Guide on how to choose the correct chain size for your Pit Bike

Guide to Differentiating Between 420 and 428 Pit Bike Chains

In this guide I will walk you through how to work out which chain you need when buying for your Pit Bike or Chinese Quad.  These bikes usually only have 2 chain types, they are 420 and 428 chains.

While they may appear similar, they have distinct differences that affect their compatibility and performance. Here’s a quick guide on how to differentiate between them.

1. Choosing the correct chain link size for your bike.

The numbering system used for chains like 420 and 428 provides information about their dimensions. This system is standardized by the American National Standards Institute (ANSI).

First digit (4): Indicates the chain's pitch in eighths of an inch. That is the measurement from the centre of one pin to the centre of the next.

Both the 420 and 428 chains have a pitch 0.5 inches (12.7mm)

Second and third digits (20 or 28): These indicate the roller diameter and roller width…

Here is where the significant difference lies.

420 Chain: The roller diameter is 7.75mm, width is 6.35mm (between the side plates)

428 Chain: The roller diameter is 8.51mm, width is 7.92mm (between the side plates)

2.  Now we know the difference between 420 and 428 chain links we need to work out how LONG we need the chain to be...

Motorcycle chain is not measured in inches or millimetres; it is measured in the number of links (or pins to be precise).

Most pit bikes will typically have a chain which is between 90 links to 120 links in length, this can vary depending on a number of factors including swing arm length and frame type.

The easiest way to calculate the length required is to count the number of links in your old chain INCLUDING the joining link. As long as the new sprocket are the same size you will not need to adjust the chain length.

3. Changing sprocket size.

If you are changing the size of your sprockets at the same time as the chain you may need to adjust the length (number of links) of your new chain. Going up by one tooth on one sprocket would mean that an extra 2 links will be needed to take the larger sprocket.

Going down by one tooth on either sprocket would mean you need a chain that is 2 links shorter

4. What if I don’t have my old chain?

If you don’t have the old chain the easiest way to get the correct number of links is to buy a long chain (120 links is usually enough) and then remove links until it is the desired length.

REMEMBER: You cannot ADD links to a chain, only remove them so always go on the side of caution and get a longer chain.

If you have no chain and also don’t know if you have 420 or 428 sprockets please refer to our sprocket sizing guide HERE

6. Conclusion

For most Pit Bikes, Monkey Bikes or small Quads a good quality 420 chain is more than adequate, but if you already have 428 sprockets on your bike it may be easier and cheaper to stick with 428 so that you do not need to replace the sprockets.