Thanks a lot, for your answer.
You say that the only way to put more gears is using a new chainwheel.
is it impossible to change the 3-speed Sturmey Archer hub gears to another hub gear with more speeds (maybe 5, 6 or 7 ?? )
Thanks
This has been answered above.
http://www.bikeforums.net/showpost.p...0&postcount=18
If it had seemed practical and cost effective, I'd have changed the hub, but it seemed far too difficult and expensive.
The standard hub has a gear range of 175%. By adding the new chainwheel (VERY simple and cheap) you increase the range to about 215%. This works and is almost certainly much more efficient than having a much more complex 7 or eight speed hub. The SRF-3 is about 95% efficient in its most ineffeicient gears. Seven and eight speed hubs drop to figures like 89% or 90% efficient in some of their gears. Adding an extra chainwheel keeps the efficiency high as long as the chainline is ok, which it is. This is very like what Brompton have done in recent years. Their six gear bikes have a three speed hub with a two speed derailieur on them. You end up with two levers, but higher pedaling efficiency.