All three chainrings are Shimano Biopace!

Single-side drive makes the most sense for a tandem that doesn't have multiple chainwheels. It greatly reduces the strain on the rear bottom bracket area, a chronic problem with crossover drive trains. The stresses on the rear bottom bracket are actually less than they would be on a single bike, since the two chains pull in opposite directions on the same side of the bike, mostly cancelling out the loads on the rear bottom bracket.