Driving the 2015 Mazda MX-5 Miata roadster is like letting loose of heavy burdens. The smartly styled, 13-foot-long two-seater is so efficient in design, there’s not a lot of room to carry extra baggage. The car, itself, weighs less than 2,600 pounds and is energetic and eager to dash down the roads in a lighthearted and sprightly manner. Heavy thoughts and responsibilities go out the windows as the Miata, with close to 50-50 front-to-rear weight balance, takes curves as if it’s on rails. Put down the Miata’s soft- or hard-top roof and the drive can be a tonic — full of sun, warmth and energy. No wonder the rear-wheel drive MX-5 Miata, now in its 25th year, is in the Guinness World Records as the best-selling two-seat roadster on Earth. More than 900,000 of the cars have been built. U.S. models come from Mazda’s Hiroshima auto manufacturing complex.