There are a bunch of doubletrack trails as well as singletrack trails here. The best are the Waiakoa Loop which is 3 miles, the Waiakoa trail which is about 6 and the Mamane which is about 1.2 miles
How to get there:
Take Rt. 37 past Pukalani to rt. 377. At the end of Rt.377 is Waipoli Rd. (to Poli Poli Springs Park) About 6 miles up Waipoli Rd. at a hunter check-in station is a 4 wheeler road that leads to Waiakoa Loop (approx. 1 mile) About 3 miles further on your left is where Waiakoa trail begins.