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).
|Ankle Angle||Average 100-120, range < 30|
|Knee Angle||Max 140-145, Min >68|
|Hip Angle||Max 85-105, up to 120 if rider has issues|
|Shoulder Angle||Average 75-100|
|Forearm Angle||Average 0-20 (5-10 is a good starting point)|
|Torso Angle||10-15 for Elite, 20-30 general, 30+ rare|
Joint motion targets are the same as for the road position:
|Metric||Average Range||Good Range|
|Knee Lateral Travel||<40||<20|
|Knee Travel Angle||<8||0-2|
|Hip Vertical Travel||<40||<15|
|Hip Horizontal Travel||<40||<10|
|Shoulder Lateral Travel||<40||~20|
|Knee over foot||20 to 80|
|Sitting angle||78 to 86|
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.
Tri/TT fit process
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 minimise Hip/Knee motion and achieve correct knee/ankle angles
- Set reach to the armpads so that they are near to being under the shoulder and minimising Shoulder Lateral Travel
- 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/knee motion, hip angle 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?
|Neck pain||Too much drop for their current level of conditioning to the aero position.|
|Sore on outside of shoulders||Pads too narrow|
|Pressure on the nose of the saddle||Wrong saddle or too much reach / drop causing them to flatten pelvis into saddle|
|Excessive weight on elbows||If they're new to the position this may just require adaptation time. Or could be too little reach or too much drop|
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.