I don't know if you can directly. You could raise their grip a bit in the TBC and then reduce their braking and cornering performance in the hdv AI settings. Not normally something you should need though, they use the same engine as you. What's the issue?
Perhaps you can do it modifying longitudinal grip for rear tyres, which is the most demanded 'type of grip' when accelerating..... But i am not sure. And you must reload the mod to test changes on that.
Besides tires you can also check their gears shifting stuff. Also check upshift algorithm, it is possible that AI could be loosing a bit at that.
Also the AIW offers a Possibility (if it still works) with the Entry AISpec=(0.0000,0.0000,1.0000,0.0000) // 4 ways to express AI speed on track, limit the acceration, max speed, their cornering speed, or their deceleration. 0.0 - 1.0 But as said above, there are more Settings that affect each other and it also depends on the basic Physics of the different Cars. So maybe changing a Setting in the AIW maybe works great for Car A, but makes it worse for Car B.
Thanks everyone, using cart 98. Making an almost full 98 season for lan racing against ai. I have two cockpits. (no houston or brasil) Making my own AIW, loading screens etc for personal use. I was finding that they put the power down quick and stick so well. Not usually an issue and thought maybe it was the mod. I have them using my same setup. First fix was giving the ai the same setup with a taller 1st and 2nd. Worked well but in lan multiplayer it is all fixed setup so not possible. Anyway after some time I learned to make the car setup have more jam out of corners. clutch/preload rear Reg and 3rd spring dampers combined with pressures and I am on them much quicker. Sometimes you just have to go out there and turn more laps adjusting setups instead of the almighty tweaking. LOL Sim on people