I rode Carmel to San Luis Obispo this April (started on the first Monday after the road opened from the slide at Rat Creek).
Prior to my trip I asked the same questions as you on this forum and got the response that in California they try to never turn away bicyclists at the hiker-biker sites. On my trip I was the only cyclist in each campground so it wasn't an issue but Pfeiffer-Big Sur is one of my favorite hiker biker sites because it is a large communal circle with lots of picnic tables. I don't think they would turn you away even if they are overflowing.
However, there is still room to improve the Pfeiffer- Big Sur campsite. The Whitefish Lake State Park bicycle campground in Montana has a Park tools bicycle vise mounted on a post to make it easy to tune up your bike while you are camped there. The bicycle picnic tables have a generous roof over them so you can shelter there during thunder storms and there is a power outlet and USB power plug mounted on the post the holds the roof over the picnic table. I would suggest that these features be added to all hiker-biker campsites.
Originally Posted by
AngeloDolce
I stayed at Pfeiffer Big Sur 3 years ago for 2 nights
(1) My experience was most of the hiker/biker sites did not allow or reservations or have problems with space, since bicycles and tents just don't take up that much space.
(2) Pfeiffer Big Sur allows 2 nights (in 2018). I was impressed by the forest so I decided to stay for a second day.
The H&B camp sites at most of the parks don't normally allow reservations, and I only heard of one being full, even at the southern parks. Angel Island (SF) only has boat access, so technically the sites are listed H&B but they require reservations far in advance and charge more than other H&B sites. Angel Island really has regular campsites that prohibit cars. All the other H&B sitess had short stay limits but no reservations, and no problems with overcrowding .
The more southern (e.g. near LA or San Diego) sites had much stricter rules trying to distinguish tourists from transients, so they had 1 night limits, higher fees, etc.