We’ve all been there – you have something with a thread like a screw, nut, bolt, or even a faucet tap – you’re trying to loosen it but can’t remember which way to turn it…clockwise? Counterclockwise…?

Bike pedals can be even trickier to fathom out because the left and right pedals have a thread that goes in different directions.

Let’s see which is which (with a handy infographic) and, also, why they have opposing threads.

Which way to turn bike pedals to loosen them

Here’s the quick answer: the bike pedal that is reverse threaded is the left one (that’s the one that your left foot goes on when you’re sitting on the bike).

This means that, to loosen the left-hand pedal, you need to turn it in a clockwise direction.

To tighten a left-hand pedal, turn it counterclockwise or anti-clockwise.

Right-hand pedals (for your right foot) have a standard thread: clockwise tightens the pedal and counterclockwise loosens the pedal.

Take a look at the infographic below and compare it with your bike pedals and you’ll soon know which is which.

Why are left bike pedals reverse threaded?

Despite appearances, bike pedals aren’t threaded differently like this in order to make life difficult and more confusing than it needs to be.

This is not a global conspiracy brought about by evil bike manufacturers.

The real reason is that it stops your left-hand bike pedal from falling off as you pedal along.

And, it’s all down to something called ‘Precession’.

The physics of this are fairly complex but, distilling it down, precession acts on the bike pedals to tighten them as you pedal and it only does this because they are each threaded the opposite direction.

To demonstrate this in simple terms squat down and look at your left pedal:

• As you travel along, the left pedal crank arm rotates in a counterclockwise direction
• This causes the pedal to rotate the opposite way (clockwise direction)
• This causes the end of the threaded pedal axle (which is slightly loose inside the crank arm) to rotate in a counterclockwise direction

This precessional counterclockwise force, which is the strongest of these three directional forces, causes the left-hand pedal to tighten in the crank arm. Making sure that it stays securely fastened and allowing you to keep on pedaling.

Just remember: LEFT pedal is REVERSE-THREADED