How To Determine Bike Chain Length

Your bike's main power supply comes from its chain, that's why extra care has to be given to it. These chains come in different types, styles, and configurations, we need to know about them so that repairing comes easy. In this guide, we will discuss everything about bike chains including how to determine them properly.

When it comes to bikes, chains are the main driving force and for that, they see a lot of wear and tear, probably a lot than any other bike component. A bike’s chain over time and cycling conditions start degrading, you will actually see that the rollers and rivets wear out and as a result, the chain stretches.

The exact measurement of a brand new chain is about 12 inches across 12 links so if the measurement is actually more than that, then it would be the perfect time to replace it. If this problem is not taken care of in time then the cogs could get damaged or worse!

In order to sort the problems, the first order of business is determining the bike’s chain length. Figuring out the correct chain length will make repairs and replacements a whole lot easier. The correct length will get you the correct chain for your bike and there won’t be any room for errors.

What Tools Do You Need?

There are specific tools that you need to determine the chain’s length, but first, let’s talk a bit about the chain’s construction. Bike chains are mainly of two types- connection rivet chains and master link chains, they are not that much different from each other but they have their unique constructions.

Master link chains have two outer chain links that connect to the chain itself whereas the connection rivet chain uses a special rivet for the connection as the name says. You will mainly need two types of tools to determine the chain length.

  • Chain Tool: These tools are necessary for cutting the chain
  • Master Link Pliers: This tool helps in removing chains with master links

Bike Chain Tool

The Different Methods of Determining Chain Length

As there are different chain types, there are different methods to determine the chain length, sometimes you use the length of your old chain to get the new chain, sometimes new methods are employed, the point is that there are different methods and we have our freedom to choose the methods.

Using The Old Chain

This is one of the easiest ways to determine the length of your bike chain, also comes in very handy. For all the bike chain sizes you can use the help of your old chain. First, you need to know if the size is correct and for that, you need to shift the bike into the small sprockets first and check if there is any slack or not.

If everything is good enough then there should be no slack in the chain but the derailleur should also be in a good position, it should not pull back that much. In the next step, you have to shift to the largest rear sprocket and front sprocket. After this, the chain will be able to make the shift easily and have two slight blends, this is all very normal so be prepared for that.

Now that we have figured out the length of the old chain we need to remove it and lay it on a hard surface. Check the new chain side by side, the links should be the same. If not, the cutting point should be precise, you should make sure that the old chain and the new chain match up. You can also try getting a universal bike chain, they fit almost all the bikes.

The Big-Big Method 

In this method, we will make sure that the bike’s chain is long enough so that it doesn’t cause any kind of damage to the derailleurs. The first step here would be to put the chain around the biggest front chainring, the biggest rear sprocket, and one link just to be sure (one link is mainly a pair of outer and inner plates).

There is a common mistake that people do here, they put the chain through the rear derailleur (rear suspension), just don’t do that. In order to make sure that everything goes smoothly, the derailleur is removed.

There are some bikes that have stronger rear wheels, these are bikes with rear suspensions, they have to be compressed if you want to use the big-big method. For perfect execution, the rear wheel of the bike must be far away from the cranks. If you are using air shocks by any chance, just let the air out, otherwise for springs, you have to remove the shock first, then the spring, and then re-insert the shock. 

If you want a simpler approach than this, then just add an extra pair of inner and outer plates to the total length of the chain. Although this method is very simple it isn’t that much accurate and there is a chance that you won’t get the desired results.

Adjusting Bicycle Chain
Adjusting Bicycle Chain

The Largest Cog and Largest Chainring Method

Here is one of the easiest methods that we have ever suggested and tried ourselves. This method will be explained in steps so let’s get started!

Step 1: Shifting The Derailleurs

When you have removed the old chain, the derailleurs need to be shifted. The front derailleur needs to be shifted to the largest chainring and the rear derailleur needs to be shifted to the smallest chainring.

Step 2: Wrap The Chain

The next step involves wrapping the chain now, it needs to be wrapped around the largest chainring, we also have to make sure that the outer plate is directed towards the front chainring. If the outer plates are not directed like that, then it could lead to problems.

Step 3: Pass The Chain

In the next step, we have to pass the chain through the derailleur cage as we mentioned before. After passing through the derailleur cage, it needs to go to the largest front chainring.

Step 4: Hold The Chain

Here we have to hold the chain at the 5’o clock position.

There would be some users that would be using the master link chain, for that we have a different methodology. A half master link chain needs to be installed at the front of the chain.

Step 6: Bypassing The Derailleur

In the second last step, we will pull the chain’s lower section to the front of the chainring. This way the derailleur will be bypassed.

Step 7: Cutting Point

In the last step, we need to find the closest rivet which is at the intersection of the chain. When we find the point, we need to cut it. That’s it, that is the cutting point.

Repairing Bicycle Chain

The Chain Sizing Equation

You can find out the bike chain’s length by using a formula, you won’t even have to open the new box. The calculation will be limited to only whole-inch increments because we can only join the inner plates to the outer plates when it comes to the chain.

The Formula is as follows:

L= 2(C) +(F/4+R/4+1)

Index:

  • L: This is your chain’s length in inches 
  • C: This is the chainstay. It is the distance between the crank’s middle to the rear axle. You have to measure it to the closest 1/8 first and then convert the answer to decimal form.
  • F: This is the front chainring, these are the teeth at the front of the largest chainring. If you are having some confusion then the number is often printed at the cogs and sprockets.
  • R: This is the rear cog, these are the teeth at the rear of the largest cog. Again, the number will be printed on the sprockets.

What Could Go Wrong?

We may think that everything may go smoothly but that is not always the case, there are some problems that could occur and we need to be prepared for that. 

Not Enough Chain Wrap Capacity

One of the biggest problems that you could face has to do with the rear derailleur when the chain wrap capacity is not enough. This means that if you have a small chainring combination then the chain will be too slack or may even fall off if there are bumpy roads, this is a dangerous situation and needs to be fixed.

First of all, we can get a rear derailleur with a longer cage that will be suitable in every kind of situation. If the chain is longer than expected then we can shorten it. The chain gauge needs to be at optimal performance too. Another solution that we can use is to avoid the small sprockets at the cassette.

More Bike Maintenance Tips:

Recap

A bike’s main driving force is the chain, and in a course of time, it will experience wear and tear. When this happens, we usually have two options, either repair or it or get a new one, the best course of action is getting a new chain. By determining a chain’s length we can speed up that process.

There are many methods that we can employ to find a chain’s length, some are hard while some are easy. We hope that through this guide, you now have a broad idea about a chain’s length and how to measure it. Let us know what you think about it in the comments!

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