What's a "Crank" and Why Does the LENGTH Matter??

Let's face it, as triathletes, most of us aren't bicycle experts. A lot of us are on used bikes, or something we found on a great sale. We may or may not have had a bike fit, and bike fitters, while sometimes great, are usually just adjusting what you have rather than recommending what you really need.

OK, let's back up. When you picked out or put together your bike, what specific things did you look for to ensure it FIT you best? Frame size? Sure. But, is that it?? Sure, yea, frame size matters, but is every 5'5" person proportioned the same? Of course not. Maybe you adjusted the seat height. Maybe you adjusted the handlebars and/or aerobars a bit. Cool. What about the crank set???

You create power by pedaling. The pedals are attached to the bike (at the bottom bracket) with long levers called cranks. Did you know these cranks come in different lengths? Do you know the length of yours? How was it chosen?

Crank Length

I was lucky. When I decided to invest in my first nice tri bike 6 years ago, I went to the bike shop, told the sales guy I knew very little about tri bikes and I needed help, and he helped me with a custom build specific to me. Part of his recommendation was shorter than standard cranks. 165cm vs. the more commonly equipped 170cm (or even 175). I trusted him, and was lucky I did!

Most triathletes pick a bike based on frame size and never think about crank length. But let's think about why it matters. Envision the pedal stroke. Imagine if that lever was REALLY long- exaggeratedly so. What would happen? You'd have to lower your seat, to be able to reach the pedal at the bottom of the pedal stroke, and then at the top your knee would be hitting your chest (especially problematic in aero!). Of course we aren't talking about anything that extreme, but you get why it matters- the crank length is determining the circumference of the pedal stroke. Now imagine a child who's less than 4ft tall, vs a tall man who's well over 6ft tall. Should their pedal stroke be the same length/circumference? No, of course not. Look at any kids bike- the crank is quite short to suit their shorter legs!

So, how do you choose the correct crank length? Like anything, it's as much art and opinion as science. But here's what science does know:

1. There are far more advantages to going short, than going long. Especially if you're on the shorter side!

2. A shorter crank means less extreme angles at your hip, knee, and ankle, meaning less strain on your body, and lower likelihood of injury.

3. Shorter cranks means higher cadence which is generally better for overall power output in triathlon and road riding.

4. Shorter cranks means higher seat position and smaller pedal circle, giving your knees more space to your chest in aero position- improved breathing and comfort and possibly allowing you to become even more aero.

5. Shorter crank means smaller pedaling range, which means lower front surface area, which is more aero.

Here's our advice. If it ain't broke... you know. However, if you are having issues with pain, discomfort, low cadence, aero position- you might consider dropping you crank length! SRAM and Shimano go down to 160mm, and there are other aftermarket manufacturers that go even lower than that. Here's what the pros ride, just for a fun reference:

• Tom Piddock 1.70m (5'7") -> 160mm.

• Tadej Pogacar 1.76m (5'9") -> 165mm.

• Remco Evenoepoel 1.71m (5'7") -> 165mm.

• Fillipp Ganna 1.93m (6'4") -> 170mm.

• Mark Cavendish 1.75m (5'9") -> 170mm.

• Jonas Vingegaard 1.75 (5'9") -> 172.5mm.

• Mathieu Van der Poel 1.84 (6') -> 172.5mm.

• Wout Van Aert 1.9m (6'3") -> 172.5mm.