DIY Bike Fit at Home: Film a Phone Video, Measure 4 Key Joint Angles Free
The 4 angles and why they matter
- Knee extension at bottom dead centre: reference 140–150°. Too small = saddle low (front-knee pressure); too large = saddle high (hamstring strain, rocking hips). See saddle height & knee pain.
- Hip angle: torso-thigh angle — determines power room and lower-back load.
- Torso lean: reference 40–55° for road. Lower is more aero but costs flexibility — see torso angle explained.
- Elbow angle: reference 150–165°. Locked elbows = reach too long or weight too far forward.
How to film: 5 things that make or break it
- True side view: camera perpendicular to the bike, at hip height. An angled camera is the biggest source of distortion.
- Full body in frame, head to the lowest pedal position.
- Pedal normally on a trainer for 5–10 seconds at your usual cadence.
- Good light, clean background.
- Fitted clothing — baggy layers hide your joints from the AI.
Filmed it? Results in 30 seconds
The free quick check runs pose detection locally in your browser (video never uploads), finds the bottom-dead-centre frame, scores 4 angles against reference ranges and reports knee-angle sweep.
Open the free quick check ›Reading your results
- All green: no obvious issues — next stop, aerodynamics.
- A yellow or two: minor deviations, usually a 1–2cm saddle or bar tweak.
- Red lights: don’t panic — re-film first to rule out camera angle issues; if it stays red on a clean retake, it’s real.
The quick check gives you measurement — what’s out of range. It doesn’t tell you how many millimetres to move the saddle and in which direction; that requires your body dimensions, flexibility profile and multi-frame consistency checks — which is what the full AI analysis does.
Want to know how to fix the red lights?
The full AI analysis uses four key pedal-cycle positions plus your body measurements and riding profile to output concrete saddle height / stack / reach numbers, step-by-step adjustments and a PDF report.
Get the full AI fitting report ›FAQ
Can I do this without a trainer?
Yes — lean the bike against a wall or have someone hold it, rotate the pedal to bottom dead centre and hold your position. Dynamic pedalling on a trainer reflects your real riding position better, though, so use one if you can.
How accurate are joint angles measured from a phone video?
With a true side view, full body in frame and good lighting, AI pose estimation is typically within ±3–5° — enough to judge whether anything is clearly out of range. An angled camera is the biggest error source; re-film before trusting an unexpected result.
Do red lights mean I must get a professional fit?
Re-film first to rule out camera issues. If it stays red, that angle genuinely deviates from the reference range and is worth adjusting — via the full AI analysis for concrete numbers, or an in-person fitter. Riding long-term with severely out-of-range angles tends to accumulate knee, back or hand overuse issues.