It is not easy to understand the bike pedal threads because there are several types and different threading for left and right pedals.
It could be a costly mistake to try to put the wrong pedal on your bike. This article will cover everything you need to know about pedals and their thread sizes.
Types of Bike Pedal Thread Sizes
It would be far too easy if all pedals were the same size and required the same tools to replace. Unfortunately, this is not the case, but thankfully, only two common types are still produced today.
It would be far too naive to assume that all pedals come in one size and need the same tool to install. Nonetheless, this isn’t true. Luckily, there are just two common bike pedals on the market today.
9/16” x 20 tpi (14.28 x 1.27 mm)
The most common bike pedal thread size on the market is 9/16″ – this is what most manufacturers produce. Pretty much all adult bikes that are made in the last 15 years will have 9/16″ with 20 threads per inch – TPI.
Major brands such as Specialized, Giant, Trek, Cube, etc., will have this exact thread size on their models.
½” x 20 tpi (12.7 x 1.27 mm)
Less common than the 9/16″ pedals, this thread size is still being produced daily and used by many bikes. These are mostly BMX bikes and cruiser-style bikes for kids. On these bikes, the thread size is most likely ½”.
0.55” x 20.32 tpi (14 x 1.25 mm)
This size is not common nowadays because manufacturers have stopped producing those a long while ago.
This specific size comes from the older French bikes – back in the days, the French had their pedal size.
Once global import/export grew exponentially, they stopped producing these sized pedals and went with those mentioned above.
If you happen to have an old French bike, the chances are that the pedal thread size is 0.55″ x 20.32 TPI.
How to Measure Bike Thread Pedal Size
Fear not. There are several ways to tell what size pedals you have/require. It requires very little knowledge and will only take a few seconds.
If you wonder what size pedals you have or need, there is a way to tell! It is very easy and won’t take more than a few seconds.
Check the Cranks on the Bike
Manufacturers made it easy to put the sizing on the crank, knowing that people would look for their pedal size.
If your cranks are made up of three separate sections, two separate crank arms, and the spindle that goes through the frame, your pedals will be size 9/16″ x 20 TPI.
If, however, your bike is made of only one piece of metal that is all connected and goes through the bike as one piece, then your pedal size will be ½” x 20 TPI.
On the other hand, if your bike is made out of one big piece of metal that is all connected, then your pedal size must be ½” x 20 TPI.
Knowing this little trick, you will determine what size pedals you have.
Measure the Current Pedals Thread Size
If you are still having difficulty determining your pedal size, there is another way. First, you can measure the thread width manually.
You can use a set of calipers if you have them handy. Those will get you an accurate measure. You could also use a standard ruler, but it won’t be as easy.
Take it to your Local Bike Shop.
Another way to determine your pedal size is by taking your bike to your local bike shop. The staff there will be more than happy to help and also guide you to a new set of pedals if you need them.
Bike Pedal Thread Adaptors
If you have bought pedals that don’t fit your bike or a set of pedals that you want but don’t come in the size you need, then there are handy adapters that you can use to solve this.
There’s a chance you bought a set of pedals, but they are the wrong size and won’t fit your bike. If that’s the case, it is unnecessary to replace them because adapters are available to solve this issue.
Types of Pedal Thread Adapters
There are adaptors available to convert from a ½” to a 9/16″ pedal thread and vice versa. For example, the Alta Bicycle Pedal Adapter is one of the best on the market.
Then there’s the Lowrider Pedal Thread Adapter that converts a crank with a thread size of 9/16″ to 1/2″ Crankspedal thread. This is for using a 9/16″ pedal on a crank with a thread size of 1/2″.
How to Install Pedal Thread Adapters
It’s very easy to install pedal thread adapters, and it won’t take more than a few minutes.
First, pay attention to picking the correct adapter for each side – left one to the left, right one to the right. Then, install each adapter as you would install a pedal.
Make sure it’s tightened. After you’ve installed both adapters, install your pedal into the adapter thread. Make sure that both pedals are tightened well enough.
You are pretty much done! It’s as simple as that.
You may feel that your pedals are sticking out just a bit because adapters are now between the crank and the pedals.
Unfortunately, the information about the left and right threads comes a little too late for some.
If you have tried and failed to loosen the left pedal by turning it to the left with the 15 mm pedal wrench, there’s a chance that the thread in the crank and on the pedal is broken. This is extremely bitter and can sometimes be very costly.
However, skilled craftsmen do not have to despair at this point, as there is still one last possibility to save the thread.
Everyone else: try a good bicycle mechanic near you!
How Bike Pedal Threads Work
The Wright brothers designed bike pedal threads before they made the first-ever plane!
Their invention is why the left bike pedal has a reverse thread, and the right side has a normal thread. The Wright brothers developed this kind of thread as it means with the motion of pedaling, the pedals will move in the direction of tightening rather than loosening.
The frictional force of the bearing assembly can loosen the threaded attachment of the pedal. In this regard, the thread on the left pedal is reversed. But the reason does not come from the very fact of bearing friction but from a phenomenon called “precession.”
The phenomenon can be illustrated as follows. If you freely grasp the pencil with your fist and spin it in a circle, the pencil itself will rotate in the opposite direction.
It’s their brilliant idea to have a reverse thread on the left bike pedal and a normal thread on the right. This is to prevent the loosening of the pedals when they are moved.
This prevents the accidentals from loosening and coming off your pedals, which would be an issue! Even more so if you were riding at higher speeds. You can learn more about thread directions in the video below.
In addition to the saddle and handlebars, the bicycle pedals on the bike are the only contact points between the rider and the bike. The pedals convert the pedaling force of the cyclist into propulsion and thus propel the bicycle.
This means that the pedals are essential for every bike and should meet certain safety, grip, and handling requirements, depending on the type of bike and area of use.