Mach 3 is 'the route daddy, taking you way out into the wilderness'.
This route shares some trail with Mach 2, before heading off south through the forest and onto the moors before returning along some sweet track and grass descents. From the furthest point, the adventurous can take a spectacular cross country ride all the way to Nant yr Arian.The highlight of the return leg is 'the Chute', very steep and very rocky, and then to top it off it gets very dark.
More information can be found here: http://www.dyfimountainbiking.org.uk/