How to Determine Your Correct Crank Length

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Wisconsin Marathon 2020
 

Whether you’re a veteran cyclist or new to the sport, you know that finding the correct size bike is extremely important to efficient and comfortable riding. What you may not know is that changing smaller elements on your bike can change and improve your cycling experience as well.

Before you assume that the crank length that comes standard with your bike (typically around 175mm) fits your particular needs, think again! The slightest size adjustment can make a huge difference for comfortable cycling.
So how do we exactly determine the perfect crank size for your bike? Unfortunately with such a huge range of variables including leg proportion, foot size, flexibility, comfort and overall movement there isn’t one simple formula. However, there are several methods used by cyclists that will give you a give you a good idea- Let’s dig in!
Method #1: 9.5% of Your Height

Graham Obree, a Scottish racing cyclist suggests that correct crank length can be easily formulated by taking your total hight and multiplying it by 9.5%. For example, if you are 185 cm tall your crank length would be 175.5 mm.
Method #2: Inseam of leg x 1.25 + 65

This method, known as the Machine Head Method focuses on more than just your height. Because each person has different body proportions, this method will take into account your leg length rather than your overall height. For example if your inseam is 87.6 cm x 1.25 + 65, your correct crank length would be 175.4. mm.

Now that you have two different methods to try, give them a go to see which works best. In the end, it’s all about your personal comfort. If you have shorter legs, you most likely could benefit from a shorter crank length than your taller cyclist teammates.
From a visual perspective, you want to take a look at when your foot is in the 12 o’clock position because that’s when your knee is at the tightest angle and most affected by crank length. Riding with the wrong crank length can lead to knee pain and back pain which we definitely want to avoid.

With all of that being said, do what feels best to you. Listen to your body. If you’re experiencing any sort of knee or back discomfort, try a different size crank length. Most importantly- enjoy the ride, be safe, and have fun!

If you need help in determining your correct crank length, please contact me.

Train Right, Tri Right,
Coach MJ

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