Thru axles are becoming increasingly popular these days. Over the past 10 years, they have pretty much become the standard on mountain bikes. Now, more and more touring and road bike manufacturers are making the switch. After some research and testing, I created this thru axle vs quick release pros and cons guide to help you decide which axle style is best for your next bike. I’ll also explain the difference between both systems and outline thru axle sizing.
What Are Thru Axles?
Thru axles are a wheel attachment system. They secure the hubs between the dropouts in the frame and fork. Thru axle dropouts have holes, rather than slots. The thru axle itself is a thick, solid pin that is threaded on one end. It inserts from the side of the wheel.
After threading through one dropout and the hub, the thru axle screws into the far dropout. This way, the wheels are essentially bolted to the frame and fork. The thru axle secures in place with a cam lever or hex bolt on the end that tensions the axle so it doesn’t come loose. There are no slots so the axle must be removed completely in order to remove the wheel from the bike.
Standard front thru axles measure 15 mm in diameter and the rear measures 12 mm. Different lengths are available to fit different hub spacing. I’ll talk more about thru axle sizes later.
What are Quick Release Axles?
Quick release axles are the standard wheel attachment system used on most bikes. They allow you to remove and replace the wheels quickly and without any tools. You don’t even need to remove the axle from the hub.
A quick release axle system is composed of a thin metal skewer that runs through the hubs. The skewer is held in place by an acorn nut on one side and a quick release cam lever on the other. Two small springs sit on either side of the hub.
The dropouts on a quick release frame and fork have u-shaped slots. The wheel secures to the bike by slotting the skewer into the u-shaped dropouts, slightly tightening the acorn nut, and clamping the quick release lever closed. A cam mechanism tensions the axle and holds the wheel in place with friction. The quick release axle stays in the hub when you remove the wheel.
Most quick release axes measure 5 mm or 9 mm in diameter. Various lengths are available to fit different hub spacing.
A Bit of Quick Release History
While racing through freezing weather in the Dolomites in November of 1927, Italian cyclist Tullio Campagnolo was slowed down by a stuck wingnut on his axle. He needed to remove the wingnut so he could remove his wheel to change gears. (At that time, bicycles had a sprocket on either side of the rear wheel. In order to change gears, you would remove the wheel and flip it around.) The misbehaving wingnut on Tullio’s bike cost him precious time which ended up costing him the race.
This experience inspired Tullio to develop a quick release wheel locking mechanism. This invention allowed cyclists to remove and replace their wheels in seconds. The quick release axle was patented in 1930 and became the standard for over 90 years. Tullio went on to patent numerous cycling and non-cycling inventions and founded the cycling company Campagnolo.
The Invention of Thru Axles
Tullio couldn’t anticipate the ever-increasing demands of downhill mountain bikers. During races, quick release axles began bending and breaking.
Quick release axle failure became particularly common on mountain bikes with disc brakes and suspension forks. The fork legs were not moving in unison when the suspension compressed and during braking. This resulted in poor brake rotor alignment, poor tracking in turns, and even detached wheels.
As axle failures grew more and more common in downhill mountain biking, it became evident that a more robust axle design was needed. In the early 2000s, thru axles were invented.
The axle was made thicker so it wouldn’t bend or break under stress. The dropouts were redesigned with holes so the wheel couldn’t detach. Thru axles bolt the fork legs together to reduce fork torsion from braking and uneven suspension loading. This creates a much stiffer front end, which improves handling and stability. The more robust design improves safety as well.
These days, quick release axles have pretty much been replaced by thru axles in competitive mountain biking. Road cyclists are in the process of adopting the technology as well.
Thru Axle Pros
1. Thru axles are safer- This is probably the biggest benefit for the average cyclist. Thru axles improve safety by making it nearly impossible for the front wheel to come out of the dropouts while you’re moving. The dropouts can’t lift off of the axles vertically because they have holes instead of a u-shaped slots. In other words, the dropout completely surrounds the axle. Thru axles also screw into the dropout, forming a much more secure connection.
This design prevents disc brakes from ejecting the axle under heavy braking force. Thru axles also make the fork more robust and less likely to fail. The axles themselves are unlikely to break because they are thicker and stronger. Finally, the axles are less likely to come loose after being improperly tightened. All of these features improve safety. I’ll outline each point in more detail in this section.
2. Thru axles reduce brake rotor rub and improve braking force– When you stand up to pedal hard, the fork can flex. Sometimes it flexes enough that a disc brake pad rubs on the rotor. This is possible because disc brake pads rest just a couple of millimeters away from the rotor.
Brake rotor rub creates drag that slows you down and reduces efficiency. It’s also simply annoying because it makes a rubbing sound.
