What you need
- A phone, and something to stand it on that doesn't move: a tripod, a chair, a stack of books.
- An indoor trainer or rollers, so the bike stays in one place.
- Bright, even light, and fitted clothing such as bib shorts.
How to film
- Side-on and square to the bike, lens at about hip height, far enough back that you and the whole bike are in frame.
- Light. In a dim room the phone uses a slow shutter and fast-moving legs blur. Open the curtains, switch the lights on. Avoid a window behind you.
- Ride normally. Warm up first, then a moderate effort at a steady cadence with your hands on the hoods. 20–30 seconds is plenty.
- Check the footage. Step through it frame by frame: the leg should be sharp at the bottom of the stroke, and the framing shouldn't move.
The four measurements
| Measurement | What it sets | Common target |
|---|---|---|
| Knee angle with the crank at 6 o'clock | Saddle height | 143–153° |
| Front of the knee over the pedal spindle, crank at 3 o'clock | Saddle fore-aft | Roughly above it, within about ±5% of leg length (±40 mm for an 80 cm inseam) |
| Back angle: hip to shoulder, from horizontal | Handlebar height | Racer 30–45°, fitness 40–50°, casual 50–65° |
| Elbow angle | Handlebar reach | 155–175° (racers 145–175°) |
Knee angle is the one with the clearest target; see knee angle at the bottom of the pedal stroke. Knee over pedal is a starting point, not a law: a rider who is comfortable and balanced doesn't need to chase an exact number. Back angle is mostly comfort against aerodynamics, and flexibility matters a lot.
Change things in this order
- Shoes and cleats, if you have pain on the inside or outside of the knee or numb feet. A side video can't see these.
- Saddle height.
- Saddle fore-aft, then check saddle height again: moving the saddle back 10 mm raises it by about 3 mm.
- Handlebar height and reach. Setting the bars before the saddle usually means doing them twice.
Make changes safely
- One change at a time, in small steps: saddle height 5 mm, fore-aft 10 mm, stem 10 mm, spacers 5 mm.
- Mark the starting position so you can go back.
- Ride two or three times before judging, then film and measure again.
- Tighten to the torque printed on the part, especially carbon parts.
What a side video can't see
Cleat position and rotation, how your knees track seen from the front, saddle tilt and shape, crank length, and differences between your left and right side. For sharp or lasting pain, numbness, or a known injury, see a professional bike fitter, a doctor or a physiotherapist.
Measure it on your own video
Film yourself pedalling on the trainer, upload the clip, and Fix My Fit measures your knee, hip, back and elbow angles through the stroke and checks them against these ranges. Free for 3 analyses, no card needed.
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