looking for easy fire road type riding in any of the many national parks. Trip starts in san francisco then north to mendocino over to lake tahoe, grand canyon then south to San Diego then north up the pacific coast highway back to san francisco.
Ah... sorry I can't help much with fire road type rides, it's just never been on my radar.
But I have other suggestions, if you're looking for any. If not, just ignore me as I ramble on. The coast up to Mendocino is beautiful. Depending on how you head across to Tahoe, you might find yourselves somewhere between Napa and Calistoga. Plenty of excellent wineries to visit. If you're coming across near Grass Valley, there's the Empire Mine. It might give you a peek into our Gold Rush, and the massive industrial and cultural changes that it brought.
Tahoe offers plenty of hiking opportunities, gorgeous waterfalls, forest, etc. We just had a massive snowstorm up north, and sometimes the passes are closed due to snow, so you'll need to keep a close eye on conditions.
Depending on where you are visiting the Grand Canyon, there's Navajo National Monument and Zion. Depending on your route to San Diego, you might be passing by Joshua Tree.
The coast back up north has lots to do. In San Simeon is Hearst Castle. The road was washed out a year ago, but repairs might be finished by the time you're there. Also near San Simeon is the Elephant Seal Rookery. Depending on whether it's time to hump or give birth, there could be thousands upon thousands of elephant seals on the beach. It's close to the highway, so it's just a short detour, and more amazing that I could ever describe.
There's Big Sur, of course, and just a little north is Carmel. Carmel is a nice place to stay, nice place to dine, and a nice place to shop. Nothing is cheap in Carmel. Oh, and there's 17 Mile Drive. Just do it. Trust me. Just north is Monterey and the Monterey Bay Aquarium. Just north of there is Santa Cruz. Stop by the Santa Cruz or Ibis factories, and maybe they'll loan you some bikes. And just north of there is San Jose, where you might want to take in the Winchester House. And just north of there is San Francisco, and we're back to the hookers and cocaine.