To optimise bike performance, cycling biomechanics is where it's at. Cycling biomechanics refer to the forces that act on the human body and the effects these forces produce. This involves having the bike set up properly, and the rider correctly positioned.
There are a number of key areas involved in cycling biomechanics:
- Saddle height
- Crank length
- Seat tube angle
- Saddle position (fore-aft and angle)
- Shoe-pedal interface
Saddle height is perhaps the most important element in cycling biomechanics. There is an optimum saddle height, which has been calculated as between 105% and 107% of leg length - this requires the lowest oxygen consumption, and is thus the most efficient position, allowing you to ride for long periods.
A saddle which is too high will cause you to 'rock' from side to side with each pedal stroke, while a saddle that is too low places extra stress on the knees.
Saddle height is perhaps the most important. There is an optimum saddle height, which has been calculated as between 105% and 107% of leg length - this requires the lowest oxygen consumption, and is thus the most efficient position, allowing you to ride for long periods. A saddle which is too high will cause you to 'rock' from side to side with each pedal stroke, while a saddle that is too low places extra stress on the knees.
Seat tube angle (STA) is a crucial factor, and not one you can change without buying a new bike! In general, road racing and touring bikes have STAs between 72? and 76?, while triathlon and time trial bikes have steeper STAs, typically between 76 and 78?. These allow the rider's body weight to be positioned further forward for greater comfort, efficiency and power production when using aero handlebars.
Saddle position: There are two factors here - the fore-aft position, which refers to the location of the rear of the saddle behind a vertical line drawn to the centre of the crank axle, and the angle of the saddle nose - either pointing up, down, or neutral.
The ideal fore-aft saddle position allows for a plumb-line dropped from the patella to bisect the pedal axle when the crank is in the horizontal forward position. This allows the hip and knee muscles to be fully utilised, minimising strain on the knees.
Saddle angle is trickier - many people prefer the saddle tipped slightly upwards - they feel like they are falling off if it slopes forward at all - but research has shown that an uptilted saddle can cause back pain, as it forces the pelvis and low back to oppose each other when you lean forwards on the bike.
Shoe-pedal interface. The ideal position is with the ball of the foot directly over the pedal - this helps to decrease stress to the knee, and is the most efficient cycling position.
If you have any doubts about the efficiency of your riding position, talk to a professional at a bike shop. They will have the knowledge and experience to evaluate all the factors and help you make the right adjustments.
