Two very interesting mountain bike trails are mapped and available on Everytrail.
Both are located east of Bonanza area, the first one crossing nearby hills and forest
Trail 1, 20 miles 4 hours
Saturday Ride at EveryTrail
Trail 2, 20 miles 3 hours
Bangkok Bike Hash – Sunday Ride at EveryTrail
Khao Yai Travel Guide 
The Bangkok BIke Hash head out to Khao Yai 3 or 4 times yeas for some amazing riding, I’ve enjoyed there relaxing Sunday rides a couple of times. If you go to there website proper you can give plenty of GPS trails to download and include not just the one listed above, but be careful the Saturday rides can be very punishing.