As Spain began to emerge from the Franco Era, Herrero became the country's most promising international motorcycle racer until he died from injuries sustained while competing in the 1970 Isle of Man TT race.

He soon moved up to a Bultaco Tralla 125 and caught the eye of Luis Bejarano, the owner of Lube (a Spanish motorcycle marque) who recognized Herrero's talent.

Around this period, Eduardo Giró, lead designer of the Ossa motorcycle company developed a revolutionary bike with a monocoque chassis.

[2][3][5] Recognizing Herrero's riding talent as well as his mechanical skills, Giró offered him a job to develop the Ossa 250cc race bike.

[2][3][5] Herrero was able to take advantage of the Ossa's light weight and superior handling characteristics to remain competitive, especially on tighter race tracks.

[1] He followed this with third place at the Isle of Man TT, a considerable accomplishment considering his horsepower deficit on the infamous Snaefell Mountain Course.

[2] Most observers considered his championship hopes dashed, but Herrero showed true grit by coming back just three weeks later to finish in a remarkable fifth place at Imola.

Herrero crashed at the 13th milestone (Westwood Corner), losing control of his motorcycle on melted tar during the sixth and final lap of the 250cc Lightweight TT.

[2] Despite a previous setback at Braddan Bridge when he went up the slip road and crashed, breaking his windscreen, he had battled back up to third place.