Ideally, the chain tension of a fixie will be as high as possible while still allowing the rear cog and the front chainring to rotate freely. If the chain tension is low, the chain may fall off. If it’s too high, the rider will be fighting the drivetrain.
Why Fixed-gear Chain Tension Is Critical
Fixed-gear bikes do not have a coasting mechanism. If the rear wheel is moving so are the chain, the rear sprocket, and the chainring. This property can result in dangerous scenarios when the drivetrain isn’t in top condition.
If the chain is too loose, there’s a chance for it to derail and fall off the sprocket or chainring fully or partially. If that happens on a standard bicycle, the rider can coast until it’s safe to stop and remedy the issue.
On a fixed-gear bike coasting is not an option. Thus, the rear wheel may begin to “chew” the chain and bind against it. Due to the blocked wheel, the rider may fall off the bike. Whether this will happen depends on the bike’s speed, the rider’s reaction, and the surroundings.
If the chain tension is extremely high, the chain may grab the cog or chainring and prevent it from rotating freely. This makes riding inefficient and unpleasant.
For the reasons above, it is crucial to set a fixed-gear bike’s chain properly.
How To Set The Chain Of a Fixed-gear Bike
There are different methods to achieve proper chain tension.
Below you will find a general guideline.
Step 1: Place the bike on a repair stand or upside down on the floor.
Step 2: Partially untighten the rear axle nuts.
Step 3: Pull the rear wheel back and place it at an angle towards the non-drive side. Tighten the non-drive side axle nut.
Step 4: Pull the drive side of the wheel towards the drive side of the bike. Don’t try to center the wheel just yet. Tighten the drive-side nut.
Step 5: Free the non-drive side nut and center the wheel. Tighten the non-drive side nut.
Done.
The first part of this procedure creates a fixed pivot point on the non-drive side. Without it, one will lose a lot of time moving the wheel back and forth.
Once you’re done setting the chain, observe it. If there’s noticeable slack, it’s not tight enough. If the drivetrain doesn’t rotate freely, the chain is too tight.
Note: Over time, bicycle chains stretch and become longer. Thus, even if you never take your wheels off, the chain tension will gradually drop over time.
FAQ: How can I know if the chain is binding?
Spin the cranks. If at a certain point of the rotation, the cranks are prevented from rotating freely, the chain could be binding.
That said, chain tension isn’t the only possible source of the culprit. Some of the other possibilities are:
- Worn cog and chainring
- A tight chain link (this usually happens after adjusting the chain’s length)
- Excessively short chain
- A loose chainring
FAQ: Does a fixed-gear bike need a chain tensioner?
No. A chain tensioner is not needed because the rear-facing dropouts of the frame allow you to tension the chain. Furthermore, most chain tensioners aren’t strong enough to handle the tension generated by a fixed-gear bike and could bend backward and create a dangerous situation. A chain tensioner could be used only when the bike is single-speed (able to coast) rather than fixed-gear.
Another problem with chain tensioners is that they are unsightly and take away from the simple look of a fixed-gear machine.
FAQ: How can I measure chain tension without a device of some sort?
It’s difficult to measure chain tension without the use of sophisticated tools. That said, there’s a general rule according to which the chain’s slack should be around 1/2 inch (1.3cm) at the tightest spot.
FAQ: My drivetrain is loud. Does this mean that my chain tension is not correct?
One cannot say with certainty whether drivetrain noise is the result of an excessively tight chain.
The noise may be the result of:
- Dry/non-lubricated chain
- Improperly tightened rear cog and/or chainring
- Twisted chain line
- Damaged chainring or rear cog
- Twisted frame
…etc.
FAQ: Is it true that a worn chain harms the cog and chainring?
Yes. In general, chains and cogs wear down simultaneously. Thus, if you have to replace a rear cog or a front ring due to wear and haven’t changed the chain fairly recently, a new chain will be needed as well. Otherwise, the chain may skip and will wear down the rear cog and chainring faster.
Since chains aren’t the most expensive part of a bike, people tend to replace them along with the rest of the drivetrain anyway.
FAQ: The chain tension of my bike feels uneven. It’s high at one spot and low at another. Why?
It may come as a surprise, but it’s rare for cogs and chainrings to be 100% round. This means that at certain locations the radius of the cog or chainring gets longer or shorter by a very small amount. As a result, it feels as if the chain tension is alternating.
That said, most people will not perceive the difference. In some cases, the source of the problem will be a damaged chainring, cog, or frame.
In some cases, the noise may be “natural” for the drivetrain in question. Some combinations of chains, chainrings, and cogs are simply loud.
FAQ: Why do some track cyclists run low chain tension at the velodrome?
On the velodrome, speed is the name of the game. A looser chain provides less resistance and thus allows the rider to pedal faster. Since track cyclists rarely backpedal, there’s a lower chance for the chain to come off. When riding in traffic, however, the rider faces many unpredictable situations and cannot afford to ride with an extremely loose chain.
