Road Bike = Triathlon Bike

In this article, I am focusing on 2 things related to triathlon bike fitting. 1) How "steep" you can get a standard road bike and 2) Front-end positioning.

1) STEEP SEAT TUBE ANGLE

Before

This client came to me with a road bike that was optimized in a triathlon position using a Thomson forward set seat post and a set of Syntace aerobars. The initial angle of the rider's virtual seat tube was 77 degrees (I say virtual because the forward bend of the seatpost significantly changes the position of the seat in relation to the bottom brakcet), about 4 degrees steeper than the traditional road geometry that this bike has. After optimization this rider was at 80 degrees, with a nearly ideal body angles and a better position for creating power in the aerobars. All this on a standard road bike. A steeper angle also meant a higher saddle height (1.5 cm higher than initial), less saddle setback from the bottom bracket (1 cm post vs. 2.5 cm pre-optimization) and more drop in the front-end (1 cm lower).

After

2) FRONT-END

Before

This client was also concerned about discomfort in the shoulders when down in the aerobars. We moved the pads further apart to bring them roughly in line with his knees eliminating shoulder discomfort and at the same time promoting good airflow. Take a look at this picture from John Cobb: http://www.johncobbresearch.com/wp-content/uploads/2008/05/forearm-smoke-on-trek.jpg. In this side shot you can see the air flowing between the aerobars and exiting along the sides of the rider. Cramping the cockpit by bringing the extension pads very close together may actually restrict airflow and increase turbulance, thus increasing the power required to move through the air. One of the things that I remember John teaching me is that you want to let the wind move by the rider with the least amount of disturbance possible (paraphrasing at best, sorry John). While I don't have access to a wind tunnel up here (and lighting a pile of leaves in front of a fan in a client's living room is probably out of the question), I hope that we have improved the aerodynamics a little bit, on top of addressing the comfort issues.

After

Update June 12, 2008: Due to the smooth clamping surface of the Thomson seatpost the saddle slipped up^, causing some discomfort as the nose was now in the way of this client's "bits". We switched the seatpost out for a better functioning Bontrager Race Lite with 20mm of set back, turned it forward and achieved this client's desired positioning with a level saddle.