Right then, Quick Mech related question...
I've got an old Sora "8 speed" rear mech (version with the Plastic B-knuckle cover) which has lived in the spares bin for a while, basically unused...
I now need an emergency stop gap replacement for a broken Tiagra on a 9 speed road drivetrain, can anyone convince me that this old Sora won't work on a 9 speed drive seeing as pull ratio is the same and cassette width is the same from 8 to 9???
Anyone know?

