The size of standard BMX chains is 1/8″ (3.2mm). Fixies use 1/8″ (3.2mm) and 3/32″ (2.4mm) chains. A BMX chain can be used on a fixie when the chain’s size matches that of the original chain.
It’s also possible to combine a 1/8″ chain with a 3/32″ cog and chainring, but the fit will not be maximally secure.
BMX and Fixie Chain Width
A bicycle chain has two widths – inner and outer.
The inner width is the distance between the inner plates. The outer width is the distance between the outer plates.
The chain size indicated on the label is the inner width. If a chain is labeled as 1/8″ (3.2mm), the inner links are spaced apart by 1/8″ (3.2mm).
The standard BMX and fixed-gear chains are 1/8″ (3.2mm). However, there are also thinner /3/32″ (2.4mm)/ and wider /3/16″ (4.8mm)/ BMX chains.
The thinner chains are designed to save weight whereas the extra-wide models provide additional strength which is quite helpful given the impact and overall tension generated during BMX stunts.
Chain, Cog and Chainring Compatibility
For best fit, the chain, the cog, and the chainring of a single-speed drivetrain should be of the same size. Otherwise, the user may experience problems.
For example, if the cog and/or chainring are made for a 1/8″ chain, they won’t fit between the inner plates of a 3/32″ chain. Thus, this combination is unusable.
If a 3/32″ cog and/or chainring are combined with a 1/8″ chain, the teeth will fit, but there will be a possibility for side-to-side play. That said, the drivetrain will at least be operational. Many riders have used this combination without reporting serious issues.
Chain Length
BMX bikes have significantly lower gearing than a fixie. For example, a typical freestyle BMX can have a 22/8 gearing. This means that the chainring has 22 teeth whereas the rear cog has 8.
Race BMX bikes are built for speed and thus have a higher gear e.g., 44/16. However, fixies have even higher gearings. Some people run 52 chainrings.
The larger the gearing, the longer the chain needs to be. Consequently, it’s possible to buy a BMX chain that’s a few links too short for a fixie drivetrain. Whether this will happen depends on the fixie’s gearing and the length of the chain.
In the worst-case scenario, the user will have to buy two chains and use one as a “donor” to add a couple of extra links to the main one. This move makes no financial sense if the user has access to a single-speed chain long enough for a fixie.
FAQ: How can I calculate the chain length of a single-speed bike?
If you get a single-speed chain designed for a road bike or a fixie, there’s no need to worry about buying a chain that’s too short because most chains come longer than necessary.
The length of a chain is dependent on three parameters:
- Chainstay length (the longer the chainstays, the longer the chain has to be)
- Chainring size
- Rear cog size
Once, you have the necessary data, you can enter it into a single-speed chain calculator and get an approximate number of links that you will need for proper chain tension.
Example:
- Chainstay length – 443mm
- Chainring size – 48 teeth
- Small cog size – 12 teeth
Chain length – 51in/129cm (101 links)
Half-link of Full-link Chains?
Some BMX chains are half-link. Each link of the chain is much shorter than a standard one.
The advantage of those chains is that the user can set the rear wheel more precisely in the dropouts to tension the chain. In addition, half-link chains have the potential to be stronger.
The downside of half-link chains is that they’re heavier and stretch (wear down) faster due to the extra pivot points.
For that reason, some people install one half-link to a standard chain to benefit from the extra customization without adding unnecessary weight to the bicycle.
FAQ: Why are BMX and fixed-gear chains so wide and thick?
Single-speed chains are notably wider than chains designed for geared bicycles for the following reasons:
- The stress on the chain is very high, especially when pedaling uphill because the rider cannot switch to a lower gear. To survive, the chain has to be stronger and larger.
- Chains built for geared transmissions have to jump from one cog to another without rubbing. More speeds/gears/cogs require a thinner chain. Thin chains are still very strong but do not offer the same degree of toughness as single-speed models.
- Single-speed bikes use a single rear cog and chainring. Consequently, there isn’t an opportunity for chain rubbing, and the outer width of the chain is unrestricted.
Summary: What You Need To Know
BMXs and fixies are single-speed bicycles. Consequently, the same type of chain can satisfy the need of both models.
If a BMX chain is 1/8″ wide, it will fit best if the rear cog and the chainring of the fixie are designed for the same chain size.
That said, a 1/8″ chain can still operate when installed on a cog and chainring built for a 3/32″ chain, but the fit will not be as secure as possible.
If the BMX chain is 3/32″ wide, it can work on a fixie only when the cog and the chainring are designed for a chain of that width. 1/8″ chainrings and cogs will be too wide.
In some cases, a dedicated BMX chain can be too short for a fixed-gear drivetrain.
There are also 3/16″ BMX chains built for extra strength. While those chains are wide enough for a fixed-ear drivetrain, the fit will not be as secure as possible unless the user relies on a thicker than usual cog and chainring.
