The AI has many, well documented short-comings.
a) It's unaware of the players car. I don't know why that wasn't ever fixed. It's been there since GT2 (and probably GT1 as well). The AI drivers "don't see" you, which is why they senselessly pile into your car at any given opportunity. They don't try to punt you into the Armco, they just don't know you're there. The ridiculous thing is that we had an AI in Geoff Grammonds GP2 (1995 vintage) and that was when PC's had less processing power than today's mobile phones and were still running MS-CLOT. That they were unable to produce something remotely similar on a PS3, which looks like a CRAY in comparison to a 1995 PC is completely beyond me. There've been freeware simulations like TORCS, which have shown some amazing feats of racing AI programming, so saying that it isn't possible is not true. It is and I claim a right to evaluate, since I've been a professional programmer since 1994, so I know a thing or twelve about what can be achieved these days.
b) The AI slavishly sticks to the cheat line, which is pessimistic at best to begin with, which is why they start to break yesterday, just as a precaution. Just watch your B-Spec nOOb in an oval throwing the anchor at Daytona. Also the AI does not seem to grasp the concept of slipstreams or the fact that one can take some corners by just lifting the throttle, they always break. This is when you slingshot past as if they're going backwards.
c) The AI also seems to "give up". This is very predominant in B-Spec modes. You often watch your B-Spec chauffeur duke it out with a single opponent, who rides WAY faster than the rest of the field (not to be mixed up with the 'rabbit') That often goes for several laps and if your B-Spec finally manages to slip past, the über-opponent immediately falls to pieces. Seeing his lap times instantly drop by more than 5 seconds is not rare. Often he's even caught by the pack, no matter how far the two battling cars had already run away from the pack. Looks like a cheap arcade game style AI boost to me.
That phenomenon rarely happens if your B-Speccer is first by the 1st corner, but pretty much always if it is second by the 1st corner.
Just some observations I've made about it.
,Toyota 7, Nissan R89c, Audi R8 Race Car with a lowly little Lamborghini Gallardo so either im pretty quick or the AI is abit slow, Here's some pics to prove it enjoy 
, What about testing cars top speeds MIRA Testing Facility down south somewhere the banked oval or what about VW's secret test track both have banked corners that you try to go round at warp factor 7, Also add into the equation that I think the Mclaren F1 when it set the world record was going round an oval and consequently they worked out though logic and maths how fast it would be on a straight factoring in the steering angle
