from Rookie’s keyboard
Hello, friends
I have prepared a short piece that will reveal a few important details regarding BMX chain sizing. Even if you aren’t a mechanic, you need to know the info below as it will be useful when purchasing a new chain. After all, chains and sprockets are consumables.
BMX Chain Width
All bicycle chains have two widths – inner and outer.
The outer width is the distance between the external/outer plates.
The inner width is the distance between the inner plates.
The official size of a chain always refers to the internal width.
If the chainring and/or the rear cog are tоo wide for the particular inner width, the combination will not work.
The standard BMX chain size is 1/8” (3.2mm).
There are also 3/32″ (2.4mm) and 3/16” (4.8mm) chains.
The idea of of 3/32″ chains is to save weight via skinner outer links.
3/16” chains are built for strength. Hence they’re thicker and heavier.
Weight Comparison
The table below compares the weight of all three BMX chain sizes.
| 1/8” (3.2mm) | Weight | 3/32″ (2.4mm) | Weight | 3/16” (4.8mm) | Weight |
|---|---|---|---|---|---|
| Wippermann conneX 100 | 403g (110L) | KMC K1 Narrow | 377g (100L) | KMC 415H (98l) | 800g |
| K1 Wide | 411g (110L) | Shadow Conspiracy Interlock V2 RACE | 362g (98L) | ||
| Mission 410 | 329g (102L) | KMC HL810 | 385g (100L) | ||
| Odyssey Bluebird | 263g (100L) | IZUMI Izumi-V | 362 (116L) | ||
As shown, the 3/32″ chains are not always lighter than 1/8″ models. In fact, there are 1/8″ models that weigh less than their 3/32″ rivals.
3/16” are not only heavier but also difficult to find.
1/8″ vs 3/32″
1/8″ chains dominate for the following reasons:
- Robustness
When all parameters are equal, a thicker chain is a stronger chain.
- Compatibility
If a chainring designed for a 1/8″ chain is combined with a 3/32″ chain, the teeth of the chainring won’t fit between the inner plates.
But a 3/32″ chainring can be combined with a 1/8″ chain. Some people say that the combination will result in a sloppy feeling due to side to side play as well as faster wear of the chainring’s teeth, but many have done it without experiencing major issues.
The outcome is dependent on the model of the chain and the chainring.
For ultimate results and safety (lower chance of a dropped chain), combine a 1/8″ chain with a 1/8″ chainring.
- Market choice
1/8″ chains are the standard. Consequently, the demand and the supply are high.
- Weight
As you saw in the table, 1/8″ chains are not necessarily heavier than 3/32″ models.
Therefore, the main advantage of 3/32″ chains is smaller than some riders believe.
- Stiffness
Another pro of 3/32″ chains is that they’re more flexible laterally. This property facilitates shifting and is therefore beneficial to geared bicycles.
But since classic BMX bikes have no gears, the extra flexibility of 3/32″ chains doesn’t matter.
Calculating/Finding Chain Width
Method 1: Labels
The easiest way to find the width of a chain is to read the label. Most models have either a 1/2″ x 1/8″ or 1/2″ x 3/32″ indication.
The first number (1/2″) indicates the distance between the chain pins whereas the second (1/8″ or 3/32″) specifies the width of the chain.
Method 2: Measure the Inner Width
If you’re trying to find the width of a chain without original packaging, you can use a digital caliper to measure the distance between the inner plates.
Method 3: Measure the Rear Cog
Another option would be to measure the thickness of the rear cog.
Rear cogs designed for 1/8″ chains are about 3mm thick.
3/32″ cogs are usually a bit over 2mm.
A Note On Chain Length
The length of a chain is dependent on the following parameters:
- Cog size
- Chainring size
- Chainstay length
A frame with short chainstays and a small chainring will need a shorter chain than a bike with longer chainstays and a bigger chainring.
New chains are much longer than a bike needs them to be. It’s up to the user to shorten the chain with the help of a chain tool.
The process is as follows:
Step 1: Slide the rear wheel towards the bottom bracket.
Step 2: Put the chain over the cog and the chainring.
Step 3: Take a short but strong wire and make two 90-degree bends on both ends. (You can use a cut spoke).
Connect one end of the wire to a chain-link closer to the chainring.
Connect the other to a chain-link closer to the rear cog. Ideally, the chain will be slack but not too much.
Step 4: Push the wheel back to tension the chain.
If the connection points are too far apart, you won’t be able to tension the chain. If they’re too close, you won’t be able to move the rear wheel much.
If you experience those issues, one of the connection points needs to be changed.
Step 5: Determine where the two ends of the chain should connect to maintain the desired chain tension. Then cut the chain with the help of a chain tool.
Until next time,
Rookie
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