To increase the development range on a folding bike, I'd like to replace its three-speed SRAM IGH with a Sturmey-Archer X-RF8(W) IGH.

The page says that it accepts a "20 to 23 or 25 teeth sprocket".

I read somewhere about IGHs that they impose a limit on the chainring/sprocket ratio because of the torque: Does someone know what the limit is for that IGH, so I know which chainring/sproket to get?

I'm thinking of using either a 44T chainring + 20T sprocket combination, or if space allows, using a compact 50/34T chainring and a 20T sprocket.

Thank you.

  • FYI, the 60's Raleigh 3-speed I have came with a 48T chain ring with a 18T rear sprocket. The spec sheets you linked too didn't have that info on there. It is possible they use some large chainring size (without disclosing) when giving the rear sprocket compatibility. – BPugh Jul 9 '15 at 20:05
  • You are getting a good range of rations with the RF-8, from 1 up to 3.25. Not sure why you would want to turn it into a 16 speed. Also, IGHs normally use the single speed sprockets and 1/8" chains. . The compact chain ring is is narrower, designed for 3/32" chains. If you want more ratios you could get a Shimano 11speed IGH. How many teeth in your current chairing? I would stick close to that number. – Kim Ryan Jul 10 '15 at 5:09
  • Thanks for the infos. The OLD on that bike is 120mm, so the SA X-RF8(W) in the only alternative IGH available. I'll try to give it a 44 + 20 to get started, and try a 50/34 later. – OverTheRainbow Jul 12 '15 at 20:06
  • Ok, but be wary that the rear sprocket and chain may be too wide for the double chain ring. IGH I've see all use single speed chain and sprockets. – Kim Ryan Jul 13 '15 at 6:29
  • The chain and cog on the IG hub are not compatible with a double crankset, as others have mentioned. Nor would the chain line work. In addition, you would have no tensioning device without a rear derailleur, and so the chain would not be able to adjust length to shift between front chain rings. It would either bind or fall off. Definitely not recommended. – zenbike Apr 2 '16 at 6:45

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