Shimano Pedaling Dynamics

[1][2] The first model, PD-M737, was aimed at mountain biking enthusiasts who, prior to this, had to use toe clips and straps or "road" clipless pedals which clogged with mud and made walking very difficult in unrideable situations.

Shimano makes a number of different SPD-type cleats, and not all cleats are compatible with all pedals, mainly between the recessed metal "mountain" (SPD) [2-Bolt] line and the protruding plastic "road" (SPD-SL) [3-Bolt] (a.k.a.

The former can only be released from the pedal by twisting the heel directly sideward, while the latter can be released twisting the heel in 'any direction' (sideward and upward) and are therefore easier to learn/use for novices to clipless pedals.

[3] SPD-SL pedals offer a larger contact area than SPD for long road rides, at the expense of ease of walking.

Both SPD and SPD-SL have a small adjustment screw (per side on dual-side SPD) on the pedal that can be used to alter the resistance required to release the cleat from the pedal, so beginners can have it 'soft' and easy to get out, and then tighten it up as they progress.