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Sizing It Up

Sizing-It-Up

Sprockets and chains come in a variety of sizes. Each of those sizes is assigned a three-digit number that is, quite frankly, a great mystery to most riders. Yet, understanding how the numbers work and what setup is right for your bike or ATV is essential. Plus, once you grasp the terminology, you can impress your riding buddies with your knowledge. So let’s get started.

Size matters.

The size of your bike or ATV’s sprockets and chain are determined specifically for that vehicle. A lighter weight, lower horsepower bike will put less stress on the drivetrain and will benefit by the weight savings afforded by a smaller, narrower chain and sprocket. A heavier, more powerful bike requires more robust drivetrain components to withstand the forces being transmitted from the engine to the ground. The size used must be in line with the motorcycle or ATV and must always be a perfect match with each other. So … what exactly are we measuring? Let’s explore the two primary size considerations.

Pitch perfect.

The first measurement is what’s known as the chain’s pitch. That’s the dimension of the linear space between the pins or rollers along the length of the chain. This is measured from the center of one pin to the center of the next pin in line, forward or backward. Got it? Great.

Through thick and thin.

The second measurement is the width of the chain. The chain width is determined by the distance across the chain at the points between the innermost plates of the chain. In other words, measure across the hole where the sprocket teeth would fit in.

As mentioned, sprocket size must match the chain size. Even if the pitches match, if the chain is wider than the sprocket, the sprocket will mesh with the chain accurately, but will have excessive side-to-side play, allowing the chain to slide back and forth as you ride. Not good. Conversely, if the chain is narrower than the sprocket, the gear teeth will be unable to slide into the chain and engage the chain rollers properly, if at all. The ideal fit of a matched sprocket and chain is where the gear aligns with the chain rollers (pitch) and has minimal side-to-side movement (width). To assure you’ve got the right matchup and grasp what those designated sizes mean, it’s time to brush up on some basic math skills.

Understanding the numbers:

So, what’s the difference between a 530 chain and a 520 chain? The difference may seem slight if one looks only at the numbers, but the difference is actually quite significant, especially when it comes to chain and sprocket width. The key is to begin thinking in eighths.

Chain and sprocket sizing is based in inches. More specifically, in eighths. Each inch is divided into eight equal parts, resulting in 1/8-inch increments. Don’t ask why, it just is. This is the base unit of measurement applied to all chain and sprocket sizes. Now, let’s explore that mysterious numbering system.

Chains and sprockets are identified with a three-digit number that commonly begins with the number 4, 5 or 6 followed by two more numbers. The first number in the series refers to the pitch of the chain. The second two numbers define the width.

Consider a 520 chain and sprocket. The “5” in 520 represents the pitch of the chain and is used as a multiplier. In this case we take that 1/8-inch base unit and multiply it by five, resulting in, you guessed it, a 5/8-inch total. A 520 chain has a pitch of 5/8-inch.

The second set of numbers represent the width of the chain. In this case, the “20” in 520 describes the inside width of that chain. For simplicity, think of that number as “2.0” instead of 20. Again, using an inch divided into eight parts, we multiply 1/8-inch by 2.0, which equates to 2/8-inch, or what is better known in its reduced form as 1/4-inch.

But what about a 525 chain? Thinking of the “25” as “2.5,” take the 1/8-inch unit and multiply it by 2.5, for a total of two-and-a-half 1/8-inch inch widths, which is also known as 3/16-inch. 

Putting it all together, that means that a 520 chain has a pitch of 5/8-inch between pins and a ¼-inch wide opening. Similarly, a 525 chain has a pitch of 5/8-inch, but a width of 3/16-inch. From there, it’s straightforward to determine that a 530 chain would be 5/8-inch pitch with a 3/8-inch width. A 630 chain would have a pitch of ¾-inch (6 x 1/8-inch) and a width of 3/8-inch, and so on.

The number mystery is solved and now you know how to size it all up.

Explore the full range of sprockets and sizing charts for your particular bike by visiting the SUNSTAR website at sunstar-braking.com. Need help selecting the right parts for your needs? Just ask!

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