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Why Is My Seat Tube Dented?

Repair & Tech Info - Featured Tech Articles

When a manufacturer uses a large diameter seat tube, the front derailleur is naturally pushed slightly further away from the center point of the seat tube.  When you are dropping the front derailleur from the large to the small ring (or the middle to the small), if a round tube is used one of the pivots of the derailleur can actually hit the seat tube and interfere with the derailleur being able to drop the chain to the smaller ring.
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To allow the derailleur to swing closer to the center point of the tube many manufacturers indent the frame a few inches up from the bottom bracket.  Many types of frames and many different manufacturers use this design - be it mountain, road, or cyclocross.  Another place you may see some indents can be on the chainstays to allow more room for the cranks/chainrings.  So don't worry, the dent is just there to give more clearance, Clarence.
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