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Why Is My Seat Tube Dented? |
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Written by Bikeman
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Wednesday, 29 August 2007 |
Seat Tube Indent for Front Derailleur Clearance
Finally, the UPS guy has arrived with your new bike frame. You tear the box open, and - Buzz kill! - you see a dent in your seat tube a few inches above your bottom bracket. Fear not - that's actually there for a reason.
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.
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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