The US GT Championships are open to any GT-style, four-wheel, closed-fender cars that meet NARRA safety requirements. The sanctioning body separates cars into four classes based on a sliding power-to-weight ratio: GT-U = No minimum weight/unlimited horsepower; GT-1 = 6.25 pounds per horsepower or more; GT-2 = 7.50:1 or greater; and GT-3 = 8.75:1 or greater.
Drivers must provide a "dyno affidavit" of their car's horsepower from an accepted commercial facility, NARRA said.
NARRA did not specify which Pirelli tire or tires will be used. Pirelli replaces Hoosier as the US GT Championships' spec tire.
Pirelli's deal on the Viper Cup parallels Pirelli's gaining the OE fitment on the 640 horsepower V10-powered 2013 STR Viper and Viper GTS with its P Zero and P Zero Corsa UHP radials. Pirelli replaces Michelin as the Viper series' spec tire.
Having a quality spec tire creates a level playing field for all drivers and takes the unknowns, and expense, of tire choice out of the equation, NARRA said.
To encourage new USGTC and SRT Viper Cup entrants, NARRA is offering a one event "grace period," where competitors will be allowed to try out the new control tire before committing to the entire series.
Regarding the Whelen US TimeTrial Championship, JX2 and Pirelli will offer a contingency of up to six sets of Pirelli performance tires for top finishers, and NARRA will award 10 bonus championship points to competitors using Pirelli tires supplied by JX2.
The USTTC uses the same power-weight ratio formulas for entries; competitors, however, compete against the clock rather than head-to-head.
JX2 Performance Group is a Greenville, S.C.-based motorsports marketing agency and race tire distributor.
NARRA has scheduled nine race weekends for the USGTC and SRT Viper Cups. The season started Feb. 15-17 and runs through Nov. 22-24 at Sebring International Raceway.
