Racing in the Rain

The NASCAR XFINITY race at Charlotte Motor Speedway — aka the Roval in the Rain — prompted some fans to suggest NASCAR ought to be able to race anywhere in the rain. But ‘can’ and ‘should’ are two different concepts. Let’s see what science has to say about it.

The Roval in the Rain

Let’s start by comparing this year’s XFINITY Roval race with the two previous years for which we have data.

Cautions

The Caution-O-Gram breaks down how many laps were run under the green flag vs. the yellow. Additionally, I color code the yellow-flag laps to identify the cause of each caution.

Comparing the caution-o-grams for the XFINITY Charlotte Roval races. The 2020 race was run in the rain.
The 2020 race (top) was run in the rain, while the 2019 (middle) and 2018 (bottom) were dry.

The Caution-O-Gram shows how much the race run in the rain differed in character from the non-rain races.

Firstly, when accidents happened during the race is different. There were no accidents until the third stage in the first two years. This year, the accidents happened in Stages 1 and 2.

Secondly, there were more stalled cars this year, and those stalls happened at different points in the race.

There was only one stalled car in each of the first two years. Both times, the stalls happened near the start of the first stage. Of the four stalled cars in 2020, all occurred in the last half of the race.

Finally, there were not only more cautions with the rain, but the cautions lasted longer.

2020201920182018
(norm)*
Cautions10756.1
Caution Laps24141012
Because the 2018 race was shorter, I normalized it to 67 laps in the last column.
A column chart showing the larger percentage of the race run under caution in 2020, when it rained.

Because cautions increased, the average length of a green-flag run dropped.

Racing in the rain decreased the average length of a green-flag run.

Finishing and Playoff Contenders

A lot more cars (almost double the number) didn’t finish the 2020 race. There were 6 DNFs in each of the first two XFINITY Roval races and 11 this year.

A column chart comparing the percent of dnfs at XFINITY races at the Charlotte Roval from 2018-2020

Perhaps more importantly, 3 of the 11 DNFs this year were playoff contenders, whereas no playoff contenders DNFed in previous years.

Two of the DNF cars in 2020 led laps, but no car in previous years that failed to finish the race led any laps.

Any Positives?

Yes. There were more lead changes; however, we know that:

We also had more green-flag passes and more quality passes. Note the low ratio of quality passes (passes of cars in the top 15) to total passes at all the Roval races.

The passing at the 2020 XFINITY Roval race was up, despite the rain.
As a percentage, quality passes were 18.8% of total passes in 2018, 19.6% in 2019 and 24.5% in 2020

Time: Not on My Side

If you go by laps, this year’s XFINITY Roval Race was 35.3% cautions. But the reality is even worse because caution laps take a lot more time than green-flag racing laps.

2020201920182018
norm
*
Time of Race2:43:052:06:301:32:351:52:46
Red Flag38:22000
Total Race Time (min:sec)201:27126:30112:46
* Because the 2018 race was shorter, I normalized it to 67 laps in the laps column

The 2020 race was 75 minutes longer than the 2019 race, which was only one lap shorter. That’s about 1.6 times longer because of the rain.

Using timing data from Timing 71, let’s break down how long we spent under each flag.

A pie chart that shows how the 2020 XFINITY Charlotte Roval was divided among time for green, yellow and red flags given the rain.
Many thanks to NASCAR’s Josh Hamilton, from whom I learned that the red-flag time is not included in the total race time reports.

The surprising result is that we spent a little more than 1/3 of the race time under the green flag.

While some people may say that excitement (in the form of crashes) might hold viewers to the television longer, I got a little weary. The cars just kept crashing! No one wants to watch three hours of cars running a few green laps and then crashing again.

Talladega in the Rain?

Let’s consider the most extreme case: Talladega. Why not race in the rain there?

Accidents and Safety

I’ve explained before the physics of racing in the rain: the need for different tires and the dangers of hydroplaning. But let’s also remember that rain tires are necessarily softer than slicks to improve the grip.

We saw tire chunking — blocks of tread breaking off — at the Roval this year. A 33-degree banked turn would stress rain-tire tread even more. Not only would we need to worry about blowouts and accidents, we’d probably need a lot of tires. That means more cost to already struggling owners

Talladega already eats a lot of cars. Combine rain with pack racing and we’ll have more accidents and even more torn-up cars.

The number of cars involved in accidents almost doubled in the rain at the Roval. In fall 2017 at Talladega, 26 out of 40 cars didn’t finish the race. Double that, and we end the race early with the last car on track proclaimed the winner.

Talladega without Drafting?

Rain means slower speeds because tires have less grip. That, in turn, might translate to drivers not having to run every lap with the throttle wide open.

And that might mean they don’t have to draft. Is it even Talladega if there’s no pack?

And even if they can draft, do you really want someone following a few inches behind you at high speed when they can’t always see where they’re going?

Time

The last race at Talladega (October 2020) was just over four hours, including two ten-minute red flags for accidents. 27% of the Talladega race was cautions if you count by laps run. But again, caution laps take longer than green-flag laps.

At 70 mph (caution car speed at Talladega), one circuit would take around 137 seconds. A green-flag lap typically takes about 49 seconds, so that’s almost three times longer for a caution lap than a green-flag lap. If we had the same percentage of caution laps as at the XFINITY Roval in the Rain, we’re talking 94 caution laps. Now the race is approaching five hours.

We’re not just talking a really long race, but one with a lot of accidents and cautions in the first two stages. I bet a lot of people turn off the television set.

Conclusion

So even if you could race in the rain at a track like Talladega, what kind of a race would it be? Is it worth the risk to drivers and track personnel, point standings and owners to run a race with a lot of opportunity for catastrophe?

Most importantly, would it even be fun to watch?

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