In urban areas the speed limit is usually 50 km/h, unless there is a different signage. Sometimes you are also allowed to drive up to 80 km/h. Just have a look what the signage says. In rural areas the speed limit is a 100 km/h, but you will realize soon that it’s not possible to drive a 100 km/h most of the time. If there is a signage with a different speed limit, follow the regulations.
Yellow signs with speed limits on are advisor for you and to warn you of an upcoming tight curve or bend in the road.
Plan more travel time, than you would normally think of.
Make sure you don’t speed – first because of your safety, second for your wallet. Speeding is expensive in New Zealand.