Knee angle at the bottom of the pedal stroke

The target: 143–153°

Measure the angle at the knee, between the thigh (hip to knee) and the shin (knee to ankle), with the crank at its lowest point. A fully straight leg is 180°. Most fitters aim for 143–153°, which is the same as 27–37° of knee bend. Fitting schools differ by a few degrees; this range is a common middle ground.

It is measured while you pedal, not sitting still with the crank down: your ankle drops and your hips settle when you ride, and that changes the angle.

Below 143°: leg too bent, saddle likely low

• Less power, because the leg works in a cramped range.
• Load on the front of the knee, around the kneecap.

Above 153°: leg too straight, saddle likely high

• Hips rocking side to side on the saddle.
• Toes reaching down at the bottom of the stroke.
• Pain at the back of the knee or in the hamstring, and saddle soreness.

Pain on the inside or outside of the knee usually has other causes too, such as cleat position, which a side view can't show.

How to measure it yourself

• Film from the side on an indoor trainer, camera perpendicular to the bike at about hip height, on a tripod or anything that doesn't move.
• Plenty of light. In a dim room the phone slows the shutter and the leg turns into a blur exactly where you want to measure.
• Ride normally: warmed up, moderate effort, steady cadence, hands on the hoods.
• Use several strokes. Measure the angle at the bottom of four or more strokes and take the average; single frames vary.

A video measurement is good to about ±3° when the camera is set up well, so 1–2° outside the range is within measurement error and not worth acting on. A camera that isn't square to the bike, or well above or below hip height, makes the angles less accurate.

Our phone video guide covers filming in more detail.

How much to move the saddle

Raising the saddle opens the knee angle. As a rough guide, 1° of knee angle is about 2–3 mm of saddle height, depending on your leg proportions and how your ankle moves.

• Change it in steps of 5 mm or less, and measure again after each step.
• Ride two or three times before judging a change.
• Moving the saddle back 10 mm also raises it by about 3 mm, so check the knee angle again after a fore-aft change.

Need a number to start from? The saddle height calculator gives one from your inseam.

When to see a professional

Sharp pain, pain that lasts after riding, numbness that doesn't go away, a known injury or leg length difference, or discomfort that stays after a few careful changes: that's the time for a professional bike fitter, a doctor or a physiotherapist.