What Is a Mountain Bike Dropout? Everything You Need To Know
Mountain biking is fun, and even the maintenance process can be exciting for mountain bike enthusiasts. However, in all the excitement, most people overlook an important part of their bike: the dropout. So, what is a mountain bike dropout, and what should you know about it?
A mountain bike dropout is the opening in a bike where the rear axle fits. This rear axle is the tool that holds the wheel in place. Furthermore, the dropout and rear axle allow users to remove the back wheel without derailing or removing the chain.
Some mountain bikes do not come with this opening, but if yours does, you need to learn all about it. This article will cover all there is to know about a mountain bike dropout, the different types, and an alternative to quick-release axles. Furthermore, the article will cover the benefits and drawbacks of the quick-release axle and the alternatives.
Facts About the Mountain Bike Dropout
Dropouts have been in existence since the 1920s. This mechanism came into fruition in 1927 when Tullio Campagnolo, an Italian bike racer, had issues changing gears during a race. Because of this, he decided to make a quick release.
The dropout is a simple mechanism. Its name even explains what it does. This bike section allows the wheel to “drop out” without any hassle. Thanks to the innovation of this mechanism, bikers can now effortlessly change their rear wheels without touching the chain.
Most people classify mountain bike dropouts as a technical part of the bike. Yet, they are as simple as they come and a basic part of your bike. While a dropout is convenient for quick wheel changes, especially during competitions, it can lead to accidents if you do not maintain it.
The position of dropouts varies. Some manufacturers produce their bikes with the opening facing forward, while others make theirs facing straight down. When the latter is the case, you call them vertical dropouts.
Technically, the name “dropout” should only refer to the opening at the back of the bike where you insert the rear wheel. However, most people use the term to describe the fork (slot) where the front axle slides into and holds the front wheel in place.
Types of Mountain Bike Dropouts
There are three types of mountain bike dropouts. These include the front fork dropout, rear derailleur dropout, and rear horizontal dropout. Most dropouts require a quick-release skewer that holds the axle and your wheel in place regardless of the type.
Front Fork Dropout
The front fork dropout is the most common of the dropout types. You can find these on the front fork of most modern-day bikes. That said, the function of the front fork dropout remains the same irrespective of how the manufacturer makes the front suspension system.
The opening where you fit the axle is the “dropout.” You slide a quick-release skewer into the front axle to hold the wheel. You must hold the wheel in place properly using the skewer, as weak tightening can lead to the wheel falling out.
Rear Derailleur Hanger With Dropout
The rear derailleur hanger with a dropout is the most affordable option of all the dropout types. First, you attach this hanger to the rear fork of the bike. Then, you can fasten your quick-release skewer into the dropout of the hanger. Ensure to fasten this skewer properly to keep it from coming loose.
The best thing about the rear derailleur hanger is that it is cheap and easy to replace. However, it is also prone to bending. You can bend the hanger back into shape a couple of times, but it will eventually break. Rest assured, you do not want the hanger to break while riding your mountain bike. Therefore, you should be careful and aim to replace it as soon as it bends.
Additionally, this dropout is useful because it takes most of the impact and spares your bike when you hit an obstacle. Keep in mind that it is better for your derailleur hanger to bend than your bike’s frame. If your hanger bends, it is easy and cheap to replace or repair, and you can even do it yourself. The situation is a lot different if your bike frame bends.
How To Replace a Rear Derailleur Hanger With Dropout
If an accident damages your hanger, you’re in luck because you can likely solve the problem on your own. First, you need to examine the extent of the damage. You need to determine if the hanger requires realignment and if you need to bend it back into place or replace it altogether. Once you know how out of shape the hanger is, you can easily fix the issue.
Horizontal Rear Dropout
Horizontal rear dropouts are the least common, and you are less likely to find them on a modern bike. With this mechanism, you can find the opening for the rear axle in a horizontal position. This opening either faces the front or rear of the bike.
This type of dropout works best with track bikes and single-speed mountain bikes. You can find rear-facing dropouts on track bikes, while you will most likely see front-facing dropouts on a single-speed mountain bike.
