We were on a New Zealand South Isle tour (not exclusively cycling) last summer and from the window of our van we were glad not to be cycling on many stretches. They have a limited number of roads and often there is no alternative to the main highway -esp. on the west coast there are long stretches where I wouldn't be happy riding I would really read up about the different routes and be prepared to skip a few of the more remote west coast stretches. Otherwise it is a great place to visit, watch for orcs at night!