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 made contact with the disc, the disc applied a torque to the caliper in the same direction as its rotation.
This was the most natural, logical, and also the simplest solution to implement from a manufacturing standpoint—especially with conventional forks, where it's enough to provide two lugs on the cast fork leg.
The drawback of this solution is that, if the lower end is free, the entire caliper could undergo significant deformation during braking.
These deformations create issues, as it is solely the caliper’s stiffness that ensures the proper positioning of the friction materials 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.
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Despite this, mainly due to the lack of alternatives, up until the 1990s the axial caliper remained the reference model across the entire motorcycle industry, with no viable alternative even being seriously considered.
For Brembo, everything was running smoothly, and there was no real reason to take risks with new or untested solutions.
In those years, in fact, all the most competitive teams in the 500cc class were using Brembo brakes, and the Italian company’s engineers were respected and valued in the paddock both for their technical expertise and for the reliability of Brembo components.
Nevertheless, within the lively minds of Brembo’s engineers, the idea of a seemingly revolutionary motorcycle brake caliper began to take shape.
The inspiration came from a world that was both close to and distant from Grand Prix motorcycle racing: Formula 1.
The company had been active in Formula 1 since 1975 and had already introduced radial brake calipers for single-seaters in 1982, with excellent results.
Thanks to the experience gained and a clear understanding of the advantages offered by the radial system over the axial one, Brembo engineers began to seriously consider the idea of applying the concept of radial mounting to the motorcycle world as well.
Mechanically, the radial mounting would have allowed for greater caliper stiffness. Since the caliper would follow the disc during its rotational phase, it would be subjected to less mechanical stress, resulting in reduced deformation.
In the radial-mounted caliper, in fact, the lower part of the caliper is no longer free but is instead rigidly secured to the structure.
This would make it possible to treat the caliper and the fork as a single integrated unit, leading to a wide range of advantages.
On one hand, the radial mounting would allow for significantly greater resistance to torque compared to an axial caliper, precisely because it minimizes elastic deformations—which otherwise absorb energy from the braking system.
On the other hand, in addition to providing a notable increase in braking performance, the radial mounting would eliminate the brake lever’s dead travel caused by improper pad alignment after hitting uneven road surfaces.
Aware of how bold the idea was, before building a prototype, they decided to present 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, the presentation of the sketches featuring the new solution ended in bitter disappointment.
The Japanese Honda technician, visibly disoriented, closed the bundle of drawings that had been presented to him, pushing them away with an expression of bewilderment.
Not only was he convinced that the solution was unfeasible, but he even regarded it as sacrilegious for the time—comparable to mounting a steering wheel on a motorcycle.
Such a rejection, pronounced by one of the industry’s top experts, would have discouraged anyone. In fact, at Brembo, the idea was temporarily shelved. But in reality, it was merely a pause for reflection.
Brembo’s axial-mounted calipers had no rivals and continued to dominate in the 500cc class.
In the years that followed, seven world titles were secured: two with Rainey’s Yamaha and five with Doohan’s Honda—all equipped with Brembo braking systems featuring axial-mounted calipers.
Yet the Brembo engineers couldn’t stop thinking about the radial-mounted caliper.
They were firmly convinced that the radial caliper, by leveraging its attachment to the fork, could stiffen not just the caliper itself but the entire braking system, resulting in a significant improvement in overall performance.
Mechanically, the radial mounting would indeed provide greater caliper stiffness which, combined with more precise pad positioning relative to the disc, would offer the rider increased braking sensitivity.
Moreover, the radial attachment would also make it extremely easy to increase the brake disc diameter.
It was just a matter of waiting for the right moment.
The right opportunity came a few years later. It was 1997, and Aprilia—at the time competing against the Japanese giants in the 250cc World Championship and constantly seeking technical solutions to gain an edge over its rivals—approached Brembo with a request for something innovative.
The Brembo engineers didn’t need to be asked twice and came back with the idea of the radial-mounted brake caliper.
