Four materials and just one disc
The history of the rise and fall of the materials that make up Brembo brake disc rotors
1982 - Aluminium fixed disc. This solution was adopted to reduce the masses on 125 and 250 cc GP bikes
1985 - Cast iron floating disc with aluminium hat
2000 - Floating disc with aluminium hat and stainless steel rotor
2004 - MotoGP carbon disc
When you look at the shiny, sparkling steel brake discs of your motorbike, it’s hard to imagine that this type of material was not commonly used in the history of the major motorbike competitions.
Right from its début in the world of bike competitions in the early ‘70s, of the four different types of material used by Brembo for its brake discs (cast iron, steel, aluminium and carbon) it was precisely steel that lasted the shortest time, especially if we’re talking about MotoGP.
For the earliest motorbike races, Brembo used cast iron for its brake discs; the first ones had a cast aluminium housing with the rotor screwed directly onto it. It didn’t take the Brembo technicians long, however, to understand the intrinsic limit of discs whose rotor was joined to the housing - in fact the rotor heats up and needs to be able to expand thermically without any restraints like the housing.
This gave rise to floating discs that could optimise their weight and performance. In these discs, the rotor is free to move radially thanks to the aluminium bushes that connect it to the housing.
This system allows the rotor to dilate freely, eliminating the lateral deformation that causes a variation in the master cylinder lever stroke and reduces the rider’s confidence in the bike’s braking response.
During the 1980s, the need to lower the weight in the 125cc and 250cc classes induced the Brembo engineers to try out aluminium discs coated in plasma. The results were positive, with a notable weight reduction on the lower engine capacities without compromising braking efficiency in any way.
In the 500cc class however, Brembo continued with its discs in cast iron - a material that ensures excellent performance levels right up to the highest thermal conditions.
At the end of the 80s, the ban on using asbestos for the brake pads changed the values at stake. The cast iron brake discs were, in fact, characterised by a high friction coefficient when combined with brake pads containing asbestos. The prohibition on the use of this material forced Brembo to come up with another solution for its racing discs.
The choice was steel - an alloy that not only had a good friction coefficient if used with the new asbestos-free brake pads, but also guaranteed a weight reduction compared with the cast iron discs thanks to its improved mechanical characteristics.
But the material most widely used for the brake discs of street bikes - stainless steel - has a somewhat short working life in the racing world. Within a few years, it was quickly replaced by an innovative material borrowed from the aerospace sector: carbon.
The early 90s saw the first appearance of this new material with its revolutionary characteristics, subsequently used for the discs of the top class competitive bikes, first the 500cc and then MotoGP. Carbon discs ensure considerable weight savings on non-suspended masses, greatly reducing the gyroscopic effect and improving the agility of the bike whilst guaranteeing far higher performance levels compared with their steel counterparts. They do have one flaw however: they don’t brake effectively until they’ve reached the right working temperature. That’s why the riders have to be especially careful during the warm-up lap and on the first bends of the race itself.
And it’s also the reason why steel brake discs are still used today in MotoGP, when it’s raining or when the weather conditions prevent the bike from reaching its working temperature range.
Unlike MotoGP, steel discs are used in all the other main racing competitions (like Moto3 and Moto2 of the Road Racing World Championship Grand Prix, the SBK World Championship, and the AMA Superbike Championship). And they’re still the best choice for street bikes, guaranteeing good performance, comfort, duration and reliability in all conditions.