1. Not Washing Your Bike
This is especially important if you use your bottle cage for sugary drinks that might slosh onto the frame. Bike + sticky, sugary liquid = gradual disaster in the form of deteriorated shifting from sugar collecting at the bottom bracket. It's better to clean it off before it disaster strikes. A regular cleaning will also remove any buildup of dirt in the drivetrain to keep it spinning smoothly. Plus, cleaning your bike involves examining it up close, which gives you the opportunity to find minor damage before it becomes major. Clean your bike every time you get it dirty—and even if you don't get it dirty, clean it every 20 to 25 rides.
2. Using Too Much Chain Lube
Overcoating your chain with lube could turn it into a giant revolving grime magnet-—collecting dirt and dust that will slow you down and ultimately accelerate wear on the whole drivetrain. Apply one drop of lube to each link, spin the cranks backwards a few times to distribute the lube, and then use a rag to wipe off as much of it as you can. What's leftover will be evenly spread over the chain without any excess dripping onto other parts of the bike that shouldn't be lubed.
More: The Anatomy of a Bicycle
Here's the correct way to lube a chain.
3. Neglecting Your Bar Tape
Handlebar tape collects all kinds of muck throughout its lifespan (think rainwater, sweat, possibly even blood). When that gunk is trapped between your handlebars and the tape, it can slowly eat away at your bars. If yours is ripped or loose, consider replacing it. Bonus: Your hands will thank you for the restored padding.
4. Leaning Your Bike on its Top Tube
This could scratch or even dent the tubes, and the more frequently you do this, the worse the damage will be. Your best bet for bike storage is a bike rack, but if there aren't any available, lean your bike against a building so that it makes contact with the wall at the handlebars and saddle. If you're propping the bike against a pole, use the rear wheel—the rubber will grab the pole and make the bike less likely to slide.
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