The right size bicycle is important for comfort, easy of handling and efficient energy transfer -- for faster riding times. A properly sized bicycle is also a wise safety precaution. But fitting for a bike isn't an exact science because there is no industry standard for bike measurements. Various brands may measure their bikes in slightly different ways.
Defining Size
Bike sizes vary depending on the type of bike you're looking at. Generally, bike frame sizes are based on the length of the seat tube, the tube that holds the seat post. Mountain bike sizes are usually given in inches while road bike sizes are usually in centimeters. Comfort or cruiser bikes are sized from small to extra large. Children's bike sizes are based on the size of the tire. They typically run from size 12 to 24 inches.
Since bicycle sizes vary slightly from one manufacturer to another, don't be surprised if your size changes depending on the brand of bike that you're looking at.
Measuring Inseam
If you're shopping for a road- or mountain bike, determine your bike size based on your leg length or inseam. Without shoes on, put a book between your legs with the book spine firmly against your crotch. Ask someone to measure the length from the floor to the book's spine. Measure in inches if you're looking for a mountain bike or in centimeters if you're sizing a road bike. This measurement is your leg length or bicycle inseam, which is different from a clothing inseam.
Guidelines
For a road bike, subtract 23 to 25 centimeters from your leg length to estimate bike frame size. The measurements will give you a good starting point, but then check for a good fit by straddling the bike. You should have enough clearance so you don't touch the crossbar when your feet are flat on the ground. If you like to sit upright on a bike, choose a larger frame in your range.
Athletic mountain biking requires a smaller bike, so subtract 12 inches from your leg length to find an appropriately sized mountain bike.
For children's bikes, try a bike size that is the same size or one size larger than the child's inseam measurement. The handlebars should be no higher than the shoulders, FamilyDoctor.org recommends. Take a child with you when you shop so you can be sure to get the right size.
Considerations
If you fall between two bike sizes, opt for the smaller size, advises Sierra Trading Post. Smaller bikes are easier to control. You can easily raise the saddle height if needed.
Handlebars can make a difference too. For the average road bike rider, look for handlebars that are the same width as your shoulders. Narrower handlebars will provide for a more aerodynamic ride; wider ones for added leverage and more room for your chest, resulting in easier breathing.
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