Thru axles eliminate this problem by reducing fork flex. They create a rigid connection between the hub and fork legs, which makes the whole front end structurally stronger. As an added benefit, braking performance marginally improves because the brake rotor stays better aligned in the caliper.
3. Thru axles don’t bend or break under heavy stress- Some disciplines of cycling put an enormous amount of stress on axles. This is the case with freeride and downhill mountain biking. Thin quick release axles can bend or break during a hard landing after a jump or drop.
This problem is particularly common on bikes with suspension forks. The legs compress unevenly and bend or break the axle. A bent axle can ruin a hub. If the axle breaks, the wheel can come off.
Thru axles, being 3-4 times thicker, have a much higher tensile strength. They don’t break under stress. The extra material greatly increases the axle’s strength, improving safety, handling, and braking. This problem is the reason why thru axles were invented in the first place.
4. Thru axles prevent disc brakes from ejecting the wheels- When disc brakes came into widespread use in mountain biking during the early 2000s, a safety issue with quick release axles became apparent. Cyclists found that heavy braking force created by disc brakes can eject a quick release axle out of a U-shaped dropout.
James Annan documented this issue in this old thread from 2003. You can also read about a few cyclists experience wheel ejection in this thread.
This phenomenon occurs because the braking force created by disc brakes pushes the wheel down and forward. This means the wheel wants to push itself out of the dropout every time you brake. After repeatedly braking, the QR axle can slowly loosen. If the axle gets loose enough, the wheel can eject out of the dropout. (Wheel ejection isn’t a problem on rim brake bikes because the braking force pushes the wheel back into the dropouts.)
Cyclists suggested a simple solution: to move the brake caliper to the front of the fork arms. This would change the direction of the braking force so the wheels don’t want to push themselves out. Manufacturers instead decided to change the orientation of the dropout slightly to reduce the risk.
Thru axles completely solve the disc brake wheel ejection problem altogether. Because the dropouts use holes instead of U-shaped slots, the axle can’t pull out vertically. For this reason, thru axles are a better choice for bikes with disc brakes.
5. Thru axles improve handling, cornering, and stability by stiffening the front end of the bike- This is the most significant performance enhancement. Thru axles bolt both fork arms together. This makes the bike’s front end structurally stronger. Fork flexing from powerful pedaling or torsional forces created by disc brakes is greatly reduced. The thru axle dropouts are also a bit beefier, which makes them more robust.
When the front end is stiffer, you can steer more accurately and precisely. The front wheel also tracks better while cornering when it is more rigidly attached to the bike. You can steer better while braking as well. Handling is better overall. The extra stiffness is particularly useful while hauling heavy loads while touring.
Thru axles also prevent suspension forks form compressing unevenly. Because the fork arms connect through the axle, both fork arms synchronize. Suspension forks absorb shocks better because they compress evenly. This improves stability and handling off-road, allowing you to navigate rough roads and technical terrain more easily. Mountain bikers benefit from this design.
6. Thru axles prevent fork fatigue and failure- When you apply the front disc brake, the fork wants to twist and flex. The reason is that disc brake calipers and rotors mount on one side of the wheel. Braking creates a torsional force, causing the fork to flex. Over time, this flexing can cause the fork to fatigue and eventually fail. Thru axles bolt the fork legs together. This makes the fork much more resistant to torsion forces than a quick release.
7. More consistent wheel alignment when removing and replacing the wheel- When you put your quick release wheel in the u-shaped dropouts, they don’t line up exactly the same every time. This is because the ridges on the quick release that bite into the frame to hold the hub in a slightly different position every time. There is some margin for error. Your wheel can end up slightly misaligned. This can lead to two issues.
First, your brake rotor or rim isn’t properly aligned. This can cause your brake pads to rub. Second, your cassette or freewheel can sit crooked if the rear wheel is misaligned. This can prevent your drivetrain from working smoothly. You might have to loosen then re-tighten the quick release to get the wheel to sit properly.
Thru axles solve these issues because the hubs sit in the dropouts exactly the same every time. There is no room for error.
8. Thru axles reduce injuries from user error- When replacing a wheel with a quick release axle, it would be easy to attach it too loosely. Particularly if you’re new to cycling. If this happens, the wheel could pop out unexpectedly. This mistake has caused many cycling injuries over the years. Thru axles greatly reduce the likelihood of human error. They are simple and intuitive to use.
9. Thru axles are more modern- These days, most mid-range to high-end road, touring, and mountain bikes come with thru axles instead of quick release. If you like to use the newest and most modern cycling equipment, thru axles are a good choice. I imagine over the next 10 years, most manufacturers will switch to thru axles, even on lower-end bikes.
