Are you using HOT bobs? If not fire your guys and get HOT Bob's, I don't use any other type of Bob, they are all terrible drivers. Hot Bob's beat this no problem. I mean think about it Senna, Schumacher, Alonso, they are all A-Holes (ie HOT).
If you are using Hots, and I mean all the way Hot HOTS, try using a fully tuned scudi, worked for me no problem.
If still no, fire your Bob's, some just weren't meant to race...