The three races were never design to be equal. The conditions change, race
length changes and who knows what the horses feel like at any given time.
Here are the race tracks involved:
1.Kentucky Derby, run over the 1 1/4-mile (2.0 km) dirt
track at Churchill Downs in Louisville, Kentucky;
2.Preakness Stakes, run over the 1 3/16-mile (1.9 km) dirt
track at Pimlico Race Course in Baltimore, Maryland;
3.Belmont Stakes, run over the 1 1/2-mile (2.4 km) dirt
track, the longest in USA thoroughbred racing, at Belmont
Park in Elmont, New York,
The races are those distances, not the tracks. Just that Belmont runs one perfect circuit around for the stake.