The granddaughter of the German immigrant blacksmith and carriage builder who invented the semi-trailer in Detroit 100 years ago has published a history of August Fruehauf's iconic Fruehauf Trailer Co. Ruth Ann Fruehauf will sign copies of Singing Wheels: August Fruehauf & The History of the Fruehauf Trailer Company from 2-5 p.m. Nov. 15 at the Detroit Historical Society, 5401 Woodward Ave.