The Hutt valley connects Wellington to the Rimutakas, the Wairarapa, and the southern end of the Tararuas. There are several options for riding through it, and it has some hidden treasures of its own; well worth a look, whatever type of riding you like.
Pass through or fly over the Hutt Valley and you will see that it was once a very beautiful river valley, but now has Lower and Utter Hutt built on top of it. Luckily it's easy to get a flavour of what it once looked like... because lurking over the low hills to the east is an unseen parallel valley, almost the same size. The lower half of this is Whitemans Valley, and the upper half is called Mangaroa Valley. There's a stiff climb in at each end, then sweet backroads riding all the way through. Strong riders can do this loop as a day trip from Wellington, others might prefer to take a train to Utter Hutt or Maymorn.
The mapped route starts from the excellent Espresso coffee shop in Silverstream, and heads up over the Blue Mountains hill to the southern end of Whiteman's valley . From there, ride a few kilometres north to the start of the Wallaceville hill road. At the junction there, turn right into Mangaroa Valley Road (over the bridge), and follow that to Flux Road. Turn left there, then right on Parks Line which will take you to Maymorn station. From there you can train back to Wellington, or make a longer ride by riding down Maymorn Road and following the river trail or one of the other routes on this page down to Petone.
The northeastern part of the Hutt river valley is a fine place to ride, whatever kind of riding floats your boat. The Belmont, the Akatarawas, the Rimutakas and the lovely small secondary valleys of the Hutt are all up here, and most of the people are down at the other end, 25km away. There are numerous ways to cover those kilometres by bike. Here are the best four options Dodo has found; all start at Petone station and go to Utter Hutt or Maymorn.
Note: all the trains up the valley except certain commuter trains at rush hour will take bikes, at no extra charge; so if you don't want to ride, no problem.
For several years an easy, mixed-surface shared use trail has run up the eastern bank of the Hutt River. A pleasant, often busy trail, the route is meandering and prioritises avoiding traffic and staying close to the river over directness, so it goes along the seafront at Petone before heading up the river, and the route is considerably longer than a direct route by road. The surface varies from sealed to gravel, with short sections of easy singletrack at the northern end. Since 2013 the signage on the trail has been progressively upgraded and now mostly says "Rimutaka Cycle Trail", into which the Hutt River Trail was absorbed. Probably took DAYS of meetings.
Dodo sees plenty of road bikes on the river trail (it's easy peasy), but if you want a faster route, there is one: take the main road from Petone station which, although it looks a motorway, isn't, and you can ride along the side of it on an ample shoulder most of the way through Lower Hutt. Not my favourite kind of riding, but it is quick.. 8km up the road (just after you go under the footbridge), turn left onto Hebden Crescent which runs parallel to the highway for 4km, then follow River Road and Whakatiki Street to the station in Utter Hutt.
This route uses trails on the west bank of the Hutt river, then hops onto Western Hutt road about halfway up, where the track disappears into a golf course. A cycle trail through here is needed and apparently planned, since it could easily connect with other trails at the north end. I did once negotiate the golf course and an adjacent railway path; see the moonshine road ride on the Belmont & Akatarawas page.