Although portions of Saddle Road have been upgraded over the years, several rental car companies still discourage drivers from taking vehicles on it. If you're concerned, your best bet to fully explore Mauna Kea is to take a 7-8 hour guided tour with a company such as Mauna Kea Summit Adventures. The fully narrated tours include pick-up and drop-off at central locations, warm Arctic style parkas, supper, hot drinks, sunset at the summit, and stargazing after dark. It's a fun and otherworldly experience for the whole family!