How are performance points calculated in Gran Turismo 5?

Question

Somehow it feels like horsepower has a greater influence on PP than weight, obviously because horsepower will always means higher speed and better accelerations at higher speed, but it won't really efficiently describe performance on very low speed raceways like eifel kart or autumn ring mini.

I also noticed some cars have better "base" PP than other cars with the same horsepower/weight ratio, but I don't really know how one can properly calculate cornering performance, since it depends of vertical and horizontal center of gravity, car length, the size of tires (type of tire has nothing to do with PP), stability in corners, suspension, etc: any car will perform differently.

I guess it's of the form ((horsepower^constant1)/weight)*constant2 + constant3.

constant1 being between 1.2 and 2.

Oddly, I also noticed increased power on very PP cars does not increase PP so much.

The other thing, I don't think PP precisely describes the exact potential for a car to outperform other same-PP cars on the same raceway, since weight will play a more important factor on slower tracks than faster ones, especially with comfort and sport tires.

What I'd love to know for sure, is how to rate certain tracks for either speed or slow cornering, so I can choose car for the same PP limit, either a lighter or more powerful car.

Answer 1

The other thing, I don't think PP precisely describes the exact potential for a car to outperform other same-PP cars on the same raceway, since weight will play a more important factor on slower tracks than faster ones, especially with comfort and sport tires.

Not to be facetious, but that basically states that some cars are better than others on a given track, which seems an obvious truth.

PP isn't perfect, but it gives you a fair comparison of car performance. It takes into account all power related characteristics (not only the engine power but also spoiler downforce and car weight).
It doesn't take handling (suspension, tyres, TCS, ABS) into account.

Note that, although tyres change acceleration characteristics of a car, their effect is not permanent and will change over the course of the race. It seems only permanent characteristics of the car are taken into account, to provide an objective number that isn't related to your handling of the car.

I seem to remember the points being directly related to a "simulated drag race" (testing straight line speed), but I heard that about GT3 and cannot find any confirmation on this anymore.
Given which characteristics influence PP and which do not, it's possible this is still used today (or a derivation thereof).