UDH is the big bike buzzword these days – with SRAM’s latest direct-mount Transmission derailleurs requiring it – but Sour thinks they’ve found a better way to future-proof their steel bikes. Instead of fully adopting the universal hanger standard, Sour tweaked it a bit so they could still make a lightweight dropout well-suited for small-diameter steel tubes, but with T-type direct mount derailleur compatibility. And importantly for some adventure riders… Tailfin compatibility, too.
Sour goes Almost-UDH for Transmission compatibility
OK I know, I know…
We finally got a universal derailleur hanger standard that brands were whole-heartily adopting, and these steel bike builders decided to screw with it and make another standard!
What are they thinking?
Well…
What they are thinking is that UDH is really not quite as ‘universal’ as well all thought. And it was really optimized for the flat wide dropouts of carbon bikes.
It requires a 13mm thick dropout with a pretty big 30x40mm flat area on the inside and 25mm diameter flat spot on the outside. Transmission derailleurs simply require ~30mm in diameter flat on both sides. That’s pretty standard on carbon bikes. And alloy bikes with big machined dropouts can also easily make that work.
But many quality steel and titanium bikes use much smaller (often hooded or flat plate dropouts), optimized to weld or braze-on small diameter seatstays & chainstays. And they simply don’t have enough free real estate to work with UDH.
Yes, it’s possible to make it work. Some steel bikemakers have switched to bigger or interchangeable dropouts, completely rearranged the layout of their stays to fit, or some have come up with a good UDH-ready compromise.
Sour’s solution was to tweak the standard, just a bit.
What’s that mean?
That means, the Sour Not-UDH is pretty much the same as a regular UDH, just with a bit of that inward-facing plastic upper fin chopped off. Sour says it’s about 15% smaller overall. That lets them fit it into a compact hooded dropout, and doesn’t get in the way of their integral rack/fender mount.
And on the outside, there’s just an alloy spacer since steel dropouts aren’t 13mm thick. Because, steel is just stronger, so they don’t need to be so wide, and can save quite a bit of weight.
Plus, unlike the SRAM UDH which is partly plastic, the Sour Not-UDH is entirely made of machined aluminum. So, the Sour one might even offer more precise shifts?
Of note: Sour’s Not-Quite-UDH is all aluminum – much like Robert Axle or Wheels Mfg‘s all-alloy UDH replacements. Sour’s also uses a standard M17x1 lefthand thread pitch to assemble the 2 hanger halves. A big driver of this was simplified manufacturing. But also, a lot of people (qualified bike shops included) have been breaking some of SRAM UDHs when installing them. A good portion of that might be because of the high UDH torque rating, the non-standard left-hand thread pitch between the bolt & hanger, and the fact that many (most?) torque wrenches weirdly enough don’t work or are inaccurate for reverse threads. That and the fact that they are about half plastic.
Some more bits of ‘universal’ hassles…
One is that the SRAM UDH hanger is a ‘standard’ and works with 12mm x 1.0 thread pitch thru-axles. But some OEMs use the UDH interface, but their own hangers have a different thru-axle pitch (since that’s not technically part of the agreed-upon ‘standard’). Why some would use a M12x1.75 axle inside a UDH is inexplicable to me, but it exists. Sour sticks with M12x1, like SRAM, and like all of SRAM’s Transmission derailleurs (which also curiously each have different assembly bolts, presumably because of slightly different hangers integrated into each T-type derailleur).
The last bit is that SRAM’s standard UDH solution is not Tailfin-friendly, because they require special axles that extend through the hanger (or T-type derailleurs) to mount the unique bikepacking racks. Since Sour is popular among bikepackers and adventure cyclists, they reworked their axles to bolt together with a 12mm hex wrench as soon as they realized this issue. So, many of the photos I have to illustrate this show a 8mm hex interface, but they’re now building bikes with the 12mm (and a 8mm adapter) and will send the new bolt to everyone who needs it.
In the end, the Sour ‘Almost-UDH’ is “100% Transmission compatible”, since SRAM direct mount derailleurs don’t make contact with the portion with the fin anyway.
Sour Not-Quite-UDH – Availability
All new made-in-Germany Sour frames welded since last fall feature the new Not-UDH dropout. Sour says the new dropout & hanger is also a bit lighter than their previous dropouts, even with the added compatibility.
But YES, you can just fit any SRAM T-type derailleur or any conventional derailleur to your new Sour bike. And even a Tailfin rack with their special M12x1 thru-axle. Plus, Sour will deliver all of their new steel bikes with an extra spare hanger, too. (And it sounds like you could use it as a replacement for your regular UDH-equipped bike if you damage a hanger there.)
Pick a Sour steel gravel or hardtail mountain bike if you want wide mountain climbing Transmission gearing. Or, now that Red went Xplr 13-speed, you can get a tighter-spaced 1x race setup for a gravel or all-road Sour.
