Just over three weeks after he broke both the tibia and fibula in his right leg, Valentino Rossi (Movistar Yamaha MotoGP) secured a front row start at the Aragon GP and came in fifth in the race – having also held second for 11 laps. Such a finish was unimaginable only a few days before the race, and was made possible through Rossi's incredible talent - and through a specific braking solution Brembo made available to remedy the problem of having a right leg working at less than 100%: the special thumb brake master cylinder. This enables the rider to control the rear brake without using his right leg to operate a pedal. Instead, he simply relies on a small lever mounted under the left handlebar that is controlled by his thumb.
The Italian had already tested the system after the Brno race. The configuration he tested was the “standard” version with a thumb master cylinder and a pedal connected to the same rear master cylinder. With this version it isn't possible to operate the rear brake with the thumb master cylinder and the pedal simultaneously, only one of the two can be used. But after the injury, Valentino wanted a solution with two separate circuits in order to operate the thumb master cylinder and the pedal at the same time. Technicians made this change in record time with a new rear caliper.
Even though this technical solution was conceived of and built 25 years ago, only recently has Rossi begun to use it. It was Mick Doohan who asked for it when he was the victim of a serious accident during test runs at the Dutch GP in 1992. Dutch doctors had operated on his right leg but there were complications during the night that put him at risk of amputation. The Australian made an urgent call to Dr. Claudio Costa, who loaded him on a stretcher and brought him to Italy.
The founder of the Mobile Clinic managed to save Doohan's leg, however it never regained the strength it once had. Doohan was no longer able to operate the rear brake with the right pedal. He needed a control on the handlebar that could carry out this same function, and this is how the thumb-controlled rear brake master cylinder came into being. As the months passed, Doohan developed increased sensitivity and went on to win five consecutive World Championships in the 500cc class from 1994 to 1998.
So the thumb master cylinder is by no means new to MotoGP™. This solution has been adopted, with varying degrees of continuity, by Maverick Viñales at Movistar Yamaha and by Andrea Dovizioso, Jorge Lorenzo and Danilo Petrucci with Ducati. The manner in which Brembo's thumb master cylinder is used changes only slightly from rider to rider since all of them rely on it to slow the bike down in overtaking and to balance the bike when accelerating in order to avoid skidding in the corners.
Practically speaking, the thumb brake works like a kind of traction control: It is activated mid-corner in order to stay close to the tyre traction point, straightening out the bike as quickly as possible. And on right-hand turns, riders with big feet find it easier to use in the peak lean angle because there is no risk of the right boot making contact with the asphalt.