If you're replacing a rear wheel, buying a new hub, or building a mountain bike from the frame up, you've probably run into Boost and Super Boost spacing. They sound similar, but they aren't interchangeable.
The biggest difference is simple: Boost uses a 148 mm rear hub, while Super Boost uses a 157 mm rear hub. That extra width affects the hub, frame, axle, wheel build, chainline, and in some cases the crankset you need. Here's what actually matters.
What Is Boost Spacing?
Boost was introduced as a wider mountain bike hub standard designed to give bike manufacturers more room to work with when designing modern frames and wheels. A standard Boost setup typically uses:
- Front: 15 x 110 mm
- Rear: 12 x 148 mm
SRAM describes Boost as a wheel and drivetrain specification that allows for things like wider and stiffer wheels, additional tire clearance, shorter chainstays, and more flexibility in frame design. Today, 12 x 148 Boost is one of the most common rear-hub standards on modern trail, enduro, and all-mountain bikes.
Why Did Boost Replace 142 mm?
Before Boost, 12 x 142 mm rear spacing was common. Increasing the rear hub width from 142 mm to 148 mm gave manufacturers additional room to move the hub flanges outward. That can improve spoke bracing angles and allow the wheel to be built with greater lateral stiffness.
The wider platform also gives frame designers more space around the rear tire, chainring, suspension pivots, and chainstays. For riders, the important part isn't necessarily the engineering behind every millimetre. It's that Boost created a wider platform that works well with modern wide rims, bigger tires, and increasingly aggressive mountain bikes.
What Is Super Boost?
Super Boost, often called Super Boost Plus, takes the same idea further. Instead of a 148 mm rear hub, Super Boost uses: 12 x 157 mm rear spacing. That's 9 mm wider than Boost.
Current hub manufacturers including Industry Nine offer separate 12 x 148 Boost and 12 x 157 Super Boost hub configurations, meaning they need to be treated as different standards when you're choosing wheels or hubs. Super Boost is primarily found on aggressive trail, enduro, downhill-oriented, and some e-MTB frames where manufacturers want additional room and stiffness at the back of the bike.
Boost vs. Super Boost at a Glance
| Boost | Super Boost | |
|---|---|---|
| Rear hub spacing | 148 mm | 157 mm |
| Typical rear axle | 12 mm | 12 mm |
| Front spacing | Usually 15 x 110 mm | Usually 15 x 110 mm |
| Availability | Very common | Less common |
| Wheel/hub compatibility | Boost specific | Super Boost specific |
| Main advantage | Balance of stiffness, clearance and compatibility | Additional width and frame-design flexibility |
The key thing to remember is: Boost = 148 mm and Super Boost = 157 mm
What Does the Extra Width Actually Do?
Nine millimetres doesn't sound like much, but on the rear of a mountain bike it gives designers some useful extra space.
Wider Hub Platform
A wider rear hub allows the spoke flanges and other hub components to be positioned differently. The goal is generally a stronger and stiffer rear-wheel platform, particularly useful for bikes built around aggressive riding, bigger impacts, and longer-travel suspension. This becomes increasingly relevant with large 29-inch wheels. A larger wheel naturally gives the spokes more leverage, so manufacturers look for ways to maintain lateral stiffness.
More Room Around the Tire
Modern mountain bikes need to fit a lot into a relatively small space. You've got:
- The rear tire
- Chainstays
- Seatstays
- Crankarms
- Chainring
- Cassette
- Suspension pivots
- Linkages
Making the rear end wider gives frame designers more flexibility when trying to package all of those components together. That can be especially useful on long-travel bikes with large tires.
More Freedom for Frame Design
Super Boost isn't simply about making the hub wider for the sake of it. The additional space can give engineers more freedom when determining suspension layout, chainstay dimensions, tire clearance, and frame stiffness. Whether that translates into a noticeably better bike depends much more on the overall frame design than the hub standard alone. A well-designed Boost bike isn't automatically worse than a Super Boost bike.
Does Super Boost Make a Wheel Stronger?
Potentially, but don't look at hub spacing in isolation. Hub geometry affects spoke bracing angles, which play a role in lateral wheel stiffness. A wider hub platform can give wheel designers more room to optimize those angles. But wheel strength also depends heavily on:
- Rim design
- Rim material
- Spoke count
- Spoke type
- Spoke tension
- Hub flange dimensions
- Wheel diameter
- Build quality
A properly built Boost wheel can easily outperform a poorly designed or poorly built Super Boost wheel. Think of Super Boost as giving wheel and frame designers more room to work with, rather than automatically making every 157 mm wheel stronger than every 148 mm wheel.
What About Chainline?
This is where compatibility gets more complicated. Making the rear end wider can also change where the cassette and chainring need to sit relative to the centerline of the bike.
