Every week I get an e-mail or two from some pour soul with a Specialized SCS bike who wants better wheels but doesn’t know what to do.  I wrote about this a little while back here, but this post (that you’re reading now) is the latest and greatest info.

SCS – What It Is

SCS stands for Short Chainstay System.  Specialized used it for a few years on disc-road/cx/adventure bikes.  It uses a proprietary rear hub, it has a 135×12 thru-axle or a 135mm QR axle, but (here’s the kick in the nuts), the freehub body is 2.5mm further inboard.  This allows for the same chain line as a road bike with a 130mm wide hub.  This also means you can’t use a normal disc hub on an SCS bike.  There is only one SCS hub on the market, it’s made by Hope, it’s 24 spoke only, and uses straight pull spokes.  It’s not a great fit for most riders IMO due to the low spoke count, and it can only be used on SCS bikes.

Non-SCS Derailleur Hanger

Ah ha, a solution! Sorta.  Specialized offers a non-SCS derailleur hanger that allows you to use a non-SCS hub.  My understanding (but I have no first hand experience with this, so, grain of salt and all that) is that the QR bikes can use a QR non-SCS hanger and then any 135mm QR disc hub will work, easy peasy.  Again…as I understand it.

Thru-Axles, Derailleur Placement, and Spread Your Stays

Lets talk about thru-axle SCS bikes.  At first I couldn’t find a non-SCS thru-axle hanger, but, eventually one of the local Specialized dealers was able to find someone at Specialized who knew that the hanger does exist and what the part number is (FYI, it’s S162600004 I believe…that’s the number printed on the hanger at least).  Even the folks at Specialized are confused with this stupid rear end.

The non-SCS hanger is a really poor design, in my humble opinion.  The goal of the hanger is to move the derailleur 2.5mm further outboard.  If I were designing this hanger, I would have made it exactly the same as the SCS hanger, except, 2.5mm thicker at the derailleur mount, with all of the added material on the outboard side, so the derailleur is pushed further out.  That is not what Specialized did.  And to be fair, with the SCS hanger designed as it is, you just put a non-SCS hub into it the cassette lockring will hit the frame.

Looking at the inboard (hub side) side of an SCS hanger (left) and a non-SCS hanger (right).

The SCS hanger, on the inboard side, has a channel for the hub to fit into. It acts as a guide to move the hub up and align it with the hole for the axle.  That channel, as it turns out, is 2.5mm thick.

Looking at the thickness of the hangers. SCS on the left, non-SCS on the right.  The derailleur mount is at the bottom of the pic.

So, what Specialized did, instead of just moving the derailleur out, the non-SCS hanger doesn’t have that channel, so it’s thicker at the hub. What that actually does is reduce the spacing of the frame from 135mm to 132.5mm – so when you put a 135mm hub into the frame you have to spread the frame a bit.  So instead of moving the derailleur away from the freehub, they’re moving the freehub away from the derailleur.  This does keep the cassette lockring from hitting the hanger.

There’s two concerns with this.

1 – The axle is still the same length, and due to the thicker hanger it doesn’t engage as many threads in the frame.  Specialized says this is okay, it still engages enough threads, and I haven’t heard any reports of anyone having issues with it loosening or failing.  This does worry some folks though.

2 – Since the frame is spreading, for the rim/tire to be centered in the bike you’re dependent on both the left and right side of the frame spreading evenly.  This doesn’t always happen.  I’ve built the same set of wheels for two different customers, both used the non-SCS hanger, non-SCS Hope Pro 4 hubs, and both had the same model year carbon Diverge frame.  One of them the frame spread evenly and the rim/tire were centered perfectly.  The other did not, and the tire wasn’t centered, and was really close to the NDS stays.  That customer had a dishing tool and was able to check the wheel and confirmed that the rim was centered on the hub, so the wheel was built correctly.  I reached out to a few folks at Specialized and didn’t get any answers as to why one frame behaved differently than the other.  Ultimately the customer had to re-dish the wheel to fit his frame, which means if he moves the wheels to another bike in the future he’ll have to re-dish the wheel again to the put the rim back over the center of the hub.

This wheel was built perfectly centered – but the frame spread required by the non-SCS hanger was uneven, putting the rim/tire too far towards the non-driveside stays.

GOOD NEWS :: Specialized has discontinued the SCS standard.

BAD NEWS :: Specialized sold a whole lot of SCS bikes before they decided to kill the standard, and they’re nice bikes other than the stupid axle standard.

SUMMARY: What to do if you have an SCS bike and you want new wheels

  • QR Axle Frame :: get a non-SCS hanger and any 135mm QR hub should fit (SHOULD)
  • Thru-axle Frames
    • Use the SCS Hope hub, if 24 spokes is enough for you.  Remember – this hub can’t be moved to another bike in the future unless that other bike is also an SCS bike.
    • Use a non-SCS hanger and any* 135×12 hub.  This will allow for a proper spoke count to fit you, and you can move the wheels to another bike in the future.  You *may* have to adjust the dish on the wheel to fit your frame (and then re-adjust it back to center if you move them to a non-SCS bike).
    • *Note :: My understanding is that DT Swiss hubs will not work with these SCS bikes, even with a non-SCS hanger.  This is because the hubs were originally designed as MTB hubs, and with the longer 11spd road Shimano freehub body the cassette lock ring will hit the frame.  It may work with a SRAM XD driver if you’re using a 1×11 drivetrain.  Maybe.  And maybe I’m wrong, I’m just going with what I’ve read.
    • *Another Note :: 135×12 11spd Shimano road hubs are a bit rare.  Many 135×12 hubs are only available as MTB hubs with a 10spd freehub body.  Hope and Hadley do both make 135×12 with an 11spd Shimano road freehub FYI.

I hope this was somewhat helpful.  I have a few non-SCS hangers in stock still, which I’ll happily sell for $40/each including shipping in the lower 48, or for $30 when ordered with a wheelset.  Once I get rid of them, I won’t be buying more though.

Thanks to Adam for the pics.