Wes Duenkel
September 8, 2015

Some consider the SCCA’s Trans Am series of the late ‘60s and early ‘70s to be the high water mark of production-based sports car racing in the United States. And in some respects, it was. But manufacturer-supported street-stock endurance racing didn’t die with waning interest in the Trans Am. The assembly line-to-racetrack concept lives on in the IMSA Continental Tire SportsCar Challenge.

The popularity of the Trans Am series was fueled by fans eager to see their favorite sports cars battle for bragging rights, and manufacturers eager to capitalize on a “win on Sunday, sell on Monday” marketing opportunity. Sure, the Trans Am series carried on, but the purpose-built tube-frame halo cars competing under today’s Trans Am banner are a far cry from what fans find in their garages. Other street-stock endurance road racing series picked up the pieces of the original Trans Am formula and kept the concept alive. Shared fan and manufacturer interest in racing cars that fans drive every day makes the IMSA Continental Tire SportsCar Challenge one of the most exciting road racing series today.

The 2015 IMSA Continental Tire SportsCar Challenge consists of ten 2.5-hour endurance races. Two drivers share a car, and must both drive at least 45 minutes to earn championship points. Dean Martin and Roddey Sterling drove Rehagen Racing’s MoonPie-sponsored Ford Mustang Boss 302R during the 2013 season.

On the track and in the showroom, the stakes are higher than ever. Manufacturers are again selling street-legal performance variants of their hot-selling sports cars so they can take them racing. Shoppers are again ticking order sheet boxes next to names like “BOSS 302,” “Z/28,” and “GT350.” So it seems only natural that manufacturers and fans are interested in watching their favorite sports cars battle door-to-door on America's legendary road courses.

The 2015 IMSA Continental Tire SportsCar Challenge consists of ten 2.5-hour endurance races. Two drivers share a car, and both must drive at least 45 minutes to earn championship points. Each car carries about a 20-gallon fuel load—enough for about an hour of green-flag running. So, most races include two pit stops where crews can change drivers and tires. Races are run in all conditions (provided the track surface isn’t flooded or there’s lightning).

As with most sports car racing, multiple car classes share the track simultaneously, and compete for individual class honors. There are two classes: ST, and GS. The former class includes smaller-displacement cars such as the Honda Civic, Porsche Cayman, Mini Cooper, and Audi S3. Faster cars such as the Camaro Z/28, Shelby GT350, BMW M3, Aston Martin V8 Vantage, Nissan 370Z, and Porsche Carrera GTS race in the GS class. While the format has remained “street stock” over the decades, the rules have evolved to accommodate more advanced safety equipment, and specified modifications to each type of car to somewhat level the playing field.

Racing modified production cars sometimes means things break—like engines. Teams come to the track with spares and the tools to complete the job quickly.

To keep one model from dominating the class, IMSA officials adjust each model’s relative performance via a combination of factors, including engine air inlet restrictor size, minimum vehicle weight, and engine RPM limit. For example, a Camaro Z/28.R must use a 60mm intake restrictor, weigh 3,575 pounds, and the engine cannot exceed 6,400 RPM. A Shelby GT350R-C uses a 58mm restrictor, weighs 3,400 pounds, and cannot exceed 8,200 RPM. By contrast, a Porsche Carrera GTS can weigh as little as 3,075 pounds and doesn’t require an engine restrictor or an RPM limit. All the cars use Continental Tire racing slicks.

Additionally, IMSA officials monitor car performance with small data-logging boxes mounted inside select cars. The data these boxes gather are used to determine if the officials are getting the formula right, or if further adjustments are necessary.

To keep a model from dominating the class, IMSA officials adjust each model’s relative performance by mandating a combination of several factors, such as engine air inlet restrictor size, minimum vehicle weight, and an engine RPM limit. Here, a technician prepares to install an IMSA-supplied restrictor in the air box of a BMW M3.
In this highly competitive racing series, every little bit counts. Drivers and engineers use data gathered from on-board cameras and loggers to hone their driving skills and chassis setups for maximum performance.

Because the series requires two drivers per car, many entries are of a “pro/am” nature (a professional racer shares the car with an amateur). It’s a symbiotic relationship where the professional is paid to race with the amateur in return for helping the amateur improve his/her racing skills—and chances of winning. Typically, the amateur will start the race, and the professional driver will finish. Drivers that start the race also must qualify the car for its starting position. The pro/am makes the series extremely competitive, as it attracts many of the top drivers in sports car racing. Amateurs also have a unique opportunity to test their mettle in competition with the best in the sport.

Because of the multiple pit stops, driver changes, and two classes of cars involved in each race, strategy plays a huge role in winning an IMSA Continental Tire SportsCar Challenge race. Often times, it’s not the fastest drivers or cars that win the race, but rather the strategist calling the shots from pit lane. Fuel economy, tire use, caution periods, track position, and weather conditions all must be mastered to spray the champagne in victory lane!

The high-stakes nature of each race, manufacturer involvement, and nationwide television coverage make the IMSA Continental Tire SportsCar Challenge one of today’s most competitive and popular road racing series.

Prior to the start of every race, officials open the grid to spectators during the “Fan Walk.” It’s a great time for fans to see the cars up close, get their favorite driver’s autograph, and wish him (or her!) luck in the race.
A diverse field of makes and models makes the IMSA Continental Tire SportsCar Challenge popular with fans.

Photo Gallery

View Photo Gallery