Thru Axle Cons
1. More expensive- Even though thru axles are incredibly simple, they cost more than quick release axles. Probably because they are a newer technology and are considered to be higher end. Thru axles cost $30-$60 each. Quick release axles cost just $10-$20 for a pair.
Thru axle frames and forks also cost more than those designed for quick release because they are more complicated and time consuming to build. The axle holes in the dropouts must be perfectly aligned and sized for the wheels to roll straight. There is very little margin for error. It takes more man-hours and precision to build the frame. This may be worth considering if you’re having a frame custom built.
Frames with u-shaped dropouts for quick release axles are cheaper to make because they allow for more adjustibility during manufacture. There is more margin for error. They also take less time to build.
2. Thru axles are heavier than quick release- Standard thru axles weigh 60-80 grams each depending on the size. Quick release skewers weigh around 40-50 grams each.
There are lightweight thru axles available that are made of aluminum, titanium, or carbon fiber. These weigh about the same as quick release skewers but cost much more.
Thru axle frames and forks are also slightly heavier because it takes more material to wrap the dropouts completely around the axle. The extra metal adds a few grams to each dropout. The weight penalty is so minor that it would really only matter for weight weenies or those who ride competitively.
3. Parts are harder to find in some parts of the world- Thru axles are really only common on higher-end bikes. In much of the developing world, high-end bikes and components are not common. If you lose a thru axle or need a new hub, it may be hard to find a spare while traveling somewhere remote. Small town bike shops may not carry thru axles. You may need to travel to the nearest capital city or have parts shipped in. For this reason, bicycle tourists usually stick with quick release axles at this time.
Having said this, more and more touring bike manufacturers are switching to thru axles. For example, Surly’s new disc trucker has thru axles. The axles are also one of the least likely parts to fail while touring because they are so robust. With globalization, it is becoming easier and easier to have parts shipped in as well.
4. Removing a wheel takes more time with thru axles- You have to unscrew the axle and remove it from the bike completely. Removing a wheel takes a few seconds longer with thru axles than it does with quick release. There is also the possibility of losing the axle while it is removed because it does not stay in the hub.
This is really only a problem in racing. To solve this issue, many teams on The UCI World Tour have begun using a spare bike instead of swapping out wheels in the event of a puncture. For recreational riders, having to spend a few extra seconds here and there doesn’t really matter.
5. Thru axles are not compatible with some bike racks and work stands- Many racks secure the bike by slotting the front quick release dropout into the rack. You remove the front wheel, place the u-shaped dropout over a pin, and lock it in place with some kind of locking mechanism. This is particularly common on car rooftop bike racks.
With thru axles, these racks become obsolete. Thru axle bikes are not compatible due to the dropout’s circular design. If you transport your bike on one of these racks, you may need to buy a new one if you switch to quick release axles. Adapters are available for some models. For example, this Filzer Fork Adapter will work with most racks.
6. Thru axles are overkill for most riders- Most riders never have to worry about breaking a quick release skewer or having the skewer work its way loose. This kind of thing really only happens in racing or hardcore mountain biking where a considerable amount of stress is put on the bike.
Performance improvements with thru axles are marginal at best and aren’t really worth the cost or hassle of upgrading for most riders. Some riders aren’t even convinced that thru axles offer any benefits at all.
Quick Release Axle Pros
- Cheaper- Quick release axles cost next to nothing. You could probably buy a used one for a couple of dollars. A new set can be had for $10. Thru axles, on the other hand, are ridiculously expensive for being such a simple part. They’re essentially just a big bolt that costs $30-$60+.
- Better parts availability- Quick release axles have been a standard bike part for over 80 years. Millions of bikes use them all around the world. If your quick release axle breaks or bends or a hub fails while you’re cycling through a remote region, you can find a replacement in even the smallest of villages. For this reason, quick release axles are still the best choice for expedition bicycle touring and bikepacking. Finding a replacement thru axle would be nearly impossible in many developing countries. They are a specialty part that isn’t available everywhere yet.
- Quick release makes it faster and easier to remove the wheels- You just pull the quick release lever and lift the dropouts off the wheel. It takes just a matter of seconds to get the wheels off. This is why Tullio Campagnolo invented them in the first place. Once the wheels are off, you don’t have to worry about losing the axle because the quick release skewer stays in the hub. This is a great feature if you have to remove your wheel often for security purposes when locking your bike up. It is also a great feature for racing where every second counts.
- Quick release axles are lighter- On average, a quick release axles weigh around 20 grams less than a thru axle. Quick release frames are lighter as well because the dropouts contain less material. You might save 60-100 grams by using quick release axles instead of thru axles.
