Update : Here’s a cool site called Manawatu Trails. The site has a collection of Back Country trails, Mountain bike trails and Back Country Tours that allow you to experience the best riding and scenery around the Lower North Island of New Zealand, including Whanganui, Rangitikei, Manawatu, Tararua, Wairarapa and Horowhenua.
If you’ve been riding north out of Wellington on an early approximation of the National Cycleway and you’ve ridden through the Horowhenua, north of Himatangi (which you can get to on the Foxton Cycleway) there’s the beach ride to Tangimoana and onto Marton, and Mangaweka and Taihape. For maps and descriptions see Rangitikei Cycleways
It seems to be the similar info as provided by some Mountain Bikers from Massey University
And likewise from the Manawatu Standard here’s a report on the progress of the Palmie to Feilding cycleway. Fielding is just one back road wth a big hill from Marton.