I'm looking for a dual drive type hub. At least that's what SRAM calls them. Hubs that are both internally and externally geared. SRAM and Sturmey Archer are the only manufactures of this class of components that I know of, and I'd like to know of more.

SRAM made the DD2 and DD3, but I think those are both out of production now. I can find several NOS on eBay, but I'd rather have something still in production so it can be serviced or replaced later.

Sturmey makes the CS-RK3, but it's 200 grams heavier than the SRAM, from what I can find.

So there are three models I'm aware of: CS-RK3, DD2, and DD3. Are there more?

Reading about these, it seems like they should have a strong niche, being used commonly in folding bikes and 3-4 wheelers. So it's a head scratcher as to why they would be hard to keep on the market.

I'll need it to be disc brake compatible.

If I can't find one I may go for NOS SRAM on eBay, and just rely on eBay for spare parts if I ever need to. 🤷‍♂️

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    Sachs originated the SRAM design before SRAM bought them. I don't know the model lineage very well. One of the Sachs ones is the Spectro 3x7. What I'm not sure of is if there were any Sachs ones that are meaningfully different from the SRAM models that took their place later. Aug 24 '21 at 6:50
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    Maybe they are not on the market anymore because most of their need can be fulfilled by wide range internal hub. The CS-RK3 you mention has a range of 177%, good internal hub can have the double (360% of Enviolo for example, 408% for an Alfine 11). They may be heavier, but maybe not if you can save the weight (and "complexity") of an additional derailleur (and as a bonus if the frame allows it, you can use a belt instead of a cassette).
    – Renaud
    Aug 24 '21 at 7:26
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    @NathanKnutson: I think the Sachs one was named Torpedo.
    – Carel
    Aug 24 '21 at 8:58
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    Classified Cycling has a 2-speed IGH that takes an 11-speed cassette. It also separates the hub "works" from the hub shell, so you can have multiple wheels and one IGH.
    – Adam Rice
    Aug 24 '21 at 13:07
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    I can still buy sram dd3 disc from the distributor so it's a current part.
    – JoeK
    Aug 26 '21 at 19:45

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