Myths of Crank Arm Length

Myths of Crank Arm Length

I have had a lot of questions and comments over the years about crank arm length and thought it would be nice to share some of the myths with you today.

MYTH : I am 5’2″ and I will loose power. I was told by my friend who is 6’5″ on 175mm cranks that if I go from my 172.5mm cranks to 165mm I will loose power.

RESPONSE : All of the published scientific studies do not show a rider would experience a loss in power. I have not seen one scientific study professing that going to a different crank length decreases power output. Research does not support power loss except at the extremes of function. What does that mean? Basically, there are EXTREMES that a rider could see decreased function on both ends of the spectrum of too short or too long. A 6’5″ rider on 120mm may be an extreme.

MYTH : Compact cranks are shorter cranks.
RESPONSE : I frequently hear from riders whom were told to go to a compact crank ( thinking shorter length ) and it will help their pedal stroke. Their cranks look too long for them. “Compact” has nothing to do with crank length. Compact cranks offer a smaller gear ratio up front. Compact cranks are typically a 50/34 ratio and standard 53/39. As with standard cranks, the lengths can vary. Commercially available cranks vary in length from 145mm to 180mm.

MYTH : I am a triathlete therefore I need shorter cranks.
RESPONSE : I do not change crank arm length just because we can but based on active measured pedaling gate. I look at the hip, the knee and the foot. The active pedal stroke is what is important.

MYTH : The stock crank that came on my bike has to be the optimal length or they would not have put it on the bike.
RESPONSE : The manufacturers are looking at averages. I find that for the mid height range, the length that comes stock on the bike is usually adequate. With that said, the dominant 3 crank lengths (170mm,172.5mm,175mm) do not support the entire population. 165mm cranks are becoming more common now but only on the smallest frame sizes.

MYTH : I found a formula online for calculating crank arm length that will work for me.
RESPONSE : I have seen a few formulas floating around but none of them address the body as a whole in motion on the bike. Some look at inseam, others height or a combination of. We have already learned that we can be the same height but have shorter/longer legs. You have to look at the knee, the hip and the foot in motion.

MYTH : Only riders with short legs should be concerned with crank length.
RESPONSE : Crank arm length can be a factor for riders of all heights.

MYTH : I am a triathlete therefore I need shorter cranks.
RESPONSE : I do not change crank arm length just because we can but based on active measured pedaling gate. I look at the hip, the knee and the foot. The active pedal stroke is what is important.

MYTH : The stock crank that came on my bike has to be the optimal length or they would not have put it on the bike.
RESPONSE : The manufacturers are looking at averages. I find that for the mid height range, the length that comes stock on the bike is usually adequate. With that said, the dominant 3 crank lengths (170mm,172.5mm,175mm) do not support the entire population. 165mm cranks are becoming more common now but only on the smallest frame sizes.

MYTH : I found a formula online for calculating crank arm length that will work for me.
RESPONSE : I have seen a few formulas floating around but none of them address the body as a whole in motion on the bike. Some look at inseam, others height or a combination of. We have already learned that we can be the same height but have shorter/longer legs. You have to look at the knee, the hip and the foot in motion.

MYTH : Only riders with short legs should be concerned with crank length.
RESPONSE : Crank arm length can be a factor for riders of all heights.
54321
(0 votes. Average 0 of 5)