How iRating works

Randy Cassidy from iRacing staff puts some light over iRating system. This is a question many newbies are eager to know and understand. As always we’ve said you race against your own, iRating is only a number, don’t be mad about it and enjoy racing.

“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.
If you finish ahead of someone with a higher iRating than yours, you take away more points from them than if you finish ahead of someone with a lower iRating than yours.
Nothing else is included in the calculation. Not how many incident points you got, not where you started, not where you finished, not how many positions you gained/lost compared to where you started. Nothing.
The iRating system uses the Elo rating system from the chess world as its inspiration.

Many people will comment “you have to finish in the top half of the field to gain iRating”. That’s an extremely rough approximation that doesn’t always hold true, but it’s a half-way decent rule of thumb. You finished 13th in a 17 car field. That’s pretty solidly in the “it’s impossible to gain iRating” category.

While you did lose iRating for finishing 13/17 in a field of mostly higher-iRating drivers, you lost a lot fewer iRating points than you would have lost if you finished 13/17 in a field of similarly-rated drivers. And, assuming there are a sufficient number of drivers in future race sessions to form more than one split, your new lower iRating makes it less likely that you’ll get put into a higher-rated split, where you’re more likely to finish near the back. Meaning the system is doing exactly what it’s supposed to do.”

Strength of field is not part of the calculation, size of field is. Strength of field is just the (properly glommed up) average iRating of the field, and iRating is already included in the calculation – no need to include it again! The size of the field (number of cars) is included to keep from getting a huge iRating bump (or drop!) simply because the field is large. If field size wasn’t part of it, then because you’d exchange iRating with many more people, the total number of points you could gain (or lose) would be larger. “

“The number of points you exchange with any other driver in the field does depend on the difference between your iRatings. Think of it this way:

The iRating is a predictor of whether you should beat the other person in a race.

If your iRating is much larger than the other guy’s iRating, and you beat them, then your iRating already predicted that outcome. So there’s no need to make your iRating much larger to meet that prediction in a future competition between you two. So the exchange is small.

If your iRating is about the same as the other guy’s iRating, then the number of points exchanged between you two will be medium-ish (technical term!). Regardless of who finished ahead of whom, your similar iRatings mean the prediction wasn’t very far off, so there’s no need to make big a adjustment. But to ensure that your iRating doesn’t take forever to move to where it should be, the points exchange also shouldn’t be tiny.

If your iRating is much lower than the other guy’s iRating, and you beat them, then your two iRatings incorrectly predicted the outcome, and by a large margin. They both have to be updated significantly because the prediction was significantly wrong.

So if the calculator you’re using only considers how many people finished ahead of/behind you, without regard to the actual iRatings, then it’s only a rough guess.”

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