Will Sunday’s warm weather drag down Chicago Marathon finish times? The data say yes.

Chicago Marathon
Runners participate in the Chicago Marathon on Sunday, Oct. 9, 2011. Nam Y. Huh / Associated Press
Chicago Marathon
Runners participate in the Chicago Marathon on Sunday, Oct. 9, 2011. Nam Y. Huh / Associated Press

Will Sunday’s warm weather drag down Chicago Marathon finish times? The data say yes.

The Chicago Marathon is back on after last year’s cancellation due to COVID-19. To mark the occasion, we’re breaking down some data from previous races.

Logistically, this year’s race will look different from previous ones in a few ways. In order to participate, registrants must provide proof of vaccination or negative results from a COVID-19 test administered 72 hours before the start of the race. Participants are encouraged to wear masks while in the start corrals and in tented areas, but they may doff them while running.

Still, if all goes smoothly, tens of thousands of runners and almost as many spectators will take to the streets on Sunday, just as before, come rain or shine — and as of Oct. 6, it looks like shine.

One of the hotter races

This year, you can expect sunny conditions with a low of 68 degrees and a high of 80 degrees — warmer than in past years but not unprecedented.

When it comes to weather, temperatures can impact your performance as much as anything. In 2007, race day conditions were so hot that hundreds of racers became dehydrated and ill and one runner died. By 11:30 a.m., about 3.5 hours into the event, the marathon officials called off the race.

According to a WBEZ analysis of climate data from the National Centers for Environment Information, temperatures on the past 10 race days ranged from the high 20s to the low 80s. Rain and wind were not usually much of a factor.

The data show that in general, the cooler the race day, the faster the average finish time.

The race kicks off in the morning, which is typically the coolest part of the day. The wheelchair and handcycle racers start first, followed by the runners in waves, with the last wave starting around 8:30 a.m.

Elite runners are more than twice as fast as the average marathoner

The first wave of the marathon is usually reserved for qualifying athletes based on previous race finish times. The fastest finish times over the past 10 years are tightly clustered around an average of 2 hours and 6 minutes. In 2017, Dennis Kimetto tied the 1977 race record at 2 hours, 3 minutes, and 45 seconds.

Brigid Kosgei
Brigid Kosgei of Kenya, poses with her time after breaking the world record with a time of 2:14:04 during the Chicago Marathon Sunday, Oct. 13, 2019, in Chicago. Paul Beaty / Associated Press

By the time the typical marathon winner has run the corner on Roosevelt approaching Museum Campus, the ordinary racer would have yet to cross the halfway point in River North. The average finish time is about 4 hours and 35 minutes — the same amount of time it would take to ride the ferris wheel at Navy Pier 19 times or listen to “LSD (feat. Chance The Rapper)” by Jamila Woods 79 times.

Racers must be able to complete the race in under 6 hours and 30 minutes, according to official marathon policy. Data from the past 10 races show that most do, but roughly 1-6% of racers take longer — sometimes several hours longer. The slowest finish time was in 2011, at 10 hours and 53 minutes; if the runner had started at 8:35 a.m., they would have crossed the finish line back in Grant Park at 7:28 p.m.

Runners from more than 160 countries have competed in the last decade of Chicago Marathons, but the race remains most popular with locals. More than a third of all runners from the past 10 races were from Illinois. The next two most represented states are New York and California, followed by our much closer neighbors, Indiana and Michigan.

Chicago Marathon
Runners start the Chicago Marathon on Sunday, Oct. 9, 2011. Nam Y. Huh / Associated Press

Over the past ten years, the race has had almost as many runners from Maryland (3,065) as it’s had from France (3,087), and three times as many runners from South Korea (384) as it’s had from Wyoming (128).

More men than women run the Chicago Marathon, and the number of racers in both sex categories have increased since then, according to data analyzed by WBEZ dating back to 2009. One in five of the female participants is between 25-29, and one in three is in their 30s. The age distribution among male participants over the past 10 years is more uniform, with near equal splits between runners between 30-34, 35-39, and 40-44.

Charmaine Runes is WBEZ’s data/visuals reporter. Follow her @maerunes.