There are at least two things that contribute to rusting :
- humidity - pH
Two examples
1. A Raleigh International 1974 bike, left in a garage in Santa Cruz CA for most of its life until 2003, every 1" square on the bike had rust coming through and the aluminum chainrings were bubbling (although crank arms and rear mech were hardly affected, suggesting that chainrings are plated with something special like nickel ...) One tire on the bike was an original tubular.
2. A Schwinn Paramount 1974 bike, left in the oft-flooded basement of our house in Illinois from 1980-2002, When it was retrieved there was rust on every 1" square on the bike HOWEVER, this was actually vapor rust deposition from other parts of the basement, as even the brake calipers had rust. Long hours with NEVR-dull have managed to remove this pond-scum almost completely although the top-tube plated cable guides and headset lower race were in bad shape and were replaced with stainless / replated.
So, the saltwater pH of coastal areas is imho a much more serious problem than freshwater vapor.
- Don Gillies
San Diego, CA