What Size Bike Do I Need?
One thing you will notice when you go to any bike shop is that the bikes are not one size like you will find in department stores. Rather than forcing a 6'2" person to ride the same size bike as a 5'2" person, higher end brands design and manufacture frames for specific measurements. So that 6'2" person will be riding a bicycle frame designed for their inseam, torso, and arm length. The frames found in a bicycle shop differ because they get longer as they get taller. Each brand has its own sizing charts, so it is important to look at the charts of each brand you are considering purchasing from rather than assuming, for example, a Medium Scott bike will be the same as a Medium Jamis. Another factor to consider is that the geometry of different brands' bikes can vary greatly even if they are the same style of bike, e.g. full suspension mountain bike
Part of Size Sheet Found on Scott's Website
How Do I know What Frame Size I Need?
The first thing to know is that mountain bikes and road bikes are measured differently. Hybrid bikes generally coincide with the measurements of a mountain bikes. Mountain bikes have a shorter seat tube and longer top tube than road bikes. The other thing to keep in mind is that road bikes are usually measured in centimeters while mountain and hybrid bikes are measured in inches.
Seat Tube Length-measured from the bottom bracket (where the crank arms are) to the top of the seat tube (seat post is not included in this measurement) is an indication of Stand Over Height.
Stand Over Height-is exactly what it sounds like, how much room there is between you and the bike when you stand over the frame. If the bike contacts you, the frame is too small.
Top Tube Length-This measurement is important because you do not want to be too stretched out, or too cramped on your bike, and it effects the handling, and fit of the bike.
How Much Stand Over Height Do I Need?
Road Bikes-1-3 inches clearance
Mountain Bikes-minimum of 2 but could be up to 3-5 depending on your style of riding and how aggressive you are
What's My Frame Size?
There are several measurements that you can take to help you dial in your fit, short of getting a professional fitting. Here we will focus on height and inseam because these will usually get you on the right frame.
Height-Easy enough, how tall are you? If you aren’t sure, stand against the wall with your feet a few inches apart and have someone run the tape measure from heel to the top of your head.
Inseam-While you’re standing against the wall have someone measure from your crotch to the bottom of your arch. If you don’t have a spouse or friend around to help you out, you can use a book to put between you and wall (you face the wall) and mark the wall at the top of the book and then measure to the floor
All size charts, like those below, should be taken as a guide, not as hard and fast rules. Every body is different and every manufacturer has their own take on sizing, particularly when it comes to the different frame styles of mountain bikes. For example, a Medium Jamis Portal might fit the same person differently than a Medium Scott Genius. You should always check the manufacturer’s size chart before making a purchase, if you are not going to go into a shop to give it a test ride first (which we highly recommend).