If you’ve ever tried to replace a mountain bike hub, you’ve probably wondered the same thing:
Why are there so many hub standards?
100mm, 110mm Boost, 135mm QR, 142mm, 148mm Boost, 157mm Super Boost — and that’s before considering axle diameter, freehub type, spoke count or brake rotor interface.
It can look like the bike industry simply keeps inventing new standards. But most MTB hub standards appeared for a reason: mountain bikes changed, and hubs had to change with them.
Here is how we ended up with the hub standards we use today.
It Started Simple: 100mm Front and 135mm Rear
For many years, mountain bike hubs were relatively straightforward.
A typical MTB used:
Front: 9×100mm
Rear: 10×135mm
These dimensions worked well with quick-release wheels, narrow tires and the drivetrains of the time.
You’ll still find 100/135mm hubs on many XC bikes, entry-level mountain bikes and older frames today.
But mountain bikes became faster and more capable. Suspension travel increased, tires became wider, disc brakes became standard, and riders began pushing bikes harder.
The hub had to evolve.
Thru-Axles Changed More Than the Axle
One of the biggest changes was the move from quick release to thru-axles.
Instead of a thin QR skewer passing through the hub, a much larger axle passes through the fork or frame and hub together.
Common standards included:
Front: 15×100mm
Rear: 12×142mm
The goal wasn’t simply to make the axle bigger.
Thru-axles improved wheel positioning and created a stiffer connection between the wheel, fork and frame. This became increasingly useful as suspension forks became longer, disc brakes became more powerful and trail riding became more aggressive.
Interestingly, 142mm rear spacing wasn’t a completely new wheel geometry.
Compared with the older 135mm system, the wider external dimension helped create a more precise and repeatable interface between the hub and frame while retaining similar cassette and flange positioning.
But MTB development didn’t stop there.
Then Came Boost: 110mm and 148mm
Today, one of the most familiar MTB combinations is:
15×110mm Boost front
12×148mm Boost rear
Why add another 10mm at the front and 6mm at the rear?
Because designers wanted more room.
Moving the hub flanges farther apart can improve spoke bracing angles and wheel stiffness. The additional space also helped bike designers accommodate wider tires, modern drivetrain layouts and evolving frame geometry.
Boost arrived during the rapid growth of 27.5-inch and 29-inch mountain bikes, where wheel stiffness became particularly important.
A larger wheel creates more leverage on the spokes and hub. Improving the spoke bracing angle became one way to build stronger and stiffer wheels without simply adding more material.
Boost therefore wasn’t just about making the axle wider.
It changed the geometry of the entire wheel.
If you’re unsure whether your bike uses 135mm, 142mm, 148mm Boost or another standard, check our Bike Hub Compatibility Guide before choosing a replacement hub.
And Yes, There Is Super Boost
Just when 148mm Boost became familiar, another number appeared:
12×157mm Super Boost
The idea follows similar logic.
A wider rear hub provides designers with more space to optimize flange position, wheel stiffness, tire clearance and frame geometry.
Super Boost is particularly relevant to some aggressive trail, enduro and long-travel bikes.
But it also demonstrates why riders sometimes become frustrated with new standards.
A 142mm hub doesn’t fit a 148mm Boost frame.
A 148mm hub doesn’t automatically fit a 157mm frame.
Each change may offer an engineering benefit, but it also creates another compatibility boundary.
What About 141mm QR?
This is where things become even more confusing.
You may also encounter:
Boost 141 / 5×141mm QR
It is commonly found on some more affordable mountain bikes that use Boost-style wheel geometry while retaining a quick-release rear wheel system.
Despite the similar numbers, 141 QR and 148 Boost are not the same axle standard.
This is a good example of why choosing a hub based only on the word “Boost” can lead to the wrong purchase.
Always check the actual axle and frame specification.
Did We Really Need All These Standards?
Probably not every single one.
Some standards became widely adopted because they solved important engineering problems. Others appeared during transitional periods as manufacturers tried to balance performance, cost and compatibility.
But the overall direction makes sense.
Mountain bikes have changed dramatically.
We now have larger wheels, wider tires, longer suspension travel, more powerful brakes, 12-speed drivetrains and bikes capable of riding terrain that would have been extreme by XC standards twenty years ago.
Hub standards evolved alongside those changes.
The unfortunate result is that better performance often came at the cost of simpler compatibility.
A Simple Way to Understand MTB Hub Standards
Instead of memorizing every standard, think of MTB hubs as a few major generations:
|
MTB Generation |
Typical Front |
Typical Rear |
|---|---|---|
|
Traditional QR |
||
|
Thru-Axle / Non-Boost |
||
|
Boost |
||
|
Super Boost |
15×110mm |
12×157mm |
*Front specifications can vary depending on bike category.
For most riders replacing a hub, the important thing isn’t knowing the entire history.
It’s identifying what is already on your bike.
Different Standards, Same Purpose
Looking back, MTB hub standards tell the story of how mountain bikes evolved.
135mm QR was enough for generations of mountain bikes. Then thru-axles improved wheel retention and stiffness. Boost changed wheel geometry for modern 27.5-inch and 29-inch bikes. Super Boost pushed the same idea further.
So why are there so many MTB hub standards?
Because the mountain bike itself never stopped evolving.
The numbers may be confusing, but behind most of them is the same goal: build a wheel that better matches what modern mountain bikes are capable of doing.
Looking for a hub for your current MTB standard?
The KOOVA S10 is available for several common QR, non-Boost and Boost configurations. Explore the S10 MTB Hub →