SPD pedals have become synonymous with pedal systems featuring a clip-in or click mechanism, essentially a quick-coupling between the pedal body and the shoe, which ultimately connects to the foot. The "S" stands for Shimano, the manufacturer, while "P" and "D" represent "pedaling dynamics." Such clipless pedals have established themselves across all cycling disciplines on sporting bikes. However, there's potential for confusion when purchasing, especially when it comes to replacement parts. 

Pedals and corresponding cleats for road bikes must include the "SPD-SL" designation. Pure SPD models are intended more for off-road use on mountain bikes or gravel bikes. The form, material, and screwing mechanism are entirely different and not compatible. Similarly, competitor Look offers road pedals with the model name "Keo," which, along with their shoe cleats, bear a confusingly similar appearance to Shimano SL but are not interchangeable. Look and SPD-SL are the predominant clip systems on road bikes, which is why mix-ups occur unexpectedly often. 

Tip: Look cleats are single-colored, while Shimano SPD-SL shoe cleats are dark with three colored corners each.

For mountain bike and touring bike owners, fundamental questions arise depending on their sporting aspirations: should they use clip pedals or not? With cycling shoes or street shoes? For road bikes, system pedals with corresponding cycling shoes, stiff soles, and pedal cleats underneath are standard equipment for the vast majority of riders. Very few are still seen with flat pedals (mostly beginners) or classic toe clips or pedal baskets with corresponding straps (typically found among retro enthusiasts). The clipless pedals and shoes designed for road bikes are even more uncompromising than systems for off-roaders. 

The soles are even stiffer, but they have no tread or even a rubber sole, which means the cleat—the cleat screwed to the shoe that ultimately holds the pedal and shoe together—cannot be hidden in a tread layer. Walking in road bike shoes is, therefore, more of a balancing act with guaranteed attention from your surroundings than a pleasant way to get around.

Using cycling shoes and clipless pedals makes pedaling more efficient than with any other type of pedal. On a road bike, you use your feet almost exclusively for pedaling and proportionally very rarely for walking or standing. The pedaling frequencies are above average, as is the pedaling portion - the time in the saddle when you're actually turning the cranks. To move the pedals quickly and securely, a firm connection is ideal. This makes classic flat bicycle pedals less suitable for use. The old toe clips are also no longer a welcome alternative because it's challenging to get your feet out. Additionally, such a strap buckled over the instep cuts rather uncomfortably into the top of the forefoot. With road bike shoes and cleats, pedaling is ideal - walking or running with them is a more than worthwhile sacrifice. 

Historical Note: In the 1990s, a theory established itself for a specific period that, in (then) modern cycling, about a third of propulsion came from pulling up on the pedals. This isn't even remotely achievable by top athletes. Physiologically, the muscles involved are far too small and their arrangement far too inefficient to expect such power. Anyone who doubts this can try pedaling with only one leg on a flat road without great effort for three minutes while spreading the other leg to the side. The hip flexor muscles aren't even capable of lifting the leg's own weight in the long term, let alone providing such significant propulsion for hours. 

Despite this, no professional road cyclist, and virtually no amateur, forgoes the tensile connection of feet to pedal. However, their primary concern is guiding the feet along the circular path and ensuring the straight alignment of the entire leg axis (foot, knee, hip), rather than propulsion. At a recommended 90 to 100 revolutions per minute, it's not coordinatively simple to precisely follow the pedal's circular path with the soles and thereby achieve efficient power transfer. You would often lose contact with the pedal surface, wasting power in the propulsion-effective downward pressure phase. 

Additionally, the two pedals are among the only five total contact points between the rider and the bike; losing contact here can mean losing control. Clipless pedals, therefore, make road bikes additionally safer. In the early days of their success story, such clipless pedals, then exclusively from Look, were also sold as safety pedals. 

Side Note: For road bike beginners, it's a kind of unwanted initiation rite to at least once in their life not release the pedal connection in time or on the wrong side and simply fall sideways for others' amusement. In dangerous situations, however, precisely this firm connection increases riding safety. You never accidentally slip off the pedal body, never lose contact at high pedaling frequencies, and there are situations where a small jump with the bike is the only solution to avoid an accident. Lifting the bike's rear end is much easier and more intuitive with clipless pedals!

Pedal systems are generally categorized into those for mountain bikes (MTB) and those for road bikes. However, even within each category, some manufacturers aren't compatible with one another. The first provider of road bike clipless pedals and thus the namesake of the system was the French brand Look. The mechanism and cleat already looked remarkably similar to today's "Look standard." Later, Shimano, Time, and Speedplay followed with additional variants and manufacturers. 

