Description of the Situation
You’re unsure whether a frame with vertical dropouts can be used for a fixed gear conversion.
Condensed answer: A frame with vertical dropouts is not ideal for converting a bike into a fixed gear. The fixed position of the dropouts makes it very difficult to safely maintain optimal chain tension. In the long run, it’s best to invest in a dedicated fixed gear frame with rear-facing dropouts.
The Chain Tension Dilemma
The number one problem with vertical dropouts is that they come with a pre-set place for the axle. As a consequence, one cannot move the wheel forward or backward to respectively decrease or increase the tension of the chain.
Conversely, dedicated fixed-gear bicycles have rear-facing-dropouts allowing you to adjust the bike’s chain tension by manipulating the wheel’s position.
There are some workarounds that can help you set adequate chain tension on a frame with vertical dropouts but most are either inconvenient or too expensive to justify the investment.
Below you will find the most common methods to tension a chain when using a frame with vertical dropouts:
1. Finding The “Magic” Gear Ratio
You can increase or decrease the chain tension by trying different gear combinations.
The bigger the gear, the greater the chain tension for the same chain length. The smaller the gear, the lower the chain tension.
For every frame and chain length, there’s a gear ratio that results in acceptable chain tension. The combination is known as the “magic gear ratio“.
This chain tensioning method has three major downsides:
a. You are restricted to 1 or 2 gear combinations that may be sub-optimal for your style of riding.
b. You have to buy more than one rear cog and chainring.
c. As the chain wears down, the chain tension will drop, and you will have to rely on a different method to re-tension the chain.
2.Half-link (pintle) Chain
The standard chains found on most bicycles consist of narrow and wide links. To increase or decrease the length of the chain, you have to add or remove two links – one wide and one narrow. Since each link is a half-inch long, the user has to work up or down in 1-inch/2.54cm increments.
In different, half-link a.k.a. pintle chains use identical half-inch links and allow you to add or remove one at a time. As a result, you can work in half-inch increments and fine-tune the chain tension with greater precision.
This method requires you to periodically remove a chain link to optimize the tension. Some people will find the process somewhat annoying.
Note: Half-link (pintle chains) aren’t designed for long mileage because they stretch very quickly and have a tendency to break unexpectedly. Hence why they’re more common on stunt bikes (e.g., BMX) which don’t cover long distances.
3. Normal Chain + Half-link
If you don’t want to use a pintle chain, you can add a half-link to your standard chain. A half-link a.k.a. a cheat link is as long as a regular link but has two sides of different width. One side is wide, the other is narrow.
Тhe cheat link allows you to make a 1/2-inch change without having to replace the entire chain with a pintle model.
The benefit of this approach is that you get the strength of a regular chain and the adjustment versatility of a pintle model.
4. An Eccentric Hub
Eccentric hubs have a mechanism that offsets the axle. As a result, one can use the hub to increase or release chain tension.
The pros of this approach are:
- Clean, aesthetically pleasing look
- Fast adjustment of the chain tension via a wrench
- You can run multiple gear ratios
Having said that, eccentric hubs have major downsides too:
A new eccentric hub retails for close to USD 200. You also have to buy a proprietary cog that would fit on the hub as well as the tools needed for assembly.
In addition, your rear wheel will have to be rebuilt around that hub. Thus, the expenses add up to:
- New Hub
- New Cog
- Rear-wheel rebuilding
For the same money, you can buy a new frame with rear-facing dropouts.
Truth be told, you may even buy an entire fixed gear bike on the second-hand market.
Therefore, this solution makes sense only if you can comfortably afford such a product and truly love the geometry of your existing frame.
5. Аn Eccentric Bottom Bracket
Eccentric bottom brackets allow you to increase or decrease the chain tension by offsetting the bottom bracket. The principle is very similar to that of an eccentric hub except that the rotation happens inside the bottom bracket shell.
The pros of this approach are:
- Discrete, aesthetically pleasing
- Contrary to the case of eccentric hubs, you don’t have to rebuild the wheel or use proprietary cogs and chainrings.
The cons are:
- Expensive. An eccentric bottom bracket is about USD 150-180. When you add the tools needed to install and set it, the bill goes over USD 200. As already mentioned, you can get a proper frame for the same amount of money.
- Inconvenience. Some people may find the installation of the bottom bracket and its adjustment complicated.
6. Filing The Dropouts Backward
Some riders file the dropouts of the frame backward ever so slightly so that the axle can move a bit.
Similar actions are done at your own risk and void the warranty of the frame because you’re modifying the product in a non-approved manner.
A Chain Tensioner Cannot Be Used On Fixed Gear
An aftermarket chain tensioner disintegrates when installed on fixed gear bikes due to high chain tension.
