We have the tandem TT, have ridden hills most of season, but recently started riding on a paved bike trail. I'm not real experienced at figuring out gearing, and since there are no numbers to go by, how do I best utilize the 27 gears I have? The gears on the left side affect the rear wheel right? Hate to sound like a bit of a dummy on this, but I guess I am. We want to get the most speed on a flat terrain with the least amount of effort. Did some experimenting today, but don't think I got it right. We both have sore knees.