It's how well he manage to take action.
If he doesn't have any strength hell not take corners as well since he needs strength to hold the steering wheel right.
He also brakes worse.
^^ What he said. Pretty much that he'll be a few seconds slower than normal, other than that you're fine. If your driver has a trouble-corner, expect him to struggle with it when the Strength is gone, even if your pace is Cold.
