2DM: Triathlon Metrics
While the majority of the metrics are the same for a Tri/TT fit as a road one, there are a few key differences.
The major change in body angles is a much lower torso angle than on a road bike (possible thanks to moving the saddle forward). Tri mode offers Forearm Angle to aid in refining the riders hand height.
Joint motion targets are the same as for the road position
If you are fitting the rider for both Road and Tri/TT bikes. The hip angle and associated metrics should fairly closely match between the road drops and aerobars positions.
The process for a Tri/TT fit is (loosely):
- Set saddle fore/aft such that their Sitting Angle is the correct range
- Refine Saddle height to achieve correct knee/ankle angles
- Set reach to the armpads so that they are near to being under the shoulder
- Set reach to the shifters so that the riders elbows are on the pads with the shifters easily accessibly to their hands.
- Set drop based on hip angle, observation and rider feedback
- Iterate through whichever steps are needed to hit a stable, comfortable position
Questions to ask the rider:
- Neck pain
- weight on elbows
- pressure on nose of the saddle
- Pain on outside of shoulders
Other problems to look for:
- Rider is stretching shoulders (dropped Scapula) to reach bars rather than lowering Torso (bars too low)
- Rider is moving on the saddle a lot (wrong saddle, bars too low or too long)
Note that short crank arms can make a significant difference to the sustainability of an aero position by opening the minimum knee angle and hip angle.