FurryOnTheInside
In Memoriam
Oh, thanks.
According to bicycle forums, FDs can handle up to a 24 tooth difference if well set up and gear ranges are changed very carefully. Shimano info states 22, but that's a conservative figure. So if keeping within that 24 tooth difference, the smallest low range chainring you could pair up with a 50T high range would be 26T; but that would still give slightly more pulling power if used with the 21T, than you currently get with the 17T and a 24T low range chainring.
I haven't seen any technology currently available that tackles this chain slack take-up problem specifically. Plenty on managing/stabilising long chains but not specifically maintaining a high degree of tension with large changes in chain length.
According to bicycle forums, FDs can handle up to a 24 tooth difference if well set up and gear ranges are changed very carefully. Shimano info states 22, but that's a conservative figure. So if keeping within that 24 tooth difference, the smallest low range chainring you could pair up with a 50T high range would be 26T; but that would still give slightly more pulling power if used with the 21T, than you currently get with the 17T and a 24T low range chainring.
I haven't seen any technology currently available that tackles this chain slack take-up problem specifically. Plenty on managing/stabilising long chains but not specifically maintaining a high degree of tension with large changes in chain length.