Likely only a fraction are actually racing online or >90% is doing oval and dirt. If you just open the browser-window for the forum or racing against AI you will be listed there as well. Most road-series are practically dead, like all vintage content and every fast open wheeler series. Certainly it's getting full in the GT3-series, MX5, Skip Barber and a few others. It's week 13 and on the road-series-servers there are roughly 850 people online at best at the moment while the iRacing-page is counting 12453 iRacers online
First off, you can't only count people racing in the "main" races (the 850 mentioned) and forget that:
1) lots of people are racing or practice in the hosted servers section. Right now there's at least 600 in that section alone.
2) I'll bet that lots of people are doing AI races for various reasons.
3) lots of people are running hotlaps/hotstints offline in prep for the next season.
Most importantly, Steam counts anyone that opens a game, for whatever reason (online race, offline AI race, practice, career mode, open but idle, customising car/character etc.) as an "online" player as well. So you can't imply that iRacing advertising 10K racers online is false/misleading, when all other Steam stats report for all other titles in the same way. Forza might have 20K "online" but with at least 25% of them designing a character or customising a car...not racing online or offline...so same thing.
As for which cars are active: what you're saying is partially true, but it doesn't tell the whole story, there's so many facets to it. First off, iRacing is practically the only game in town in all of sim racing if you want to do online oval or dirt road/dirt oval racing with the proper flags/rules
and don't have time for the time restrictions of finding buddies to race or leagues...Oval is also the most promoted discipline where, if you're alien good, you have a chance of racing for actual money. So it's not surprising that's a large chunk of the subscriber base.
Also related to that, there's a big reason why GT3 and similar cars are all the rage in all online sim racing: they're easy to pickup (not saying easy to master) compared to vintage cars and fast open wheelers. I love the fast open wheelers (the iR-01 has become my primary focus), but not many people can handle it; it's not something you pick up and are capable of getting on the pace in a few mins. I want them to be popular, and I don't think sim racing should ever be made arbitrarily more difficult than the real car, but let's face it: Driving a Lotus 49, Lotus 79 or a V10 F1 car without TC or ABS has never been easy. How many online races do you see for similarly difficult cars in other sims? Even when you do enter one, it's usually a wreckfest unless you're in a league of drivers at a reasonable level. Also compounding the problem is tuning iRacing's FFB to feel like it should isn't as intuitive as other sims, and that's extremely necessary to keep those more difficult cars under control.
Finally, the big difference between other sims and iRacing is that there's a ratings system and championships for each series and many people care to keep their rating at a certain level, either for the quality of racing, the higher points you get in championships, or both. If you're highly rated due to being an excellent GT driver, but then jump into the top level open wheelers, you're expected to be at that same rating level over there too...and as I said, it's not easy for everyone to switch over from GT to Formula...so most try them out, can't keep the car on track after 15 mins of trying (or not up to the level they expect), crash into others (or get crashed into) and then give up and go back to GT3/MX5/skip barber etc. Same for the primarily oval guys who want to dip their feet in road racing...oval racing definitely has its many challenges, but going from Ovals to a road track in 300kph capable open wheelers is a big ask.
Having said all of that, multiclass road races in iRacing are almost always packed 24/7 as well as F3. Also, if you read the iRacing subforums for each series, they'll tell you when are the most packed times so you'll know when to look for a race (helpful for the vintage and fast open wheeler races). Road racing far from dead.
