You have to drive to work in the rain, so why can&#8217;t NASCAR race in wet weather?</p><p>For one, it would force drivers to slow down &#8212; and no fan wants that. More importantly, though, is the tires on the race cars.</p><p>According to Diandra Leslie-Pelecky&#8217;s book <em>The Physics of NASCAR</em>, the tires are totally smooth. No treads means better gripping of the track.</p><p>&#8220;Rubber has very good frictional properties,&#8221; Leslie-Pelecky writes. &#8220;When two metals rub, microscopic protrusions scrape along each other. Rubber, in contrast, deforms to wrap around protrusions and fill dips, which makes rubber ideal for producing grip. Goodyear develops different tire compounds for different races, taking into account track banking, speeds, and the surface type.&#8221;</p><p>At Kansas Speedway, where NASCAR will be racing this weekend, there is 15-degree banking in the turns.</p><p>While more friction equals more grip, it also means more heat and wear on the tires. The flat surface of a racing tire helps dissipate heat. NASCAR tires have a thinner treads (1/8&#8221; compared with 3/8&#8221; on a passenger-car tire), which helps with heat dissipation as well.</p><p>Each tire has five or six small holes known as wear pins or wear holes. Larry McReynolds, a race analyst, explained their purpose at Foxsports.com.</p><p>&#8220;Once the tire is used either in practice or the race,&#8221; McReynolds wrote, &#8220;you can get a lot of information from that tire like tire temperature and air pressure build up. But if you want to see how that tire is actually wearing, you go back after it has been run and check those wear holes after a substantial amount of laps.</p><p>&#8220;As the driver comes off the racetrack, so much debris and rubber has built up on the tires from them being hot. The only way to get back to those wear pin holes and get an accurate measurement is to scrape that build-up off. To do that a lot of times you have to take a putty knife or scraper and (blow-)torch it up a little bit to be able to get back to those wear pin holes.&#8221;</p><p>Another difference between your car and race car is the size of the tires. In particular, all four tires on the cars that will run at Kansas Speedway are not the same.</p><p>&#8220;At all races, except the two road courses, left-side tires have a slightly smaller circumference (the distance around the tire) than right-side tires: 87.4 inches vs. 88.6 inches for Atlanta,&#8221; Leslie-Pelecky writes. &#8220;The difference in circumference (called stagger) helps the car corner. The outer tires have to travel farther than the inner tires when the car turns. The larger right-side tire helps compensate for the longer distance.&#8221;</p><p>At Kansas Speedway, which is a 1.5-mile track, the tires all contain an inner liner, which is basically a second tire mounted to the rim inside the first tire. It has its own air supply and is required on tracks that are longer than 1 mile, so that if a tire blows, the driver can still control the car.</p><p>And while you put air in your tires, NASCAR&#8217;s pit crew takes it out. Most use nitrogen instead.</p><p>&#8220;Air is 78 percent nitrogen, 21 percent oxygen, and 0.9 percent argon,&#8221; Leslie-Pelecky writes. &#8220;The remaining 0.1 percent is a mixture of other gases. Air is mostly nitrogen already, so why bother with the 22 percent of air that&#8217;s not nitrogen? The problem isn&#8217;t the oxygen &#8212; it&#8217;s water vapor that is often mixed in with the air. The pressure exerted by water molecules in the tire can change significantly near water&#8217;s boiling temperature of 212 degrees Fahrenheit. &#8230; Small changes in that region can produce large pressure changes. Races are sometimes won and lost by thousandths of seconds, so a team can&#8217;t overlook any possible advantage.&#8221;</p><p>That&#8217;s why they rely on physics to help win the checkered flag.</p><p>TERMINOLOGY</p><p><strong>Friction</strong> is the force between surfaces that opposes their relative motion. The chief causes of friction are the interlocking of the minute irregularities on the rubbing surfaces, adhesion between the surfaces and the indention of the softer by the harder body. Friction between solid bodies may be classified as sliding and rolling.