Friction is your biggest enemy to good shifting performance, we suffered through bad shifting on our speedster for years until I solved all the problems. Over the years I've found three main points of friction;

1) Particularly on the tandem for some reason I find that over time the cable housing will deform where it enters the shifter. This allows the inner reinforcing wire to partially enter the shifter and squeeze the shift cable. Check the ends of the housing and if you see bare wires just trim it back a bit and reinstall the housing.

2) the point where the cable wraps around the bottom bracket is a huge source of friction. The cable should not be running on bare metal. I take a section of shift cable housing and strip away the outer casing and reinforcing wires so I am left with just the smooth inner liner. Slip a 6 inch piece under the bottom bracket and run your shift cable through this. Makes a massive difference in performance.


3) Cable housings are the obvious source of friction but most tandem setups don't have much housed cable. Still, it doesn't hurt to just replace it regularly. I buy in bulk and it's quite cheap.

We run a race face crankset with a mix of brands of chainrings and a gearing range far outside that recommended by Shimano with excellent performance.