Steamers vs drifters: what the data actually shows.
A steamer is a horse being backed heavily enough that its price shortens quickly. A drifter is the opposite, a price that lengthens as money stays away or moves elsewhere.
Neither is a guaranteed edge on its own. The distinction that matters is not steamer versus drifter, but moved price versus pre-move price. Backing a steamer once it has already shortened has, in the data behind this product, been a losing position against Betfair SP. Backing the same horses earlier, before the bulk of the move happened, has been the profitable side.
That is the reason HorseWhale exists as an early-warning tool rather than a results page. It is built to catch the gap between the first books cutting a price and the last books catching up, not to report the move once it is finished.