I’d rank the 10 days I spent road riding and training on Hawaii’s Big Island as likely (highly likely) the best riding I’ve done anywhere. I based all of my rides out of the Waikoloa Resort area, which is 40km north of Kona. Most of the ride distances below are based on starts in Waikoloa.
Here’s a Google Map of some routes I did, either from reading online forums, riding with a small club on the Island, or discovering on my own. It’s usually straight forward (there aren’t that many roads), though there are two side roads in particular that get you away from traffic:
If I could only do one ride, it’d be Mauna Kea for sure. Epic. Next best is the North Waimea + Hawi loop, followed by the one around Kona.
There’s some riding in the south and south-east, too, that I never got around to, and of course the east coast. But as I understand it the west and north-west stuff I did is the best riding with the most options.
80–100km, 1300m: North Waimea + Hawi Loop
Probably one of the best rides, period. Big 24km climb starting from sea level near the Sam Spencer Park up to just before Waimea (halfway point), and hang a left to go north to the top of the hill in the grassy farmlands. The downhill to the very north tip is super fast, smooth, great turns, from the high plains down through the rainforest. Except for the first half of the climb to Waimea, very little traffic. Snack in Hawi, then cruise back along the coast.
162km, 3500m: Mauna Kea
The big volcano, where the telescopes are. From sea level it’s an 80km climb, 70km of which aren’t too hard. You go through all sorts of landscapes. The first part, Waikoloa road, from the west coast to Saddle Road, is gradual-ish climbing. I recommend hitting that portion in the morning: the rush-hour traffic flows east-to-west from 6–8am, so you want to be going against it (you’ll have more of the lane to yourself). The next section is old Saddle Road (it’s the road that cuts across the whole island between the two big volcanoes) is super awesome going up or down. Seriously one of the best 20km I’ve ever ridden. Then you’re on the 4-lane Saddle Road past the military base and through a lava field before a sharp left up the mountain. This last 10km going up to the visitor centre is super hard, like 14–15%. It’s paved, though (and the Visitor Centre is still very high elevation)—there’s a dirt road after that for another hour to the top and the telescopes. I didn’t try it: you should, might be doable on 25mm tires and your easiest gear.
52km, 800m: Kona Loop
I started and ended this one in Kona. Great little loop. I did it multiple times. Basically it goes south through Kona, then climbs up and east (mostly 5–8%, with a 2x 500m of steep ass shit), then 180º back towards Kona, but elevated on the hillside along the old Mamalahoa highway above Kona—narrow, but traffic isn’t too bad, and it’s super great pavement and twisty and fun. Descends back to west coast highway, then back into Kona. The local club showed me the route. There’s a little out-and-back extension at the southern most portion into Captain Cook area, further south, that I hear is nice.
90km, 1000m: Waimea Loop
Starts on the same climb that the epic Mauna Kea ride does, but instead of going all the way east to the volcano on Saddle Road, you cut north half way up and head to Waimea. OK little town for a snack stop, lots of ranch land. Then you descend on a super fast, wide shoulder, nearly straight shot to sea level again (it’s actually going down the first half of the climb in the North Waimea + Hawi Loop above). Prety much the fastest single long descent I’ve ever done. Again, start out early against the morning rush hour traffic (or do the loop backwards in the evening).
125km, 1750m: Waimea Loop + Honokaa
Same loop as Waimea Loop above, but with an out-and-back tacked on half way. Nice because you’ll see you can skirt off onto the parallel Old Mamalahoa Highway which is nearly as fun as the north loop, and has the same amount of traffic—almost none. When you get to Honokaa (sleepy little town, with a teenage-run diner on the main drag with ice cream and burgers) you could even head north-west another 30km to the Waipio Valley lookout (which is where the excellent Waimanu hiking trip starts from). Note: the Waipio Valley Lookout is where the “Steepest Road in America” is, which you walk down to start the hike, and which Lance Armstrong has the KOM on. I didn’t ride it because it was wet the day I was there and you need hella traction (26% grade or something).