In the past on Sierra road the CHP has closed the road to cars in the early morning. I would not be surprised if they either kept the entrance gates closed or closed the road to cars the same time they opened the gates. The off road parking on north gate at the ranger house below the junction is very limited... maybe 10-15 cars. Maybe they would let cars park on the road but I kind of doubt it. The state park people like to enforce rules and generally don't care much about cycling. Since the park is closed at night you can't drive up there and camp.

I would not try to drive it at all.

In the past on Sierra they have closed the road to riders some time before the race arrives. Starting about 30 min before the race there are a lot of vehicles coming through, sometimes CHP at high speed. I plan to have picked my spot and gotten off the road at least 30 min before the race arrives. If you're an hour before the race, no worries- there's a lot of other cyclists hanging out. Bring plenty of food, hang out and party.