World Rallycross supercars rear wing comparative

After our review of how RX Supercars generate downforce at the car front, we will cover in this post the main device for rear downforce generation in the RX Supercars. As in the case of WRC cars, this is the rear wing. In opposition to the rear diffuser, WRX technical regulations allow much more freedom in the design of the rear wing. We will review the different designs used by each car, as we previously did in the comparative of the rear wing of the 2017 WRC car generation.

Janis Baumanis (Ford Fiesta) and Timur Timerzyanov (Hyundai i20), RX Catalunya 2019

Current WRX technical regulations allow the inclusion of a rear wing with the material and shape are of free design. It must have the maximum dimensions defined in the Drawing below, independently of the car size. And must be contained within the frontal projection of the car, and within the projection of the car seen from above.

Maximum dimensions allowed by WRX Technical Regulations for the rear aerodynamic device of supercars – Art. 279, App. J 2019

All RX supercars include developed aero devices as rear wings, with different solutions in order to contribute to transfer all the power generated by their 600 hp engines to the track. In all cases, the rear wing is a biplane, following the shape of an inverted airfoil.

The rear wing of the new Ford Fiesta designed by Stard is a biplane wing with no end plates, but supports on both sides, very similar to the rear wing of the Hyundai i20 WRC (2014-2015). Note the vertical fin at the rear of the upper plate: this is called Gurney flap, and it is incorporated to increase wing efficiency. The main benefit is an increase in downforce generated by the wing. The presence of the flap allows the flow to remain attached for longer than without any flap; if separation happens later, the wing can be set at higher angles of attack (as the risk of premature separation is avoided), and higher angle of attack means higher downforce. Although at a higher drag cost.

Janis Baumanis, Ford Fiesta Evo, Team Stard, RX Catalunya 2019

The rear wing of the All-inkl.com Muennich Motorsport‘s Seat Ibiza is similar to that of the new Fiesta, with the addition of vertical fins on top of the upper plate. These fins have been added this year, to the wing design used in last season. The presence of vertical fins contributes to generating downforce when the car is moving sideways, which is very usual in RX supercars races.

Timo Scheider, Seat Ibiza, Team All-Inkl.com Muennich Motorsport, RX Catalunya 2019

The rear wing of the brand new Skoda Fabia WRX designed by ESmotorsport also incorporates vertical fins, higher than that of the Ibiza, for what the grip when cornering is probably higher. The vertical fins of the Fabia are regularly distributed across the main profile, while the Ibiza includes two fins in the center and two additional fins on both extremes of the main profile. In both cases, a Gurney flap is included at the rear of the profile.

Rokas Baciuska, Skoda Fabia, Team ESmotorsport – Labas Gas, RX Catalunya 2019

The Fabia also includes end plates (the piece with a GBY sticker). The goal of end plates is double: on one side, they prevent low-pressure air under the main profile flow to the upper side, which would result in a loss of wing efficiency. On the other side, endplates allow generating downforce when the car is sideways. Note that the end plates are bent in on the lower portion. This is one of the singularities of the Fabia, as no other supercar or rally incorporates such feature.

picture by Anna Solé Genescà

Rokas Baciuska, Skoda Fabia, Team ESmotorsport – Labas Gas, RX Catalunya 2019

Peugeot is the only car taking advantage of one of the features allowed by the technical regulations: the rear aerodynamic device may be adjustable. The Peugeot 208 designers took advantage of this feature and included an adjustable rear wing main profile, allowing the angle of attack to be changed. Higher angle attack means that the wing is able to generate higher downforce, due to a higher surface facing the air flowing from the roof, but at the cost of higher drag. The picture below corresponds to the configuration used in RX Catalunya 2019, which makes sense, as the Montmeló RX circuit includes only two short straights and numerous high and medium speed turns. The reduction in top speed caused by the additional drag was probably smaller than the gain obtained in downforce while cornering. And probably it will be the configuration used in most of the RX circuits, as they are similar in configuration.

