Most bicycles are bought without any kind of bike fenders. This is unfortunate since there are many good reasons to use bike fenders. Fenders come in various lengths for different purposes. Those who are riding their bikes for the purpose of commuting will want to get fenders that give as much coverage as possible. On a mountain bike, the main reasons for the fenders are to keep the rider from getting more muddy than necessary and to keep dirt and mud out of his face. They are interested in less coverage, but more ruggedness.
Bike Fender Material
There are bicycle fenders made from high end plastics (polycarbonates and polymers) as well as simple sheet metal. There are even bamboo bike fenders. Each type of fender material has its advantages and disadvantages.
Metal fenders are usually very light and can be modified (bent) as necessary to accommodate the individual bike. If not installed properly, or maintained regularly they can become noisy.
Plastic fenders are also modifiable to fit the bike, but only to an extent. You can cut away the plastic to fit, but you can't easily add the material back on. Plastic bike fenders are quieter than metal ones. Interestingly, plastic fenders can be much heavier than metal fenders.
Other bike fender materials can be variations of those or include wood and bamboo. Bamboo bike fenders are very expensive (starting at $80 a set instead of $10 for metal). Bamboo can be more effective than other types of wooden bike fenders. Wooden fenders are usually flat and don't offer much coverage. Bamboo bike fenders look great and can be made to offer as much coverage as metal and plastic fenders.
Bike Fender Types
There are bike fenders that cover the top of the tire along with enough of the front and back to keep the rider's feet dry. There are also short fenders that keep the majority of the water out of the rider's face. It depends on the purpose of the fenders and the type of bike as to which fenders the rider will need to buy. Generally, however, the longer the bike fenders, the more satisfied the rider will be with their purchase.
Full-length bike fenders
Full-length fenders cover a great deal of the rear wheel. They start about even with the chainstays in the front, go over the top of the tire and down the back until they are pointing down again. The front fenders start well in front of the forks (6 inches or more) and come down the back of the wheel to at least the half way point. Often the front bike fender will have a flanged mud flap to give extra protection for the rider's feet.
Full-length bike fenders give the greatest coverage and protection. They will be most effective in keeping the rider and bicycle clean in wet road conditions.
Half-length bike fenders
There is not really a class of fenders called half-length bike fenders, but these are fenders that don't fit in the full-length category, nor the clip-on category. Sometimes they are called beaver-tail bike fenders.
These half-length fenders cover less of the wheel than full-length bike fenders. They barely cover enough to provide protection for the rider. If the rider is not concerned about getting his feet and clothes a bit dirty, but is wanting to protect himself from being completely drenched, then these may be a good choice. Sometimes bikes are not designed for fenders. Half-length bike fenders can often be installed in a bike like this.
Clip-on, or quick release bike fenders
Clip-on fenders are made to help the rider keep grit and grime out of their face, but they do little to protect the bike or the rider's clothes. Clip-on bike fenders can be installed on just about any bike and can easily be moved from bike to bike.
Clip-on fenders are most often seen on mountain bikes and bikes that are used in very muddy conditions. They sit higher off the tires than other types of fenders and therefore don't get clogged with mud and rocks.
Buying Bike Fenders
Many bicycle shops will only have a couple of models of fenders available. It is worth dropping in to see what they have though. It is also helpful to take the bike so that the shop can recommend specific types of bike fenders for that model.
Bike shops are not the only place to look though. There are many places online that sell bike fenders. Amazon has a large selection as well as other online retailers.
There is the possibility of finding used bike fenders on old, discarded bikes. Sometimes used fenders will be too bent to be useful. It is good to check with a local bike repair shop because they may have parts, like old fenders, that they will sell for cheap, or give away. This may not be an option for someone wanting to install new bike fenders on a freshly polished bike. But it is an even greener way to be a bike commuter.
There are different types of bike fenders for different purposes. Each rider will have to determine what is best for their situation and their type of bike.