the stretch from long beach to irvine can be done mostly on bike paths. the la river bike path that starts/stops about 5 miles south of union station in the vernon area of los angeles leads into the long beach bike path which continues south along the beach to the naples area of long beach. you jump
back on pch for a short distance coming into seal beach/sunset beach and can stay on pch which has a decent shoulder or make a right and follow a handful of parallel streets to huntington beach. once in huntington beach, there is a bike path that runs all the way to the edge of newport beach. this is your biggest exposure to pch and where you’ll encounter the most traffic. it’s approx 3 miles from the edge of newport beach to the back bay area where you pick up the trail that head’s inland past uc irvine and into the irvine bike path trails system.

if i remember correctly, it’s about 50 miles from union station to the back bay area of newport beach going this route. you’ll be on/off pch for a few miles here and there but the shoulders are wide. i definitely like the parallel roads in seal/sunset beach with the quiet and low traffic. i last did that entire stretch this april and the roads were all fine. (with the exception of two roads from union station to the la river bike path-alameda st. which was very very good but busy dtown traffic and then very very bad pavement to washington...and a short bad pavement stretch on downey street). the bike path alongside the
huntington beach part of pch needed some repaving here and there but nothing too bad. biggest issues were watching out for traffic/trucks/bad pavement on alameda street and watching out for sand (and usual peds, dogs, surfboard carrying beachgoers, etc) on the beachside bike paths starting in long beach. i like alameda st for the directness of exiting the union station/dtown area but also dislike it due to the traffic volume and some high potential pinch/puncture flat pavement before making a left/heading east on washington st. next time i do the ride tho, i’ll prob take alameda again. it’s just an area that requires your complete attention and rolling conversations with the group should wait till you’re on the la river bike path. there was also a short (nearly a mile, maybe a mile) detour off the la river bike path when i rode in april in the area of imperial ave that had the alameda st. mix of railroad crossings, blah pavement and road debris. that short detour may still be in place but hopefully not.

https://www.strava.com/activities/1499642002

pch is tightest in long beach but wider with a shoulder once it starts to exit long beach and head into seal beach. you could stay on pch all the way from long beach to newport beach
but the mix of bike paths and quieter parallel streets is nicer imo.

Like others said, why go thru Irvine. As stated in LB take the beach path, you have to do a little jog to cross over Alamitos Bay, then onto Marina Drive, then along the beach thru Seal, Sunset, Huntington and Newport. Stick together and take the right lane on PCH from Newport Blvd past Tustin Ave. after crossing the back bay bridge turn right on Bayside, a couple of ways to get to Ocean in corona Del Mar, stop for a picture on the bluff, then left on Poppy right on PCH to Laguna. Right on a Cliff (the second one), then it will cross PCH, turn right on the other side of PCH to stay on Cliff, the right on Beach, then L on Broadway, R on Forest L on Glennyre to the end and back on PCH to Dana Pt.

Here here is my route last month thru Newport and Laguna as far as Oceanside.

https://www.strava.com/activities/1876723786