Roughly half of all thoroughbreds that have won the Kentucky Derby in the 21st century went on to win the Preakness Stakes. Most of the time with ease. And yet these same horses routinely fail at winning the last leg of the triple crown at Belmont.
Why is that? Why is it so common for a Derby winner and Triple Crown favorite to go on to win the 2nd leg so often, and then so rarely ever win the final big race at Belmont?
It comes down to 4 main reasons in my estimation, all with equally effecting points to consider:
1) Preakness Stakes is the shortest track. Belmont is the longest.
This is the easiest factor to point to. The numbers never change, and the variable hurdles are always the same. Pimlico Race Course for the Preakness Stakes is simply the shortest track:
Kentucky Derby length - 1 1/4 mile dirt track at Churchill Downs. --->>> 10 furlongs.
Preakness Stakes length - 1 3/16 dirt track at Pimlico Race Course. --->>> 9.5 furlongs.
Belmont Stakes length - 1 1/2 mile dirt track at Belmont Park. --->>> 12 furlongs.
This equates to shorter furlong stretches. A furlong is an 1/8 mile, and if the track's straightaway stretches have less of them, the horses will have less opportunity to use their fuel to outpace a lead horse. This equates to lead horses more easily being able to hold leads, while having to burn less energy to do so. Bodes well in favor of track favorites.
When it comes to the Belmont, the struggle is more apparent. Horses have more training geared toward shorter tracks, as the Derby and Preakness are similar in size, with the Belmont standing out as the real challenge to train for.
2) Less horses enter Preakness than Kentucky Derby, usually close to only half.
With the shorter track also comes less horses wanting/able to compete, compared to the Derby. Where the Derby typically has 18-20 horses, the Preakness typically has only 8-14 in the race. That smaller field of contenders for the favorite and Derby winner to overcome makes it all the more likely for a repeat win.
Especially when you consider that some of the other 'odds favorites' from the Derby that lost are more likely to opt out of the Preakness, as their Triple Crown prospects have been shot. They'd rather rest and then try to play the upset, come Belmont time.
Here are the number of horses that raced in each Triple Crown leg, from 2011-2015, to give you an idea of how the Preakness' competition is far less than it's 1st leg counterpart:
Kentucky Derby - 18
Preakness - 8
Belmont - 8
Kentucky Derby - 19
Preakness - 10
Belmont - 11
Kentucky Derby - 19
Preakness - 9
Belmont - 14
Kentucky Derby - 20
Preakness - 11
Belmont - 10
Kentucky Derby - 19
Preakness - 14
Belmont - 12
And the reason why I think that the field also being smaller at Belmont doesn't equate to the same edge is this --
3) Easier competition at Preakness; Belmont competition typically has much fresher legs.
Even though Preakness and Belmont routinely both see less horses on the track over the Derby, it also comes down to the level of competition that shows up.
Here's a real world example, to justify this thought. If you are a Derby odds-on favorite to finish in say a top 5 spot, and you do not win, you have the very real and appealing option to opt out of the Preakness race (that's just 2 weeks after the Kentucky Derby) and instead give your horse a valuable rest for Belmont.
Not having to race the Preakness, but instead waiting to play spoiler in the Belmont is a strategy many teams chose to go for. For if you race your horse in all 3, you are that much more likely to lose all 3. Better to hope to win the final leg, than assuredly be more likely to lose every single race. With a purse of $1.5 million at both Preakness and Belmont, it's no wonder why some opt to just race 1 or 2 legs, outside of the Triple Crown pursuer.
And last point here, if the current Derby winner wins the Preakness, that means that the best horse in the country at the moment is tired as hell. And much more likely to lose his final race, priming you to play spoiler. If no horse wins both first races, even better; that means the field competition is more proven to be wide open, and your horse has fresh legs. Decided advantage, always.
4) Momentum from Derby win, with less pressure than Belmont race.
This final point all comes down one of the most valuable phenomenons in all of sport, momentum. Much like the strange story behind running a faster than 4-minute mile, it's harder to pull something off until it's happened. And the more it's ever happened, the more likely it will happen again. This idea seems almost built-in to the laws of psychics.
Until 2015, no horse had been able to pull off the Triple Crown feat for 37 years. That momentum of failure has the feel to it that every horse that wins the first 2 legs are never the less fated to still lose at Belmont. History tells this story time and time again. Of course American Pharaoh bucked this drought. But that made history.
Taking all the factors into consideration, a Kentucky Derby winner is almost set up to win the Preakness. It's a shorter track, the shortest actually. Less horses enter than the prior race. Other favorites opt out. And they have the momentum of their last win.
But for all those reasons, in reverse, make it exceedingly difficult to win the Preakness AND Belmont. Belmont's the longest track. Different horses jump into this race, many being former favorites from the Derby that want to play upset, and are rested enough to pull off the challenge. And the pressure for a Derby and Preakness winner to go on to win 3 races in a row often times proves too daunting, especially to a horse that's usually the most tired of any other horse at Belmont Park.