Part 2: Dirt – Under the Hoof: The Science and History of Horse Racing Track Surfaces
Welcome to part two of our racetrack surfaces series! Today, we will discuss the significance of dirt racing in the United States. Dirt consists of sand, silt, and clay, and is the country’s most popular surface for Thoroughbred racing. Currently, there are approximately 56 Thoroughbred dirt racetracks throughout the US. The American Thoroughbred has been bred to excel on dirt across various distances and conditions.
You might be wondering–WHY do Thoroughbreds in the U.S. race primarily on dirt surfaces, when we already read that turf is most popular globally? The main reasons are dirt surfaces are easier to maintain, and how breeding has adapted. Turf is a living, breathing surface that gets torn up with divots when horse hooves gallop over it. It must be intricately watered, reseeded, and rested for periods of time to keep it thriving. While dirt surfaces also require meticulous care, they don’t need any regeneration time. Many US racetracks host racing over multiple consecutive days, for weeks at a time. This continuous use is better suited to a dirt track, with a small number of races carded on a turf course. In England and Ireland, where nearly all racing is on turf, each racecourse hosts a far more limited number of races over their grass tracks thanks to a “fixture list” that rotates race dates from track to track. This gives the grass time to regenerate between fixtures.
To maintain proper moisture levels on a dirt surface, many tracks have various layers that serve as the foundation for their racetrack surface. For example, Keeneland Race Course was built over a drainage pipe, and consists of multiple layers: dense-graded aggregate base, drainage stone, porous asphalt, and limestone screenings. The top 6” of the track is referred to as the “cushion,” and is composed of sand, silt, and clay. This ensures that the horses have an even and consistent surface to run over that is not too hard or too compact. Another example is Saratoga Race Course. Saratoga has deeper layers than Keeneland, due to the geological nature of the location. Saratoga* has 4 ¼ - 4 3⁄4” of sandy loam cushion, 10” of a clay/sand/silt mixture, and a sand base drainage layer on top of natural soil.
A rating system was developed over time to classify the consistency of a dirt racing surface, based on the level of moisture in the track. These ratings are listed below with definitions from equibase.com:
FT = Fast: Completely dry and at optimal efficiency.
WF = Wet Fast: Occurs immediately after a heavy rain; track has surface water on it, but the base is still solid, accounting for times similar to (or even faster than) a fast track.
SY = Sloppy: As the track continues to accumulate moisture, the base is still solid but water is beginning to seep into the base; Surface water is evident. A superscripted S beside a sloppy track indicates the track has been sealed.
MY = Muddy: Moisture has permeated the base of the track; times are somewhat slower and running tires the horses more.
SL = Slow: The racing surface has begun to dry out; the base is still soft, but surface drying is evident; times are generally slower than normal.
HY = Heavy: Similar to Muddy, the track surface is deep and consistency is thick, an obvious slowing of times will be apparent as will the tiring of front runners.
GD = Good: The drying process continues, times improve and the track is approaching a FAST condition. Some flying dust may be evident.
FZ = Frozen: As a result of sustained low temperatures, ice particles have formed on the racing surface. Racing is typically canceled for the protection of our equine athletes.
Along with the ease of care, breeding of the US Thoroughbred has also had a role in the popularity of dirt racing. The most famous dirt races in the US include the Triple Crown series: the Kentucky Derby (which dates back to 1875), Preakness Stakes (first run in 1873), and Belmont Stakes (originated in 1867). These are known as the crown jewels of racing, with only 13 horses in history having conquered all three. A full list of 2024 Graded Stakes Races–meaning some of the most prestigious racing events around the country–along with their designated racing surfaces, can be found here. With many of the most prestigious horse races held on dirt, over time, US breeding of horses adapted from the more refined appearance of an English Thoroughbred, to a slightly stockier animal with a large shoulder and hip that can dig into the dirt with force.
Stay tuned for the next segment of our series, which will cover synthetic surfaces!