When checking a bike frame, it also helps to know what to look for.
There are only a few ways in which a bike frame can be damaged, I will go over the most important ones below:
Rust – Rust is a clear sign that your bike has been exposed to too much water, compromising the actual frame material. Common problem areas are the seat tube, bike chain and rear cassette. Make sure you do what you can to address the leak or problem and get your bike checked out by a professional.
Dents and Bends – Your bike frame can sustain a few dents and bends after a bad crash. If unaddressed, these dents and bends could eventually compromise completely, leaving you in a world of hurt on the way out.
Cracks – Cracks in your bike frame are the most dangerous to ride with, as they severely diminish the structural integrity of your bike. If you develop cracks in high stress areas, it is time to get a fitting and evaluation from your LBS. If you sustain a crack after a bad crash, always have a professional check it out before you start riding again.
Scratches – Scratches are not always too much to worry about, unless you see them around any suspicious areas like the head tube or rear axle. Regardless, always fully inspect your bike, no matter how small of an issue you think a scratch may be.
All connections of frame to components for tubes