Chris if you're reading this, you once asked me for feedback on the Sturmey Archer RX-RK5. After doing the testing, I can not give this IGH a passing grade for ebike use.
The immediate things to point out are that the axle is a bit small at 8mm flat and while it held strong, I'm not sure I'd want to drop off anything all that high with 8mm. Also, the sprocket is 1/8" so only single speed chains, bmx etc. will work, which limits what you can have on your front chainring (mtb wise anyway). I was using narrow/wide and obviously those didn't work, had to switch to a cheap steel chainring for testing. As for performance, this shifting is okay but note there were times where it had trouble shifting in to gears (despite indexed shifter). I would have to either stop pedalling, then pedal some more then try the shifter again, not ideal when you're riding. I tried a few times with cable adjustment as you would with a normal derailleur but could only get 90% at best.
But those weren't the big deal breakers. The thing I just couldn't get around no matter what was the engagement. I'm not sure exactly what's on the inside as far as mechanics, but what it felt like and performed like was a hub with only one prawl. So if you were just past the engagement point, you would have to pedal almost a full revolution without moving (or engagement) till it connected again. It's a very unusual feeling (like pedalling without a chain) and there's just no getting around this "delay". It can even be felt when you twist the throttle and there's a delay in engaging.
It is however a very robust hub, but perhaps not for this application. Needless to say, it's off my bike now.
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