Tech - 157Trail
When Boost 148 was launched, we chose to remain on the sidelines 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 wheelsets 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 chainline 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 & chainline 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 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 chain line is the same as what it was when 12x150 was released in the early 2000's. The only difference 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-drive side, 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 centerline), 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, Race Face Cinch based cranks (Next, Turbine). Over the past two years, all major crank manufacturers have come on board to support the 55-57mm chainline 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 chainlines.
At Knolly, our 157mm bikes 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 chainline) 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.
157TRAIL allows us to eliminate tire width and focus on tire diameter. Riders can pick their wheel and tire combination based on intended purpose: be it a razor-sharp handling rocket ship, or a rock crawling monster truck (or anywhere between).
157mm hub spacing can be implemented using a flipped chain ring to maintain existing Q factors on XC / lightweight cranksets such as XTR, XO1 and Race Face Next SL.
157mm has a massive increase in stiffness over 142mm and even Boost 148. In fact, the increase in stiffness between 142mm and 157mm is almost three times more than 142mm to 148mm Boost.
157TRAIL provides the most options for tire size across all models. All Knolly 157TRAIL frames will easily clear tire widths up to 3.25".
We have re-designed the entire rear-end area to keep things as tight as possible. The 157TRAIL spacing increases rear axle width by 15mm (7.5mm per side) and yet heel clearance has only moved outward by 1.5mm per side! Our 157TRAIL rear-end remains the same or in some cases narrower than existing Boost 148 bikes currently on the market.
Due to our Fourby4 suspension and Knolly’s forward mounted seat tube we do not need to extend chainstay lengths to accommodate larger wheel sizes, including standard sized 29" tires and high volume 27.5 Plus tires. Fourby4 also allows us to use 73mm bottom brackets shells and is front derailleur compatible.
Chainring clearance remains huge: at 36T for 29" models and 38T for 27.5" models.
Knolly has a reputation for producing bikes that last and we are known for not jumping on the latest trends. We have thousands of loyal riders that, year after year, have ridden our brand because of the performance of our suspension, the longevity of the product and the customer service we provide. Our move to 157Trail enabled us to design, build and deliver the highest performing mountain bikes in the industry.