Just when you thought things might be settling down for a bit, with 650B wheels all but taking over the mid/long travel segment, 29ers owning the XC field and 26″ bikes relegated to entry level, youth and gravity bikes. Alas, the 148mm thru axle that seemed to be a novelty when introduced on Trek’s 2015 Slash and Remedy bikes may soon be ubiquitous.
But why?
Surprisingly, there are a lot of reasons why this makes sense. Ones good enough to actually justify the annoyance of another axle standard that’ll require new hubs and new frames to take advantage of. Ones that will make mountain bikes better in quite a few ways. And while most companies we talked to wouldn’t provide details of their own forthcoming products on the record, some would speak in generalities. We have it on good authority from some of the biggest parts suppliers that the 148mm axle standard will become the major new feature of 2016 bikes from almost every major company. SRAM is on board since they’re providing the wheels for Trek’s new Remedy 29er, the first bike to use Boost 148. And Norco told us outright they’re “planning … a couple of new platforms to use this standard.”
Here’s what we learned…
FIRST OFF, WHAT IS BOOST 148?
In the beginning, we had 135mm quick release hubs. The 135mm number is the measurement between the dropouts, not accounting for the slot that the hub’s axle ends sit in. When 12×142 came about, it was simply a new axle size, not a new standard per se. It just opened up the internal hub diameter to allow for a larger diameter thru axle to be used. This made the rear end stiffer and, since it was fully enclosed by and threaded into the frame, eliminating any chance for the hub to move in relation to the frame.
All was good…until 29ers came along and lengthened the distance from the hub to the rim. This had the effect of decreasing the spoke bracing angle, narrowing the triangulation and generally resulting in less stiff wheels. The solution Trek developed was to widen the hubs.
But wait, why not just use the 150mm standard that’s already on downhill bikes?
Because, the 12×150 axle sat on the inside face of the dropout area, without any notch in the frame to hold it in place. That meant you had to hold the wheel in line with the holes and slide the thru-axle into place. It was a pain, which is why every bike we know of went to the 12×157 standard. It’s the same 3.5mm extensions the 142 uses to slot into the dropouts, just with a wider axle to get wider wheels. It’s not as big a deal on DH bikes since many of them are running shorter 7-speed cassettes. That, and you’re not pedaling all day on them. In reality, there’s a massive 15mm difference between 157 and 142, and it’s just too wide for normal riding. Thus, Boost 148 was born:
So, the new Boost 148 really and truly is a new standard, not just a new size, since it requires a new hub shell and new frame. It is similar to 12×142 in that it’s using the same measurements from cassette to dropout and rotor to dropout, as well as the same 3.5mm hub catches in the frame. Where it becomes an entirely new hub is that extra 6mm in the center of the hub shell, widening the entire system.
On the one hand, this is good because it will use existing standards for disc brake mounting and spacing, as well as cassette mounting and spacing. On the other hand, it’s going to cause headaches and cursing because it will require an entirely new hub shell. There is no simple end cap swap as with 12×142, the Boost standard will be an entirely different hub shell. And it’ll require a new frame to put them in.
But, as you’ll see, it may just lead to much, much better bikes in the very near future.
WHAT’S TREK USING IT FOR?

STIFFER FRAMES, BETTER SUSPENSION
SHORTER CHAINSTAYS (OR BIGGER TIRES)
THE CHANGE TO CHAINLINES
ANY BACKWARD COMPATIBILITY?
“Boost 148 was something SRAM has been wanting to do for a very long time, but up until Trek being willing to dedicate a bike platform to it, SRAM never had the chance to make it a reality. But with SRAM and Trek partnering up, they came up with the first bike to have this new interface (Remedy 29er in MY15).
Boost148 is a complete system. You must have the front and rear chainline move out by the corresponding 3mm. Rear end gets 6mm wider symmetrically and the front chainline moves out 3mm to correspond with rear chainline movement. SRAM 1x systems have a chainline of 49mm. A SRAM 1x Boost148 system has a chianline of 52mm. 50mm or 52mm is not correct for a SRAM 1x system, and you will have compromised drivetrain performance with any other chainline.
SRAM is THE component brand that brought Boost148 to the market. We are the first company to have wheels and cranks to support this new standard. We will continue to expand our offering moving forward as well.”