Northeast of Kingston, the Blue Mountain Peak Trail is a 15 mile out-and-back singletrack heading 3,000 feet up the namesake peak. While mainly a hiking route, the Blue Mountain Peak Trail is very bikable. The view from the top of the other islands is fabulous and the descent is epic.
To reach the mountain biking trailhead from Kingston, you will need to make your way in a 4WD vehicle to the village of Mavis Bank, which takes about one hour. From Mavis Bank, it is another 5 miles up a narrow steep winding road to the main trailhead at Penlyne Castle near Abbey Green Coffee Plantation (4,500 feet). The trail starts just east of Penlyne Castle on a service road for the coffee plantation, known as Jacobs Ladder, which is arguably the steepest part of the mountain bike ride. Continue on Jacobs Ladder for one mile into Portland Gap where there is a ranger station. The trail continues to the north across the open field.
Note: If you plan to bring your own bike to the island, make sure it is very clean in order to avoid problems with Agriculture Officers at the airport. Otherwise, they may want to pull your bike out and spray it with some chemical. Also, there really are not any maintained trails. All the vegetation grows very fast and the trails become brushy. And, the rain makes the trails very slippery so it is better to try during the dry season from January through April. It is guarenteed to be hot and humid.