Clipless pedals are the great unsung mountain biking innovation. Suspension, indexed shifting and lighter/stronger kit get all the adulation, but it could be argued that clipless pedals have quietly done the most to change the face of off-road riding.
They give more control over the bike with feet not slipping or bouncing out of the pedals on bumpy descents, and allow legs to pull up on the pedal as well as push down for XC efficiency. Everyone remembers the first time they simply stomped and clicked into a clipless pedal. Once mastered, it's rider and bike in pure harmony.
Clipless pedals seem to have even slipped in under the retro radar, witness the grouches that eschew suspension and gears in favour of the 'purity' of rigid and gearless bikes that just happen to have state-of-the-art clipless SPDs.
So what makes a clipless pedal?
Determines how much force it takes to clip in and out of the pedal. Beginners like to adjust this so it's nice and loose for nervous toes and gradually tighten as they get more confident. It's also handy to lessen the tension when things get a bit muddy as clag has its own tenacious agenda.
Sometimes it's nice to have something to rest the foot on, especially during tricky trail sections, or for wearing casual shoes to pedal down the shops. They can also provide a bit of a platform for clipped-in shoes.
This is the part of the pedal that engages onto the cleat and holds your foot in place. Different manufactures have different design but they all work around some sort of spring mechanism. If you ride in muddy conditions look for a mechanism that will clear the mud reasonably well.
The bits of metal that bolt to your shoes and then clip into the pedals. It is these that determine how much your foot floats around and the angle of release. All mtb cleats fit into the twin holes found at the bottom of all clipless-ready mtb shoes.
This is a measure of how much your fott can rotate once clipped in to the pedal. Knees and ankles usually don't like being rigidly stuck to things whilst being pushed up and down, they prefer a bit of wiggle, the float in a cleat and pedal allow the foot, and therefore everything above to pivot and rotate around the cleat. Time pedals allow the foot to slide from side-to-side a little bit as well.
not to be confused with float, this is how much heel rotation it takes to release the foot from the pedal. Too much release angle can be quite a strain for those with a delicately turned ankle.
Some don't have any spanner-flats but have an allen-key shaped hole in the axle that has to be tightened from the back. The drive side pedal (right) tightens in a clockwise direction. The non-driveside (left) pedal tightens in an anticlockwise direction. An easy way to remember this is pedals tighten to the front of the bike and loosen to the rear.
some pedals have grease ports to squeeze grease through to prolong bearing and pedal life, others require disassembly to get at the bearings for servicing. The best pedals are the ones where you don't have to do any of this for a very long time. Most pedals can be serviced to some degree but sometimes, and horribly, it's more cost effective to buy a new set of pedals.