Well, sizing is an issue that calls for in-depth deliberation when it comes to mountain bikes.

First of all make up your mind primarily where you want to ride your mountain bike. You may want it for cross country (XC), all mountains (AM), Freeride (FR), downhill (DH), trials, racing, touring and single speeds. Other equally important issues are - your height, age group, sex, (Male/Female).

Ideally speaking, comfort should come at the top of your list. Comfort has a direct bearing with the clearance. Clearance – clear cut gap between your crotch and top metal tube (the one that is parallel to the ground) of the mountain bike, when you are standing over this metal tube resting your legs on the ground. As a general guide, a clearance ranging from roughly 3 to 5 inches is considered to be comfortable for Mountain bikes. Comfortable clearance will vary between 3 to 5 inches depending upon men and women, cool rider or an aggressive rider.

Though in most of the mountain bikes adjustments in the seat, handle bars and other parts are possible but it is best if you make a complete list of your requirement.