Private Track Days vs Regular Track Days
If you're fortunate enough to be invited to a private track day, there are a few things to be aware of and how they operate differently from traditional Fast/Intermediate/Novice (A/B/C, etc.) track days.
If you're reading this, then you likely are already familiar with how normal track days operate so I'll list the differences that I've seen having attended private track days with two different organizers.
The biggest attraction--low head count
Usually no sessions - this means anyone can go out at any time
Tech inspection is usually about the same
Riders meeting is usually about the same
Some of them will reserve the first 30 minutes of track time for the newer/slower riders
Track side services will likely be limited since it's not usually worthwhile for the vendors to hitch up a trailer or load a van and drive to the track for a low headcount event
Details about the event will likely not be as formally available (i.e., on a public-facing web site)
The cost will be higher since the coordinator's track costs are the same as a regular organizer but the headcount is lower so the expenses are divided by a smaller number of riders, however, they are usually looking to break even or very little profit so if the overall headcount is 1/2 of a track day provider, the cost is less than double. To note, it seems that track days with lower headcounts, from my casual observation, tend to have fewer incidents and fewer ambulance runs.
I've now done a couple of private days this season, both at Thunderhill East. One was through Dylan Thieu, an individual in the Bay Area (California) and the other by Dysturbed Riders, a riding group out of central California (Stockton/Modesto or such).
So, my takeaways after my 2nd private track day this year...
The biggest thing is it's just nice having relatively little traffic on track, however being on the faster end of the riders, it can be a little disconcerting to come up on what would be C group riders when you're at an A group pace. I made sure to keep my eyes up and glance into the horizon for upcoming traffic but there were a couple of times when the speed differential was very significant. It was fantastic to be able to go do two 15-20 minute sessions in an hour's time. I think I rode about 150 miles that day, riding from 10:00 - 4:00 PM. Since I was there with friends, we swapped bikes a few times which was super fun. There's nothing like sampling bikes at a decent pace and not worrying about being able to work on your own objectives because you'll miss a session. While I was able to do new PBs on both of my track bikes (the Ninja 400 was a bonus because I wasn't planning to focus on it, I just brought it in case I was getting tired at the end of the day, which I was but still managed to trim a second off my former PB), I lost time on my best lap on the Daytona due to traffic but it was still a good improvement. That's not to say that I wouldn't have encountered traffic on a regular track day but if I'm riding in the A group, most people are running a pretty decent tempo so I think the probability of encountering traffic would be lower. The ability to go run laps whenever you want though is huge. If it's going to be hot, just go run laps in the morning until you need fuel, and leave at lunchtime. If it takes you 15 minutes to build pace but then you see the checkered flag at a regular track day, that kind of sucks. With open sessions, just go run until you build your pace, and don't worry about the session ending soon. If you're getting to the top of your normal riding group but are apprehensive about bumping, you'll likely encounter some faster individuals and be on track at the same time so you can see what the differences are and due to a lower headcount, the risks are lower.
It's a fun experience that I heartily recommend. You'll have to try one out to see if it fits with your riding objectives and preferences.
I've put some of the riding videos below (at the time of writing this, the embedding function isn't working quite right so traditional YouTube links are there as well).