Speed when unchallenged will usually win.

The past performances furnish what is called the Speed Rating. A formula is used to analyze the running times of horses in races, and then give a numerical statement of how fast they ran. This figure is the basis for speed handicapping.

The speed rating is derived from the track record
for that distance. The track record is 100. For every fifth of a second, faster or slower, a horse runs,
the number is adjusted. This figure reflects only
the finish time of a race, and ignores the earlier fractions of the distance.

The speed rating should only be used when comparing horses that have run at the same distance and track. Horses that acquired their
speed rating at another track were compared to
a different track record. This can be highly significant.

A major factor in the finishing time is the condition of the race track on the race day. In the maintenance of race tracks, the surface may be changed to add depth to the inner rail area. As time goes by, and races are run, this will change.

Another factor of finish time is the post position of a horse. Horses closer to the rail run shorter distances that the horse posted further out.

Speed ratings present a fairly accurate picture of the physical condition of a horse.  Increases or decreases in recent races become a major factor in determining the condition cycle that all horses go through.

A very successful speed handicapper is Andy Beyer.
Check out his several publications.

Since the inclusion of Beyer Speed Figures into the Daily Racing Form in 1992, horseplayers have had a new tool to use in their day-to-day handicapping. Learn what Beyer Speed Figures are, how they consistently point to the fastest horses in each race, and how to apply them correctly to produce winning wagers.  Speed to Spare written by Joe Cardello in a easy to understand fashion, the book provides useful examples of how to use Beyer figures and when the top figure is vulnerable. Very good treatment of bounces and form cycles. The statistical studies in the book are worth the price alone.

Anyone who has read Beyer on Speed should also read this!