We can start the answer by checking out the Guinness World Record which is 43.97 mph (70.76 km/h) over 2 furlongs. The horse was a thoroughbred racehorse named Winning Brew, a two-year-old filly. The world record occurred at the Penn National Racecourse, Grant Bill, Pennsylvania, United States of America on 14 May 2008. Two furlongs is 402 meters and Winning Brew covered the distance in 20.57 seconds. The Guinness record is not definitive because a horse may have run faster but no one was timing it or it was not reported to Guinness. For example it is said that some America’s quarter horses have been timed at 55 mph but the times have apparently not been formally recorded.
Over 1.5 miles (2,414 m) the fastest horse was three year old Hawkster at Santa Anita Park, Arcadia, California, USA on 14 October 1989. Hawkster covered the distance in two minutes 22.8 seconds.
Dr Desmond Morris in his book Horsewatching which was published in 1988 says that the record over a quarter mile was 43 miles an hour and at that time the speed was exceptional. He says the record over 3 miles was an average speed of 33 miles an hour.
Horses galloping flat out can regularly reach speeds in excess of 30 miles an hour. If they are healthy thoroughbreds they can maintain this speed for several miles.
Quarter horses race over short distances of a quarter mile and are trained sprinters.
Perhaps the most remarkable record of horse speed is Red Rum’s record for the Grand National which is over 4.5 miles. He covered the distance in 9 minutes 1.9 seconds in 1973 at an average speed of 29 miles an hour. Remember that this course is over jumps and they are very high and dangerous jumps as well.
Authors on the internet repeat the information that the Asiatic wild ass can run at 43 mph (70 km/h) I don’t have any firm confirmation of this but the Asiatic wild ass also has have a high level of endurance.
A horse with amazing stamina was Champion Crabbet who travelled 300 miles in 52 hours. This averages about 6 mph.
Why are horses so fast?
Racehorses are, of course, selectively bred and the founding horses are fine examples of fast horses. It is said that eighty percent of modern thoroughbred racehorses have in their pedigree an undefeated 18th century horse named Eclipse. The lady in the video, Melissa Mazan, Professor, Large Animal Internal Medicine, Cummings School of Veterinary Medicine at Tufts University says that also in their pedigree is a mare called Pocahontas (1837–1870). She was an English thoroughbed referred to as “one of the most influential thoroughbreds of all time, male or female” by Thoroughbred Heritage.
Fastest horse in South Africa
Kasimir is the fastest horse in South Africa at the date of this post:
KASIMIR(Captain Al) confirms his status as South Africa`s fastest race horse, winning today`s Mercury Sprint #Greyville
— Racing Guru (@RacingGuru) July 27, 2019
Note: Videos such as the one above sometimes stop working for reasons beyond my control. If it has happened I apologise.