Triathlon seat stays (behind the top of the downtube) are sometimes open at the top. (see below, or Kestrel Talon vs 4000 for example)
and sometimes closed
What are the advantages/disadvantages? I would think the obvious answer is in the drag properties and possibly weight savings, but really don’t know, anyone?
and-
2. Seat stays–how can they be so thin? Rider weight limits? Frame flex issues? Weight savings?..how, why!?
Thinking of upgrading my road bike frame. I’m @ 6’3" and 200 so a broken carbon skewered ass is not favorable.
Generally, if the stays are shaped correctly, thinner is better for drag reduction. And the stays meeting low on the seat tube is also (typically) good.
Structurally, seatstays can afford to be thin because on a bike they are mostly in compression. It would take an enormous amount of force to buckle adequately designed thin carbon or metal seatstays.
I think you are seeing the results of advanced materials and production methods. Typical steel bikes have the seat stays mounted up high for stiffness and strength even while using light tubing. My steel 90’s KHS Aero attaches them above the top tube.
Interesting. Why don’t all modern carbon road bikes do this?
And for the aero hole behind the top of the seat tube on the tri bikes-- this seems like and obvious aero vortex or area of drag.
Having the seat stays attach as high up as possible also yields the most rigid frame (with a more rigid design you can use lighter material and save weight).
With a full carbon frame you can do basically what ever you want, but people tend to make minor mods to existing designs.
Regarding aerodynamics, having the seat stays attach lower both reduces the frontal area, and changes the way the wind sees the shape. If you look at how the wind sees a cylinder that is tilted at an angle, the greater the angle from vertical, the more the wind sees the cross section as an elongated oval (more aero). http://www.shodor.org/media/M/z/V/hMGY1NTNhNWNlZTUxNDEzYjU1MTA1M2IyYTBiOWU.png
The lower the attachment though, the weaker the structure, so the more material (weight) is needed to deliver adequate stiffness.
A great example of this is the QR Illicito frame. One side has a traditional seat/chain stay combo, the other a single chain stay. The single stay is more aero, but needs a lot more material to be structurally sound (which is probably why they didn’t do both sides). http://triathlon.competitor.com/files/2010/09/NK4_6263.jpg
