Alex,

Metrolink will also get you to Oceanside easily. Irvine to Oceanside for 8.75, in a little under an hour (most trains). That would be an excellent way to get away from the traffic closer to Irvine, and it would be a great starting point [along with San Clemente (24 to 29 minutes, 6.75); and the other stations on that line] for a wide variety of possible rides.

That part of the coast is beautiful, and there are many side roads up into the hills, with a variety of touring possibilities there. Bike clubs in that area could tell you a lot about the best local roads.

Enjoy the rides.