iRacing
Online racing is a large part of sim racing. The most popular simulator for online racing is by far iRacing. This sim had been built from the ground up to be an online only racing simulator, and has a lot of features designed to keep the racing fair and competitive. Firstly, it has a subscription fee, unlike other simulators. On top of this fee, you are required to purchase the content you wish to use (apart from a small amount you get for free with the subscription, just to get you started), cars cost $8, while tracks cost $12 (with the exception being the Nordshleife, which is $20). The tracks are also laser-scanned, like Assetto Corsa. This means that the game can be quite expensive, in order to run a full "series" (iRacing's version of a championship) you'd have to purchase a car in that class, along with any tracks. You do, however, get some money back if you participate in more than 80% of the races in that series.
The game also features a license system. It is split into two categories, road and oval. Each upgrade separately. The first stage is the Rookie license, this is made up of a couple of road and oval championships using the base ("free") content. Each series has a race running each hour, and you are able to participate as many times as you want, this ensures there is always something to do. As you race, you earn iRating and safety rating. iRating is based on your overall skill, I.E, where you place in the qualifying and races. Safety rating is based on how safe you are as a driver. You start the race with 18 points, each contact with another car, runoff, or contact with a wall depletes points depending on the severity of the impact, this will either increase or decrease your safety rating at the end of the race. In order to be promoted you must participate in a certain number of races, and attain a minimum safety rating.
All series have a schedule, at the end of this schedule, the season ends. There are four seasons in a year, and you'll be promoted automatically at the end of a season, if you have the requirements. Outside of the Rookie license, you gain access to more and more series, and more and more cars, ranging from GT cars to open-wheelers, to NASCARs. This keeps the races fair, and ensures that you do not run across people who simply want to cause trouble and annoy others, usually by crashing into them.
Public Racing and Leagues
Outside of iRacing, there are two other ways of playing online, racing on public servers, or running with a league. Most sims have multiplayer, so it's usually not hard to get a race going. If you're running on a public server, however, there is no guarantee of a good race. A lot of servers can be infested by people who simply want to annoy people, usually by ramming them across the road, or by cutting the course. The only way around this, is to join a league. A league is a group of people who race to a specific schedule, these are usually moderated, and people who do not follow the rules get banned.
All screenshots on this page are taken from the Steam page for iRacing: http://store.steampowered.com/app/266410/
