Seat tube failures (or cracks) at the base of the extended mast are becoming all too common.

IMO- this is a poor design and has always been despite it's current popularity. It's an especially poor design in aluminum, and my comments apply to almost all aluminum frames with extended masts, not only Montagues.

There are 2 main things owners of these frames need to know.

1- the seat post must extend at least 1-1/2 diameters (about 2") below the top of the highest cross brace, ie. top tube or seat stays. If the post doesn't extend that far, all the load is borne by the unsupported seat tube which isn't strong enough. Unfortunately, many owners are misled by the minimum insertion mark on the post, because they're not told that that mark is only about the post, and may not apply to extended mast frames.

2- even if the post is deep enough (more than 2" below top tube), there's no assurance that the mast won't fail. Seat posts are flexible, as is the mast, and if the post is not rigid enough, it won't reduce flexing of the mast, which will fatigue over time. When depends on the rider weight, saddle height, and ride conditions, but all are likely to fail there eventually (eventually can be many years+).

The bright side is that if the post extends deep enough, the tube will crack over time and the likelihood of a sudden catastrophic failure is low.

So, in fairness, it's impossible to blame Montague without knowing if this is the original post and what their instructions say about insertion depth.


BTW- the above is my opinion, and not everybody agrees with me (obviously), but I'm not without knowledge of metals and structures, so it's not a totally uninformed opinion. I offer this qualification to avoid getting drawn into a back and forth debate.