For 2016, the Specialized Crux cyclocross bikes get thru axles and disc brakes across the line for all carbon models, alongside other minor frame and fork updates. The Roubaix endurance road bikes get thru axles on carbon bikes from the top down to the SL4 Expert level.
That’s a big update from 2015 models, where all bikes still used standard quick release dropouts on the rear (forks were already thru axle). Generally, thru axles are a good thing, offering a stiffer frame and wheel, and a safer mounting system when used with disc brakes. What’s got some riders in a tiff is the way Specialized went about adding them, creating a proprietary system that locks you into their Roval or Axis wheels…
UPDATE: Read the development story behind the SCS 135mm disc brake thru axles in our interview with Spec’s Road Brand Manager Mark Cote!
The controversy of the design comes from the axle spacing, which remains at a standard 130mm in order to maintain proper chainline and short chainstays. The gap inside the dropouts is 135mm, which accommodates the additional 2.5mm per side required for the slots that the wider thru-axle hub endcaps slot into. The difference is that the 135mm spacing is not the same as 135mm mountain bike spacing (stay with us… the diagram below provides visual comparison and will help make sense of it all).
The design does indeed allow for perfect chainline, for which there are recommended guidelines. Those guidelines prescribe ideal placement for the chainrings in relation to the cassette, with different variances based on how long the chainstays are. For shorter chainstays, there’s less wiggle room in order to maintain proper shifting and prevent the chain from accidentally rubbing the other chainring in a 2x setup.
Specialized runs their narrow 68mm OSBB, and they want short chainstays, so they had to get creative to maintain a good chainline.
The result is SCS (Short Chain Stay) hubs and spacing. For the new thru axle version of SCS, that means a 135mm spacing at the ends of the hubs, which keeps the traditional hub spacing at 130mm. In other words, as far as the cassette’s position on the hub is concerned, this is a 130mm road hub.
For practical purposes, this simply means you’re getting a 130mm disc brake road bike hub on a modern bike…the downside being that most (ie. all) modern disc brake road bikes have switched to 135mm QR rear spacing, which becomes 12×142 with a thru axle. So, with the new Specialized Crux and Roubaix, you’re locked into using their SCS Roval or Axis wheels because no one else makes 135mm thru axle hubs.
- It limits your ability to use existing high end wheels, either as primary or pit wheels.
- It locks you into Specialized’s wheel system, unless you’re willing to buy a wheelset and then rebuild them with your own rims.
- The desired chainline could have been accomplished by either using a wider bottom bracket and 12×142 rear thru axles, or using an offset chainring spider or direct mount ring with 12×142, similar to how mountain bikes are moving the chainline out to accommodate Boost 148 rear ends.
- With 1x drivetrains, maintaining ideal chainline for the best front shifting is less important, although we’d add that having incorrect chainline can cause premature drivetrain wear and extra noise.
