Crank Length Calculation

It is important to use the correct length of crank to ensure that your legs can work efficiently. You risk damaging your knees if you habitually use cranks which are too long, especially as you get older. 170mm cranks, which most cycle manufacturers fit as standard to most bicycles, are unsuitable for anyone shorter than the average European adult male and are therefore too long for most people in the World!

Normally fit adult riders should use cranks which measure about 20% of their effective leg length, rounded to the nearest 5mm, whereas growing children can safely increase this figure to 22%. This length goes all the way to your hip joint and cannot be measured directly. Ask a friend to measure your height twice – first when you are standing upright against a wall, without shoes on, and second when you are sitting squarely against it. Then subtract one measurement from the other one, as shown below.

The following table shows recommended crank lengths for normally fit riders on upright bicycles, based on the 20% to 22% range. Even shorter cranks may be required by disabled riders with restricted knee movement and by users of faired racing recumbents (due to space restrictions). Additionally, riders with very long legs may need shorter cranks on standard upright bicycles, to prevent their toes hitting the front wheel or their pedals hitting the ground when cornering.

	leg :	50	52.5	55	57.5	60	62.5	65	67.5	70	72.5	75	77.5	80	82.5	85	87.5	90	92.5
	child : adult :	110 100	115 105	120 110	125 115	130 120	140 125	145 130	150 135	155 140	160 145	160 150	165 155	170 160	175 165	175 170	180 175	180 180	185 185