I'm looking at http://www.specialized.com/ca/en/bikes/road/tarmac/tarmac-comp#geometry and would like to know what "Seat-Tube Angle" means. For say the 56, I would assume that angle is like this


Where the horizontal black in parallel to the earth, the red is the bike frame and the blue is the angle.

Am I correct in my assumption?


  • Unfortunately this stuff is not all that well standardized. Seat tube length, eg, may be to the center of the BB or to the bottom, depending on whose system you're using. Apr 3, 2015 at 12:03

1 Answer 1


Yes, you are correct. The seat tube angle is measured relative to horizontal.

There is also a separate angle called "derailleur angle", which is measured between the seat tube and chainstays. You'll rarely find it specified in the geometry data though...

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