Furthermore, the horizontal rear dropout is beneficial if you plan on turning a mountain bike into a fixed or single-speed gear.
That said, this dropout does not come without its drawbacks. For one, despite the functionality of the rear-facing dropout, you might find it hard to set and maintain chain tension.
In addition, the axle bolts of front-facing dropout can affect disk brake systems, hindering them from performing to their full capacity. This is why most people do not recommend these dropouts for regular, recreational bikes.
An Alternative to Quick Release Axles
Dropouts have been around for decades; interestingly, nothing about the mechanism has changed since then. However, a newer design is slowly becoming more popular than the mountain bike dropout. The dropout may become obsolete with time and give way to this new axle system. The name of this system is the thru-axle.
Ultimately, the dropout and thru-axle have the same function. However, with the thru-axle, the axle goes through the bike (Hence, the name). The axle is a long tube that you insert into the wheel.
In most cases, you might mistake the tube for a quick-release skewer because they both use a cam system. But, keep in mind that, unlike the dropout, the thru-axle does not provide the axle. Instead, it only holds the wheel.
Benefits of Thru-Axles
When comparing a mountain bike dropout to a thru-axle, the latter comes out on top. Here are some reasons why thru-axles may be better than dropouts.
Safety
Safety is a factor that many consider when opting for thru-axles. These tools provide the safety that quick-release axles cannot. With thru-axles, the chances of your front or back wheel falling out are slim to none. This is because the slots on the axles are holes and not U-shaped.
Therefore, the dropout cannot detach from the axles vertically. Furthermore, you screw the axles into the dropout, making the connection tighter and more secure.
Robustness
Some types of cycling put a lot of stress on the axles. Fortunately, thru-axles are quite strong and do not break under pressure because they are three to four times thicker than quick-release axles. This increase in strength not only improves safety but also improves braking and handling. Interestingly, this is the reason why thru axles were invented in the first place.
No Brake Rotor Rub
This is a major problem with quick-release axles. The disc brake pads and rotor are so close together that pedaling hard can cause the fork to flex.
The fork might flex to the point where a pad rubs against the rotor, which reduces braking power and causes annoying sounds. However, thru axles do not have this problem because they limit the fork flex by making the front end stronger.
Prevents Ejection of Wheels
There was a safety concern during the early 2000s when disc brakes became popular. Some cyclists noticed that hitting their breaks with force caused the quick release axle to eject from the dropout.
This issue occurs when the force from the disc brakes pushes the wheel forward. This motion causes the wheel to attempt leaving the dropout each time you hit the brakes. If you keep hitting the brakes, the quick-release axle will eventually loosen, and the wheel will fall out of the dropout.
Luckily, you do not have to worry about this with thru-axles because they utilize holes instead of the standard u-shaped openings. Hence, they cannot pull out vertically.
Drawbacks of Thru-Axles
Although it is the better choice, a thru-axle is far from perfect. Here are a few disadvantages that come with this innovation.
More Costly
Thru axles are expensive for their size. Granted, they have numerous features and benefits, but their price is way higher than quick-release axles’. However, this could be because the technology is still new, and most might consider it high-end.
Hopefully, this price drops with time. Furthermore, thru-axle forks and frames are more time-consuming and complicated to build, so they cost more.
Heavyweight
Due to their robustness and material, thru-axles are pretty heavy. They are much heavier than the quick release. Thru-axles usually weigh between 0.13 to 0.17 pounds (60 to 80 grams), depending on size. On the other hand, quick-release axles weigh about 0.09 to 0.11 pounds (40 to 50 grams).
With that said, you can find aluminum, carbon fiber, or titanium thru-axles. These axles are lightweight and weigh nearly the same as quick-release axles but are costlier.
Wheels Are Harder To Remove
Thru-axles are not the option for speed because removing a wheel requires more time. When removing a wheel, you will need to unscrew and completely remove the axle from the bike.
While the difference in time between thru-axles and quick release is just a few seconds, this difference can cost you a race if you ride competitively. Also, you might lose the axle when you remove it because it does not stay attached to the hub.
