Since searching for MTB tours in the Caribbean can be challenging, I just thought I would share some knowledge: Detour Bike Trails is currently closed, but may re-open at some point. I was sad to hear this, as I rented a bike and did a tour with them last time I was there.

BTW, at first I rented a bike from Paradise Rentals in Jolly Harbour -- bike was in bad condition and they didn't have a pump or a wrench to adjust the saddle. Luckily I came prepared, adjusted the shifting and braking, but bike was still awful so I returned it and rented from Detour Bike Trails. They may be the only game in town now, so if you rent from them bring your tools.