I know you're all opening a new browser window to find out what the title means. To save you a little time: Spurious is essentially defined as something that is plausible but ultimately deceptive. I think that is an apt description of speed figures. They look pretty straightforward and some people take them at face value but the deception lies in the fact that singular figures are very misleading.
The last 5 horses that entered the Derby off the highest last out Beyer Speed Figure all lost and only two of them even hit the board. Since the inception of Beyer Speed Figures the horses who could boast of having earned the highest figure in their final Derby prep went just 5 for 21. It may be seen as decent performance but these horses are often favored. 3 of the 5 winners were actually just the co-highest earners and some of them like Charismatic did get overlooked. But in general you'll have horses like The Cliffs Edge, Empire Maker and Bellamy Road.
Certainly there is a connection between speed and winning the Derby. The horse that runs the fastest race on the day gets to the line first and more often than not they receive a nice Beyer Speed Figure for that performance. The Average Derby winning Speed Figure since 1993 is 109.47. The record of horses that ran a 109 or more prior to the Derby is 23-4-2-2. That is a fairly successful group in isolation however you will find many years, like 2006 for example, that had no horses who had run a 109 prior to the Derby.
Another popular Beyer Speed Figure guideline is the 105 mark. Trainers are hoping that the Derby is their charges best performance ever. Many horses are still improving so it is not necessarily accurate to expect them to run fast enough to win the Derby prior to the Derby. The 105 mark became the benchmark because the majority of Derby winners had run that number. In the last 12 years there have been 62 horses that ran a 105 or more in a two turn race as a 3yo. Their cumulative record is 62-8-5-6, a flat bet on all of them nets you a tidy 64% ROI. So again we see a decent performance and a good return on investment as well. The problem with this statistic again is that in certain years you won't have any horses that ran a 105 in a prep. Is it then safe to conclude that no horses in that race are fast enough to win the Derby?
The obvious answer is that a horse will always win the Derby no matter how slow it is run. Horses do not have to win any past runnings of the race they only must beat the competition they face on that particular day. To truly come up with a number to determine who is fast enough to win the Derby you have to look at each Derby separately. The trick is finding out whether or not the horse is fast enough to win this Derby.
The method I came up with to quantify this idea is taking the average of every winning Beyer figure achieved in two turn graded prep races. But I only included the races that were represented in the Derby itself. For instance what bearing would the Arkansas Derby have on the Kentucky Derby is no one from that race was running?
What I found was that it eliminated far fewer horses but most importantly (and not surprisingly) every single Derby winner in the last 12 years was "fast enough" to win their Derby. The most important part of this factor is not the horses that it includes (which compiled a record of 124-12-9-11) but rather it is most useful for identifying horses to toss. Horses who did not achieve a Beyer Speed Figure that was equal or superior to the average two turn prep winning figure compiled a record of 89-0-3-1.
That's right, 89 starters and no winners, only 4 of them even managed to hit the board. 41% of the Derby starters in the last 12 years were not fast enough to win the race and almost none of them ran well. That is the real value of this statistic.
The downside to using this method is that it's not exactly clear who is or isn't fast enough until the Derby field has been drawn. In this day and age we seem to want to able to figure these things out months in advance. But there are a few ways you can rough a idea. In the last 12 years the average Beyer necessary to be "Fast Enough" has always been somewhere between 97 and 106.
I also have data from all the TC for 2004 to the present and a look at the average Beyers achieved so far in the prep races can give you a rough idea of how fast the current crop is.
Two Turn Prep Beyer Average (Jan-Feb)
2004 - 92.53
2005 - 90.92
2006 - 96.00
2007 - 91.86
2008 - 90.61
As you can see this year's prep races in January and February are the slowest in the last 5 years. They most closely compare with 2005 when Giacomo was the eventual winner. That may be slightly tempered by the fact that Santa Anita's prep races are being run on a different surface this year so the figures might be skewed. But overall the crop looks quite slow. It would not shock me if 97 ended up being the "Fast Enough" figure this year.