Last week I went out bike shopping for my daughter. She's tall, but not quite fully grown. So, in the course of trying to find a great deal on a kid's bike I came across a beautiful bike for her, a Marin Lucas Valley. The price was right and I knew it would be good for her in the long run as she grew into it. The only problem was that it was just a bit too "long" for her. She felt stretched out and the flat handlebars were a different experience from her previous hybrid/comfort bike. So what to do? The answer was to install an adjustable stem, which would solve the only aspect of this bike that wasn't ideal for her.
1. What is a stem anyway? Will it grow flowers or something?
Your stem is the part of the bike that attaches the handlebars to the fork. It's a key part of your steering, and what channels your action on the handlebars into the front wheel being pointed in the direction you want to go.
The size of a stem varies between bikes of course but in general it's usually about as long as the width of your hand. A small adjustment in the stem length can make a big difference in the way things feel. Just 10-20 mm difference in length can have a significant impact on a rider--whether one feels overly stretched out, or tucked in and nice and comfortable. Most of the time, you can only accomplish this change by swapping out the stem completely.
Any easy solution to the problem that my daughter had with improper handlebar fit (beyond what you can do with normal bike adjustments to make it fit you better) can be found in swapping out your current stem for one that is adjustable.
Like its name implies, an adjustable stem can be modified in a way that brings your handlebars up and down as well as forward and back. This is accomplished with a two-piece design allowing the stem to bend in the middle, with a bolt fastener that clamps down to hold it in the preferred position.
Note there are two main styles of stems - the newer style, called a threadless stem and the older version, called a threaded or quill stem. What we're describing here applies to a threadless stem only.
3. How an adjustable stem modifies handlebar height and length
By bringing up the adjustable stem, the natural result is that it raises the overall handlebar height while bringing in the overall length as well. A person sits more upright and not so stretched out -- in a way that is more comfortable for many riders. The photo is of the same Marin bike that I bought for my daughter, only with the new adjustable stem installed. Compare that with the photo of the original stem above, the one with the red arrow. See the difference? With the new stem, my girl can sit more upright, not hunched over and stretching forward to reach the handlebars.
4. An adjustable stem can help maintaining a bike's fit over time as a kid grows
5. Also offers an easy modification to fit your style of riding
An adjustable stem can be modified literally in seconds, in most cases with a plain 'ol Allen wrench. Though you might not be the kind of person to make these constant modifications to you bike, there are those who'll dig this type of easy customization.
Consider a situation where you're going to go on a relatively short but pretty intense ride with somebody you know really likes to spin the pedals and go fast. You take your handlebars down to give you a sleek, more aerodynamic stance on the bike. Or, maybe you're going out with a friend on a leisurely afternoon ride that'll take 2-3 hours. You can then simply bring the handlebars up so you are sitting more upright and relaxed. Seriously, it's about a 30 second adjustment.
6. Helps make it easier if you need to share a bike
From time to time I'll have friends come visit from out of town who want to find a way to go riding when they travel. An adjustable stem can make the difference in typical frame sizes a lot easier to manage. I'm tall, so in many cases just bringing the handlebars up and back makes my big bikes still workable for shorter friends. In fact, between that and adjusting the seat height as needed, frequently a person can safely and comfortably ride a bike that may be a couple frame sizes different than what they'd normally select, especially if it is a smaller person riding a larger bike.
I'm not saying two roommates sharing one bike would love this constant adjusting, but it can make the occasional loaner use very much possible and easy.