One extra observation I would make on top of the sibling's detailed answer is why I believe iRacing is by far the best online racing game. iRacing has an MMR v

One extra observation I would make on top of the sibling's detailed answer is why I believe iRacing is by far the best online racing game. iRacing has an MMR value called iRating which is used to match you against drivers of a similar skill level (like every online game) but it also has the unique concept called 'safety rating'. Safety rating is based on your 'incidents per corner' over some recent history of corners (in the 1000 to 10000 range). Safety rating controls which official racing series you're allowed to enter - higher level stuff like F1 cars requires a better safety rating than the entry level Mazda MX-5. Having the need to maintain (or improve) this safety rating gives the 'risk' incentive to drivers which most online games are lacking. In real racing a desire not to put your car into a wall at high speed controls how dangerously people drive, but that risk doesn't exist online and so in a lot of games (e.g. the F1 games) people attempt stupid dive-bomb overtakes, take out their competitors and make it less fun to play. Safety rating puts that incentive back. It's not perfect of course, but it does help iRacing feel more 'real' and 'fair'.