@Alex Sawczuk and @Renato Simioni , you may want to take a look at it. Yesterday I've finally could spare some time to do my tests. So, I did the same race I had 3 days ago (Endurance Brasil @ Autopolis), since I was already trained. Race was set for 30 minutes, with a 30 minutes qualifying session. I change some setting according to Renato's suggestion and completelly turn off Track Usage and Track Progression, to avoid the track rubbering's extra grip to mask AI times somehow. Also set Fuel Usage to X2 to force a pit window with MCR in the specified time, and set Tyre Wear to normal, to check it's relevance in AI lap times. A note for clarification: the Endurance Brasil skinpack consists of multiclass racing with MR18 and MCR2000. I've raced with MCR2000, and ran a qualifying session first to ensure the two grids will be fully separated in race start, thus preventing one class mess with other's lap times. (I explain this tip in the OP). The picture below shows my findings: In the left column, we have qualifying times. You can skip the first 10 positions (they are MR18 class, don't apply to our test). Then, after 11th position, I isolated 4 AI Cars (subjects marked A, B, C, D), which I think could best describe the issue. The complete qualifying and race results, laps, gaps, positions for this test race can be found here: http://simresults.net/170119-Xo1 In the RACE LAPS columns, I isolate race lap times for ours subjects. The first two laps can be discarded, since in race start all cars are very close, some AI breaks too much to avoid touch, there's fight for position, etc. So, after this phase in race, I've marked in green a reference lap time for each AI. You can notice that, for this car/track combo, lap times are 1s to 1,5 higher than qualy times. As the race goes by, you can see that AI lap times start to decrease. Of course, there are some very slower times, due to AI errors, off-tracks, fights for position. But this behaviour is desirable, that's ok. Marked in orange are the lap AI performed a pit stop, and the lap after. You can notice that lap times before pit are much faster, closer to qualifying times. Those laps are marked in blue, the same color I've marked qualifying times as well. Interesting to notice that subject A could even be 1 tenth of a second FASTER than his qualifying lap. In those laps, AI have very low fuel, they are ligher and get faster times. At this point, we can observe another tip of mine: the 'Pit Window'. We can see that, when MCR2000 AI cars reached a 20-30% fuel left window, they initiated their pit stops, and all cars were distributed in a 3-lap Pit Window, problably to split teammates and avoid them to pit at the same time. After the pit stops, the AI cars fill up their tanks, which make them heavier. Their lap times as now compatible with race start times (marked as green for better comparison). We can clearly see that Tyre Wear have INSIGNIFICANT EFFECT in AI race lap times, close to none. This has been happening from a long time ago, in every car and track I tried (being default content or mods). So long that I could notice, test it, and create this system I talk in OP. As a matter of fact, I've been observing this behaviour since GSCE days. But is was worse then, AMS have fixed other important issues (like fuel usage influencing too much lap times, but this is past). On the other hand, I've struggle a lot with my tyre wear. Got off-track once. And in my last lap before pitting, my rear-left tyre wear bar marker in HUD was already yellow. I could cleary feel the wearing effects, It was difficult to make long corners, and I almost spin in the harpin in third sector. The negative tyre effect superceeds the positive fuel consumption for me. So, with all that, I'm standing my position about my tip: to have a fair race against the AI, turn off tyre wear, since with that option on, as race goes by, you're gonna get slower, and AI will be faster, almost to the point of qualifying times.