Talk Bike Nerdy to me: Knolly's take on 157TRAIL aka: Superboost axle widths
Updated: Aug 28, 2020
by Noel Buckley
Why didn’t Knolly adopt 148mm Boost?
When Boost 148 was launched, we chose to remain on the sideline because we were not convinced it was right. At Knolly our design philosophy ensures that any performance feature change needs to be supported by a valid engineering position and proven rider performance benefits. And we were right to wait.
When 148 Boost was created, it was designed to help fix a problem with 29er wheel sets and it was marketed as "a huge improvement in stiffness". It was simply the widest possible hub width that could be implemented while maintaining normal Q-factors of existing 2x10 speed drivetrains and it was limited width wise by the rear stays of certain suspension designs. It was also designed to support the needs of 2x10 systems and keep Q factors narrow. This is why it only expanded the chain line by 3mm. Why not 4mm, 5mm, or even 7mm? It was because of the constraints of 2x10 and narrow Q Factors. Boost 148 was then adopted as a solution by the "plus size" tire community because it gave another 3mm of tire clearance per side. Unfortunately, it did not solve all the tire size issues. And in 2013 and certainly by 2014, 2x10 was a distant memory; it was all about 1x11 with 10 42T cassettes.
So why 157Trail?
We should remember that the 12x157 standard isn't "new". It's been around for close to 20 years and was originally the 12x150mm DH standard developed in the early 2000's and then evolved into the 12x157mm DH standard post 2010. Both 150 and 157 use the same hub & chain line standard, they just have different end caps. The 157mm hub width has an extra 7mm of width to support the "3.5mm shelf" in each dropout used to transfer wheel loads from the 12mm frame axle to the larger 19mm diameter hub axle. This is the same way that the current 142mm width (still used on some mountain bikes and very dominate in road/gravel) was akin to the earlier 135mm. The 157 standard is not a new standard, it's just become more widely adapted to trail bikes over the past few years.
The current 12x157mm hub shell width is the same, cassette location is the same, and hence chain line is the same as what it was when 12x150 was released in the early 2000's. The only difference that's come up recently is the idea of using the wider hub shell to maximize the width between the hub flanges. Obviously the position of the drive side flange is constrained by the cassette's location but on the non-driveside, there is room to move this hub flange outward towards the left side of the bike. Different hub & wheel manufacturers have differing opinions on this. Some are trying to maintain an even spoke tension (i.e. the left side flange is closer to the hub center line), or achieve a wider bracing angle (left side flange is moved as aggressively outboard as possible). Some are using asymmetrically drilled rims to equalize the bracing angle. And some wheels incorporate all of this. There's no right answer and it depends on what the hub & wheel manufacturer thinks is best and also, the quality of the wheel's components and build. But what 157mm does do is give you options beyond Boost 148mm and it delivers a stronger, higher performance wheel.
What benefits will the average rider see over their current 148mm boost bike?
When 157 started to become popular with a small number of trail bikes a few years ago, the major challenge wasn't at the back end of the bike (i.e. hubs). The challenge was in the center of the bike with cranksets. There were lots of 157mm hubs on the market as well as FR and DH cranksets available to support them but these cranksets were overkill for XC, Trail, and Enduro/ All-Mountain applications. They also had fairly wide Q factors in the 180mm+ range. Trail cranksets (which are what most of us purchase) were limited to one (albeit very good) vendor, Raceface Cinch based cranks (Next, Turbine). Over the past two years, all major crank manufacturers have come on board to support the 55-57mm chain line that 157mm rear hubs require. This has become easy for them as almost all modern cranks use variable axle lengths and/or chainring offsets to achieve the desired Q factors and chain lines.
At Knolly, any of our 157mm bikes (the Knolly Fugitive and new Warden) can run a sub 170mm Q factor crankset (i.e XX1 or XTR or Next SL), and still have amazing tire and heel clearance while keeping the Q factor in the XC/Trail range. You don't have to run a narrow crank (a stock XT crank has around a 177mm chain line) but it's possible. That's the benefit of 157; it provides a stronger wheel at almost no weight penalty (literally 10g or so). It also maintains compatibility for narrow cranksets for those that want to use them, and provides a ton of tire clearance.
Why use this standard when Boost 148 is almost ubiquitous throughout the industry?
The first answer is simply because it's better. The second answer is because it's not based on 2x10 technology that had a very short lifespan in the bike industry and almost no one uses anymore. The third answer is because it's an established older standard and it's super well supported at all levels of OEM and aftermarket manufacturing.
In addition, a large part of the market is building 29" bikes and wider bracing angle supports these wheel diameters better, in every way. For high end wheel sets, it allows lots of options on how to build the wheel and vary compliance and stiffness (which means a higher performing wheel). For low end wheels, it builds a more tolerant wheel. It’s good all around.