- You can use any bike carrying rack- Many racks secure the bike by locking the front dropouts to a mechanism in the rack. These require u-shaped quick release dropouts. You may have to buy a new rack if you buy a thru axle bike because the dropout style is incompatible with the old style rack. Adapters are available for some racks. This is an extra expense to consider. Of course, manufacturers designed newer racks for compatibility with thru axles.
- Quick release axles are a tried and true technology- Millions of cyclists have relied on quick release axles over the past 90 something years. The technology has proven to be simple, durable, reliable, and affordable. There is really no reason to upgrade bikes just so you can get thru axles unless you’ve experienced problems with quick release axles breaking or bending due to the type of riding that you do. The difference in performance between QR and through axles is imperceptible to most riders.
Quick Release Axle Cons
- Quick release axles are more dangerous- Under certain circumstances, a wheel can come off. If the quick release loosens over time, gets knocked loose, or wasn’t tightened enough in the first place, the u-shaped dropout can simply lift off of the axle. As you can imagine, this could result in a horrible accident if it happens while riding at speed. Over the years, there has been quite a bit of litigation over quick release axles. Most accidents are caused by human error but cycling companies have recalled bikes on several occasions. For example, in 2015 the Consumer Product Safety Commission issued a recall for 1.5 million bikes for a defect that could cause the QR lever to hit the disc brake rotor when improperly tightened or left open. Manufacturers included Cannondale, Fuji, Specialized, Giant, Raleigh, GT, and more. It is important to note that this was a voluntary recall that was made to prevent potential accidents from misuse or user error. The axles functioned fine when properly used. Lawyer taps or lawyer lips started appearing on QR dropouts in the 90s to prevent frivolous lawsuits from cyclists claiming that their QR axles caused an accident. Thru axles attach the wheels more securely and reduce the likelihood of wheel attachment caused by human error.
- Quick release axles allow for more flex in the front end of the bike, which hurts handling- Disc brakes can cause the fork arms to flex. If you’re using a suspension fork, the arms can move independently from one another. This happens because the fork arms are not firmly connected. Quick release axles don’t provide much structural support for the front of the bike, allowing the wheel to wander. This results in poor tracking and handling in some situations. Having said this, the difference is usually very minor or even imperceptible. You can read a side by side comparison here.
- Quick release axles can bend or break- Jumping and downhill mountain biking puts a lot of stress on axles. Skinny quick release skewers can bend. A bent axle can ruin a hub over time. With enough force, the axle can break. If this happens, the wheel could lodge in the fork or come off completely and cause you to crash. Thru axles can withstand much more force.
- Brake rotor rub- Because disc brake pads sit so close to the rotors (sometimes less than 1mm), they can rub if there is some flex in the fork. Quick release axles allow the fork to flex which makes brake rub more common. This can also cause reduced braking power because the rotor isn’t perfectly aligned.
- Less modern- Quick release axles are an old cycling technology that seems to be on its way out. Most bicycle manufacturers are moving toward thru axles. These days, most high-end bikes use thru axles and lower-end bikes still come with quick release.
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The Third Option: Bolt On Skewers (Solid Axles)
Bolt-on skewers work exactly the same as quick release skewers except they tighten with a bolt instead of a cam lever. They have the same diameter as QR. The bolt-on design allows you to tighten the axle tighter than you can with just your hand. Using a wrench or hex key to tighten the axle gives you more mechanical advantage.
Bolt on axles offer a few advantages over standard quick release. First, they make it less likely for your wheel to come off simply because they hold the wheel tighter. For this reason, many quick release disc brake bikes come with bolt-on skewers. They make it much less likely for the axle to loosen or the wheel to eject during hard braking.
Another benefit of bolt-on skewers is that they make it slightly harder for a criminal to steel your wheels. They would need a wrench to remove the bolt. They can’t just use their hand like they can with a lever. The bolt also looks a bit sleeker than the lever.
There are some disadvantages to bolt-on axles. First, you’ll have to carry a tool to take your wheels off. This adds a bit of weight to your tool kit. It also takes a few seconds longer to remove and replace the wheels. This can be annoying if you take your wheel with you when you park your bike to avoid theft.
Thru axles are also available with in both bolt on or lever options.
Thru Axle Sizes: Diameter, Length, and Thread Pitch
Three measurements define the size of a thru axle. The front and rear are almost always different sizes. When buying a replacement thru axles, you’ll need to know the following to ensure that you buy sizes that are compatible with your frame, fork, and hub.
