Description of the concern: Unlike classic round chainrings, oval chainrings do not have the same radius across the entire unit.
Or in other words, the distance from the center of an oval chainring to the periphery differs.
As a consequence, the chain tension varies during a pedal stroke.
When the “oval” part of the chainring is pointing forward, the chain is stretched ever so slightly more.
For that reason, many people wonder whether it’s possible to use an oval chainring on a single-speed bike that doesn’t have a derailleur to eat up the chain slack when the chain tension lowers during a crank revolution.
If the oval chainring is shaped properly, the changes in chain tension are incredibly small and almost permanent, especially during pedaling.
As a result, you can put such an oval chainring on a single-speed bike without suffering from a dropped chain. The chainring needs to have a narrow-wide teeth pattern for maximum chain retention.
Requirements for Installing an Oval Chainring on a Single Speed Bike
A successful installation of an oval chainring on a single-speed bike requires:
1. A Quality Oval Chainring
A well-made oval chainring ensures that the same number of teeth engage during every segment of a crank revolution.
This design greatly reduces the variations in chain tension caused by the unusual shape of the chainring and minimizes the likelihood of a dropped chain.
2. Horizontal Dropouts Or a Chain Tensioner
If the chain tension isn’t adequately set, the chain can fall regardless of what chainring is used.
There are two ways to tension a chain on a single-speed bike:
a. Horizontal Dropouts
If the frame has horizontal dropouts pointing backward, you could increase the tension on the chain by sliding the wheel back.
Such frames are found on dedicated single-speed bikes such as track bikes, urban fixies, BMXs, and dirt jumpers.
b. A Dedicated Chain Tensioner
Geared bikes do not have horizontal dropouts. When you decide to convert such a bike into a single-speed machine, you’re left without a way to modulate the chain tension because the derailleur is no longer present.
To battle this problem, people install dedicated chain tensioners that mount to the dropouts and push the chain up or down to increase its tension.
3. A Narrow Wide Chainring
The main purpose of narrow-wide chainrings is to maximize chain retention.
Narrow wide chainrings have teeth with alternating thickness. One tooth is slim; the next is thicker.
The design mimics the gaps on a chain which are also following a narrow wide pattern – the inner links have a narrow gap whereas the outer links have a wider one.
A narrow wide chainring keeps the chain tighter because the space between the chain links is maximally filled.
As a consequence, the chain is almost locked and doesn’t move from side to side as much as it would with a standard chairing.
For that reason, narrow wide chainrings are recommended when running a single-speed bike or a 1x drivetrain, especially if you don’t use a chain guide.
3. A Perfect Chain Line
In the ideal scenario, the chain is perfectly straight without any deviations to the left or right.
This set-up ensures efficient power transfer and reduces the chances of dropping a chain.
If you have a “real” single speed frame, the chain tension is straight by default.
But if your single speed bike is a conversion, you will have to do a lot of measuring to get the chain line as straight as possible.
If you don’t have a good chain line, the chances of a dropped chain increase notably.
4. A Good Chain
A high-quality chain with a consistent distance between the links is necessary to minimize the variations in chain tension.
Many oval chainrings are designed for 1x drivetrains and aren’t as thick as dedicated single speed chainrings.
As a result, the user has no choice but to combine the thin chainring with a geared chain even when the bike operates in single-speed mode.
(Geared chains are narrower than 1-speed chains to fit between the rear cogs.)
5. A Dedicated Single Speed Cog
It’s tempting to take a cog out of a cassette for a single speed conversion, but the approach has two major downsides:
a. Possible Hub Damage
Single-speed bikes put a lot of torque on the rear cog. The stress is continuous and always on the same spot.
When you use a thin cassette cog for a single-speed conversion, you risk damaging the hub because the cog has a narrower profile and can dig into the hub’s driver.
(Cassette cogs are thin because a cassette has to fit many of them.)
b. Ramped Shape
Cassette cogs have a special relief meant to facilitate shifting.
When such a cog is put on a single-speed bike, this property turns into a negative because it increases the chance of a dropped chain.
Conclusion: To avoid damaging the hub and dropping the chain, it’s best to use a true single-speed cog.
Setting The Chain Tension On an SS Bike With an Oval Chairing
1. Place the Cranks In The Proper Position
Rotate the cranks until the biggest radius of the oval chainring is pointing straight up.
The purpose of this step is to maximally stretch the chain.
If the chain tension is set when the chainring is in a position that doesn’t stretch the chain as much as possible, the tension won’t be optimal during the more demanding part of the pedal stroke.
2. Set The Chain Tension
The common standard for chain tension is to have 1/2″ (1.27cm) of up and down play at the tightest spot.
If you have horizontal dropouts, the classic way to set the chain tension is as follows:
- Tighten the non-drive side of the axle.
- Grab the entire wheel and use it as a lever to set the chain tension on the drive side. Check the play. Let go a bit or turn the wheel more if necessary.
- Once the tension is sufficient, tighten the drive side of the axle.
- Untighten the non-drive side and turn the wheel until it’s pointing forward.
- Tighten the non-drive side.
Note: There are other ways to tighten a chain on a frame with horizontal dropouts. The one above is a common method when doing the procedure alone.
If you’re relying on a tensioner, the tension is set by moving the unit up or down until the right setting is reached. The process is easier and cleaner too.
FAQ: Should my oval chainring be smaller or bigger than my regular round chainring?
In general, it’s recommended to match the size of your previous round ring when installing a new elliptical one.
If your old chainring has 32 teeth, the new oval should have the same number as well.
The idea is to make the current gear ratio more efficient without switching to a new one.
An Oval Chainring On a Fixed Gear Bike?
Putting an oval chainring on a fixed gear bike is not a popular choice, but it’s not unheard of either.
The legendary bicycle mechanic Sheldon Brown was running an old Biopace elliptical chainring on his fixie.
Here’s a brief paragraph that reveals part of his take on the subject:
People are often astonished to learn that I ride Biopace chainrings on fixed-gear bikes. They imagine that there will be tremendous changes in chain slack as the chainring rotates. In practice, this is not the case. A 42 tooth chainring will generally engage 21 teeth against 21 chain rollers, regardless of its shape.
You can read the full article here.
That said, some riders are unhappy with oval chainrings on fixed-gear bikes and consider the variation in chain tension annoying and even dangerous.
Why?
Because the chain on a fixed-gear bike is also part of the bike’s rear brake system. If the chain falls or breaks, you will immediately lose your ability to brake with the rear wheel.
And while an oval chainring may work just fine, a round chainring designed specifically for a fixed-gear bike is a more conservative and safer choice, at least for beginners.
If you’re new to fixed-gear riding, it’s best to stick with the classics.
Summary
1. An oval chairing can work on a single-speed bike as long as the drivetrain is of good quality, and there’s a way to efficiently pre-set the chain tension.
2. The chain tension will vary ever so slightly, but the discrepancies shouldn’t be big enough to result in a dropped chain.
3. When setting the chain tension, the highest point of the oval should be pointing up.
3. It’s recommended to use a narrow-wide chainring for extra chain retention.
