We have a Sunday Morning Coffee Jam on the west side and that’s close to Koolina. It can be a spirited ride if certain people show up. More of a social ride through residential neighborhoods rather than a sight seeing ride.
If you’re going to be renting in town, you can go splurge at The Bike Shop Honolulu and they have some nice rentals like the Venge or Tarmac Disc. Bikeadelic is also a good place to rent.
Riding from central Oahu up Kunia to the North Shore is nice. Not much of a shoulder for most of it though and cars can be speedy depending on the time of day. North Shore riding east of Haleiwa can be a bit sketchy if you don’t know what you’re doing as there’s not much of a shoulder for many sections and lots of potholes open up during winter. If you’ll be hanging around Dillingham airport, there’s not much traffic there. Not much of anything over there except for mountains air and beach.
In town, riding up and down Tantalus, a cat 2 climb, is nice. Lots of potholes so be careful on the descents. Going around Diamond head, toward Hawaii Kai and up to Makapuu is a common east side ride. Lots o riding in Kailua area too. Also, another The Bike Shop up there with rentals.
If you want to check the routes, you can look up the segments like Tantalus TT, Honolulu Century, Haleiwa Metric Century or DEMRR (Dick Evans Memorial Road Race) then you’ll see what’s rideable.
I do not recommend riding anywhere from the downtown to pearl harbor area. Not for vacation at least. It’s just somewhere you have to go through but can be sketchy if you don’t know what you’re doing. Also, rush hour in the afternoon starts around 3:30 and the vehicular rage doesn’t temper until after 6:30. It’s not bad, but people are more in a rush around that time so yea…