Wednesday, April 10, 2013

What Makes a Race Competitive? A mathematical look at the factors that cause more lead changes in a race.

(This is a cross-post with

Lead changes in any NASCAR race are always a big topic in the media. Lead changes are used as a barometer for how entertaining or competitive a race is from a product and TV spectator standpoint. To give you a reference point, on average there were about 20 lead changes per race in the Chase Era.

What if we could predict lead changes? Let's look at the factors that cause lead changes to vary in a race.

For this exercise, we look at all the races in the 9 full seasons of the Chase Era (2004-2012), or 324 total races.

After running many linear regressions with various combinations of factors, here are the four that dominate how many lead changes a race will have:

Length of Race (in miles, not laps): Every 100 miles adds 4.7 lead changes.
Number of Caution Laps: Every 20 laps of caution adds 1.5 lead changes to the race.
Restrictor-plate race: Being a plate race itself adds 22 lead changes on average.
Saturday race: The effect of racing on Saturday decreases lead changes by 2.6 on average.

What Can We Infer from These Factors?
  • Obviously the longer a race, the opportunity for more lead changes can only increase, not decrease.
  • The more caution laps in a race, the more chance for different pit strategies, problems on pit road for the leader, drivers staying out during the pit sequence to pick up a lead lap bonus, bunching up the cars on restarts so that somebody else could take the lead.
  • We know plate racing has always resulted in more lead changes (because the cars are all bunched up together, racing in a large pack), now we have quantified that factor.
  • The one factor that sticks out is Saturday racing. There are fewer lead changes for a Saturday race. Why is that? Does the shorter week make it harder for teams in the shop to work on their cars and get them ready for the weekend? Do the Saturday races have compressed practice schedules, making it harder for the lagging teams to improve their cars? Is it because Saturday races are usually at night, and the cooler temperatures make it harder to compete? This is a very interesting factor to focus on in the future.

These four factors explain almost 60% of the lead changes in any race.

Now let's focus on the factors that DO NOT have a statistically significant effect on lead changes in a race, even though a lot of these might get discussed in the media as having an effect:

  • Month of the year: Lead changes don't change over the course of the year.
  • Number of LAPS in a race: As we saw above, it's the race length measured in MILES that matters, but not the number of laps.
  • Road course: Races at Sonoma and Watkins Glen don't affect lead changes.
  • Track Length: Whether the track is half-mile Bristol or 2.5-mile Pocono, this doesn't affect how many lead changes will occur.
  • Race speed: Some tracks are faster than others, and average speeds can vary from track to track. But this is another area where there is no effect on lead changes. This is interesting because it suggests that you don't need a fast track to have a more competitive race.
  • Winner's Starting Position: One factor considered was the original starting position of the winner. If a winner started on the pole, versus if the winner started way in the back of the pack, would that make an impact on lead changes? Nope; theoretically, this suggests that inverting the field (starting the fastest cars in the back) would not increase lead changes. (This finding is not terribly surprising: remember my earlier post showing how starting position often has little bearing on finishing position.)
  • Race purse: Here's one more interesting, unexpected quirk from the data: the amount of money at stake does NOT increase the number of lead changes! In fact, there was one FEWER lead change for every extra $734,000 added to the average's race purse.

In conclusion, what have we learned today? We learned that the number of lead changes is a number that doesn't move on most factors. Even factors that you would think might make a difference (namely race speed, track length, amount of money at stake) don't actually contribute much at all. Ironically, so many of the changes that are suggested to make races more viewer-friendly (shorter distances, fewer cautions, more Saturday night races) all actually reduce the number of lead changes!