Known as a popular challenging Maui bike ride, the West Maui Loop, offers incredible views and a little bit of everything that the island has offer, especially when completed by foot. The start/finish point in Ma'alaea was selected to be central and most accessible, though you may start anywhere along the loop and run in either direction. The route is described clockwise, moving over the Pali which can have a lot of car traffic during the day with little shoulder. Once you hit Ukumehame, this is the flattest section of the route staying on the lower Honoapi'ilani highway past popular Launiupoko and Puamana surf spots. Continuing through Lahaina town, past Ka'anapali and into Napili- the road is fairly flat as you approach the first marathon of the route. The hill climbing up to Kapalua will wake you up for the rest of what's ahead. Be prepared for often rain showers and high winds, also there are few to no places for water, nutrition and fuel past Kapalua so plan accordingly, espcially if you are doing this route self or unsupported. From here on out it's rolling hills and incredible views of steep cliffs and open ocean. "Mr and Mrs Steepy" (aka the Wall and climb immediately after) are highlights of the route. Dropping into Kahakuloa Town, you'll pass the historic church and can stop for banana bread to fuel the next few miles of steep climbing. Once you top out you'll carry on with a few steady climbs, mixed in with steady descents as you make your way through the windy and often narrow roads past Maluhia. Once you hit Mendes Ranch, prepare your quads for a few steady miles of downhill and spectacular views of the north shore, town and Haleakala on a clear day. Dropping into Waihee town you'll run past the elementary school and "back to civilization" as you climb up Kahekili Highway into Wailuku town. Less than 10k to go once you past Wailuku Elementary School. Most days the wind will pick up by the afternoon and you'll be pushed to the finish as you past the Tropical Plantation, main access roads back to Kahului and north Kihei where you'll finish back at the start in Ma'alaea.
Here's a link from a local bike shop detailing the route from their shop starting and ending in Lahaina, West Maui Cycles.