Every year, the Peachtree Road Race presents a new challenge for Ty McCormack. On Monday, it was the unusually excessive morning heat — almost 80 degrees — for the 10-kilometer Independence Day race through the streets of Atlanta. “I’d say it probably was the warmest it’s been in any Peachtree I’ve run,” said McCormack, who started with the Elite A Division around 7 a.m. in the world’s largest race of its size.