Welcome to Pedal Science, the weekly bike fitting blog by Nick Thomas of The Endurance Coach. This week we look at the subject of saddle height and cycling performance.
Along with height and tilt, the third consideration when establishing the correct saddle position is how far forward or backwards it should be. The exact position affects power transfer, comfort and handling characteristics. Whereas many people arrive for a fitting with saddles far too high or low the fore/aft position usually requires less adjustment.
For a road bike the primary reference point for saddle position is where the forward knee is positioned with the cranks in a horizontal position. The measurement is taken by dropping a plumb line from the tibial tuberosity (bony lump below the knee) and observing where the line bisects the pedal.
The textbook position is the line passing directly through where the pedal attaches to the crank – this is the aim but the entire bike fit needs to be taken into consideration before making any adjustments. Exact position is affected by several factors including the angle of pelvis rotation (e.g. through hamstring tightness), cleat position and length of the femur (thigh bone).
The most common reason people deliberately move the saddle too far forward or backwards is to achieve a more comfortable position because the existing bike fit and/or riding posture are incorrect. A sort stem can lead people to push the saddle back but the more common reason is to move the saddle forwards as the rider feels overstretched. There are three main reasons for this:
- The frame is too big
- The stem is too long
- The rider is sitting in a slouched position causing their centre of mass to be positioned too far back
Once the correct stem length has been established (with top tube length being taken into account) and posture has been improved there should be no need to for the saddle to be positioned too far forward.
Because time trial bikes feature a steeper seat tube angle than road bikes there are different factors to be taken into account. The steeper frame geometry enables the rider to be positioned further forward on the bike thereby providing a more efficient, powerful riding position: this is especially beneficial on flat/rolling courses.
As the saddle can be moved forward considerably more than on a road bike it’s reasonable for the knee to be positioned several centimetres in front of the pedal centre. The exact position is dependent on many factors but the rider’s experience, ability and nature of event play a key role in the final decision.
Nick Thomas is the resident bike fitter at The Endurance Coach. He is a fully qualified bike fitter and expert in lower limb mechanics, holding a BSc (Hons) in podiatry. You can contact him using the email address: email@example.com or see more about his fitting services by GOING HERE.