In the tires .tbc file, edit the lines
DryLatLong=(1.335, 1.335) // Lateral/longitudinal coefficients in dry weather
WetLatLong=(1.290, 1.290) // Lateral/longitudinal coefficients in wet weather
Make small changes and test, higher numbers are more grip; there will be settings for front and rear tires, for each compound, so scroll through the entire file. And there are many tire files throughout the vehicles folder; some cars may have more than one, and several cars may share one.
In the .hdc file for each car are:
TractionControlGrip=(1.00, 0.20) // average driven wheel grip multiplied by 1st number, then added to 2nd
TractionControlLevel=(0.30, 0.90) // effect of grip on throttle for low TC and high TC
ABS4Wheel=1 // 0 = old-style single brake pulse, 1 = more effective 4-wheel ABS
ABSGrip=(1.00, 0.20) // grip multiplied by 1st number and added to 2nd
ABSLevel=(0.30, 0.90) // effect of grip on brakes for low ABS and high ABS
This may be more what you are looking for; I've not used driving assists so never tweaked these.