It's counterintuitive and it's only true in an "all other things being equal" scenario, but it's true. In the real world, you more often than not get better performance and lower lap times with the wider tire. But it's important to understand how much of that is due to the width and how much is due to the zillion other things that influence how the tires interact with the pavement. Believe it or not.
Start here
http://insideracingtechnology.com/bookorder.htm
You need to read what I wrote again if you think that's what I'm saying