The enthusiasm shown by Aprilia, combined with the renewed energy Brembo’s engineers poured into the project, resulted in new technical drawings and thorough testing. The time had finally come to move from paper to prototype.
Confident in the project, Aprilia decided to test the new system with test rider Marcellino Lucchi during private testing at the Jerez circuit in Spain, in February 1998.
Lucchi was immediately enthusiastic, and in the following days, Aprilia’s other riders joined the testing phase: Tetsuya Harada (1993 250cc World Champion), Loris Capirossi (two-time 125cc World Champion), and Valentino Rossi (newly crowned 125cc World Champion) all began successfully testing the new Brembo calipers.
The radial-mounted caliper made its debut at the opening round of the 1998 World Championship in Suzuka, Japan.
The new technical solution adopted by the Aprilia 250s caused quite a stir among insiders, and there was no shortage of skeptics in the paddock.
But when, in the following race, Aprilia nearly achieved a one-two finish—Harada taking the win and Rossi crashing on the final lap while running second—everyone realized that the radial-mounted caliper represented the future.
For Aprilia, it was a triumphant season, with 12 Grand Prix victories and the top three positions in the final World Championship standings: Capirossi as champion, Rossi second, and Harada third.
The first to bring the radial caliper to the 500cc class was Suzuki in 1999, achieving a surprising second place in the championship.
Kenny Roberts Jr. started the season using Brembo’s axial calipers but switched to radials during the year—securing the first-ever victory for a Brembo radial-mounted caliper in the 500cc class.
But this was just the beginning.Despite Yamaha also replacing Brembo’s axial calipers with radial ones the following year, it was the American Suzuki rider who clinched the world title—becoming the first 500cc World Champion with a radial-mounted caliper.
From that moment on, the use of radial calipers on track grew rapidly. Within just a couple of years, all teams—including Honda—swiftly converted to Brembo’s new and more effective solution.
From Grand Prix racing, the Brembo radial-mounted caliper made its way into Superbike, and then gradually filtered down into lower-tier competitions.
For riders, it was love at first sight, and the previous axial-mounted calipers were quickly replaced by radial ones on racetracks around the world.
The very same technical director of Honda Racing Corporation (HRC), with great class and elegance, later admitted he had been wrong and apologized to the Brembo engineers for his abrupt reaction years earlier.
After all, since the introduction of MotoGP in 2002, every single Grand Prix has been won by bikes equipped with Brembo radial-mounted braking systems.
From the racetrack to production road bikes, the transition was quick. The time was right, and the outstanding effectiveness proven on the track provided solid guarantees for series production. Even the last taboo was about to fall, and once again Brembo was succeeding in its mission: transferring innovation and know-how from racing to the road, making it accessible to all motorcyclists.
Once again, it was the Noale-based manufacturer that believed in the solution.
In 2003, in an effort to relaunch the latest evolution of the RSV Mille R, Aprilia decided to equip the twin-cylinder bike with a pair of newly designed Brembo calipers, directly derived from competition use. The RSV Mille R thus became the first production motorcycle fitted with radial-mounted calipers.
The innovation was soon adopted by other manufacturers, who feared falling behind the times.
On road bikes, the radial-mounted caliper confirmed all the advantages previously demonstrated on the track—and added new ones.
Being free from any kind of lateral constraint, the caliper adapts more effectively to minor disc oscillations during rotation, allowing the pads to make full use of the disc’s braking surface.
This not only improves braking performance but also benefits the lifespan of friction materials, which tend to wear more evenly.
After an initial application limited to supersport motorcycles, radial-mounted calipers began to spread to naked bikes and touring models as well.
Today, there is no category—scooters included—that doesn’t feature at least one model equipped with radial-mounted calipers.
What just a few decades ago was considered a quirky idea from a group of engineers is now the de facto standard of the industry—the trusted ally of every racer on the track, and the object of desire for every motorcyclist.
Vision, ingenuity, creativity—but above all, tenacity and perseverance—enabled Brembo to break through prejudice and resistance, asserting itself against all odds: they enabled Brembo to innovate.