Though the Queen Charlotte Track is primarily for hikers, mountain bikers can ride the whole thing in a day or two. There are two steep ascents but it is not overly technical, and with pack transfers and abundant accommodation you won’t need to lug heavy panniers. Most of the track is open to bikers year-round, though the northern quarter (Ship Cove–Camp Bay) is off-limits from December to February.
Marlborough Sounds Adventure Company operates a three-day Freedom Bike Ride with bike rental, transfers and comfortable accommodation at Punga Cove and Portage Resort.
Alternatively you can rent a mountain bike and organize your own trip, either camping or staying in cheaper accommodation.