yeah, can be like the proverbial iceberg - i noticed a small crack in my CR's front rim. eventually took front tyre off to change, and holy moly, the aluminium on the tube side of the rim was all bubbled and flaking off in layers halfway round it, and looked bloody shite. end result was the thickness was reduced by heaps. guess caused by water sitting in there for years somewhere along the way. i bought new excel rim and spokes, looks a beaut now.