When you’re pedaling forward, the chainring bites against the chain and pulls it. Then, the chain rotates the rear cog and subsequently the axle and the wheel.
During a forward pedal stroke, the upper part of the chain (the one closer to the seat) is under the greatest tension. In different, the bottom part of the chain (the one closer to the ground) is somewhat slack.
A spring chain tensioner operates on the lower part of the chain. It either pushes up or pulls down the chain to create proper chain tension.
There isn’t a lot of stress on the chain tensioner when pedaling forward because the bottom part of the chain isn’t maximally stretched.
If you pedal backward, the chainring spins in reverse (anti-clockwise) and stretches the bottom of the chain a bit more.
If there’s a freewheel (the bike has the ability to coast), the rear wheel itself isn’t part of the equation as it’s rotating independently. (If you want to learn more about how a rear hub works, check out this post).
As a result, the tension of the chain doesn’t increase greatly during backpedaling because the wheel has no effect on it.
On a fixed gear, the outcome changes drastically because the rear wheel is never disconnected. When the rider tries to brake by skidding, the chainring stops moving and so does the chain. However, the wheel wants to remain in motion due to inertia. The cog is also spinning and pulling on the chain. As a consequence, the bottom part of the chain stretches and reaches high tension.
The spring on a chain tensioner is too weak to cope with the extra tension. If there’s a chain tensioner, the chain will either push it or pull it aggressively until the spring twists or brakes. Damage to the body of the tensioner is also possible.
Another downside of using a tensioner on a fixed gear is the slack in the lower part of the chain. Every time a cyclist skids, the first part of the braking sequence is “slack elimination” rather than locking the wheel right away. The result is a jerky motion that negatively affects the control over the bike.
For the reasons above, people don’t use aftermarket chain tensioners for fixed gear bikes. That said, chain tensioners work just fine on single-speed bikes with a freewheel.
What About a Ghost Ring?
A ghost ring is a free chainring added to the drivetrain to increase chain tension. The ghost ring isn’t connected to the frame. Only the chain is keeping it in place. One can increase or decrease the chain tension by playing with the position of the chainring.
Ghost rings look cool, but they have the following downsides making them a sub-optimal choice:
- Potential injuries or damages
The chain is the only component securing the ghost ring. If the chain wears down without being readjusted, it may become too loose, and the ghost ring may break free, especially if the terrain is bumpy.
If the ghost ring jumps out, it can get into the spokes or jam into the cassette and cause major damage to the rear wheel. The accident may result in injuries too.
- Annoying set-up
If the chain tension is off or the chain and chainring don’t agree with each other, the ghost ring will keep coming out until you get the set-up “just right”.
Ultimately, it’s best to avoid using a ghost ring, especially as a long-term solution.
What About Horizontal Dropout Adapters?
Horizontal dropout adapters are an aftermarket product designed to turn frames with vertical dropouts into frames with rear-facing dropouts. The adapters attach to the frame via bolts tightened to the existing dropouts.
The idea may seem great on the surface, but it raises some red flags.
First, a bolt link isn’t as strong as а proper weld. Second, on a fixed gear bike, the rear dropouts are under a lot of stress. It makes sense to keep them as strong as possible. Adapters can compromise strength.
Third, horizontal dropout adapters lower the aesthetics points of the bicycle.
Therefore, it’s highly questionable whether it’s worth it to rely on a “hack” instead of investing in a proper frame.
A frame with vertical dropouts will always be sub-optimal for а fixed-gear conversion because all aforementioned solutions have major limitations and downsides.
This leaves us with three logical approaches:
1. Sell the frame and buy a new one
There are no irreplaceable frames. If you can find one comfortable frame, you can find another. The only exceptions are frames that have sentimental value. In that case, you can keep your existing bike and build a new one with a proper frame for the task.
When it comes to frames for fixed gear, there are only two viable options:
- An old frame with semi-horizontal dropouts
Some old road bike frames have semi-horizontal dropouts giving you the option to slide the wheel backward to increase chain tension. The downside is that the dropouts are still forward-facing. As a consequence, you can’t use standard chain tugs to tension the chain.
There’s also a chance that the wheel will slide forward in the dropout and cause a drop in chain tension.
The most attractive point of this approach is that a similar frame can be found for cheap on the second-hand market.
- A track frame with rear-facing dropouts
If you’re serious about fixed-gear riding, this is the best long-term approach.
- Switching to single-speed instead of fixed fear
Another option would be to use a freewheel and ride your bike as a single-speed rather than fixed gear. In that case, you can rely on an aftermarket chain tensioner or an old derailleur to tension the chain.