The choice of mountain bike stems or MTB stems are vital for a number of reasons. First, the types of MTB stems you use will ultimately determine your riding position, which will subsequently have a great effect on how the bike handles.
For example, many people choose to go for longer bicycle handlebar stems if they are planning on cross-country riding. In fact, a length of at least 120mm is recommended here as the increase in the stretch of the rider's position will serve to stabilize the bike's steering.
On the other hand, shorter stems are recommended for downhill or four-cross riders. A maximum length of 80mm will ensure that steering is significantly quickened. In addition, using a shorter stem will ensure that getting off the bike at the back is facilitated as the distance between saddle and handlebar is reduced. This will mean that making snap direction changes is far easier.
Whenever possible it is always a good idea to try a number of different stems before reaching a final decision. Even a 10mm difference in length will have a huge effect on handling, depending on your own size and position. So experimenting with various stems is vital.
Many people believe that if they are experiencing an uncomfortable ride, then a shorter stem is the answer. Unfortunately, this is not always the case as often a longer stem can serve to distribute your weight more effectively.
Often the best way to experiment with stems is by using spacers to alter the position of the stem, moving it up and down to suit.