Knee Flexion at TDC
Target≈105°–110° included (≈70°–75° of flexion)
included hip–knee–ankle angle with the crank at top-dead-centre (12 o'clock).
Why this matters
The top of the stroke is where the hip and knee are most closed. If the knee is pinched too tightly at TDC the hip can impinge and power is capped; if it's very open the saddle is probably tall.
What good looks like
The knee clears the top of the stroke with a comfortable bend (≈70°–75° flexion) and no sense of the thigh jamming into the torso.
Common faults
- Pinched top (knee very closed) — often a low or far-forward saddle; pairs with a closed hip angle.
- Very open top — usually fine if BDC extension is still in range, but worth confirming.
Coaching cues
- Read TDC and BDC together — they bracket the stroke and cross-check saddle height.
- If the top feels jammed, look at hip angle at TDC and bar height, not just the saddle.
How to draw
- Pause with the measured leg's crank straight up (12 o'clock).
- Thigh line: greater trochanter → knee. Shank line: knee → ankle.
Related measurements
- Knee Extension at BDC — the bottom of the stroke.
- Hip Angle at TDC — the hip side of the same closed position.
General bike-fit guidance, not a clinical recommendation.
source · sports/cycling/learn/cycling_knee_flexion.md