The Heaphy Track
Land Owner: Department Of Conservation
Trail Manager: Department Of Conservation
You can mountain bike the the Heaphy Track in the winter season from 1 May to 31 November.
Most people ride the trail from east to west as the Mackay-Lewis downhill is more fun. See Classic New Zealand Mountain Bike Rides (South Island) by the Kennett Brothers for a good mountain bikers description of the trail and what to expect.
There are plenty of shuttle options for either end of the trail. To find them, a quick internet search or contact the Nelson, Golden Bay or Westport Information Centres. Some will no doubt be listed below in the links section.
The Heaphy Track is a tough ride and you need to be prepared. See the Department of Conservations Heaphy Track webpage for more info: http://www.doc.govt.nz/parks-and-recreation/places-to-go/nelson-tasman/places/kahurangi-national-park/things-to-do/tracks/heaphy-track/