SCS and Axle Standards

Posted by Jerry Chabot on

Hi Everyone. Lets to try to unravel the many mysteries of the bike industry and their various "standards".... or lack there of. There is no current lack of standards, they are just all different!

The most important thing that I want to address here is Specialized SCS. This is their "short chainstay system", which in concept is very valid. Specialized is an engineering company that sells bikes, I am an engineer that rides bikes, so I get where they are coming from. Not sure I agree with the implementation in this case, but that is OK cause we have it figured out.

SCS is basically a road hub (130mm OLD) mated to an MTB hub (135mm OLD). (OLD is "over lock nut distance". As always, refer to Saint Sheldon for more info.) Imagine you cut two hubs right in the center of the hub shell and took the disc brake mount half of an MTB hub and magically grafted it onto the freehub side of a road hub. Actually, its not magic because Specialized did it.  The reason they did it was to allow a road length chainstay on their road disc product. Prior to SCS, Shimano and SRAM had a 420mm minimum chainstay length to run a disc brake hub. No issue there, that is pretty standard on CX bikes. But on a road bike, say a Tarmac, that is unacceptably long. If you shorten them to normal road length, the 135 OLD does not play nice with the road crank Q factor and you get cross chain noise, and maybe even some chain grab. So, Shimano and SRAM would not sell product to Specialized for that configuration. The solution? SCS hubs.

Read more here and here if you are interested, or take my word for it. 

How does this affect you, the bike consumer? It is yet another axle standard to worry about. Let's review current axle standards:

Road QR: Good old fashioned quick release.  100mm OLD front. 130mm OLD which means RIM BRAKES <<< Can't stress this enough!! 130mm OLD = RIM BRAKE ONLY

MTB QR: Same as above, only the rear is 135 OLD and can be disc OR rim brake. Wider rear axle, longer chainstays on MTB, zero issues for disc.

XC Through Axle: 15mm axle in the front, 100mm OLD just like QR. 12mm axle in the rear, 142mm OLD. 142mm because you need some "extra" axle to stick into the frame so the wheel self locates prior to stuffing the axle through. Otherwise this would be VERY finicky. The net dropout spacing and effective OLD is still 135mm.

Road Through Axle: This is the new kid on the block. It is the same 12x142 on the rear, but now with a 12mm front axle as well, still with 100mm OLD spacing, that better matches the generally slimmer blades of a road fork. Don't forget the drop outs are now closed, and threaded for the axle, and they need some beef, so a 15mm axle results in a rather "heavy" looking fork, and is not aesthetically pleasing.

SCS Road Through Axle: This is Specialized being good engineers and solving a problem that would otherwise pretty much derail the road disc bike market. If road disc means long chainstays, no one is going to want to race on it. Because they made a hybrid MTB (disc) and Road (low Q factor) hub together, they end up with a 12mm through axle but only 135mm OLD, already wider than your current rim brake road bike. If they went short chainstay and 142mm OLD, your heels would very likely hit the chainstay. NO GO!  

You really can't fault Specialized for BUILDING A BIKE CORRECTLY, now can you? You can't. The devil is in the details, and as an engineer, I agree with them.  The problem is that they are way out in front on this, and the 2016 Crux cyclocross bikes are shipping and people are just now getting them and realizing that none of their wheels fit. Literally. And the bikes come with clinchers only this year. And the only wheel you can buy that will go on EVERY 2016 CARBON CRUX SOLD is Specialized Roval Carbon.  A sweet wheel, to be sure, but $2,700!! 

Enter NEXT.  We called all the major hub companies and no one is getting near this. No one even has 12x100 front road TA adapters ready (DT will ship them in December). Ok this is a problem. But we are engineers! We can do this! And in fact we have done just that. We have designed, and are moving into expedited production on, both a Road TA kit and an SCS Upgrade kit. Both will be available to ship with NEXT wheels in a few weeks. Bear with us, but once we have them, no one else will. 

So go home, tell your friends. Unpack your shiny new 2016 Crux (or Roubaix or Ruby or Diverge) and once you have convinced yourself that that just happened, come back over here and visit the wheel store. We've got your back on this one. And we won't even judge you.