Why is Bike Fit So Important?

Friday, 15 June 2012


~ Special guest post from Ian Harker of Different Bikes. Learn more about them at our sponsors page.

I was recently talking to an experienced, but injured cyclist who was telling me he broke his leg at a repair clinic for kids. He hopped a bike that was way too small for him. He isn’t sure how, but after a few feet of peddling he ended up on the ground with a broken leg. He told me it was a great example of the importance of riding a bike that is fit properly.

I couldn’t agree more, but the importance of a proper fit includes more than safety. A bike that fits properly will also be comfortable and perform more efficiently. Numbness or pain in your back, legs or hips may be signs that your bike isn’t sized quite right. Adjustments may need to be made.

What size should my bike frame be?
A properly fit bike starts with the frame. You will need to comfortably straddle the top tube, but sizing a frame is a little more complex than a simple straddle test. The length of the top tube will also affect how comfortable or aggressive your position is while on the bike. If your handlebars are too far away, and your elbows are straight you will not only feel stretched, but you will not absorb impacts and vibration efficiently. If your handlebars are too close you will feel cramped and suffer fatigue from hunching over your bars.

How high should my seat be?
Once a properly sized bike frame is chosen it is time to make adjustments to the seat to help you achieve the perfect fit. Your seat moves in three separate ways, vertically, horizontally and seat angle, to ensure an efficient pedal stroke that reduces fatigue and injury.

A proper saddle height will allow your leg to be roughly 80-90% extended when the pedal is in the lowest part of the stroke (cranks in vertical position. Once the seat height is adjusted the seat needs to be moved to the proper position (forward or backward) along the rails. Your goal is to ensure the knee is in line with the pedal axle when your cranks are in the horizontal position. This can be measured using a plumb line dropped from the knee while sitting on your bike with your pedal in the forward position. The final step for seat adjustment is the seat angle. As a general rule, you want to level your seat so that it sits parallel to the ground. As you ride you may find that needs to be adjusted so the nose of the seat angles slightly up or down to relieve numbness or pain.

How do the stem and handlebars affect my bike fit?
Fine tuning of you bike fit can be done through adjustments in the stem and handlebars. The length and height of the handlebars will affect your overall body position to suit your needs and style of riding. Your position can be more upright by running a shorter stem with bars that sit a little bit higher. This will provide a more comfortable, yet less efficient body position. A longer stem with lower handlebars will provide you with a more aggressive position

While these are general guidelines, they can be beneficial in helping you get the most out of your bike. Buying a bike from someone who can help you get the right fit is important. Any bike that is purchased from Different Bikes includes a basic bike fit, an analysis similar to what has been described above. Professional services that include laser and video analysis are also available for those who spend a significant amount of time commuting, training and racing on their bikes. Different Bikes has their professional bike fitting partners listed on their website.

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