iRacing uses a ranking system to keep track of everybody's performance so its matchmaking system can provide close wheel to wheel racing. It's not unique in itself as lots of competitive online games use some sort of ranking system. Think of Dota's MMR or League of Legends' ELO.
Wondering why you gained (or lost) iRating points at the end of a race? There's many factors that come into play when determining whether you earned or lost points at the end of the race. First we will explain what iRating is before we jump into how it's used for matchmaking.
iRating is a numeric value that iRacing's algorithm calculated based on your performance and is then used in matchmaking to achieve close matched racing. Simply put how fast iRacing thinks you are.
iRacing uses their iRating system to determine how fast you are and who should be put together in a race.
This system is quite advanced, but please allow an iRacing team member to explain.
"Everyone that finishes ahead of you in the session takes iRating points away from you. You take iRating points away from everyone that finishes behind you. The number of points in each exchange depends on the two iRatings involved, and which finished ahead of the other. The iRating system uses the Elo rating system from the chess world as its inspiration."iRacing Staff - Randy Cassidy
A really dumbed down version is that if you finish in the top half of the field you should gain iRating. There are outliers, but as a general rule of thumb. Now this depends heavily on the Strength of Field metric which simply put is a combination, or average if you will, of all the drivers iRating who are part of the session.
Imagine on a Saturday afternoon where people are signing up for a popular MX5 or Skip Barber race. There are 80 iRacers who signed up for the race, though we can't fit 80 drivers on any (road) grid or would it be good for your framerate or session stability. Now those 80 drivers will be split up into 4 races, featuring 20 racers each. At this point iRacing's algorithm will create those 4 sessions and try to put people of equal speed (iRating) together.
Now if your iRating is somewhere around a thousand to fifteen hundred ratio, you maybe be put in the 2nd or 3rd split, while if you have an iRating of over 3k, you are likely fiding you int he fastest session, also known as top split.
Simply put, by finishing races in a better position than where you started. Please note that this is a very dumb downed version, and there are a lot of details and caveats to take into consideration.
First of all, your race has to go official. This means that enough people signed up to participate in the event.
Although it's a relative score that will always be changing, there are some ballpark figures to use when trying to determine how you weigh up against the rest of the iRacing community. We also highly recommend reading some of these top rated comments on what's considered a good iRating.
Generally speaking anywhere between the 0 - 999 range is considered on the slower side. Races with only iRatings in this range are usually a little hectic and may also contain players that are not at that pace levels, but for other reasons received this iRating. For example a player who :
Now if you have an iRating that sits between one and two thousand, than you are getting into an interesting mix of players who are likely very evenly matched with you. This will also mean you often find yourself in high participation races in the top split or second split. Both of which will most likely be very hard to win for you, but should give you plenty of opportunity to learn and have some wheel to wheel action.
Somebody with an iRating between two and three thousand has likely sunken a good chunk of time into the sim and is a sim racer with a lot of passion. Exactly the crowd you want to race, most of them are experienced and you will be having a great time.
Wait what, it's over 9000?! Yea it's possible, usually people who are this fast are referenced to as aliens in the sim racing community. Their speed is simply unnatural and therefor it's believed that these are actually aliens showing us a thing or two.
Now this is a bit of a controversial one as both iRating and your Safety Rating should be a result of you participating in races. By trying to game the system you might have a higher iRating than the system designed for you to have. It will be great to post in your forum signature or boast your ego (which is totally fine), but you might end up in races against stronger opponents and iRacing still believes you should be on the podium in order to not lose any points. Which is also the beauty of the system, the more you race the more likely you will race against equally skilled opponents.
With all of this in mind, you can approach each race from an analytical standpoints before considering joining. There's a great post that focuses on Oval series and how to boost your iRating.