Originally Posted by Fat Boy Biker
I was wanting to get double sided SPD type pedals, and some day I will buy better road shoes. But what is the real difference? Are double sided SPDs not considered road worthy? I saw the Look pedals and think I would prefer to stick with one type for both bikes.
When talking about pedals, it's always best to distinguish between the four basic parts.
- Pedals
- Cleats
- Mounting pattern
- Shoes
SPD pedals accept Shimano-style/compatible SPD cleats. There is a variety of flavours of SPD pedals and each accept their own respective cleats. Technically SPD pedals are Shimano MTB pedals. There are also clones of that design which can be found from other manufacturers such as Wellgo but the design strictly originated from Shimano. What most of them have in common however is that they use the SPD-style mounting pattern which is the side-by-side two-hole arrangement. When many shoe manufacturers print that their shoes are SPD compatible, what they mean is that they have drilled their shoes for SPD-style mounting pattern. Many non-SPD cleats will also work with this mounting pattern. Almost all MTB shoes are drilled with SPD-style mounting patterns. Some road shoes are drilled to accept SPD cleats too since there are some road cleats which use the SPD-style mounting pattern.
Most road shoes are also drilled for Time (4-hole) and/or Look (3-hole) mounting patterns. Some shoes are only drilled for one type of pattern. These were patterns that, much like Shimano's SPD, were standardised based on the introduction of those pedal systems a long time ago. Many different pedal manufacturers produce cleats which adhere to one of these types of mounting patterns. For everything to fit and work properly, you must find a pedal (which will determine cleat) and shoe combination that have compatible mounting patterns.
Road cleats are generally larger than their MTB counterparts but they were also not really designed for walking on and thus not designed to be recessed into the shoe. Many of these cleats can be damaged if walked on so cleat covers are necessary for any amount of offbike activity. Additionally, due to the size and shape of road cleats, walking on them can be tricky at best. Running or negotiating stairs with them can be treacherous. Think walking around in skates. However the size of the road cleats allows them to more efficiently distribute loads and thus produces less chances for hotspots.
Generally speaking, cleats that use SPD-style mounting patterns are prone to giving their users hotspots because they have a relatively small contact area between the cleat and the shoe. This is further ascerbated if the shoe has a relatively flexy sole. A very stiff sole is required to prevent hotspots with SPD-type cleats.
SPD pedals themselves are known for being prone to clogging and jamming under really muddy offroad conditions. This is due primarily to the design of the SPD bindings which why most MTBers prefer other pedal systems such as Crank Brothers Eggbeaters or Time ATACs which have a more open body design that allows the mud to clear. Additionally, SPD pedal designs are known for having too little free-float thus they try and lock your knees into a certain position. This can be bad for some people. SPD pedal designs also couple release angle and tension. Once you overcome tension, you release. Other pedals systems make these independent. First you have free float until you hit tension or release angle. Some pedal systems have all three and each can be independently adjusted. This is to say that your feet are allowed some amount of free float before they hit a tension region. Then you are in restricted float until you get to the release angle at which point you release. Such a system is superior especially for offroad riding where you need to be able to move the bike around underneath you but still not inadvertantly release.
Most offroad pedals as well as MTB SPD pedals are double-sided and offer things like multiple entry/release methods making them more user-friendly for cyclists who continually have to mount/dismount. Road pedals are generally designed assuming the rider will spend the majority of his/her time attached to the bike so they usually only have one side and one entry/exit method. There are some road pedals that are double sided however. These include Speedplay Zero and X series pedals, Crank Brothers Quattro, Coombes Pro Pedal System and the BeBop Pedal System. Most road pedals have a lower stack height meaning they place the foot closer to the spindle vertically thus making them more efficient. Some have adjustable float and adjustable release angles too.
Most road shoes are designed with very stiff soles to start with. They are also designed to not have much tread. And due to the nature of road cleats, they're designed to expose as much of the cleat as possible thus they're pretty unfriendly to walk around in. With road-specific shoes, you pretty much walk around on your heels and look like a duck.
That pretty much covers the basics. I'm sure others will chime in on points I might have overlooked. There are also plenty of related threads both in the past and recently on this topic. If you do a search, you'll find ones that are more specific to a make and model of pedal and/or shoe.