LeMond's Formula for Bike Sizing

Greg LeMond popularized a precise formula for bike frame fitting.
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Once upon a time, you straddled the top tube of a bike and if you could stand over it without too much trouble, “the bike fit you,” recalls three-time Tour de France winner Greg LeMond in his book “Greg LeMond’s Complete Book of Bicycling.” A bike shop mechanic watched you spin the pedal backward and took an educated guess at how high the seat post should be, and off you went. All that changed as LeMond advanced from the juniors to the pros, and he publicized a completely different approach to fitting a bike.

Greg’s Bike: Too Small

    LeMond turned pro in 1980, joining the Renault team managed by French coach Cyrille Guimard. The Californian was just in time to benefit from Guimard’s tests of the most efficient bicycling position and how to fit frames and seats. In 1978 and 1978, Guimard had taken champion riders to Renault’s wind tunnel to test the racers’ aerodynamic efficiency and pedaling power. He found that most riders kept their seats far too low, and Guimard raised LeMond’s seat an inch and a half. “That is like increasing your shoe size three sizes,” LeMond writes. It was a shock to LeMond, but he got used to it and rode better: lower on the bars and more comfortably, his legs able to fully extend.

Guimard's Formula

    Before you even set the seat height, you need the right frame size. Guimard came up with a formula based on your inseam length, essentially the distance from the floor to your crotch. You need to take this measurement in centimeters, or in inches multiplied by 2.54. Say you are a 5-foot-4 woman, with an inseam length of 30 inches or 76 centimeters. Multiply your inseam length by 0.67, yielding 51 cm in this example. That means you need a road bike frame of 51 cm as measured from the center of the bottom bracket to the top of the top tube. For a mountain bike, take off 10 to 12 cm, for net of 39 to 41 cm in this example.

Measuring Tips

    If you want to get your measurement correct, LeMond advises a few tips. Wear a pair of high-quality chamois cycling shorts for your measurement and thin riding socks. Track down a hardcover book about 1 1/2 inches thick and 5 inches long. Stand in an uncarpeted area where you can mark your walls, such as in a garage. Place the book between your legs and press it lightly upward to mimic saddle pressure, and backward, level, against the wall. Mark the top of the book with a pencil -- having an assistant helps with this part -- and measure from the floor to the mark.

Women-Specific Tweaks

    The LeMond formula doesn’t change for female riders, in terms of frame size, so you can still use it to start your hunt for the perfect bike. But you still may want to look for a women-specific design, or WSD. On unisex road bikes, women may find the top tube and cranks too long, and the handlebars too wide. Mountain bikes present similar issues, such that you may want to find a WSD version with narrower handlebars and a shorter top tube for great comfort and efficient pedaling.

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