Mountain Bikes
Before you choose a mountain bike, you need to understand that it is not designed to be a street racer. Bikes designed for speed have you leaning forward over a short wheelbase, giving you complete control over the bike. Mountain bikes are designed to get you safely across rough terrain over long distances. Even among mountain bikes, there is some variation in purpose, so it may be helpful to determine what kind of terrain you want to ride on before you choose a mountain bike.
If cost is a factor, then you need to understand that the materials used to make the bike are the greatest determinant of cost. If you're into stunts and the real tough off-road biking, then you may want some high-tech materials or titanium. But that costs more than the average mountain biker wants to pay. Most importantly, you don't need the best materials in a mountain bike that will mostly be used to go on light trails and roads.
Several other bike features will impact the price of your mountain bike. If you want precision brakes, precision gears, and derailleurs, you'll pay extra. But, for the adventurous biker these are all a must. It is worth paying for the high-end versions of this type of equipment, as the price difference isn't that much.
Good tires may cost a little more, but they are worthwhile for riders of almost every type. In particular, having Kevlar tires comes in handy on long rides and trail rides. You get all of the usual bike control with these tires, but with added durability.
Going Beyond the Price to Meet Your Needs
No matter what you pay for your bike, if it isn't designed for the terrain you'll be riding on or if it doesn't fit your body well, it isn't going to be a very good mountain bike for you. For example, the right bike for you should allow you to stand and straddle the bike without you having to stand on your tip toes. Most people recommend at least 4” of extra space above the bike when standing, to ensure you can comfortable stop and stand.
Similarly, when you're sitting down the seat needs to be at a comfortable height. In order to maintain control of a mountain bike on rougher terrain, the seat should be placed lower than it would for a street bike. For best comfort, you will want a seat that is wide enough in the rear to fully support your pelvis. This will be wider for women than for men.
When the bike is docked and you are sitting on it, you should be able to comfortably hold the handlebars while resting the balls of your feet on the center of the pedals in the 6 and 12 o'clock position. While in this position, your lower leg should be bent slightly and your upper leg should not be pointing up.
It is generally recommended that you take a short test ride of the mountain bike before you purchase it. You should feel comfortable at all times, without any need to curl up, stretch out, or strain your neck. All controls should be easily grabbed.