5Dev Mullet Mod Puts SRAM MTB 1x Transmission on Non-UDH Gravel Specialized

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    Maker of some of the wildest machined mountain bike cranks on the market, 5Dev turns their attention to road & gravel bikes with a game-changing UDH Mullet Mod for non-UDH bikes. What it means is that you can run a new direct mount SRAM mountain bike Transmission (T-Type) derailleur on Specialized bikes that have a conventional hanger.

    That’s right, T-type derailleurs on a bike that does NOT have a UDH.

    Yes, for the time-bring it is Specialized only. But, we can’t imagine that will last forever, as this could really be a game-changer for updating tons of existing bike!

    Why not make road and gravel bikes UDH & T-Type compatible?

    (Photo/Tyler Benedict)

    Micro-refresher here, first. SRAM spent a few years convincing the bike-producing world that the universal derailleur hangeror UDH – was the way of the future. Mountain biking makers got on board pretty quickly.

    sram transmission direct mount rear derailleur installation closeup
    (Photo/Tyler Benedict)

    And that later turned out to be because SRAM had an all-new direct-mount style T-Type MTB rear derailleur & Transmission in the works. Without tons of different hangers, they could bolt the derailleur directly to your frame, ensuring improved stiffness, perfect alignment, and promising better shifting. All you needed was a UDH-equipped frame. Tons of mountain bikes have already made the leap, so there’s tons of compatible options.

    But road bikes and gravel bikes have been slower to get on board, as there wasn’t as much demand for that wide 520% 1x gearing spread.

    At least, there wasn’t before. Now, plenty of gravel riders want that 1x simplicity. They want that mega Mullet gearing range that combines road dropbar shifters with massive MTB cassettes. But the vast majority – even with some of the most creatively innovative new gravel bikes – don’t have UDH-ready bikes.

    So, 5Dev wanted a solution. What is their Mullet Mod?

    Enter the bolt-on 5Dev Mullet Mod for Specialized bikes!

    5Dev Mullet Mod for Specialized, non-UDH conversion kit to get T-Type Transmission direct mount MTB derailleur on gravel road bikes, B&W

    Put simply, this seems to be just a smartly-designed thru-axle end nut and set of spacers.

    We’ve not seen an exploded diagram of it yet. But presumably, this is a combination of spacers on either side of your Specialized bike’s carbon dropouts. On the inside, it would connect to the same interface as Specialized’s own replaceable derailleur hanger. And on the outside it spaces everything out to the correct width for the T-Type SRAM MTB derailleur. Tying it together is likely a special thru-axle and a bolt that holds it all together.

    5Dev Mullet Mod for Specialized, non-UDH conversion kit to get T-Type Transmission direct mount MTB derailleur on gravel road bikes, up close

    5Dev says that there are “no modifications needed. It’s a bolt on mod.” So possibly, it could mean the derailleur would be removed when you remove the rear wheel/axle. But likely many owners of existing Specialized road and gravel bikes would take that compromise to fit the latest mullet drivetrain onto their bikes.

    What bikes does it fit?

    Specialized Diverge STR gravel bike dropout

    First off, 5Dev says that it is made for “select specialized road and gravel frames“. They go on to explain that it is “ideal” for the Diverge and Cruz line-ups, which includes the ‘full-suspension’ Diverge STR. Separately they also confirm that it will fit current Roubaix and Tarmac road bikes, as well.

    Specialized Diverge STR gravel bike frameset

    Further discussion of compatibility says that it “fits most 12x142mm through axle frames” with 5Dev’s patent pending design. The determining factor is going to be the width of the frame at the dropout AND the consistent interface for a replaceable derailleur hanger. Presumably, 5Dev could make options to fit other bikes/bike brands down the road.

    And how much does it cost?

    5Dev Mullet Mod for Specialized, non-UDH conversion kit to get T-Type Transmission direct mount MTB derailleur on gravel road bikes, complete

    Here’s the trick. The 5Dev Mullet Mod for Specialized bikes costs $1500, and is ONLY available in the United States.

    Yet while that sounds like an exorbitant price for a derailleur hanger mod, it is actually a pretty complete upgrade package. For fifteen-hundred bucks you get the complete bolt-on 5DEV UDH Mullet Mod, plus a new SRAM XX SL AXS rear derailleur, an XX SL flattop chain, and an XX SL 10-52T cassette. That’s already $1400 for the SRAM parts themselves ($650, $150 & $600, respectively), making the 5Dev addition sound down right affordable!

    Oh, and one more thing…

    Prototype 5Dev Aero Titanium Cranks for road & gravel

    5Dev Mullet Mod for prototype 5Dev Aero Titanium crankset for road and gravel bikes

    Did you notice those cranks on the Specialized gravel bike there? That’s an as-yet-unreleased set of CNC-machined 5Dev Aero Titanium Cranks for road and gravel bikes. 5Dev is tight-lipped on the details other than to say ‘stay-tuned’. They clearly are SRAM direct-mount crankarms that share the precisely machined ends of their signature MTB cranks. But they have a smooth outer surface and smoother rounded edges for cleaner looks and aerodynamics.

    We’ll be keeping ears and eyes open for more details!

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