toolong

I noticed in the sturmey catalog the X-RK3 disc 3 speed hub. From googling, it seems that the hub exists in the wild, but I can't find it for sale anywhere. Does anyone know if it has been discontinued or has a source where it can be bought? I assume the price would be similar to other 3speeds in $60-80 range.

A somewhat related question, are 3 speeds suitable for mountain biking? I read somewhere that their mechanism simple and robust compared to other IGH hubs. Do they survive MTB abuse well?

In particular I'm looking for a hub for my trike, so i would like something that can deal with high torque and possibly shift under pressure. Are the sram i-motion 3s worth their 2x-of-sturmey pricetag?

K6-III

The X-RK3 disc hub has 163mm over-locknut spacing and is unsuitable for most frames.

The 2 options for 3-speeds with disc brakes come from Sram (I-Motion 3) and Shimano (Nexus 3 Disc).

Of these, only the i-Motion 3 is relatively available, with the Nexus 3 Disc shipping from QBP in late March.

All modern 3-speeds have comparable internals and all are very durable. The i-Motion 3 has a slight advantage in regards to it's shifting mechanism being inboard of the chainstay, while the others do not.

Dan Burkhart 

Sturmey Archer hubs are great, but they don't seem to have caught on that to market in todays economy, you need to keep your web site current.
The hub to which you refer has no mention there, nor have they updated it to show the new, (and very nice) rapid fire style shifters.
Heck, you would think they would want to trumpet the improved ratio range and durability of their 8 speeds, but all you get is the old 305% models.
Wake up Sturmey Archer!

tcs

Yep, it's the S-RK3 three speed disc hub that has the 120mm OLD. Alas, it also seems to be a theoretical product.

There's always the AB3 three speed hub, with its big 90mm drum brake, and the alloy shelled X-RD3 with a 70mm drum brake. Both of these are available.

tcs

tatfiend 

For mountain biking, or a trike, the 3 speed hubs have a relatively limited gear range and large steps between gears. Not sure about strength as none currently made are recommended for tandems or cargo bikes except the Rohloff or SRAM P5 Cargo which are not 3 speed. Also not sure of the actual availability of the P5 Cargo as it is in the SRAM tech manual but not listed on their web site. The Rohloff was originally designed for mountain bikes apparently.

With all gear hubs I have tried the lower the torque input while shifting the better/faster the shifting is.

toolong

First of all thanks for all of the IGH trivia. From the catalog looks like sturmey 3speed hubs come in every hub spacing size imaginable, so I'm not worried about fititng the right bike. I was more curious whether the hub will survive high torque(ie while not shifting)

Yeah I just got the "old" 8 speed hub this summer. Seems to work ok, is the trigger shifter an improvement over the grip shift? I don't mind the grip shift much..except when shifting up(ie lower cable tension), those are laggy. That and I accidentally broke one shifter by riding without the "dust" cap which caused the cable to pop out then pop back in bent which then proceeded to bust the plastic piece holding it in place...not the most reliable shifter

As to sturmey's products, I found that all of the useful stuff is hidden in the "contact" page at https://www.sturmey-archer.com/contact.php under "PDF Catalog" link. It's full of all kinds of wonderful goodies.

Speaking of the new hub, is it practically better than the old one? ie would it be more suited to a cargo trike I'm currently planning to go with a 3three speed, but lack of a disc option is a little irritating.

For now I've decided to settle for the 3speed coaster brake version unless the disc one pops within the next month.