Chains

People fresh from the tech industry or their home basement lab but new to bicycles are always trying to find a better alternative to the chain. For derailer-equipped bikes without removable seat stays—normal bikes, in other words—the humble oiled chain, around since 1885 and perfected by Sedis in the '70s, still rules the drivetrain. Yes, it's greasy; but lube it with Boeshield, and it's not bad at all. If it squeaks, lube it. If it gets gunky, clean it with El Duke (see below). When it wears out, replace it.

Here's a gear inch calculator chart.