Just so you know, every car rental I have had there made me sign a paper saying that I will not not take the car over Saddle road. In the unlikely event that anything ever happened, they basically say that they are not responsible.

Also, if you've never been there, Volcano parks is HUGE, and if you want to take the Chain of Craters road all the way to ocean, be aware that it is a LONG drive just from the park entrance to the end of the road (20+ miles). After driving almost three hours to get there, we were not prepared to drive another hour to get down to the cliffs (without stopping for sightseeing). It was worth the drive, but we didn't factor in the almost two hours just for that part of it.

Many people suggest getting a cheap room in Hilo the night before so you can get an early start. I haven;t done that yet, but definitely see the wisdom in that idea.