Patrick Schwarzenegger -- I'm Riding for TWO Now

Patrick Schwarzenegger one-upped his fitness legend dad during a bike ride -- and even flashed one of his new GF Miley Cyrus' trademark moves.

PS and Arnold Schwarzenegger went cruising around Santa Monica Friday on their bicycles -- and for some reason ... Patrick was towing an extra bike. Even with the extra cargo ... he was leading pops.

Note Patrick's form -- tongue out. Looks like Miley's rubbing off in more ways than one.

As we previously reported ... the duo was spotted locking lips at a USC football game this week.