# Can We Race Stockcars in the Rain?

NASCAR and Goodyear are ready for rain at a road course with rain tires. But is that all you need race safely and competitively in the rain?

## Why Rain Makes Racing Hard

In sportscar racing, teams simply trade out their normal “slicks”  (which have no treads) for rain tires.  In NASCAR, at all course except road courses, we just stop and wait for the rain to let up.

Slicks maximize how much rubber is gripping the road at any given time.  The contact patch (the part of the tire in contact with the road) for a NASCAR tire on a Cup car is about the size of a man’s size 11 average width shoe — which isn’t all that much considering that those four tiny patches of rubber are responsible for 200 mph speeds.

the coefficient of friction tells you how grippy your tires are. The higher the number, the grippier the tire.  Regular car tires have a coefficient of friction with dry asphalt between 0.7-0.9.  That number drops when you make the asphalt wet — to as low as 0.25-0.50.  (These numbers are ranges because the specifics – the type of asphalt, how old it is, the oil content, the specific type of rubber, etc., all affect the coefficient of friction.)  Race tires on dry asphalt have coefficients of friction between 1.1 and 1.3 or so, but they drop even lower on a wet track.

Water gets between the tire and the road, decreasing friction and thus grip.  Even a very, very thin layer of water can cause hydroplaning. The faster you drive, the smaller the contact patch, and the more likely you are to hydroplane.

## Goodyear’s Solution for Racing in the Rain

Goodyear’s rain tires have grooves — just like passenger car tires.  The grooves point away from the center of the tire in the middle.  The pressure of the tire on the track pushes water away from the flat spots and into the grooves. The grooves give the water a way out from under the tire.

Goodyear supplies tires for other series, which has given them lots of experience with developing tires for racing in the rain. But it’s still a challenge.

In passenger cars, hydroplaning can happen at speeds as low as 35 mph. In the 2008 Montreal Cup race, the average speed went from 90 mph to 75 mph when the rain tires went on.

## Other Rain Considerations

In addition to tires, there are some other issues with racing in the rain, most of which have to do with visibility. All the traction in the world doesn’t help if you can’t see where you’re going.

### Windshield Wipers

Windshield wipers have to do a whole lot more work on a race car. Because high speeds mean that more spray from cars in front of you hits your windshield.

You also have to worry about tear offs, because you’re still going to get gop on your windshield. Your wipers have to work with the tear-offs.

### Condensation Inside

Remember Carl Edwards at Montreal in 2008 with a Swiffer mop trying to clear the fog from the inside of his windshield?  Moist air will condense on any cold surface.  Windshields are made of good thermal insulators, so it’s inevitable that you are going to get condensation.

A defogger uses heated air to increase the temperature of the windshield to prevent condensation. Most passenger car systems also pass the air through a dehumidifier so that you’re not making the problem worse by increasing the moisture content. That’s a lot of stuff to cram into a stockcar.

### Brake Lights

Race cars don’t usually have brake lights, although they have been used. In the aforementioned Montreal race, Joey Logano wrecked under caution when someone stopped in front of him and he didn’t see them.

And, of course, if we give the drivers brake lights, they will start playing mind games with each other.

### Safety

Rain, as you know, is often accompanied by thunder and lightening.  Lightening killed one fan and injured several more at Pocono in 2012.  The drivers are good: They’re essentially in Faraday cages. Your car is one of the safest places if you’re stuck outside in a thunderstorm. But spotters, pit road officials, etc. are all out there in the elements. Pit crews face additional hazards, including slipping (them and/or the car).

## Conclusion

Can stockcars race in the rain? They can, under some limited conditions. But it’s much harder for the drivers, the crew and everyone involved. Sometimes, the smart thing to do is wait and hope the rain delay is shorter rather than longer.

NOTE: I spiffed up this blog was spiffed up on 2020-10-08 by editing it for clarity and length.

1. Skip says:

A lot of that already exists – they ran the Nationwide race Montreal in the rain a few years back. The race started in dry conditions, and at lap eight the rain started, so everyone came in, installed brake lights and windshield wipers, put on rain tires, and went back out.

Now, the racing wasn’t very good, but they did mostly get it done.

2. Tim Woskobojnik says:

Good, well rounded coverage of the subject. Thanks again.

3. Edward Washington says:

NASCAR drivers are “the best in the world”? Really? If that is the case, then why is Formula One the only series to declare it’s champion as “World Champion?” The answer to that is simple. NASCAR drivers are NOT the best drivers in the world. The only people who believe otherwise are those who are too narrow-minded to see beyond their myopic views. Best stock car drivers? Maybe. Best drivers in the world? NOT EVEN CLOSE!!!!!!!.

• Sorry, Edward – I should have used the tag around “best drivers in the world”. Long-time readers of this blog know that I am disproportionately amused by the overblown hype surrounding NASCAR. It’s typically American – we have a World Series that only covers North America. Anyway, it was meant to be ironic, not literal.

4. Lucas says:

While I see your point, the NNS cars do have a single brake light in the rear windshield when they race on road courses. It is turned on only when it rains. Also, the NNS teams have developed a downforce device to put on the windshield wiper to make sure they do not fly off. This was done after the first time they raced in the rain. I believe racing in the rain is possible. The first NNS race in the rain was terrible because it rained too hard to race. I think even F1 would have stopped the race due to the conditions. The second time was much much better. They can race when the track is a wet after a rain or when it’s raining lightly. No one can race in a monsoon, like they had in the first race in the rain. I am unsure of the vehicle dynamics of it all, but I will know in the coming months.

Just thoughts from a Motorsports Engineering Student

• Welcome, Lucas – thanks for the comments and great to have a motorsports engineering student reading! I think the question almost becomes “Is it worth racing in the rain?” They get so little opportunity to do it — Each race is likely to feature some problem until they’ve raced enough races to encounter them all. Personally, I like watching the sportscars in the rain – you can see the aerodynamics patterns in the water coming off the rears of the cars! Thanks again!

5. Steve D says:

I road race motorcycles with enough success to have won a few national championships. When it’s raining, one of our favorite sayings is “This isn’t NASCAR”. If we can race in the rain on 2 half dollar sized contact patches, with power to weight ratios and top speeds comparable to NASCAR on 1/1000th the development budget, there is no technical reason why NASCAR cannot do the same.

Rain tends to separate the men from the boys regardless of that last 5% of mechanical advantage.