Arima rindo「有間林道」 MTB circuit (59.15km, 1140m climb, 3.5hr) 

Category: Road: 41.5km, Dirt road: 17.65km

Route: Ome, Futamatao, Nariki, Naguri, Arima dam, Arima rindo, Naguri onsen, Kurosawa, Ome

Map:

Profile

Notes:
There's very little traffic on any of these roads after you pass Arima dam - usually just a few bikers on the paved and upper dirt road. Walkers stick to the hike trails so are nowhere to be seen except for the odd time the trail passes over the road. Most of Arima rindo (20km-25km mark) is closed to traffic so is deserted!

You can start this route from Sawarabinoyuu if you just want to do mostly off road - it's about 30 mins drive from Ome with plenty of free parking space.
Drive to Sawarabinoyuu onsen (follow sign to left @ 16.2km point) and follow the route from 16.2km to 39km (+ from 14.7km to 16.2km to complete the loop).
Alternatively, from the same start point, follow the paved road up from Arima fishing reception (20.1km) instead and start the dirt trail from the 41.18 mark of MTB route 4. This way you do most of the climb on paved road so it's not so tough - you may meet more bikers on this route though.
You can relax after the ride in Sawarabinoyuu onsen for JPY 700.