A standard Boost drivetrain commonly uses a chainline around 52 mm, although newer drivetrain systems and frame designs can use different measurements. SRAM specifically identifies standard Boost as using a 148 mm rear dropout width and a 52 mm chainline in its drivetrain documentation.
SRAM also notes that chainring offset depends on chainline and rear hub spacing. Super Boost frames may require a different crank, chainring offset, spacers, or chainline depending on the manufacturer. That's why you shouldn't buy drivetrain components based only on the words Boost or Super Boost. Check the frame manufacturer's specification first.
Is Super Boost the Same as SRAM MTB Wide?
No. This is an easy one to mix up.
SRAM specifically states that MTB Wide and Super Boost are not the same standard. While certain combinations can overlap, SRAM says they generally have different requirements involving cranksets, bottom bracket spacers, hub dimensions, and chainline.
Can You Put a Boost Wheel on a Super Boost Frame?
Generally, no. A 148 mm Boost hub is narrower than the 157 mm spacing the frame was designed around. Similarly, you can't simply install a Super Boost wheel into a Boost frame. The 157 mm hub is physically too wide.
Adapters exist for certain hub designs and very specific applications, but compatibility depends on the hub and frame. Treat Boost and Super Boost wheels as different products unless the manufacturer specifically says a conversion is supported.
Can You Convert a Boost Hub to Super Boost?
Sometimes, but definitely not always. Certain aftermarket hubs use interchangeable axles, end caps, or hub components that allow different configurations. Others don't.
And there's an important distinction between making a hub fit between the dropouts and actually producing the correct cassette, rotor, and spoke-flange positioning. If you're considering converting a hub, check directly with the hub manufacturer instead of assuming a set of end caps will turn any Boost hub into Super Boost.
What About 157 mm Downhill Hubs?
This is another area where the numbers can cause confusion. 157 mm rear spacing existed on downhill bikes before modern Super Boost became common. That doesn't mean every component labelled 12 x 157 should automatically be treated as identical.
Hub architecture, flange positioning, drivetrain requirements, axle interfaces, and frame specifications can vary. If you're working on an older DH bike or trying to reuse an existing 157 mm wheel, check the exact hub and frame specifications before buying parts. Matching the number alone isn't enough.
Is Super Boost Better Than Boost?
Not necessarily. Super Boost offers some legitimate engineering advantages, particularly for frame manufacturers building aggressive bikes around big wheels, wide tires, and long-travel suspension.
But Boost has a major advantage of its own: Compatibility.
Boost 148 components are extremely common. That means you'll generally have more choices when shopping for:
- Hubs
- Complete wheels
- Replacement wheels
- Cranks
- Chainrings
- Used components
Super Boost components are available from major manufacturers, but the selection is usually smaller. If you already own a bike, though, there isn't really a decision to make. Use the hub spacing the frame was designed for. Don't choose a frame based purely on whether it says Boost or Super Boost.
How Do I Know Which One My Bike Uses?
The easiest option is to check the specifications provided by your frame or bike manufacturer.
Look for something like: Rear Hub: 12 x 148 mm. That's Boost.
Or:
Rear Hub: 12 x 157 mm. That's Super Boost.
If the information isn't listed, check:
- The manufacturer's technical manual
- The specifications for your exact model and year
- The markings on the rear hub
- Your rear axle specifications
Don't rely entirely on measuring the outside of the frame or axle. Different axle lengths, threads, and frame designs can make that misleading.
Does Boost vs. Super Boost Affect Wheel Size?
No. Hub spacing and wheel diameter are separate specifications. You can have a:
- 27.5-inch Boost wheel
- 29-inch Boost wheel
- 27.5-inch Super Boost wheel
- 29-inch Super Boost wheel
The same applies to mixed-wheel bikes. A bike could use a 29-inch front wheel, 27.5-inch rear wheel, and Super Boost rear spacing. None of those specifications automatically determines the others.
The Bottom Line
The difference between Boost and Super Boost is pretty straightforward once you cut through the terminology.
Boost uses a 12 x 148 mm rear hub.
Super Boost uses a 12 x 157 mm rear hub.
Super Boost gives bike manufacturers additional width to work with when designing the rear wheel, frame, suspension, tire clearance, and drivetrain. Boost, meanwhile, remains incredibly common and gives riders a huge range of compatible wheel and drivetrain options.
Neither standard automatically makes a bike better. What matters is that your frame, hub, axle, crankset, chainline, cassette, and wheel are designed to work together. If you're replacing a wheel or building a bike, check your frame's specifications before ordering anything. Nine millimetres isn't much until the new wheel doesn't fit.
Remember that we offer free shipping on all orders over $149CAD. Orders are all processed and shipped within 24 business hours as well. Looking for mountain bike parts? We stock hundreds of parts from multiple brands and you can shop our entire selection here.
Spend less and ride the best with TBS Bike Parts.
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