We also have a Burley Rock 'N Roll, which we bought new in 1992. Now that we have a better road tandem, we use it as our city bike, or things like
towing our Westies.
You say you've bought new tires, and these seem to be thick and knobby. Such tires are great for trails, but if you are going to be using it primarily on the road, you'll want to get thinner and slicker tires, which will greatly decrease your weight and rolling resistance. With the right tires the Rock 'N Roll can be nearly as fast as an optimized road tandem. For example, the morning loop on our Burley here
averages 18.6 mph, and on our Dragonfly on the same loop
we've done 20.1. So, maybe 1.5 mph difference on the flats. The hills are a different story.
Questions about the Rock'N Roll, as well as tires are discussed on these threads:
? for the tandam guys
26" Road wheels for tandem
Thoughts For New 26" Tires ?