At any thoroughbred racetrack in America, on both the main track and turf course; the condition of the surface will have a decisive impact upon the outcome of the race. The most significant environmental factor will be the weather, specifically, the amount of recent rainfall.
Uncover vulnerability or advantage
On a yielding turf course, Speed will have virtually no chance of winning. If the turf course is too wet, a race will typically be moved off turf; and many of the horses will scratch.
Therefore on racing days with bad weather, be sure to verify the race is still on turf.
When the dirt gets wet it gets sloppy and horses which are not in the lead get a constant flow of mud to the face.
Handicapping a dirt race over an off track, examine how horses performed under different track conditions to see if they have demonstrated weakness or advantage.
It may also be helpful, to consider the sire's performances, vulnerabilities or advantages over off tracks.