I have finally decided to try and tune my own V8 Supercars after getting a handle on tuning other cars. But I keep breaking traction just before mid corner not sure if it's my tuning or driving style. I haven't had this issue using other people's tunes
If you slam the throttle mid way to the corner you will always lose traction, if you drive it like pro drivers that only go full throttle on the straights you should be fine
You could also try to turn down your torque and acceleration on your LSD... (Limited Slip Differential) that way the power don't go to the wheels as hard when you gun it out of a corner...