You just have to man manage them extremely well, it sucks that you can't just leave them to drive because in high traffic they have a tendency to drive like a bat out of hell, whereas on the other hand with no traffic around they drive like an 80yr old that can't see over the dashboard properly.
The key is to allways keep them at medium pace, then you can't go wrong. Having said that when I chose my drivers I made sure their chatacter was dead in the middle of cool and hot! Another trick is to also tell them to "heat things up" at the start of the race in order to get clear of the field and get some fresh air. But this depends on the power of the car you are driving and the level of your driver. At anything below five this strategy is futile and you just have to struggle through events until you get your driver to a higher level. My drivers are now level 22, 23, 24, 20, 22 and 21 and they now have no issues with being "steamy under the racesuit" and can sustain racing at maximum speed.
But it's not all fun and games at maximum speed, tyre wear is immensly high so my biggest tip is to only race at medium pace, unless you realy need to get around someone or are that much faster that you can afford for your driver to drive so slow he turns to ice.