Here are a few common problems that occur when your bicycle is left outdoors for extended periods without any protection from the elements:
Seals: On older Bicycles, seals become less effective over time. This allows water and moisture to seep inside your Bicycle, affecting the bearings on your headset and bottom bracket, wheel hubs and other drivetrain components like your shifters and rear derailleurs.
Steel bike frames: While rain and moisture aren’t good for any frame material, rust can develop quicker if your Bicycle frame is made of Steel. Even if it doesn’t show on the outside, the frame can start to rust on the inside, compromising its integrity and making it less safe.
Chain: Stainless Steel chains on more expensive Bicycles rust slower when exposed to rain and moisture. On lower-end Bicycles, the metal components start to show signs of rust much sooner.
Bolts: The metal on your bolts might not be the same as the metal on your other components. The stem and stem bolts are one common combination. When the bolts and metal on the stem begin to corrode from rain or moisture, it can cause them to seize up and get stuck, making the bolts difficult to remove when you decide to replace them or remove a part.