This thread started with riding fire roads (gravel grinding), so I have quick story. This summer I converted my Cannondale Road tandem into a gravel bike by switching out the 700C wheels for 650B wheels and I couldn't be happier. I was able fit 2 inch tires with a slightly chain stay modification. I live next to a state forest with literally 100 miles of gravel roads and some amazing climbing, my wife and I ride the gravel when it is raining just to stay off the main roads and not deal with traffic. Awesome work outs, silence and super fun down hills. My wife and I are hooked and if I didn't already own 4 tandems maybe I would buy a full suspension so we could ride more single track. Hmmm 5 tandems, that is not so bad is it ?