I was in Hawaii in 2003, so things might have changed, but here are some thoughts:

1. At that time, there were no bike shops on the Big Island, so if you're planning on renting you'll either have to do so in Maui (where there are lots of options, but make a reservation asap) or see if you can get a loaner from one of the tour companies. Either way, you won't be able to replenish your supply of inner tubes and other LBS supplies.

2. Many of the planes that fly between Maui and the Big Island are tiny. Check ahead to see if they can handle a bike case.

3. If I could do only one ride on Maui, I'd climb the volcano. It's 36 miles and 10,000 feet, but very few sections steeper than 7%. Check the weather before you go, because it can get nasty at the top.

"I was on the Big Island in mid March and had a terrific time biking on the Queen Kaahumanu Highway (19) north from Kailua-Kona. This is the route the Ironman goes up. It is a wide open highway (read ""no shade"") with a huge shoulder but watch those nasty tradewinds. Pack lots of food and water as the water/food stops were few and far between. I thought the best part of the biking was just north of the intersection of 19/270 starting at Spencer Beach parking lot (near Kawaihae head north on 270 to the town of Hawi (a good stop for supplies) (continue to Pololu Valley lookout only if you are really adventurous and the weather is dry!) otherwise turn around and go back to your car at Spencer Beach (this is around 18 miles one way not including the lookout option).

You can get a decent road bike at Bike Works in Kailua-Kona (I think they rent to Ironman participants). See their web-site: http://www.hpbikeworks.com/Bikeworks/index.html

I called them 2 weeks before I went and reserved a ""deluxe"" road bike (I think it was a cannondale R1000). They had all kinds of different models in the shop but I called rather late in the game and they only had one that would fit me, so call early and they may have a better variety for your size. I brought my cycling shoes and they supplied the correct pedals. The price was reasonable, but made even better for a multi-day rental. I think it was $40 a day and I paid $60 for two days. Before I went I mapped out some routes by looking at the map of the Big Island from where I was staying at Spencer Beach (not recommended for camping by the way!) and doing one ""out and back"" on highway 19 from the bike shop and the other day I rode the Kohala mountain range from Spencer Beach going counter clockwise on 19 toward Waimea then north to Hawi on 250 and back to Spencer beach traveling south on 270. This was not a simple ride as there is a major amount of climbing and a tricky decent on 250 with a very small shoulder up the climb. I recommend doing it because of the awesome scenery, but only if you are not skiddish about close contact with traffic and have good climbing and descending skills. I have a rearview mirror on my helmet and I constantly look into it so I can see when a car is approaching. My mirror gives me the extra confidence I need when I am riding a small shouldered road cause I'll use as much of the road that I need till a car comes into view and then I'll duck far off to the shoulder.

Have fun and an additional word of advice, don't leave anything of value visible in the car as I had a horrific break-in to my rental car at the end of my vacation."

Haleakala is _only_ 10,023ft.