I always have TCS set to 0. It was tricky at first well worth the pain in the end.While you can't tinker with the cars much, it's worth looking at the Traction Control and Brake Balance settings for various cars and in the longer races with pitstops the fuel mix too.
The default TCS3 can be quite a drag on your times, I find dropping it to 2 is almost always possible and with the FWD and 4WD 0 is simple enough to drive. Some of the RWD cars can be quite twitchy though and spins are a real PITA with a wheel as the game takes ages to reset you and 3 point turns are no fun at all.
The brake balance can make quite a difference too.
BTW those settings seem to reset to default on non-owned cars when you're doing other things so worth checking each time before the start line.
Here's a few Brake Bias reference points i use as a base starting point.
MR = - (1-3)
FR = + (1+3)
MR = 0 +3
FR = +2, +4
4WD = +5
FF = +5