Hook up with Donnie from Maui Cyclery...as in give him a call now and ask him questions. He owns the bike shot at the bottom of Baldwin Ave in Paia where the climb starts. He can give you the best information on how to best plan it out and find other riders who may join you. Super nice guy.
They just finished repaving Baldwin ave earlier this year (the first few miles of the climb) so it's all buttery smooth road all the way to the top now. In December, the weather should be decent. Your biggest worry will be rain and wind that can make it very cold up over 5000'. Sea level is usually around the high 60's at sunrise and warms up to mid 70's. Of course as you climb, the temperature drops, but assuming you start riding in the morning, it doesn't drop drastically as the sun moves overhead. So if it's high 60's at sea level at 7 am, expect it to be low 60's up around Makawao at 3500' at 8-9 am. Not uncommon for the areas above 6000' to drop into the 50's...sometimes even lower if there is wind chill.
Use sunscreen...even if it's cold.
It takes about 3 w/kg of steady effort to break 4 hours on a nice day. 95% of the first timers who try to ride for time up the hill underestimate it and go out way too hard and suffer the last 3000'. Which is a real shame because that's the most beautiful part of the ride. So my advice is to enjoy it and throw out time goals. I promise you will not get to the top and think...man...I have so much energy left. If you go easy in the beginning (think Sunday coffee ride effort for the first 3500'), it just means you will be able to ride steady/strong at the end without feeling like your hamstrings and calves are about to seize up. You'll also want to save some energy to enjoy the descent. It's hard to enjoy if everything in your body feels like it's about to cramp. While descending for over an hour straight your arms, shoulders and triceps will be supporting a lot of your weight.
I usually race it with my easy gear as 34/32. And I while I don't spend a ton of time in that gear, I do use it for the short steep sections which is good to keep you out of the red zone. I generally finish around 3:30-3:45. I think most cyclists will use the 34/32 gear for at least 50% of the ride if they have that option and aren't trying to go all out.
They just finished repaving Baldwin ave earlier this year (the first few miles of the climb) so it's all buttery smooth road all the way to the top now. In December, the weather should be decent. Your biggest worry will be rain and wind that can make it very cold up over 5000'. Sea level is usually around the high 60's at sunrise and warms up to mid 70's. Of course as you climb, the temperature drops, but assuming you start riding in the morning, it doesn't drop drastically as the sun moves overhead. So if it's high 60's at sea level at 7 am, expect it to be low 60's up around Makawao at 3500' at 8-9 am. Not uncommon for the areas above 6000' to drop into the 50's...sometimes even lower if there is wind chill.
Use sunscreen...even if it's cold.
It takes about 3 w/kg of steady effort to break 4 hours on a nice day. 95% of the first timers who try to ride for time up the hill underestimate it and go out way too hard and suffer the last 3000'. Which is a real shame because that's the most beautiful part of the ride. So my advice is to enjoy it and throw out time goals. I promise you will not get to the top and think...man...I have so much energy left. If you go easy in the beginning (think Sunday coffee ride effort for the first 3500'), it just means you will be able to ride steady/strong at the end without feeling like your hamstrings and calves are about to seize up. You'll also want to save some energy to enjoy the descent. It's hard to enjoy if everything in your body feels like it's about to cramp. While descending for over an hour straight your arms, shoulders and triceps will be supporting a lot of your weight.
I usually race it with my easy gear as 34/32. And I while I don't spend a ton of time in that gear, I do use it for the short steep sections which is good to keep you out of the red zone. I generally finish around 3:30-3:45. I think most cyclists will use the 34/32 gear for at least 50% of the ride if they have that option and aren't trying to go all out.