My wife and I are considering a c'dale rt2 and were wondering if anyone has tried putting cross tires on and riding off road? We have some nice fireroad climbs in my area that I would definitely want to give a go on a tandem. Since the bike has v'brakes and/or disc brakes I'm guessing that a wider cross tire should be no problem. We are a pretty light couple - 310 lbs total so i'm guessing the frame should be able to handle a little offroad use.
The cross tires will go through a lot, but they can cut, puncture, and pinch-flat on the rocks and gravel. The faster we go, the more tire problems we get. So, I would say it depends on your riding style and the terrain. If it works well on a single bike with cross tires, it won't be that much different on a tandem.
Would 29" MTB tires fit on the Cannondale? Just a thought.
The frame will take a lot of beating. But road bike gearing is too high for our off-road riding.
We recently bought a tandem with 26" wheels so we can switch between road wheels and MTB wheels.