on the handlebars, connected by cables to the front and rear derailleurs. The derailleurs -- devices through which the bike's chain passes -- move from side to side to shift the chain from one sprocket to the next. There are two main factors that affect the derailleur's function: 1) cable tension and 2) derailleur alignment.
Begin by shifting the rear shifter to largest number indicated and place the chain on the smallest sprocket. Adjust the High limit screw so the guide pulley and the smallest sprocket are lined up vertically. Reconnect the cable, pull out any slack, and retighten the anchor bolt securely.
Shift through the gears, making sure each gear achieved is done quietly and without hesitation. If necessary, use the barrel adjuster to fine tune each gear by turning it the direction you want the chain to go. For example, turning clockwise will loosen the cable tension and move the chain away from the wheel, while turning counterclockwise will tighten cable tension and direct the chain towards the wheel.
Shift the rear shifter to the gear one and place the chain on the largest cog. Adjust the Low limit screw in quarter turn increments until the guide pulley and the largest cog are aligned vertically. Again, shift through each gear several times, checking that each gear is achieved smoothly. It may take several attempts before the rear derailleur and cable is adjusted properly. Ensure all bolts are secured tightly and the chain does not fall off in either direction.
Shift both shifters to the smallest number indicated and place the chain on the corresponding cog and chainwheel. Disconnect the front derailleur cable from the cable anchor bolt. Check the position of the front derailleur -- it should be parallel with the outer chainwheel and clear the largest chainwheel by 1-3mm when fully engaged.
With the chain on the smallest chainwheel in front and the largest cog in back, adjust the Low limit screw so the chain is centered in the front derailleur cage. Reconnect the cable, pull any slack out, and tighten the anchor bolt securely.
Shift the front shifter to the largest chainwheel. If the chain does not go onto the largest chainwheel, turn the high limit screw in 1/4 turn increments counter-clockwise until the chain engages the largest chainwheel. If the chain falls off the largest chainwheel, and into the pedals, you will need to turn the High limit screw in 1/4 turn increments clockwise until the chain no longer falls off.
Shift through every gear, using the barrel adjusters to fine tune each transition. The barrel adjuster for the front derailleur is located on the front shifter where the cable comes out of the shifter. Clockwise will loosen the cable tension and direct the chain closer to the frame while counter-clockwise will tighten the cable tension and direct the chain away from the frame.
Do not ride a bicycle that is not shifting properly. Overlooking proper adjustments may cause irreparable damage to the bicycle and/or bodily injury. Never move the shifter while pedaling standing up, or under heavy load, nor pedal backwards after having moved the shifter. This could jam the chain and cause serious damage to the bicycle and/or rider.
How do I fix a flat tire?
Remove the wheel from the bicycle and deflate the tire completely via the valve. Loosen the tire bead by pushing it inward all the way around. Press one side of the tire bead up over the edge of the rim. Use tire levers, not a screwdriver, otherwise you may damage the rim (a good substitute for tire levers are the handles of metal kitchen spoons, there are no sharp edges that may damage the tire or tube).
Remove the tube, leaving one tire bead on the rim and locate the leak or puncture. Patch it using a tube repair kit, carefully following the repair kit instructions, or replace the tube. Ensure that the replacement tube size matches the size stated on the tire sidewall and that the valve is the correct type for your bicycle.
Match the position of the leak in the tube with the tire to locate the possible cause and mark the location on the tire. Remove the tire completely and inspect for a nail, glass, etc. and remove the offending culprit. Also inspect the inside of the rim to ensure there are no protruding spokes, rust or other potential causes. Replace the rim tape which covers the spoke ends, if damaged.
Remount one side of the tire onto the rim. Using a hand pump, inflate the tube just enough to give it some shape. Place the valve stem through the hole in the rim and work the tube into the tire, taking care not to let it twist. Using your hands only, remount the other side of the tire by pushing the edge toward the center of the rim. Start on either side of the valve and work around the rim. Before the tire is completely mounted, push the valve up into the rim to make sure the tire can sit squarely in position. Fit the rest of the tire, rolling the last, most difficult part on using your thumbs.
Check that the tube is not caught between the rim and the tire bead at any point. Using a hand pump, inflate the tube until the tire begins to take shape, and check that the tire bead is evenly seated all the way around the rim. When the tire is properly seated, fully inflate the tire to the pressure marked on the sidewall. Use a tire air pressure gauge to check. Replace the wheel into the frame checking that all gears, brakes, axle nuts or quick release levers are properly tightened.
For more information on how to fix a flat check out our Guide to Fixing Flat Tires.