Brembo brakes under pressure at the WRC: not all Rallies are the same

5/17/2016

 Grip, weather conditions, the winding nature of the track and altitude all affect how World Rally Championship cars use their braking systems

​In single-seater races, the only external variable that can influence the outcome is rain. In World Rally races however, there are numerous variables that the drivers and teams have to deal with and that impact, among other things, the characteristics of the braking system. Here are the most significant:


 

1) As the grip increases, the use of the braking system increases.

           

Some of the WRC races require driving on tracks covered in snow or ice, others call for crossing over waterways. The surfaces of the WRC races also vary dramatically: asphalt, dirt, sand and gravel. All of these elements translate into differences in grip that affect how the brakes function.


 

 
 

2) But the biggest factor is the winding nature of the track because this puts greater stress on the braking systems.

           

The tracks used for the special stages also influence the use of the brakes: a rally characterised by numerous straightaways and braking sections requires a different use of the brakes than one with continuous right and left-hand curves.


 

3) And if there are many descents, there is more stress on the braking system.

           

Equally as important for the effort required of the brakes is the variation in altitude: a flat race is not the same as one with big drops or steep ascents. In light of its extensive experience matured in the World Rally Championship, Brembo has made a braking system that is differentiated according to the conditions the cars are going to face. Which is why we have split our analysis into two parts.

 

                 

 

Rallies on unpaved roads

               

In rallies that are contested on unpaved roads, the drivers are required to continually correct the path of the car. Repositioning the vehicle in the centre of the carriageway means constantly applying the brake with the driver's left foot.

 

This doesn't allow the braking system to "cycle" because it is always under pressure, therefore, there isn't enough time to cool it down.

 

On unpaved roads, large discs aren't necessary because in general, there are no abrupt stops after the long straightaways, like there are in races on asphalt.

 

For this reason, the diameter of the Brembo discs is 300 mm and the thickness ranges from a minimum of 25.4 mm to a maximum of 28 mm.

 

In less challenging races, superlight Brembo discs are used because there is no need for all the material that is essential in races where the brakes are under more stress.

 

Also, the ceramic Brembo pads are softer compared to those used on asphalt in order to avoid blocking the wheels and to prevent the discs from overheating. These pads are made of RB330.

 
 

Of the 14 races in the 2016 WRC, the one that demands the most from the braking system, according to Brembo technicians who are specialised in racing, is the Rally Mexico.

                    

The special stages are quite wavy, but they are primarily characterised by impressive descents where the brakes are crucial. On the Ibarilla special stage, the drivers go from 2,599 to 2,065 metres in approximately twenty kilometres.

                    

The Rally Italy also puts the braking systems to the test because it takes place on unpaved roads endowed with a great deal of grip and they constantly change direction, which means the brakes are continuously used to correct the path of the cars. As if that isn't enough, there are also many ups and downs that demand the use of the brakes to stay on the road.

                    

The Rally Argentina is also present in the category of rallies on unpaved roads that are very demanding on the braking systems. The problem in this race is that the cars have to cross fords which may cause thermal shock. This increases the risk of cracks forming on the discs and the pads detaching.

                    

Thermal shock may also be a part of the Rally Sweden: if it snows heavily, the backend of the car moves a great deal and can end up hitting the piles of snow that come into contact with the rear brakes.


 

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Yet, when there is a lot of snow, the grip is low. If the snowfall is light, the rivets penetrate more easily into the compact dirt, increasing grip. The combination of these two elements leads to a medium level of difficulty for the braking systems.

                       

Among the least challenging races for the braking systems are the Wales Rally GB and Rally Finland. The first is famous for the mud which makes it especially slippery and devoid of grip.

                       

The Rally of the Thousand Lakes, on the other hand, has very fast lines but the street surfaces are slippery because they are covered in gravel that destroys the grip of the first cars that pass through.

 

Rallies on asphalt

                          

In the rallies that take place on asphalt, a very clean driving style is needed to be fast, one that is distinguished by making the fewest adjustments possible.

 

In these races, the tracks feature alternating straightaways and fast curves where the brakes are used hardly at all, and then the drivers have to stop abruptly and intensely. The braking torque in play is therefore very high. Which is why for races on asphalt, Brembo supplies some of the teams with a liquid-cooling caliper and 32-38 mm pistons built entirely of aluminium alloy.

 

This liquid-cooling system aims to guarantee a significant increase in the braking performance. Indeed, with this caliper the temperature drops by about 80°-100° with up to 45% improvement on caliper temperature compared to air cooling systems.

 

Similarly, the Brembo brake discs with cast iron brake rings are bigger than those used in races on unpaved roads: the diameter measures 355 mm and the thickness ranges from a minimum of 30 mm to a maximum of 32 mm. The pads with a ceramic base are more aggressive than those used on unpaved roads, the bigger bite is due to the Brembo RB350 mix.

 
 

Of the rallies on asphalt in the 2016 WRC, the hardest on the brakes is the Rallye Deutschland. The grip is fairly high, especially in the Arena Panzerplatte special stage where instead asphalt, the cars travel on strips of cement. Furthermore, there is a notable amount of 90 degree braking sections on this track that interrupt the long straightaways.


 

As a consequence, the braking torque in play is very high. The Rallye de France has also been judged very difficult for the brakes, but only for the 2015 and 2016 versions when the competition was held in Corsica. From 2010 to 2014, it took place in Alsace and ranked medium on the difficulty index.


 

In Corsica, on the other hand, the streets are very curvy and particularly narrow, which mandates the drivers to use the brake pedal continuously to correct the car. The Monte Carlo Rally is of medium difficulty for the braking system, but this claim comes from taking the average of the two sections at the opposite ends of the track. The initial special stages, near Gap, can offer excellent grip if there is no snow, and thus become very dangerous.


 

The final special stages, above Monaco, require the drivers to deal with ice and snow and so they almost never use the brakes. The Rallye de España is similar in that it starts out on asphalt and ends up on unpaved roads: the cars begin with equipment for asphalt, brakes included. When the surface changes, the mechanics replace the differentials, suspension and even the braking system.