Bike Fitting Using a Goniometer

Written by tony guerra Google
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Bike Fitting Using a Goniometer
Get your bicycle properly fitted to your body. (man bicycling on beach image by Lijuan Guo from

A bicycle that's sized to your specific measurements will not only feel more comfortable, you'll also be able to ride it longer and with greater power. This is just as important for the occasional recreational rider on a decent mountain bike as it is for Lance Armstrong. Getting your bike set up correctly by consulting a bike fitter who uses a fitting tool called a goniometer is essential for a good ride.


A bike fitter uses a goniometer to determine your knee joint angles. The correct angle of the knees during the pedalling upstroke and downstroke, when it's efficient, delivers the greatest comfort and power. By measuring when you're sitting on your bike, pedalling in a stationary manner, a fitter can set your bike seat's height. He can also set your seat's forward or backward reach.

Bike Fitting Using a Goniometer
Correct knee angle delivers the most power (bicycle racer image by jimcox40 from


By using a goniometer, a bike fitter can quickly match almost anybody to a bike that will fit them well . She'll be able to determine how high the bike's seat should be and how big or small the bike's frame needs to be. An ill-fitting frame can leave you feeling uncomfortable during and after a ride and can even cause injury.

Bike Fitting Using a Goniometer
Poor fitting bikes can cause discomfort (cyclist in ojai nature park image by jc from


Bike fitters usually use a cycling-specific, colour-coded goniometer. They're made of clear plastic and are about 16 inches long when the two arms are folded one over the other. They're also attached to a clear plastic wheel with a full 360 degrees marked off within the wheel. Fitters take down information on knee joint angles to ensure you're on the right frame and with the right seat height. If they don't note knee joint angles, ask them why. They may be using a different system.

Bike Fitting Using a Goniometer
Make sure the bike fitter uses a goniometer (cyclist in yellow jersey image by jc from

Knee Angle

According to the experts at TriMyCoach, a website for cyclists and triathletes, knee flexion of 30 degrees when riding a bicycle is ideal. A few degrees either side of 30 is fine if your feet are larger or smaller. How your feet sit on the bicycle's pedals will help to determine how high or low your bike seat will need to be. This will help to prevent knee stress or even knee injury from pedalling at the wrong angle of knee flexion.

Bike Fitting Using a Goniometer
Thirty degrees is the ideal knee angle. (cyclists image by michele goglio from


The bike fitter will place the goniometer on the side of your knee, one arm going up the thigh, the other down the lower leg. He'll also note the degrees of knee flexion at the bottom or your pedal stroke. Once he has that, he'll adjust seat height and then measure again. Usually, a fitter also looks at where your hands are at various places on the bike's handlebars. It's important to let him know how comfortable or uncomfortable you're feeling at different seat heights.

Bike Fitting Using a Goniometer
Measure at the bottom of the pedal stroke (cyclistes image by Nath Photos from

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