When they established the PP system,tires selection was part of it (it was in the PP equation)....but not long after they removed it....so if you didn't pick that car for a long time,chances are good that it shows the PP from that period (tires selection in PP equation)....now if you go on that car the PP will be update....
The PP system was introduced in the Update : v1.06 Febuary 18th ...if you bought the car before V1.07 and didn't used the car since....PP will be off.
Update V 1.07 1 week after update V 1.06
[Fixed Issues]
- Performance points (PP), which is an index of a car’s overall performance, is now calculated regardless of your tire selection. You can now set performance point restrictions and tire restrictions separately when you race in a lounge.