[Peter P.]

Water isn't necessarily a concern; salt and water is.

Your sweat, left to dry on a steel frame can penetrate a paint job and cause rust. It's one reason why framebuilders evolved from fully enclosed brake cables along the top tube to split cable stops and a bare cable-sweat would collect under the housing and rust would form there.

Treat the inside of the the tubes with Framesaver or something similar, and wipe down your frame with a wet rag if you sweat on it, and you'll have no problems.

As an example of what can happen to your bike if rust is allowed to develop, consider my main road bike. It used to have the enclosed brake cable along the top tube mentioned above. After years of neglect and rust developing, I had the bike powdercoated and split cable stops installed. The bike is now 25 years old. The underside of the tube looks worse than the top side. I ride this bike almost daily. Dig-