Q: After a long lay off I started cycling again last year. The bike I was using was fitted with a circa 1987 Shimano six-speed 105 groupset with down tube gear levers. The transmission was noisy and when getting out of the saddle to climb a hill the rear mech always slipped into a smaller sprocket.
I decided to change the bottom bracket, chain and cassette, so I had to rebuild the rear wheel with a new hub, which I did with Shimano Tiagra nine speed. But the rear mech still jumps into a higher gear. Is this an issue of incompatibility of the rear mech with the new cassette, or the gear levers not being STI, or perhaps both?
John Morley, email
A: It would be worth checking first that the shifter itself was not responsible. In the centre is the bolt that attaches the shifter to the down tube. This bolt also governs how much force is required to move the lever.
Sometimes if this comes slightly loose then the shifter will move under the tension of the cable, which allows the derailleur to shift down the gears. Best solution would be to change to STI levers and a nine-speed derailleur.