Dirt vs asphalt: what changes for braking in the 2018 WRC

1/25/2018

Different surfaces require different braking systems and different braking styles. Brembo explains it all in a few minutes

«The winner rejoices, the loser explains» says Julio Velasco, one of the most famous volleyball coaches in the world. But at Brembo, despite winning it all in the 2017 WRC, also ready to offer explanations.

Having Brembo brakes turned out to be a necessary (though not sufficient) condition for winning the past edition, both for the WRC and the WRC 2. Necessary because both 2017 winners, WRC and WRC 2 ( Sébastien Ogier with M-Sport World Rally and Pontus Tidemand with Skoda Motorsport), were equipped with Brembo braking systems.

Not sufficient because several other drivers who were also equipped with Brembo brakes had to settle for second level positions. For 2018 simply rejoicing would have been an option here at Brembo.

Instead, we decided to explain how the braking system works for the current WRC, both on dirt and asphalt, what conditions make braking critical, and which rallies in the coming season are the most challenging for the brakes.

TECHNICAL FEATURES

Since technical regulations haven't changed compared to 2017, the technical features offered by Brembo haven't changed significantly either. Research, however, has allowed us to perfect some of the features used in the previous championship.
Regulations allow for the use of discs with a 370 mm diameter, but only for races on asphalt: up until 2016, the maximum diameter allowed was 355 mm.

Generally speaking the discs on each vehicle are changed at the end of the day, though a rally could safely be completed with a single set. However, the brakes wouldn't perform as well since the significant wear on these vehicles tends to reduce the slotting on the discs after just 150 km, which means the braking system is less effective and slower to respond and cool.

Increasing the power of the braking system however risks producing excessive heat. To compensate, the Manufacturers have made the front air intakes more efficient and crafted never-before-seen rear air intakes: Brembo told the individual teams how much air was needed to cool the disc and caliper.

The idea of a liquid cooling system was discarded after a careful analysis of the pros and cons: the option would have added extra weight to the calipers and additional components and, above all, could be unsafe if the pump were to break.

Besides, Brembo engineers are confident that having air intakes will keep temperatures in check. Brembo has designed an air intake system with two channels for each wheel: one leads to the center of the disc while the other is pointed directly at the brake caliper. For the rear, on one side, the channels can be bigger since they may be used to cool other vehicle components

THE TEAMS

For the 21st consecutive championship Brembo will be the supplier for team M-Sport Ford WRT, which is once again fielding world champion Sébastien Ogier: meanwhile the other two Ford Fiesta WRCs will be driven by Elfyn Evans, Bryan Bouffier and Teemu Suninen.

Brembo also produced almost the entirety of the braking system for the three Hyundai i20 Coupe WRCs, driven by Andreas Mikkelsen, Hayden Paddon, Thierry Neuville and Dani Sordo. Brembo produced the calipers, pumps, discs, pads and even the foot pedals for both teams.

On the other hand the three Toyota Yaris WRCs only use a few components produced by Brembo.

FACTORS THAT AFFECT THE BRAKES

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.

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 (unchanged with respect to 2017) 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 13 races in the 2018 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. 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.

Braking systems: WRC vs Dakar.
The braking systems for the Dakar stand out from those used in rallies because of their sturdiness and duration.

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.

Similarly, the Brembo brake discs with cast iron brake rings are bigger than those used in races on unpaved roads: the diameter measures 370 mm and the thickness ranges from a minimum of 30 mm to a maximum of 32 mm.

The 370 mm discs are the obligatory choice in the front while some Manufacturers have incorporated either the 355 mm or 320 mm discs in the rear: the decision is based on the road conditions and the driver's feeling. 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 2018 WRC rallies on asphalt, the most demanding are the Tour de Corse and Rally Germany. Grip is fairly elevated on German soil, especially at the Arena Panzerplatte where cement blocks are used instead of asphalt. What's more, the race features an infinite series of 90° braking sections following long straightaways. On the other hand, the roads on the French island are full of bends, requiring constant use of the brakes to keep the speed and trajectory in check, and the temperatures reached are quite elevated.

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.