A Time Trial is a competition between you and the clock (and everyone else and the clock!) You are on the track alone and must try to record the fastest sequence of laps without spinning, going off the track, or having contact with a barrier. Any such incident will invalidate your current lap sequence, and you will need to complete another full sequence in order to better your time. The Time Trial time is your average lap time for your best sequence of laps in the session. The number of laps in a full sequence varies from track to track, or from configuration to configuration.
What is an official time trial? Official means you completed the required number of consecutive incident-free laps during a time trial session. For example, Mazda Raceway at Laguna Seca requires four consecutive incident-free laps.
Essentially, you get a session rating at a track each time you complete a time trial. This session rating depends on your time trial time compared to the time trial record for that car at that track.
Your last four time trial session ratings at a given track regardless of the car are averaged to get your rating for that track. For each car you time trial at a track, you're given a normalized number, and that number is reflected by a rating, for example, 1600. Why doesn't it matter which car? Because within the formula, being x.xxx off the record in a Rookie Solstice can be equated to being x.xxx off the FSB200 record.
Your track rating from your 8 most recently visited tracks are averaged to give your overall time trial rating.
What if you haven't time trialed at 8 tracks? What happens here, is that you're given the service-wide average rating for the remaining tracks. So the table shows Driver A having time trialed at 4 tracks, leaving him 4 tracks at which he is getting the service average rating, for example, let's say the avg is 1600 for all other tracks.
Once you have time trialed at 8 tracks, your overall rating is more correct, because now you have 8 real ratings for 8 tracks, no service average ratings are included. Once you complete a time trial on a 9th track, only the 8 most recent are used, so in this case, your first track would be dropped from the average.
Having the best time trial or being at the top percentile of the standings for a given week or track doesn't necessarily equate to a positive gain in ttRating points.
Your iRating and ttRating will only appear on your competition license once you are awarded your Class "D" license.
You can find more information in the Sporting Code Section 5.5.4. Time Attack