A bicycle seat is far from a universal platform for a cyclist. Everyone's proportions are different, and the seat that comes with your new bike is almost never the most comfortable. The ideal bike seat strikes a balance between support and cushioning, and should be properly sized to the width of your hips and the size of your legs to make sure there's no chafing or pressure.
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All in the Hips
The first step to finding the most comfortable bicycle seat is to make sure you've properly measured the width of your hip. A bicycle seat supports your weight using your sit bones, the bony protrusions of your pelvis that can be felt underneath the flesh in your rear. To find the width between your sit bones, you can sit on a flat surface like a table and feel for the two contact points of your sit bones and measure the distance.
Finding the Balance
A plush seat with ample cushioning may not be the most comfortable bicycle seat you can have. Because the tissues between your legs are especially sensitive to pressure, the extra cushioning found on some bicycle seats may redistribute your body weight onto areas where it will cause pain and discomfort after a few miles. Chafing, numbness, and even potential for damage are all consequences of a poor fitting bike seat, so it's worth taking your time to find a seat that supports your weight on your sit bones with no pressure elsewhere.
Different Strokes for Different Folks
The best saddle for your riding routine is custom-designed for your style of cycling. If you enjoy a relaxed ride on a touring bike or beach cruiser, a seat with a little extra cushion is ideal, because your upright riding position puts more weight on your hips. A racing cyclist, however, usually prefers a much more firm seat that won't bend or flex under intense cadences. Racers balance their weight evenly between their hips and their hands, so there's less of a need for support.
A premium solution to saddle discomfort is to invest in a leather hammock-style saddle, a classic design that has stood the test of time. These saddles are very expensive, but the leather will break in over time, giving you a custom fit that cradles your legs for optimal comfort over extensive mileage. These saddles are a favorite for endurance and tour cyclists, because these athletes spend hours in the saddle at a time and demand the best in comfort.