Determining the right chain length for your bike may seem complicated. In reality, there is no reason to worry.
Good news, because this is something to know when replacing a bike chain.
In this article, I share with you the 4 methods I used, either in the workshop or at home, to determine the ideal chain size for my bike. By following one of these methods, finding the right chain size will be easy.
The good thing is that these methods are useful to determine the chain length of your bike whether it is a road bike, mountain bike, or single-speed.
4 methods to determine the length of a mountain bike or road bike chain
Determine the bicycle chain length using the old chain
Of course, you can use your old chain as a length reference for the new one. But it has to be a good one. In the case of replacing the original chain, this should be reliable. However, check if it had a quick release or not. This will have an impact on the type of link at the ends of your future chain.
Determine the length of a chain using the largest sprocket and the largest chainring
This method used by the transmission manufacturers Sram and Shimano is in my opinion the easiest to use on rigid frames only.
The idea here is to place your new chain on the largest sprocket and the largest chainring without going through the derailleurs, tighten and add 2 links to this loop.
The links to add are a male (2 inner plates + 2 rollers) and a female (2 outer plates + 2 pins).
This total chain length corresponds to a specific number of links. Both ends of the chain must be male links when using a quick link.
Therefore, this is equivalent to adding one link + the quick link.
To determine the chain length of a single-speed bike, the method is identical, instead of adding 2 links, you add 4.
Determine the size of a chain using the smallest sprocket and smallest chainring
This second method given by the Italian manufacturer Campagnolo consists in placing the chain on the smaller sprocket and the smaller chainring through the derailleurs. Then measure the distance between the guide roller and the chain to the chainring.
In the figure below from the Campagnolo user manual, the distance H should be between 8 and 15mm.
Tip: Checking the correct chain length
A visual way to check if your chain length is good on a rigid frame is to place the chain on the large chainring and the small sprocket and make sure that the cage of your derailleur is perpendicular to the ground.
The cage is the element of the derailleur that joins the guide and tension rollers together.
Determining a chain length for full suspension frames
When a frame is a full suspension, the distance between the wheel axle and the bottom bracket axle varies during the suspension movements (compressions/decompressions).
To adjust the chain length to this movement you must, as in the first method, place the chain on the largest sprocket and on the largest chainring without going through the derailleurs and add 2 links. But be careful, this must be done in the position where the distance between the wheel axle and the bottom bracket axle is the most important. This distance is given according to the swing axle of your rear triangle.
It is up to you to measure this distance.
Calculate the bike chain size
You can also determine the chain length of your bike with online calculators.
I admit that I don’t use this method because I think it takes more time and requires the use of a computer while I have my hands on the bike.
How do I know if the chain is too long?
To check that your road bike or mountain bike chain is not too long, place yourself on the largest chainring and the smallest sprocket. Once in this position, check that the chain is not too loose.
How do I know if the chain is too short?
To check that your MTB or road chain is not too short, stand on the large chainring and sprocket. This puts maximum tension on the rear derailleur. Therefore, if in this position you cannot lift the derailleur cage, the chain is too tight.
Does bike chain length really matter?
It is important that the chain on your bicycle is the right length. A chain that is too short or too long will have a direct impact on the life of the chain and other drivetrain components.
A chain that is too short or too long will have a direct impact on its life and that of the other components of the drivetrain, while a chain that is too short will increase friction and stress on the components.
Likewise, efficiency will be reduced.
You’ve learned how to determine the right chain length for your bike based on its drivetrain and frame type.
Now keep in mind that the right chain length is essential to the proper functioning of your components and their longevity.