A significant advantage of Look and SPD-SL is that they use the same shoe standard, requiring the same threads on the shoe side. Adapter cleats make the sole unnecessarily thicker, thereby worsening biomechanics. Most shoe manufacturers have adopted a triangular arrangement similar to that of the market leaders. The significant disadvantage of both is the wear of the plastic cleats on hard surfaces. While clipping in and out, as well as pedaling itself, produces virtually no abrasion, the plastic of the cleats diminishes quite quickly when walking on asphalt or gravel. Pedal systems with metal cleats are more durable in this regard, but are considered more finicky when entering and exiting.

The flat plastic cleats from Look and Shimano can be easily inserted and locked into the pedal. The front nose of the cleat is guided over the pedal surface in the direction of travel until it dips into a recess in the pedal frame. Then, you press down on the rear part of the cleat, whereupon a mechanism on the back of the clipless pedal engages a groove in the rear cleat using spring force. With practice, this can be executed in a single, fluid movement. Exiting via a slight inward rotation of the toes or outward rotation of the heel only causes problems if you don't think of the necessary slight rotational movement during an adjustment period. 

The power transfer of both models, especially the somewhat larger SPD-SL cleats, is excellent due to the flat design. Unlike MTB pedals, where freedom of movement on the pedal is more critical than power connection, you stand very securely on the pedal with SPD-SL and Look Keo cleats and don't tend to tip sideways.

The firm connection between the crank, pedal, shoe, and, of course, the foot has not only measurable advantages in power transfer but also positive effects regarding the biomechanically correct positioning of the cycling shoe on the pedal axis. When mounting shoe cleats in general and aligning the popular Shimano SPD-SL cleats specifically, several parameters should be observed to avoid overexertion, pain, or numbness along the sole, in the ankle joint, within the calf muscles, or even in the knee. Additionally, efficiency when pedaling decreases with an incorrect mounting position. 

Important Information: Cleats come with the pedals when purchased, not with the shoes. You can also purchase them separately for an average of €15, and it is recommended to replace the cleats regularly (see below). Besides the two shoe cleats, you get six matching screws and elongated washers in the set. Even if the old screws still appear promising, it is recommended to use the new ones. 

The color of the SL cleats indicates the freedom of movement in the pedal:

To remove cleats and attach new ones, you only need a hex key. Older models can still be loosened with Phillips or flathead screwdrivers, but since the threads often become difficult to turn due to dirt and rain, screw heads for greater torque proved sensible. It's easily imaginable that the Torx® standard might gain ground here in the future. If you don't want to screw your cleats to the shoe by feel, but simply want to mount them in a biomechanically sensible way, a ruler and pen are helpful. Alternatively, a one-time investment in Ergon's fitting tools can permanently save work and pain.

The goal of optimal mounting is to place the central pressure point, or more accurately, the force axis, directly over the pedal axis in the forefoot. This not only ensures optimal power transfer but also ensures that the metatarsal bones, toes, and even the ankle muscles work against the least unergonomically introduced forces. Both passive and active locomotor systems prefer natural movements. Since bicycle riding doesn't belong to this category, you should imitate walking or running as well as possible. And in these "gaits," you push off from the ground via the force axis between the big toe base joint and the base joint at the little toe. 

You can find an ergonomically acceptable position for the SPD-SL cleat without the corresponding Ergon fitting tool using the instructions below. Those who want to work really precisely can't do without help in the form of a bike fitter or fitting tool:

The primary indicator for wear of your SPD-SL cleats is the front plastic tongue that's inserted into the pedal. Shimano recommends watching for an angular formation here. If the edges are ground round, this means play between the cleat and the pedal. Timely replacement makes sense. But also watch for damage to the rear edge of the cleat. At the very latest, according to the manufacturer, you should replace the cleats when the colored (yellow, red, blue, gray) TPU elements are no longer visible. First, secure hold in the pedal is no longer guaranteed; second, the nylon base cleat is significantly more slippery when walking. During regular visual inspection, you should additionally check the screwing for completeness and a tight fit. When in doubt, replace the cleats early to avoid accidents.

Just a few millimeters or a few degrees can cause havoc in foot positioning on the pedal. Typically, biomechanically poorly adjusted cleats are characterized by a gradual intensification of pain in the midfoot, knees, or by numbness and burning in the toes. Ignored in the medium and long term, such minor problems can lead to even serious injuries, increased joint wear, and even athlete failure. The feet are comparable to a building's foundation. If a construction stands on unstable or uneven ground, even a solid structure can be compromised. Similarly, errors in foot position and, consequently, pedal cleat alignment persist throughout the pedaling movement, extending up to the hips and lower back.

Proper cleat adjustment is crucial for achieving comfort, efficiency, and preventing injuries in road cycling. Take time to carefully position your cleats, and don't hesitate to make minor adjustments if you experience any discomfort. When in doubt, consult a professional bike fitter for optimal results.