OP must drive to the airport anyway, so it is hardly an inconvenience to require him to be there if he's going to depart earlier anyway. Yes, there exists the risk that he gets to the airport and there is no room on the earlier flight, but most agents will game the chances (or you can check) for loads.

Later flights don't work under "flat tire" because you definitely need to be at the airport and it's iffy whether you get an agent who honors what is an unwritten perk, not a fare rule. If you don't, you are SOL buying a new ticket and trying to get other segments reinstated.