BDC

Raise it five millimetres. Pedal again.

Put the phone on a tripod, get on the bike, pedal. BDC reads your knee at bottom dead centre and says what to move.

knee · bdc —

stroke 0 of 0 in this loop

cadence — rpm, stroke to stroke

position hoods road · dynamic band

Real footage, real pose data, read by the same model the app uses. road bike · trainer · hoods

WHAT IT READS

You don't need to know the angles. You need to know why your knee hurts.

Seven angles a fitter's camera reads from the side, each at the moment in the stroke it's defined at.

Angle	Joints	Moment	What it sets
Knee extension	hip · knee · ankle	at bottom dead centre	Saddle height. Front-of-knee pain and burning thighs: too low. Pain behind the knee, hips rocking: too high.
Knee flexion	hip · knee · ankle	at top dead centre	Saddle height, checked at the top of the stroke. Knee driving into your chest: crank or saddle.
Hip, closed	shoulder · hip · knee	at top dead centre	Saddle forward or back, and bar height. A pinched hip at the top of the stroke and a sore lower back.
Hip, open	shoulder · hip · knee	at bottom dead centre	The same, read at the bottom of the stroke.
Torso	hip · shoulder	against level	Bar height and reach. Sore neck and shoulders, numb hands.
Shoulder	elbow · shoulder · hip	—	Reach. Arms locked straight or bunched up.
Elbow	shoulder · elbow · wrist	—	Reach and stem length. Numb hands, sore wrists.

These are placements inside a band, not a diagnosis. Persistent pain or numbness: see a fitter.

HOW THE LOOP WORKS

Bike on the trainer.
Phone on a tripod, side on, three metres back.
Pedal.

It counts your strokes, reads the knee at bottom dead centre, and says the number and a direction with a capped step. Move the saddle, pedal again, and it reads the change.

knee 141 — road band. raise it five millimetres. pedal again.

WHAT IT COSTS

Free to set your saddle height. One small purchase for the full fit — every angle, both legs, and the record.

FREE saddle height knee at bottom dead centre, spoken

FULL FIT every angle saddle back and forth · bars and reach · both legs · the record