from Rookie’s keyboard,

Hello, friends

Another day, another post.

Today, I decided to talk about bike pedals again – a “boring” but super important bicycle component.

What if I tell you that they have one unexpected property (from a rookie’s perspective)?

What is it?

Well, they have a built-in “self-tightening mechanism” that prevents them from falling off when you pedal.

This happens thanks to the strategic thread direction on the axles.

The left pedal has a left-hand thread. This means that the pedal is installed by rotating it counter-clockwise and can be removed by rotating it clockwise.

The right pedal has a right-hand thread. To mount it, you have to screw it in clockwise.

Despite the self-tightening function, if the pedals are not tightened sufficiently in the beginning, they will wobble and may even fall off.

Pedal Thread Directions

	Left Pedal	Right Pedal
Direction of Installation	Counterclockwise	Clockwise
Direction of Removal	Clockwise	Counterclockwise

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Crank Arms and Pedal Axles

To learn why self-tightening is necessary for optimal performance and safety, we have to analyze the motion of the crank arms and the pedals’ axles.

Drive-side

To move forward, the rider has to press the drive-side pedal down in a clockwise direction when looked at from the side of the chain.

As the crank arm is spinning, the axle of the pedal is supposed to be stationary.

(The pedal itself is rotating around the axle thanks to a simple ball-bearing system.)

Since the rotation of the drive-side crank arm is clockwise, it’s necessary for the drive-side axle to tighten in that direction too. This is accomplished by using a standard right-hand thread on the axle.

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It’s easy to comprehend what is happening by putting a finger on the drive-side crank arm and then spinning it to mimic forward pedaling.

You will see that the crank arm is rotating in a clockwise direction around your finger which in this case plays the role of the axle.

Rotation of the drive-side crank

However, since the non-drive side crank arm is pointing in the opposite direction, it’s rotating anti-clockwise when pedaling forward. (You can do the same exercise to understand the process.)

To make the non-drive side pedal self-tightening, it’s necessary to use a left-hand thread so that the pedal doesn’t untighten during riding.

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Additional Info

If the pedal is left loose ever so slightly (no threads should be visible), it will self-tighten until the axle no longer moves.

That said, it won’t be accurate to conclude that a bike pedal cannot come loose. It’s a very real scenario in the following cases:

The axle has been cross-threaded.

Cross-threading occurs when using the wrong pedals for the bike or when trying to install the pedals too quickly and with too much force.

Since the pedal axle is made of steel whereas the crank arms are aluminum, the axle damages the crank arm threads quite easily (steel is harder than aluminum).

Eventually, this could lead to a weak connection and a wobbling pedal.

• The pedal is broken/destroyed.

It’s extremely rare for a pedal axle to break. Truth be told, you’re more likely to break the crank arm than the pedal axle.

That said, every part under stress can potentially crack. In some cases, the pedal’s bearings and caps can be destroyed to the point where the entire platform falls off the axle. Of course, this is a rare situation. And there will be plenty of warning signs before it occurs.

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Thread Size

The size of most pedals is 9/16″ x 20.

9/16″ (14.3mm) is the diameter of the pedal’s threaded part.

TPI is an acronym for Threads Per Inch and shows the number of threads per 1 inch/2.54cm. In this case, the threads’ density is 20 per inch or 20 per 25.4mm which amounts to 1.27mm between threads.

There are also 1/2″/12.70mm pedals that have a thinner axle. Those are usually found on the BMX market and are designed for single-piece cranks. If you have a 1/2″ pedal, you won’t be able to mount it to standard cranks.

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The Right Wrench

Pedals require a 15mm spanner (In some cases, an 8mm Allen key can also be used.)

As long as the spanner is thin enough to get in the area and wrap around the axle, it’s gonna work.

That said, dedicated pedal wrenches are quite thin and have a long handle for additional leverage.

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Until next time,

Rookie