Kevin Hansen, Peugeot 208, Team Hansen MJP, RX Catalunya 2019

picture by Anna Solé Genescà

Kevin Hansen, Peugeot 208, Team Hansen MJP, RX Catalunya 2019

Prodrive also included vertical fins in the rear wing of the GCK Taneco Renault Megane RS. It was the result of multiple studies and wind tunnel tests, as shown in the picture below. Tests were developed during 2017 at British MIRA full-scale wind tunnel, located in Nuneaton (UK).

The result was one of the most complex rear wings of the category. It is the only wing which incorporates two winglets on each external side of the endplates, with the objective of using additional air pressure when cornering to generating additional downforce.

picture by Anna Solé Genescà

Guerlain Chicherit, Renault Megane RS, Team GC Competition, RX Catalunya 2019

Also, a complex wing design can be seen in the GCK Academy Renault Clio RS, but with smaller vertical fins, irregular endplates and a more prominent lower plate.

Cyril Raymond, Renault Clio RS, Team GCK Academy, RX Catalunya 2019

All the Audi S1 aligned in 2019 RX Catalunya included the same rear wing design, with no vertical fins, the tallest, closed endplates and a very small Gurney flap.

picture by Anna Solé Genescà

Andreas Bakkerud, Audi S1, Team Monster Energy RX Cartel, RX Catalunya 2019

Also, the Audi S1 is the only car including a flow divider in the center of the lower profile, to better channel air towards both sides of the car rear. This is the consequence of the air intakes located on both sides of the roof of the Audi S1, designed to provide fresh air to rear coolers. Due to these intakes, the flow of air in the center of the roof is higher than on both sides. So, the flow divider contributes to making the flow more homogeneous, and the rear wing more effective.

Andreas Bakkerud, Audi S1, Team Monster Energy RX Cartel, RX Catalunya 2019

The pool of RX Supercars present in Catalunya RX also included an Audi A1, driven by Tamás Karái. The rear wing of this car is different from that of the S1, with open endplates and a more prominent Gurney flap. As no air intakes are present on the car roof, the flow divider in the lower profile of the rear wing is not required.

Tamás Karái, Audi A1, Team Karái Motorsport Sportegyesulet, RX Catalunya 2019

Former World Rallycross Champion Mattias Ekström decided to make a one-event come back for the Belgian event held in Spa from May 10th to 12th. He decided to drive the car with which he got his 2016 title, prepared by JCracetecnik, but with a renewed rear wing, with four vertical fins and open endplates.

picture by Abras Loic

Mattias Ekström, Audi S1, Team JCracetecnik, RX Belgium 2019

Finally, some supercars just include the original rear wing of the race car which they are based on: it is the case of the GRX Taneco‘s Hyundai i20 (using the rear wing of the 2016 Hyundai i20 WRC car), the Knopick’s Citroën DS3 (using the rear wing of the DS3 R5 rally car) or the Stard‘s Ford Fiesta of Jani Paasonen (using the rear wing of the Fiesta WRC 2012-2016).

Timur Timerzyanov, Hyundai i20, Team GRX Taneco, RX Catalunya 2019

picture by Anna Solé Genescà

Niclas Grönholm, Hyundai i20, Team GRX Taneco, RX Catalunya 2019

Hervé Knapick, Citroën DS3, Team Knapick, RX Catalunya 2019

Jani Paasonen, Ford Fiesta, Team Stard, RX Catalunya 2019

The Ford Fiesta driven by Christopher Hoy in Catalunya RX included a different rear wing design, with open endplates and no vertical fins.

picture by Anna Solé Genescà

Christopher Hoy, Ford Fiesta, Team Christopher Hoy, RX Catalunya 2019

In summary, different cars and different solutions to improve downforce generation at the car rear, in order to better transfer the 600 hp available from the RX supercar engines. But rear wing is not the only element to achieve that: rear diffuser also plays a role, which we will review in a next post.

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