Hello, for anyone interested in taking bikes on trains in NZ, it can be confusing and hard to find the information, so we did a little research.

I hope this helps.

NZ only has 3 'long distance' trains - these are run by TRANSRAIL.
- North Island: Auckland to Wellington.
- South Island: Picton to Christchurch,  AND  Christchurch to Greymouth.

There are also some shorter but extensive 'local lines' (between Auckland/Hamilton and in/out of Wellington), that could be useful for touring cyclists - see below.

TRANSRAIL info:
"Include your bicycle or excess luggage at the time of booking under the ‘extras’ page. You can also email [email protected] or call 0800 872 467 with your booking reference number to add it to your booking.
The check-in and luggage page says:
"Bikes and E-Scooters need to be added at the time of booking. Our Luggage Carriages have limited capacity, and the number of bikes we can carry may vary by service. Please contact us for details. You don't have to deflate the tyres, but bicycles can only be accepted as Checked Luggage if:

• Handlebars are removed or turned sideways
• Pedals are removed or turned in
• Panniers removed
• Helmets removed
• Accessories removed
• Free of mud / dirt
• Label your bike with your name and phone number

The cost to carry a bike is $20 and bike with trailers (max 1, subject to availability) is $50.
Unable to carry tandem bikes.

* * * * * * * * * * * * * * * * * * * *
AUCKLAND and WELLINGTON - 'LOCAL LINES'

Southwards from AUCKLAND to HAMILTON
The 'TE HUIA' train runs from Strand station (AUCKLAND) to Frankton station (HAMILTON).
https://www.tehuiatrain.co.nz/timetables/
Their Facebook page says they can take bikes: try this link: https://www.facebook.com/tehuiatrain/photos/a.666932757339591/742307896468743

Local WELLINGTON lines:
https://www.metlink.org.nz/assets/Network-maps/RegionalRailNetwork.pdf 

From WELLINGTON, the 3 most extensive *local* lines that also take bikes are:
1.  KAPITI line (northwards, coastal, terminates at WAIKANAE) Metlink.
2. WAIRARAPA line (north-east inland, terminates at MASTERTON) Metlink.
3. CAPITAL CONNECTION (northwards, terminates at PALMERSTON NORTH) Transrail.
(More info on each of those 3 below. )

"If you're at Wellington Station, the departure screens show a bike symbol on services that allow bikes.
Some peak train services do not allow bikes on board.
Metlink trains have special low-floor carriages that can accommodate bikes on services that allow them.
Each two-car train can accommodate up to 3 bikes, on a first-come, first-served basis.
Look for the bicycle symbol on the outside of the carriage, and in the cycle area inside the carriage.
Cyclists must load, secure, and attend their bike while on board.
Bikes must not obstruct doors or aisles, and are to be stored in the bicycle area only."

LOCAL WELLIGNTON LINES:
- - - KAPITI LINE Coastal to/from Waikanae: https://www.metlink.org.nz/service/KPL/timetable

- - - WAIRARAPA Inland to/from Masterton: https://www.metlink.org.nz/service/WRL/timetable
"Wairarapa Line trains can carry bikes in the luggage car, depending on space. The luggage car will always be on the northern end of the platform when the train stops. Bikes and luggage must be lifted into the luggage car and carried up a few steps with a narrow entrance, unlike the trains on the rest of the network. Large cargo-style bikes can't be carried on Wairarapa Line trains.
Cyclists must speak to staff before loading their bikes. Passengers must load their own bikes and luggage into the luggage car while staff supervise. For safety reasons during loading, bikes and luggage should not exceed 30kg in weight, and bikes must be under 180cm in length."

- - - CAPITAL CONNECTION (Wellington to / from Palmerston North (PN) )
https://www.greatjourneysnz.com/capital-connection/

Capital Connection is a commuter train which runs only Monday to Friday, once a day in each direction, (departs PN early morning to Wellington, and departs evening to Palmerston North). No weekend service.
"Bicycles can be conveyed on the Capital Connection in the baggage van subject to space availability. Please make yourself known to the Train Manager as they will place your bicycle on board."