This road is as rugged as the Rainbow Road and just as beautiful. However, it is a good deal longer and you will need adequate supplies to provide you for a good three days. The road follows an old coaching road once serviced by two accommodation houses. The boarding houses, Acheron and Molesworth, have been restored but are not lived in.
The first stage out of Hanmer is a long climb to the top of Jack's Pass and down into the valley to your first stop at the Acheron Accommodation House (about 25k) where there is a basic DOC camp. This can be a fairly short day and consequently many riders decide to push on through to Molesworth. Consider lingering a while at Acheron though; it's a lovely place, and an early start the next morning leaves you plenty of time for a leisurely lunch and perhaps a swim in the Awatere River.
The following day is a good distance (60k) over saddles and plains that generally follow the Awatere River. The road is at its roughest between Acheron and Molesworth and much of it is quite deeply corrugated. The scenery, though, is breathtaking. At Molesworth Accommodation House there is a basic DOC camp with water and a toilet. All water should be boiled however. Across from the camp runs the Molesworth Stream, which boasts a perfectly formed plunge-pool (just upstream from the DOC Ranger's hut). This can make for a refreshing end to a long, hot day in the sun.
The following day is equally lovely but equally strenuous. The road rises and dips over 80 kilometres of gravel road before settling into a long, tarsealed straight toward the main highway (a further 20k away). One option to break up this last stretch is to camp the night at Hodder Suspension Bridge (just before Camden). There is longdrop by the bridge; ask locally and the land-owner may let you set up tent for the night.
Once you reach the main highway, you can turn left to Blenheim (a main town, approx 23k) or right to Seddon (4k, campground, store, pub, backpackers). The Molesworth Road is well worth doing. It is rugged and taxing, yet it remains one of those great journeys that you exhilarate in once it's completed. Beautiful, lonely and memorable.