Thru Axle Diameter
Front thru axles usually measure 15 mm in diameter. Rear thru axles usually measure 12 mm in diameter. This is the current standard. To measure the diameter, you can use a pair of calipers.
The front thru axle is larger in diameter than the rear because steering puts more torsion force on the axle. In the past, 20 mm thru axles were used on the fork. Downhill mountain bikers still use 20 mm axles on the front. Some road riders are switching to 12 mm front thru axles these days to cut weight.
Thru axles come in a range of lengths to accommodate different hub spacing. Manufacturers use two different length dimensions to indicate the size:
- Over locknut dimension (OLD)- This is the most common. This measurement is the distance between the insides of the dropouts. The most common rear thru axle over locknut dimension lengths are 130mm, 135mm, 142mm, 148mm, and 197mm. 148 mm is usually referred to as Boost Sizing. 197 mm is often called fat sizing. The most common front thru axle over locknut dimensions are 100 mm, 110 mm, and 150 mm.
- Overall length- This is the length of the thru axle measured from the base of the head to the end of the axle. This is the better measurement to make sure you buy the right size. It is usually about the same as the distance between the outsides of the dropouts. The overall length is typically about 20-30mm longer than the OLD.
When it comes to length, there you have about a 2-3 mm margin for error to work with. If the axle is slightly too short or long, it should still work.
Thread pitch is the distance from the tip of one thread to the tip of the next thread in milimeters. You can use a caliper to measure this. Common thru axle thread pitches include 1 mm, 1.5 mm and 1.75 mm. It’s important that you get the right thread pitch so you don’t strip your axle or dropout.
Mixing Thru Axles and Quick Release
You don’t need to use the same axle system on both wheels. For some riders, using a front thru axle and a rear quick release axle makes the most sense. This is worth considering for several reasons.
First is the cost. If you’re getting your frame custom built, it is cheaper and faster order it with a rear quick release and front thru axle. The reason is that it is harder for frame builders to keep thru axle dropouts aligned and there is less margin for error during manufacture. The frame takes more time to build which adds to the cost. Front thru axles don’t add any time or expense because there are plenty of thru axle forks on the market.
Next, rear thru axles provide very little if any benefit for most riders. Front thru axles are more important because the fork is weaker and more susceptible to flex than seat and chain stays. The front of the bike also steers. The strength of thru axles helps.
Finally, thru axles require longer chainstays because they use wider hub spacing than quick release. The standard rear dropout spacing for thru axles is 142 mm. If you combine this with 405 mm chainstays, your chain may run at too extreme of an angle while you’re using the outermost gears.
This means you won’t be able to cross chain gears by running the smallest chainring and smallest cog on the rear. Your heel could also rub on the wide chainstays while pedaling. With 142mm thru axles, you’ll want your chainstays to be at least 415-420 mm.
One interesting thing to note is that the rear dropout spacing is exactly the same for standard rear disc 135 mm quick release axles and 142 mm thru axles. Even though thru axles are longer, you end up with the same exact dropout width and cassette position because part of the thru axles sit inside of a pocket in the dropouts. This article has a great visual showing how this works.
Converting A Quick Release Bike to Thru Axles
If you’re in love with your frame but want to upgrade to thru axles, it is possible to make a conversion in some cases. There are a few ways to go about this. All involve swapping out some components.
The best and easiest solution is to swap out your quick release fork for a thru axle fork. In most cases, you will also need a new front hub that is compatible with thru axles. 15 mm is the most common diameter for front thru axles.
There are also adapters that allow you to use a thru axle hub in a quick release fork. I don’t have any experience with this. If you do, comment below.
For the rear, your best option is to swap out the quick release for a bolt-on axle. These use the same hub and drop out as quick release but provide a bit more secure connection between the wheel and frame.
You can’t upgrade the frame to thru axles without cutting off your dropouts and welding on new ones. At that point, you’re better off just buying a new frame.
Final Thoughts about Thru Axles Vs Quick Release
Some riders feel that thru axles are just a way for the industry to sell more bikes and components. There is probably some truth to this. The advantages they offer aren’t really noticeable for the average recreational cyclist.
Thru axles offer more benefits for mountain bike riders than road riders. The main advantage that everyone can enjoy is safety. Handling marginally improves as well.
Having said this, it seems like thru axles are where the industry is headed. The technology is simple, easy to use, and robust. Thru axles are definitely a step forward. Just not a big leap. If you’re happy with your quick release bike, there is no reason to go out and buy a new bike just so you can have thru axles. If you’re planning to upgrade anyway, thru axles are probably the better choice.
Where do you stand on the thru axle vs quick release debate? Share your tips and experience in the comments below!
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