{"id":7619,"date":"2020-04-23T11:54:28","date_gmt":"2020-04-23T11:54:28","guid":{"rendered":"https:\/\/www.firstcomponents.com\/?p=7619"},"modified":"2026-06-22T04:54:24","modified_gmt":"2026-06-22T04:54:24","slug":"bike-crank-arm","status":"publish","type":"post","link":"https:\/\/www.firstcomponents.com\/de\/bike-crank-arm\/","title":{"rendered":"The Comprehensive Guide to Bike Crank Arms (Right Length, Design etc)"},"content":{"rendered":"\n

Everything important you need to know about bike crank arms, including why “crank arm” is technically the wrong term, is contained right here.<\/p>\n\n\n\n

Some of what we cover:<\/p>\n\n\n\n

Types of Crank Arms<\/a>
How to Fix a Crank Arm<\/a>
What Crank Arm Length Should You Use?<\/a>
How a Crank Arm is Manufactured<\/a><\/p>\n\n\n\n

WHAT IS A CRANK ARM ON A BIKE?<\/strong><\/h2>\n\n\n\n

<\/p>\n\n\n\n

A crank arm<\/em><\/a> is just a crank<\/em>, which is specifically defined as a \u201cbent or vertical handle\u201d. It comes from the Old English word cranc<\/em> as part of crancstaef<\/em>, a \u201cweaver\u2019s instrument\u201d.<\/p>\n\n\n\n

\"Fat<\/figure>\n\n\n\n

When you add arm<\/em> to the mix, it\u2019s akin to saying DVD Disc (DVDisc), or GPS System (GPSystem) or PIN Number (PINumber). What a nerd might call a tautology<\/em>.<\/p>\n\n\n\n

\u201cBUT!\u201d, you say, \u201cCrank and arm are two different words, so it\u2019s not the same thing.\u201d<\/p>\n\n\n\n

\u201cYes, at face value,\u201d I\u2019d reply. \u201cThe difference for bike pros, though, is that crank and arm are exactly<\/em> the same thing.\u201d<\/strong><\/p>\n\n\n\n

I\u2019d guess that a weaving loom\u2014referencing the definition above\u2014included some sort of lever mechanism. Nevertheless, we often need to point out which parts of a crankset in particular (spider, chainrings, or crank arm) we are talking about, for accuracy sake. In this case, talking about crank arms<\/em> adds clarity to a conversation.<\/p>\n\n\n\n

Since the term crank arm<\/em> is widely used, and the particular part of a crankset comprised of the arm is our focus here, we\u2019ll follow convention by continuing to add arm<\/em> to crank<\/em>.<\/p>\n\n\n\n

Structurally, the non-drive side crank arm consists of the one simple lever-arm; the drive side crank arm is a little more complicated due to the addition of the spider and the chain ring(s).<\/p>\n\n\n\n

BIKE CRANK ARM DESIGNS AND TYPES<\/strong><\/h2>\n\n\n\n

<\/p>\n\n\n\n

The history of bike design largely centers on bottom brackets and their corresponding crank modifications through the decades. The most significant changes have only come in the last few decades.<\/p>\n\n\n\n

One-Piece Crank<\/strong><\/h3>\n\n\n\n

<\/p>\n\n\n\n

A one-piece crank remains close to its origins in the automotive crank.<\/p>\n\n\n\n

\"1<\/figure>\n\n\n\n

Yep, the one sticking out the front of the car that you took hold of and, literally, cranked to kick over the engine, in the days before we had starter motors (and no, I don’t remember those ?).<\/p>\n\n\n\n

The forged\u2014or cast\u2014rod zig-zags through the bottom bracket shell, held in place by threaded bottom bracket flanges that tighten against the bearings<\/a>.<\/p>\n\n\n\n

Cottered Crank<\/strong><\/h3>\n\n\n\n

<\/p>\n\n\n\n

With cottered cranks, independent crank arms are attached to the spindle through a cotter pin.<\/p>\n\n\n\n

\"Bottom<\/figure>\n\n\n\n

Crank arms slip onto the spindle and are secured by tightening the cotter pin nut. Keeping it tight avoids play and thus rapid wear of the contact area. The cotter pin tightens against the machined edge visible on the left, holding the whole assemblage securely in place.<\/p>\n\n\n\n

Square Tapers & Splines<\/strong><\/h3>\n\n\n\n

<\/p>\n\n\n\n

Square taper designs <\/a>maintain the separate crank arms characteristic of cottered cranks, but improve on the way they connect to the spindle.<\/p>\n\n\n\n

There\u2019s no underestimating the simple engineering power of a wedge coupled with bolts inserting laterally into the spindle instead of vertically through it.<\/p>\n\n\n\n

\"square<\/figure>\n\n\n\n

Four faces with a tapered wedge fitting into a corresponding tapered aperture on the crank arm creates a tight and reliable fit.<\/p>\n\n\n\n

We attach the crank arms by means of bolts threaded into the spindle; applying the correct amount of torque ensures crank arms are firmly secured to the spindle when installed, and easily removed come maintenance or upgrade time.<\/p>\n\n\n\n

\"octalink<\/figure>\n\n\n\n

Shimano\u2019s Octalink splined bottom bracket and matching crank arms were an alternative for a while. But crank design quickly moved to integrated cranks. Square taper has stood the test of time (for low-end bikes) whereas Octalink is long gone.<\/p>\n\n\n\n

Integrated Crank<\/strong><\/h3>\n\n\n\n

<\/p>\n\n\n\n

\"integrated<\/figure>\n\n\n\n

In a way this design is a step back to the simplicity of a one-piece crank, although much lighter and stiffer.<\/p>\n\n\n\n

The drive side consists of the spider, crank arm, chainring and spindle together in one piece.<\/p>\n\n\n\n

\"bike<\/figure>\n\n\n\n

The non-drive side crank arm slots onto the spindle and is secured by a bolt threaded into the spindle. Alternately the crank arm clamps around the spindle with a pair of pinch bolts.<\/p>\n\n\n\n

HOW DO YOU FIX A BIKE CRANK ARM?<\/strong><\/h2>\n\n\n\n

<\/p>\n\n\n\n

Fixing a crank arm all depends on how you damaged it and how much damage is involved.<\/p>\n\n\n\n

Pedal threads are not easy to damage, but careless installation that even partially damages the threads may render the crank unusable. Even if you could install a pedal, tightening to torque tolerance would likely be impossible.<\/p>\n\n\n\n

Re-tapping the threads may work as RJ demonstrates:<\/p>\n\n\n\n