Why can some series race in the wet and others can’t?

Whether a racing series can run in the rain comes down to a mix of track design, safety infrastructure, tire technology and vehicle type. It’s not just an arbitrary rule. 

Why F1, IndyCar and sports car road/street events can race in the wet 

• Purpose-built drainage: Road/street courses are designed with camber and drainage systems to help shed water, though standing water is still a risk in heavy rain. 
• Wet-specific tires: F1 and IndyCar carry dedicated intermediate and full wet tires with tread grooves designed to disperse water and reduce aquaplaning, unlike slick tires used in dry conditions. 
• Visibility systems: F1 cars are open-cockpit, but spray is managed somewhat by track layout, and races can be neutralized (safety car, red flag) if visibility becomes too dangerous. IndyCars have tear-off strips across the aeroscreens, and sports cars are equipped with single-blade windscreen wipers.  

Even with all of these, very heavy rain can still stop races. The 2021 Belgian GP and 2023 Japanese GP are examples where F1 red-flagged or delayed racing due to poor visibility and the risk of aquaplaning. 

Why NASCAR (and oval racing generally) mostly can’t race in the wet 

• No tire grooves for water dispersal: NASCAR's oval-racing slick tires aren't designed to channel water away like a road tire. They're built for maximum grip on dry pavement at sustained high speed, not water evacuation. 
• Banking pools water: Steeply banked ovals (especially superspeedways) cause water to pool in the corners rather than drain off like a flatter road course camber would allow. 
• Extreme speeds amplify risk: At 180-200 mph on an oval, even small amounts of water dramatically increase aquaplaning risk. It’s much more dangerous than the same water depth on a road course at lower cornering speeds. 
• No wet-specific setup: Oval cars aren't set up with wet aero or wet tire compounds the way F1/IndyCar teams prepare rain-specific setups. 

NASCAR has occasionally experimented with rain tires on road courses (a road course-specific wet tire developed a few years ago), showing it's technically possible when the track type suits it. The issue is fundamentally about oval tracks, not stock cars themselves.