Why do vehicles do this

[omega5002]

Ok, whenever I edit the handling, the npc driving the cars go alot faster and It's harder to race or do missions. When I did the mission where you had to go on the pcj600 and go onto a plane to destroy it, the plane goes too fast( I didn't even edit the plane) and when I do the pit thing in the driving school, the opponent car goes twice as fast than me and It's the exact same car. Why all of sudden the cars go too fast, it some weird program that rockstar made to make the cars go faster when the handling is edited. Also when I do the LV ring race with the turismo and I replaced it with a Mclaren F1 and made it go 240mph, the other cars go way behind me and that's not fun, what, is the vehicle limited to 120mph because that's the default speed of the fast gta cars. What's the file that control what the npc do with driving. Is there a mod or guide to fix this problem or am I going to have to live with it.