Bike Theory For Dummies: Cottered And Cotterless Cranks Demystified

from Rookie’s keyboard

Hello, friends

Today’s lesson from the series Bike Theory for Dummies (BTFD) will tell you everything you need to know about cottered and cotterless cranks. 

Let’s start with the basics.

Cottered Cranks

Cottered cranks go back to the ’70s. They attach to the bottom bracket spindle via a wedge inserted into the crank arm. 

You can easily identify them by looking at the attachment points. If there’s a small wedge (or a hole for one) perpendicular to the crank arm, the cranks are cottered.

Cotterless Cranks

Cotterless cranks are all the cranks out there that don’t use a wedge to grab the bottom bracket axle.

The attachment mechanism of cotterless cranks depends on the bottom bracket. 

For instance, square taper bottom brackets connect to the cranks via a set of bolts threaded into the axle.

The Good Sides Of Cottered Cranks

• Vintage look

Let’s be real. Cottered cranks don’t have a technical advantage over cotterless models. Their appearance is their strong point.

Some cottered cranks have a design absent from modern cranks.

Thus, if the user is looking to achieve a certain retro look, cottered cranks can help with that task.

The Negatives

Cottered cranks have many disadvantages:

• Heavy Crank Arms

The arms are made of steel and are therefore heavier because aluminum is a soft material and will be deformed by the wedges (cotters).

• Super Low Supply

Cottered cranks are available only on the second-hand market. In many cases, they’re overpriced for what they are due to the shortage of available models.

To find a good set, you will have to browse a website for used parts, a forum, or a Facebook group.

• Service Tools Are Hard to Find

Since cottered cranks are a rarity, the companies making bike repair instruments have lost the incentive to produce tools for them.

Ideally, you will have a cotter puller/press. Some people machine them and sell them online. Since the item is highly specialized, the price is often high for recreational mechanics who will need the tool once or twice.

• Low Quality

Мany of the cottered models available today are average at best. For example, most cottered cranks come with riveted chainrings that cannot be removed without replacing the cranks too.

• Few Bottom Bracket Options

Cottered cranks cannot operate with modern bottom brackets. To use them, you will need a bottom bracket spindle designed specifically for cottered cranks. Those have beds cut out for the cotters holding the cranks.

• Limited Crank Length

Since cottered cranks aren’t popular, they do not come in a variety of lengths. Most cottered cranks are 170mm. This will prevent you from using shorter cranks if you so desire.

• Limited Chainring Choice

Cottered cranks will limit the chainrings that you can install for two reasons:

1. Most cottered cranks come with riveted (non-removable) chainrings.
2. Some cottered cranks have three rather than five attachment points for their chainrings. Thus, you won’t be able to use modern chainrings with those models even when the chainrings aren’t riveted.

Cotterless Cranks = The Logical Choice

• By upgrading to cotterless cranks, you will gain access to a large variety of modern cranks, chainrings, and bottom brackets. If you want your bike to be up-to-date and use the latest components, cotterless cranks are the way to go.

• Modern cranks are fairly easy to install and remove as long as you have the right tools. For example, if you have square tapered cranks, you will need a crank extractor. That said, some of the latest models attach to the bottom bracket solely via Allen bolts. Thus, you can remove them by using even the simplest multi-tool.

• Modern cotterless cranks could be noticeably lighter than old-school cottered cranks.

• Cotterless cranks are available in a variety of lengths. If you want to experiment with shorter or longer cranks, cotterless cranks will allow you to do that.

• Cottered cranks pre-date MTBs and BMXs and were designed primarily for road bikes and commuters. Subsequently, a set of cottered cranks won’t offer top-level strength simply because it wasn’t needed at the time.

• Cotterless cranks have no technical disadvantages when compared to cottered cranks. One can argue that cotterless cranks aren’t nearly as aesthetic when installed on retro models. That may be true if one is referring to modern cotterless cranks. However, there are many cotterless cranks from the 70s and 80s that look just fine on a retro bicycle that’s even older.

From cottered to cotterless 

It’s possible to convert from cottered to cotterless cranks. The procedure is as follows:

Step 1: Remove the cranks from the bottom bracket spindle (this is the hardest part and may require you to destroy the cranks if you don’t have the specialized tools mentioned above).

Step 2: Remove the bottom bracket.

Since cottered bottom brackets are fairly old, you will need a specialized tool for the lockring and the cups.

Step 3: Measure the bottom bracket shell to determine how wide the new bottom bracket body should be.

Measure the length of the old cottered spindle and make sure that the new bottom bracket has the same total width.

Those steps are necessary to ensure that the new chainline is as close as possible to the old one.

Usually, bottom brackets have a size indicator consisting of two numbers e.g., 68×113.

The first number (68 in this case) indicates the width of the bottom bracket body whereas the second (113) shows the length of the spindle (total bottom bracket width).

Step 4: Install the new bottom bracket and cranks.

Until next time

– Rookie