My First Blog!!! Short Cranks!

Welcome to my new blog! Please bear with me as I jump into this medium to bring you information on products, technology, ideas, and more. I anticipate that much of what I share will be cycling and biomechanics focused, but who knows what else may inspire me in the future.

This blog will be a lighthearted take on things I find "COOL" and want to share with the world. I promise not to bore you, go too in-depth, or get too technical. I'll also be grading things on a "COOL" factor of 1-5 icicles—1 being totally uncool and 5 being totally rad.

Now that that's out of the way, here's what I think has recently been a cool occurrence in the cycling world.

SRAM Announces Short Cranks!

Finally, one of the 3 major component manufacturers understands what I and several other fitters have been saying for more than a decade: short cranks are essential for getting the correct fit for many cyclists.

SRAM is now offering cranks as short as 150mm.  (previously, cranks would typically come as short as 165mm, and even now Shimano only offers their GRX800 crank as short as 170mm).   In the past, I would need to order short cranks from Rotor and Appleman at a pretty steep price.  And now that Rotor has killed off their USA distributorship this SRAM option is a godsend.  

I can hear it now from many of you reading this: "Blasphemy! I need long cranks to generate more torque!" Well, not only is the physics not behind that argument, but the cycling community has been steered wrong for generations about crank length.

Let's Get the Physics Out of the Way First.

A longer lever arm will enable you to create more torque. But torque isn't the only equation in cycling—we need to think about work and power.

• Work = force × distance (where force = torque × angular distance)

• Power = work / time

So, a longer crank arm enables you to create more torque, but the radius of the circle you travel is longer and takes more time to complete. A shorter crank arm may produce less torque, but the radius is smaller and takes less time to travel through.

Therefore: more torque requires more time, or less torque requires less time. In the end, power is essentially the same. That's why you're seeing pro cyclists switching to shorter cranks that actually fit them, and they are winning.

Why Does Crank Length Matter?

It actually matters that you get on the crank length that fits YOUR needs. Biomechanics, body limitations, and riding style all help determine what's right for you.

Body height is an obvious factor. The taller you are, the longer the crank you might be able to use. A big problem has been for shorter riders, where appropriately short cranks haven't been readily available.  I frequently build bikes for customers who are 5’ to 5’4” who need cranks as short as 150mm.  

Another issue is age-related mobility loss. As we age, we lose mobility in our joints, which limits how long of a crank we can use comfortably. It's very common to lose the ability to bring our knee to our chest (hip flexion). Longer cranks demand more hip flexion by making the foot rise higher toward the chest. If you run out of hip flexion at the top, you'll be forced to exceed your hip's range of motion. This causes the pelvis to rock excessively at the top of the pedal stroke and forces the hip to close more than it should, leading to discomfort.

If you're a time trialist or triathlete who leans over to get aero, you're probably aware of how your knees and thighs can hit your chest. Shorter cranks can prevent that and reduce hip flexion, making the transition from cycling to running easier.

How Can Such a Small Change Make a Big Difference?

Cranks change length in small increments—2.5mm to 5mm. Here's why that matters more than you'd think: the amount of crank length change is doubled in effect at the top of the pedal stroke.

Think of it this way: Your seat height is a fixed distance from the bottom of the pedal stroke to the top of the saddle. Shorten the crank 10mm, and the saddle needs to rise 10mm to keep the seat height the same. Now, at the top of the pedal stroke, the pedal is 10mm lower while the saddle is 10mm higher—that's a 20mm difference! Your knee is 20mm farther away from your chest. That makes a big difference.

What Does a Shorter Crank Actually Feel Like?

Most of my clients don't even notice the change. All they know is that they're more comfortable and not running into themselves. The bike fits more appropriately. Comfort and proper biomechanics will prolong your enjoyment and can even make you faster.

So thank you, SRAM, for being on the leading edge of change and bringing helpful technology to the end user.

How cool is the new availability of short cranks?