This is the story of an innovation that was all of those things combined, but that changed forever the way motorcycle brake systems are designed. An innovation so bold it was labeled heretical, and that, because of its revolutionary nature, required patience, tenacity, and above all, time to be truly understood and appreciated.
This is the story of the radial-mount caliper, and how Brembo turned it from an idea considered too daring even for the extreme world of racing into a component capable of enhancing the everyday riding experience of millions of motorcyclists.
We are in the early 1990s, and Brembo is already the undisputed leader in racing motorcycle brake systems. A journey that began less than 20 years earlier, in 1972, when Brembo produced its first motorcycle caliper intended as OEM equipment for street bikes, had already reached the peak of success with Brembo brakes featured in the 500cc class of the Motorcycle World Championship, the highest expression of motorcycling in the world.
In those years, all motorcycles, including those competing in top-level racing, were equipped with brake calipers featuring axial mounting to the fork.
In such a system, the bracket anchors the caliper only at the upper point near the fork, while the lower point remains free. When the pads come into contact with the disc, the disc applies a twisting force to the caliper in the direction of rotation.
It was the most natural, logical, and simplest solution to manufacture, especially with traditional forks where it’s sufficient to cast two mounting tabs on the fork leg.
The downside of this solution is that, with the lower end free, the entire caliper could undergo significant deformation during braking. The deformation created problems, since it is the caliper’s rigidity alone that ensures proper positioning of the friction material on the disc surface.
This problem became particularly evident with the significant increase in grip provided by slick tires, introduced in Grand Prix racing at the end of the 1970s, which allowed unprecedented lean angles. But when the lean occurred on a bumpy section, the pads would end up hitting the discs. So, at the next braking point, the lever had to be pulled twice, because the first pull produced no braking effect.
Don’t miss this!
Despite this, especially due to the lack of alternatives, until the 1990s the axial-mount caliper remained the model to follow for the entire motorcycle sector — alternatives were not even considered.
All the top 500cc teams used Brembo brakes, and the Italian company’s technicians were respected and appreciated in the paddock both for their expertise and the quality of Brembo components.
For Brembo, everything was going smoothly, and there would have been no reason to risk new and uncertain solutions.
Indeed, in those years, all the most competitive 500cc teams used Brembo brakes, and the Italian company's technicians were highly respected and valued in the paddock, both for their competence and for the authenticity of Brembo components.
Nevertheless, in the creative minds of Brembo engineers, an idea for a seemingly revolutionary motorcycle brake caliper began to take shape.
The inspiration came from a world both close to and distant from motorcycle racing: Formula 1. The company had been active in Formula 1 since 1975, and as early as 1982 had introduced radial-mounted brake calipers for single-seaters with excellent results.
Thanks to the experience gained and the awareness of the advantages offered by the radial system compared to the axial one, Brembo engineers began considering the idea of applying the radial mount concept to motorcycles.
Mechanically, radial mounting would allow greater stiffness in the caliper, which, by following the rotation of the disc, would be subject to less mechanical stress, and therefore less deformation.
In the radial-mount caliper, the lower part of the caliper is no longer free but solidly anchored to the structure. This would allow the caliper and fork to behave as a single unit, resulting in multiple benefits.
On the one hand, the radial mount would offer significantly greater resistance to torque compared to an axial caliper precisely because it minimizes elastic deformations (which absorb energy from the braking system). On the other hand, in addition to ensuring a significant increase in braking efficiency, the radial mount would eliminate dead travel in the brake lever caused by misaligned pads after road irregularities.
Aware of the boldness of the idea, before building a prototype, they decided to submit some technical drawings to someone considered a true guru in the motorcycle world — a man of great charisma and experience: the Japanese technical director of the Honda Racing Team.
Unfortunately, presenting the sketches resulted in bitter disappointment.
The Honda technician closed the folder of drawings with a confused expression, pushing them away. He not only believed the solution was unfeasible, he even considered it sacrilegious — comparable to mounting a steering wheel on a motorcycle.
A rejection of such weight from one of the top experts in the field would have discouraged anyone. In fact, Brembo temporarily shelved the idea. But it was only a pause for reflection.
Brembo’s axial calipers had no rivals and continued winning in the 500cc class. In the years that followed, they earned seven world titles: two with Yamaha’s Rainey and five with Honda’s Doohan — all equipped with Brembo braking systems featuring axial calipers. But Brembo’s engineers couldn’t stop thinking about the radial-mount caliper. They firmly believed that, by anchoring the caliper to the fork, the entire braking system could be made more rigid, with a significant improvement in performance.
