Try the best of both worlds - a quiet meander through the backwaters followed by a bit if high speed action through the Lewis Pass. This route starts and finishes in the thermal resort of Hanmer Springs and can be ridden in one, two, three or four days in either a clockwise or anti clockwise direction. If your travelling anti clockwise you'll find that the first 110km is unsealed and can be rough at times therefore an adventure style of bike is recommended. Note also that this section of the route is OPEN DURING THE SUMMER MONTHS ONLY - more on this below.
A word of explanation - Molesworth Road is officially also known as the Acheron Road but if but if you say 'Molesworth' everyone knows what you mean.
Hanmer Springs makes a great starting point for this trip, there are plenty of holiday homes, motels, hotels and camp sites plus the thermal pools to relax in after a hard days riding. Google 'accommodation Hanmer Springs' and you will be spoilt for choice. I prefer the anti clockwise route and which passes through historic Molesworth Station, it's worth taking your time through this section, stopping off at points of interest along the way to suck in a bit of local history. The road is unsealed but generally pretty good, there may be the odd rougher patch and maybe a small ford or two but two wheel drive cars go through all the time so no worries there. This section of the road is open during the summer months only, normally the road is open from the Saturday of Labour Weekend to Easter Monday or the second Sunday in April, whichever is the later date. Note too that during the open access period, the road may be closed suddenly because of fire risk, extreme weather, road conditions or farm activities.
To check if the road is open call Department of Conservation on +64 3 572 9100
Once you've gone through the Molesworth you'll hit State Highway 1 (SH1) and turn left heading north to Blenhiem. With a population of around 30,000 this is a large town by NZ standards, it sits at the heart of the Marlborough wine area and has a wide range of places to stay, or simply grab coffee if you you intend to push on. From Blenhiem take SH63 towards St Arnaud, on to Murcheson then Springs Junction where you'll turn left onto SH65 heading through the Lewis Pass - don't forget to stop at St Arnaud for a look at Lake Rotoiti. Some great riding to be had along here, fast sweeping bends with native bush either side, if you have time turn right on to SH7 for a side jaunt to Reefton for more of the same or better (but watch out for damp sections of road under the trees). Back onto SH65 heading south before turning left for towards Hanmer Springs to relax in the hot pools. 550km of yumminess!!.