How do you make sure you can replace a 5 speed freewheel with a 6 speed one? This is on an 80s Fuji Regis. There is about 8-9mm of space between the smallest gear and the dropout, if that matters.
I ask only because 6 speeds seem easier to find than 5 speeds.
I replaced my chain and cranks/chainrings recently and now the 16T gear (next to smallest) skips. All the others are fine.