There are several ways to enjoy Maui on a bicycle, depending on your inclination and determination. Resort visitors often rent bikes and cruise around resort areas — Wailea has particularly nice bike paths.
There are some places along main roads where you can bike safely (a paved bike path runs from Ka’anapali to Lahaina), but heavy traffic and bad shoulders in some places create challenges even for those who are experienced. You can rent bikes and all the accessories at a number of bike shops.
Bicycle tours are another way to go, and there are several options. You can tour Lahaina, Upcountry and Tedeschi Vineyards, West Maui, and Hana on guided or custom tours. There are also popular Haleakala downhill tours for wimps who can’t hack the 40 miles uphill. After being bused to the summit of Haleakala, you’re given a bike, helmet and windbreaker. Then you head downhill for perhaps the longest ride you’ll ever take without pedaling.
Bikes are not allowed on the hiking trails of Haleakala, but there are mountain bike trails. Ask for details at the bike shops.