Benefits of Quick Release Axles
Quick-release axles may be going out of style, but there is a reason why they stayed at the top for so long. Here are some reasons why people love quick-release axles.
Affordability
Due to their popularity and material, quick-release axles are very affordable. You can buy used ones for a few bucks. Even brand-new ones do not cost much more than the secondhand pieces. However, thru-axles are quite pricey, and you will need to spend a lot of money on a simple tool.
Availability
Quick-release axles have been the only option for over 80 years, and millions of mountain bikes use them. Therefore, if you are ever in trouble and need a replacement, you can get one regardless of where you are. Quick-release axles are the best option for trips to remote areas because you most likely won’t get stranded.
Conversely, thru-axles are still relatively new, and you might not be able to find them in certain countries that still use the older quick-release axles.
Easy Removal of Wheels
Removing your wheel is easy with quick-release axles, and you can do it in a few seconds. All you have to do is pull the lever and lift the dropouts. Furthermore, you do not have to worry about misplacing the axle because the skewer never leaves the hub.
Lightweight
Most manufacturers create their axles using aluminum. Therefore, quick-release axles are extremely light and only weigh a few grams. Generally, a quick-release axle is 20 grams lighter than a thru-axle. You might even be able to save up to 100 grams by using quick releases as opposed to thru-axles.
Compatible With Bike Carry Rack
You secure your bike on most racks by attaching the front dropout to the rack. You do this by using the U-shape on the dropouts. However, this is not the case with thru-axles.
You might need to purchase a new rack due to incompatibility. If you do not want to buy a new rack, you can buy an adapter, which means spending more money. With that said, manufacturers understand that the thru-axle is here to stay, so they now make newer racks compatible with thru-axles.
Technology You Can Trust
A quick-release axle is not an experimental technology. Cyclists have been using quick-release axles for over 80 years, and they can trust them to do the job. The technology is simple, affordable, and durable.
Therefore, most might not see a reason to opt for newer bikes just for thru-axles. In most cases, cyclists cannot tell the difference between the two. However, if your type of riding causes your quick-release axle to break or bend often, you should consider switching to a bike with thru-axles.
Drawbacks of Quick Release Axles
Technology as old as the quick-release axle will likely have a few downsides. Here are some disadvantages that come with quick-release axles.
More Dangerous
If you do not take care of your quick-release axle or don’t notice a break or bend, you might be in danger. When a quick release gets loose, the chances of the dropout lifting off the axle are high; should this happen, the wheel might fall off. If you are riding at high speed when this wheel falls off, you might hurt yourself badly and end up in the emergency room.
Prone to Bending and Breakage
Sometimes, a pro can also be a con, which is one of those cases. Going through vigorous riding puts a lot of pressure on axles. This pressure can cause weaker quick-release skewers to bend. When this bent axle stays too long in the hub of your bike, it can ruin it.
If you keep riding the axle like that, you might even break it. If this should occur, the wheel might fall off and lead to an accident. However, you will not have this problem with thru-axles because they can withstand high pressure.
Rubbing of Brake Pad and Rotors
The disc brake pads and rotors are quite close together and can rub against each other occasionally. In some cases, they are less than 1 mm apart.
When you have a quick-release axle, this tool might cause the fork to flex and increase the chances of the brake and rotor rubbing against each other. There are no serious effects of this rubbing, but the braking power of your bike will be lower because the rotor is not in alignment.
Older Technology
As they say, out with the old, and in with the new. Indeed, quick-release axles have withstood the test of time. However, newer technology is here, and the use of quick-release axles might be coming to an end. Most manufacturers make their high-end bikes with thru-axles and leave the lower-end ones with quick release.
Final Thoughts
A dropout is an essential part of a mountain bike, and cyclists must start paying more attention to it. Riders have utilized these dropouts for close to a century, making them a quintessential bicycle part.
While a newer and better technology replaces the dropout, it is still viable equipment. Hence, if you still own a mountain bike that uses one. Ensure you fix and fasten your quick-release axles for maximum safety.
