Mike,

Drafting seems to be a factor in bicycle and human racing, so I presume it is a factor in horse racing also. It's something that rarely gets mentioned even among "trip" handicappers. I've been trying to watch that kind of thing more closely, but it's hard to accumulate evidence of it as a factor.

One idea I am tossing around is that a very fast pace in combination with some drafting could account for the occasional very fast figure you see from closers under those conditions. Figures they rarely duplicate under more average conditions.

When you look at the closer's fractions there often isn't a lot of evidence that they should have been helped by the faster pace unless they are the very deep closer type that sort of got dragged into running at a more efficient pace than usual. Another possibility is that when they finally make their move they meet much less resistance from the front runners than usual because they are all dead tired. However, maybe the biggest factor is drafting.

There's another application I'm just starting to look it, but I don't have much evidence yet.