Q. On Monday, May 20, the Spring Oaks at Parx was given an 82 Beyer. The final time was 1:43.95 for 1 mile and 70 yards. The very next day with no rain to really affect the surface at Parx, the winner of the Spring Derby was awarded an 88 Beyer. The final time was 1:44.59. How can his Beyer be six points higher when he ran three&#45;fifths of a second slower?&ndash; John O&rsquo;HaraA. We get many questions along these lines, and the explanation is usually the same: Racetracks change. They can change significantly from one day to another, even if there is no change in weather and the track is labeled fast on each day. That&rsquo;s what happened at Parx.If you look at the results for the two cards, you will see clearly that the racing surface was very fast on May 20 &ndash; fast enough that a $5,000 claimer ran six furlongs in 1:09.94. On May 21, the track had become much slower. Parx ran three six&#45;furlong races and they were all run in 1:13.55 or slower. To calculate the Beyer Speed Figures, we analyze every racing card to determine the speed of the racing surface. Parx was 11 points faster on May 20 than it was on May 21, explaining the difference in figures for the two stakes.