Hello, what ratio speedo gearbox do I need for a 1966 A65L with a 19 inch rear wheel and a Smiths ssm 5001/03A speedo , thanks Roy :-\
The 1966 parts book shows 21:10 for WM2 19 inch rim and 2:1 for WM3 18 inch rim.
Smiths catalogue shows part BG5330/111, 21:10 reversing.
Thanks JulianS forgot to mention the last four numbers on the speedo are 1600 and I respect your knowledgeable answer other forums suggest that 21:10 equates to 2/1 . My bike came back from the US and I believe it was sent out there with a 19 inch rear wheel now to confuse me more in the book Thunderbolts and lightnings on page 80 it states 1966 saw standard smiths rear wheel speedo drives introduced on all models 1.25:1 ratio on UK & US models and 2:1 ratio for export models with KPH speedos, (I know books can be wrong) I wonder if any member with 19 inch rear wheels knows what ratio there speedo gearboxes are, bit long winded but would like to get it right. Roy :-\
Roy - This is what BSA said - 1.25:1 was for 150mph speedos introduced for 1967 season.