Here is another Extralite frame I just built for Andy K. Like Marco’s from yesterday it’s a blend of Columbus Spirit and Life with a externally butted seat tube. In almost every case when building with the thinnest of the thin tube sets I prefer to sub in an externally butted seat tube. The reason is that at the top of the seat tube there is a lot going on. You have the seat stays and top tube welded in, the slot and you have to ream and hone the tube to the proper dimension for the seat post. What I have found is that when you load all that stress into one area of a very thin tube the long term durability of the frame falls into question. Even if you do everything right over a 10 or 20 year period of time the probability of failure in that area is higher than I like. Add to that poor maintenance, rust or ham fisting a post that’s to small and the likelihood of failure goes up. Using an externally butted seat tube removes that risk and does so with only a small weight penalty.