3DM: 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).

Joint motion targets are the same as for the road position

Joint alignment is where we really see the impact of shifting the saddle forward. As a starting point aim for a Sitting Angle of 80 degrees and work from there to balance the riders comfort and ability to reach the bars.

If they are constrained by UCI rules you will need to trial cut-off saddles in order to hit the correct Sitting Angle.

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):
  1. Set saddle fore/aft such that their Sitting Angle is the correct range
  2. Refine Saddle height to minimise Hip/Knee motion and achieve correct knee/ankle angles
  3. Set reach to the armpads so that they are near to being under the shoulder and minimising Shoulder Lateral Travel
  4. Set reach to the shifters so that the riders elbows are on the pads with the shifters easily accessibly to their hands.
  5. Set drop based on hip/knee motion, hip angle and rider feedback
  6. 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.

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