Mechanically, radial mounting would allow greater stiffness of the caliper, which, combined with more precise pad positioning relative to the disc, would provide the rider with better braking feedback. Moreover, radial mounting would allow for easy increases in disc diameter.
It was just a matter of waiting for the right moment.
The opportunity came a few years later. It’s 1997, and Aprilia — then going head-to-head with Japanese giants in the 250cc World Championship and constantly seeking technical solutions to gain a competitive edge — asked Brembo for something innovative. Brembo’s engineers didn’t need to be asked twice and returned to the idea of the radial-mount caliper.
The enthusiasm from Aprilia and the renewed energy of Brembo’s engineers led to new drawings and thoroughly developed tests. The time had finally come to go from paper to prototype.
Confident in the project, Aprilia decided to test the product with test rider Marcellino Lucchi during private tests at the Jerez circuit (Spain) in February 1998. Lucchi was immediately enthusiastic, and in the following days, Aprilia’s other riders — Tetsuya Harada (1993 250cc World Champion), Loris Capirossi (two-time 125cc World Champion), and Valentino Rossi (newly crowned 125cc World Champion) — also successfully tested the new Brembo calipers.
The radial-mount caliper made its debut in the opening race of the 1998 World Championship in Suzuka (Japan). The new technical solution used by the Aprilia 250s caused a stir in the paddock, and skepticism wasn’t lacking. But when, in the next race, Aprilia nearly scored a 1-2 finish (Harada won, Rossi crashed on the final lap while in second), everyone realized the radial-mount caliper was the future.
For Aprilia, it was a triumphant season with 12 Grand Prix victories and the top three positions in the final championship standings: Capirossi champion, Rossi second, and Harada third. Suzuki was the first to introduce the radial caliper in the 500cc class in 1999, achieving a surprising second place overall. Kenny Roberts Jr. started the season with Brembo axial calipers and switched to radial ones during the year, scoring the first-ever 500cc win with Brembo radial-mount calipers.
But this was only the beginning — because the following year, Yamaha also switched from Brembo axial calipers to radial ones, yet it was the American Suzuki rider who took the world title: the first 500cc World Champion with radial-mount calipers.
From that moment, radial calipers saw increasing use on track. Within a couple of years, every team — including Honda — rapidly adopted Brembo’s more effective new solution.
From Grand Prix racing, Brembo’s radial calipers moved to Superbike, and then trickled down to lower-level competitions. For riders, it was love at first feel, and axial calipers were quickly replaced on racetracks all over the world.
Even the same Honda Racing Corporation (HRC) technical director, with great grace and elegance, admitted he had been wrong and apologized to Brembo’s technicians for his earlier harsh response. After all, since MotoGP’s debut in 2002, every GP has been won by motorcycles with Brembo radial-mount braking systems.
The leap from the racetrack to production motorcycles came quickly. The extraordinary effectiveness proven on track provided full assurance for mass production. The final taboo was about to fall, and once again, Brembo succeeded in its mission — to transfer innovation and know-how from racing to the road, making it available to all riders.
Once again, the company from Noale believed in the concept. In 2003, aiming to relaunch the latest evolution of the RSV Mille R, Aprilia decided to equip the twin-cylinder with a pair of newly designed Brembo calipers derived directly from racing. The RSV Mille R thus became the first road motorcycle equipped with radial-mount calipers. The innovation was soon adopted by other manufacturers who feared being left behind.
On production bikes, the radial-mount caliper confirmed all the advantages proven on track and added more. Being free from any transverse constraints, the caliper better adapts to small disc oscillations during rotation, allowing the pads to contact the maximum useful surface of the disc; this not only improves braking but also benefits the life of the friction materials, which wear more evenly.
After initial adoption on supersport bikes, radial calipers began spreading to naked and touring models. Today, there is no category — including scooters — without at least one model equipped with radial-mount calipers.
Despite their widespread use in recent years, radial-mount calipers remain a high-end product. But what a few decades ago was just the odd idea of a group of engineers is now the de facto standard of an entire sector, the faithful ally of every racer, and the object of desire for every rider.
Vision, ingenuity, creativity — but above all, tenacity and determination — allowed Brembo to break down prejudices and resistance and assert itself against all odds. In a word: innovation.