Shimano Pedaling Dynamics

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Shimano Pedaling Dynamics, better known as SPD system, or "spuds" has become a benchmark design for clipless mountain bike pedals. The SPD pedal was invented by Shimano in 1988. While not the first clipless bicycle pedal, the important innovation of the SPD was its small cleat which fitted in a recess in the sole of a shoe designed for SPD use. The shoe could be also used for walking as the cleat did not protrude, whereas previous systems had a large protruding cleat. The same year, LOOK designed a pedal which also used a recessed cleat. However, that particular cleat was rather large and never created a "design standard" where other manufacturers manufactured pedals which would use the same style of cleat. Clipless pedals use a system of cleat retention which is quite similar to that of a downhill ski binding. Generally, clipless pedals are seen to be safer than the older style of pedal/shoe integration using toeclips, toestraps and shoeplates.

Shimano makes a number of different SPD cleats, and not all cleats are compatible with all pedals, especially between "road" and "mountain" SPD product lines. Among otherwise-compatible cleats, there is an important distinction between black cleats ("single release") and silver cleats ("multi release"). The former can only be released from the pedal by twisting the heel outwards, while the latter can also be released by a sharp pull upwards and are therefore easier to use for novices.

There is a small allen key adjustment for the strength of heel twist to release, so beginners can have it 'soft' and easy to get out, and then tighten it up as they progress.