The physics in GT5 definitely aren't perfect, as you can see if you run your car even at low speed like 25mph into a wall. If you do this in Live For Speed, you'll see some amazing body motion as the force reverberates through all four suspensions individually. This might be closely modeled in iRacing, but so far I haven't seen it in any videos of it.
Enough people like Grandi have commented that setting up your car has a lot to do with how it behaves, and how realistically, so I'm going to have to pour through the Settings boards and glean some wisdom from them. But even with stock cars on Sports or Comforts, as many have said, sports cars feel nicely authentic. Race cars are all over the map, but for now I'm happy with them because they aren't completely out the window wrong. As far as I can tell, anyhow, with my abundant non-experience with real world race cars.
With Kaz's real world experience in racing and ongoing consultation with pro racers, hopefully he and the physics team can cook up an update that will make us all cheer.
I just got done taking the LFA out for a spin in an Arcade Nurburgring race with ABS off and brake balance set low front and back, something that used to give me a challenging but manageable race prior to Spec II. I
could not keep that car on the track at first, and braking was a spinfest! If you guys don't notice any difference in the new physics, I have to wonder what the heck you're doing. I have yet to explore online physics, as I'm afraid the differences from offline might still be too great, and I don't want to go ramming people around.
ABS is still a number of assists in one, like one or two ticks of stability management and skid recovery. Even at ABS 1, brakes still refuse to lock up. The LFA was now raceable and could be pushed aggressively, but even on Sports softs, the Nurb was a handful, and I just can't say no to squeezing a bit more speed out of the car in a turn. I left the track in a few turns rather than risk a spin.
I decided to take a test run on an empty Ring and did a time test on Sports softs again, with sunny weather and time of day transition at the default of 30. I turned everything off, set my brake balance the way I used to, and the car was almost as unstable as those in Forza - which I'm questioning how realistic they are, but that's another thread. Taking turns aggressively is a chore. You have to pay attention to what the car and tires are telling you every split second or you'll lose it, which I did several times through even modest turns. Turning on stability management was only slightly better. Racing at night was eerie! I have to applaud you guys who can handle this untamed beast with everything off, because it wants to go wild at any decent speed.
I tell you what, even in race cars, if you can't have any fun in this update, I don't know what to say. Spec II is just amazing, how much it has transformed GT5 in even the most subtle ways.