I think Input-Lag is maybe the wrong word for the things happening there... V-sync is more known for causing minimal lag when displaying the Game on the monitor. In case of raceroom --> you a closer to a corner than you actually see on screen. So your steering-input is a always a bit to late...
That's great (and definitely good to know), but still, to be able to react to something, you have to see it happening first. And if there's lag to when an event is shown to you, there will be even more lag in your response to it, even if the input itself doesn't have any lag. Yes, it's fairly small, but still, every bit might help.