How to Size a Bike Chain
Determining the correct bike chain length is the basic preparation task for changing the bicycle chain. We explain why accuracy is important when sizing a bicycle chain. Furthermore, we also present various methods how to size a bike chain for your new bike chain.
Sizing a Bicycle Chain – In a Short
These exciting topics await you:
Why the Right Bike Chain Length Is so Important
On most bikes, the chain transfers your power from the pedals to the rear wheel. However, for the shifting parts and drivetrain to work one hundred per cent, the chain must be a perfect match for your bike. A key factor here is the perfect chain length.
A chain that is too long can cause to disengagement, hit the frame or a chain suck more easily, which can lead to damage to the bike or even crashes. A chain that is too short, on the other hand, may prevent you from shifting all gears. Damage to the shifting components is also possible. Wear on the chain, sprockets and chainrings can be also increased. The bike chain length has a significant influence on the riding safety and the performance of your bike.
Although manufacturers such as Shimano offer bicycle chains in various standard lengths, sizing is often necessary. When changing the bike chain, it is therefore crucial that you determine the exact number of chain links.
WHAT YOU NEED
Material and Tools
In terms of equipment, you don't need much for sizing a bicycle chain.
- New bike chain
- Chain tool (pin extractor)
- Working gloves (optional)
You have everything you need to size the bicycle chain on your bike? Let's go!
Calculating the Chain Length – Step-by-Step Instructions
There are basically four methods for determining the matching number of chain links. We explain the procedure for all four below.
METHOD 1
Counting Links (Comparative Method)
"Why not simply place the new chain next to the old chain and compare the length?" – unfortunately, this doesn't work. This would be too inaccurate due to the elongation of the worn chain. Instead, for the first method, you have to count the individual links of the old chain and then simply use the resulting number for the new chain. Please note: This method requires that the old chain was optimally sized.
Our expert tip: It's best to count two or three times. You should be sure of the number before you shorten the new chain.
METHOD 2
Calculate the Chain Length
If you are building a completely new bike, you can also calculate the optimum number of chain links.
- Sum up the number of teeth of the largest chainring (T1) at the front and the largest sprocket of the cassette at the rear (T2).
- Divide the result by two.
- Now add two chain links (one inner and one outer link) to the number of links obtained.
- Now measure the length of the chain stay – with the chain. You do this by holding the first bolt of the chain in the center of the rear quick release or thru axle and counting chain links from there to the center of the bottom bracket (NL).
- Multiply the result by two.
- Then add the result from step 3.
- Round up the result so that you will get an integer (even) number when divided by two.
Is that too complicated for you? You can also calculate the chain links using this formula:
Chain length = 2 x NL + 1/2 x T1 + 1/2 x T2 + 2
- NL stands for the number of the chain links, needed to measure the chainstay.
- T1 is the number of teeth of the largest chainring at the front.
- T2 is the number of teeth of the largest sprocket of the cassette.
Our expert tip: For Shimano or SRAM 11- and 12-speed drivetrains, however, we recommend methods 3 and 4.
METHOD 3
Chainring and Sprocket Method – Shimano
This method is suitable for all new Shimano 11/12-speed chains if you don't have an old chain for comparison. This is how it works:
- Shift the derailleur to the smallest sprocket and the front derailleur to the smallest chainring (if your bike has multiple chainrings).
- Place the chain over the largest sprocket and chainring so that the two ends of the chain meet at the back (9 pm) of the cassette sprocket.
- Hold the ends of the chain together so that one side overlaps. The point at which the chain has contact with the cassette for the last time is called the zero position
- You must add chain links to the zero position to obtain the correct length.
- Hardtail bikes + chain with QUICK-LINK chain lock: 4 to 5 links
- Hardtail bikes + chain with connecting pin chain lock: 5 to 6 links
- Full suspension bikes + chain with QUICK-LINK chain lock: 5 to 6 links
- Full suspension bikes + chain with connecting pin chain lock: 6 to 7 links
METHOD 4
Chainring and Sprocket Method – SRAM
This method is suitable for all current SRAM 11/12-speed chains (except AXS) if you don't have an old chain for comparison. And it works like this:
- Shift the rear derailleur to the smallest sprocket and the front derailleur to the smallest chainring (if your bike has multiple chainrings).
- Place the chain over the largest sprocket and chainring so that the two ends of the chain overlap on the underside of the chainstay.
- Shorten the chain at the point where three pins overlap on the longer overlapping chain part.
Further Tips for Finding the Right Bike Chain Length
- Are you riding a 12-speed flattop chain for SRAM AXS drivetrains? The US manufacturer offers its own AXS bike chain length calculator on its website to determine the exact number of chain links.
- The calculation using a formula is the simplest method. However, it is the least accurate, as it does not take into account certain characteristics of the bike model (such as the rear suspension of a fully).
- If you have accidentally shortened the chain too much, you can easily insert some links with another chain connector.
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