I'm finally getting around to getting my 1967 C25 back on the road after 40 years. The original gearbox sprocket had 16 teeth, but the new one that I bought at a classic bike show has 17 teeth. I was assured that this is the sprocket that most people now fit. Does anyone know if the standard 100 link chain can still be used with the bigger sprocket? I need to buy a new chain so need to make sure that I get the correct chain length. Thanks for any advice.
I think you will find that most packets of chain will be longer than you require, to allow for trials rear sprocket guys.
The 17t will speed your bike up a bit, typically 48 becomes 51 mph.