Aero details of 2018 WRC cars

The regulations for the current WRC car generation set that current car configuration will be maintained during the period 2017-2019, while a new WRC car homologation will be allowed for 2020…maybe with hybrid cars, according to Jean Todt impressions collected by Manufacturers had the option of five jokers for the chassis in 2017 and will have 3 in 2018 and 3 more in 2019, to make some improvements/adjustments on the cars. This is the reason why no big modifications have been introduced after initial homologation, just small changes, but still some of them with significant impact on car performance.

Up to date, manufacturers have spent their jokers mainly to improve the aero balance of the car, as well as the cooling capacity.

Hyundai was the first to spend several jokers, in the last part of season 2017, to give Neuville a car that allowed him to fight for the Driver’s title. In April 2017, Hyundai engineers started to work on the modifications, first with the aid of CFD and after, during summer and fall tests.

mikkelsen mx18.jpgpicture by Hyundai Motorsport

A.Mikkelsen/A.Jäeger, Hyundai i2o Coupé WRC, Rally of Mexico 2018, 4th

The first set of modifications, introduced in Rally Catalunya 2017, consisted in the removal of a dive plane, the redesign of the existing one and a redesigned rear wing, as we already reviewed in a previous post. The front splitter was integrated as part of front bumper (before, it had been connected to the bumper with quick-release fasteners).

A second joker was spent in the next rally, in Wales, with the aim of improving drag and lift on the rear of the car. To do that, they redesigned the frontal design of rear fender (A). The goal was to send air towards rear wing instead of to car sides, to reduce drag, as we already reviewed here.

AUTOMOBILE: WRC Monte Carlo - WRC -24/01/2018picture by Michelin

D.Sordo/C. del Barrio, Hyundai i20 Coupé WRC, Rallye Monte-Carlo 2018, ret.

Also, new air outlets were created behind the rear fender (B) and rear bumper (C). The higher the amount of air extracted by these outlets, the lower the lift at car rear, as well as the better the cooling efficiency. Compared to the original design, the outlets were enlarged to be close to the maximum dimensions the regulation allows. This also contributed to better cooling rear brakes, according to requirements of brake supplier (Brembo), as explained here.

A third modification (although not considered as a joker) was the redesign of side mirrors, first used in Rally of Mexico, after being tested since December 2017. The main goal seems to be to allow air flowing from front fender and dive planes to reach the rear wing, as we reviewed in a previous post. New mirror support configuration includes longer lever arms, which initially caused vibration and resonance problems, and although it seemed already fixed… TV images from Tour de Corse stages do not confirm, as vibration continues to be present

Toyota tested several modifications in the inter-season tests, which at the end were incorporated in Rallye Monte-Carlo 2018. The main goal was to improve the cooling capacity while re-equilibrating the aero balance. A first visible modification was a bigger air inlet in the front bumper, to increase the amount of air entering the engine bay for cooling purposes.

To deal with such flow increase, the radiators’ capacity was increased and additional coolers were added. But also bigger outlets were required, so different alternatives were considered. One of the problems was that air outlets ahead of the front wheel were banned in 2017 (while allowed until 2016).  But Toyota managed to find some areas where they could re-create the openings for the same effect, more specifically in front of the front fender, on the lateral surface of the bumper. These openings were first seen in the pre-season tests carried out in November 2017.

yaris lappi almeria fernando cruz II opening.jpgpicture by Fernando Cruz (

E.Lappi/J.Ferm, Toyota Yaris WRC, Test in Almeria (Spain), November 2017

In the Rallye Monte-Carlo, new exits were closed off, as well as during the first leg in Sweden.

pre event car circle.jpg

picture by Toyota Motor Corporation
Latvala  MC 2018 side outlet blinded.jpgpicture by Michelin

JM.Latvala/M.Anttila, Toyota Yaris WRC, Rally Monte-Carlo 2018, 3rd

New exits were opened again in Rally of Mexico, where cooling issues reappeared again (as in 2017) due to high ambient temperature, as Technical Director Tom Fowler confirmed to Martin Holmes (RallySportMagazine) in a recent interview.

JM mexico 2018 side outlet open.jpgpicture by Michelin

JM.Latvala/M.Anttila, Toyota Yaris WRC, Rally of Mexico 2018, 8th

The new air outlet is located behind radiators, to contribute to hot air removal. Arrows in the picture below show engine bay air removal alternatives for the 2018 Yaris WRC.

yaris mx18 villalpando01 arrows.jpgpicture by Jesse Villalpando

O.Tänak/M.Järveoja, Toyota Yaris WRC, Rally of Mexico, 14th

The redesign of the front fender, where much larger opening areas were included, also contributed to increasing the airflow exiting from the inside of the car.

yaris air outlet areas.jpg

Toyota Yaris WRC, Birmingham WRC presentation, January 11th, 2018

Air exit was split into two areas: 1) top of the fender for removing the hot air from the engine bay, and 2) rear exit for air from brake cooling and wheel space, with louvres sending air downwards. All air removed from these areas contributes to generating downforce at the rear of the car, as the lower the amount of air below the car, the lower the pressure.

yaris number 9 mc18 wing.jpgpicture by Rallirinki (

E.Lappi/J.Ferm, Toyota Yaris WRC, Rallye Monte-Carlo 2017, 7th

Small wings were located on top of the fender to minimize the impact of airflow exiting from the top outlet on main, external air stream. The additional air from the wheels increases the speed of the airflow on the underside of the wing (blown wing) which represents a small contribution to create additional downforce.

Even with the implementation of these modifications, cooling problems seem not to be completely solved, as drivers complained again about cooling issues in the warmest rally of the year (Mexico 2018), same as in 2017.

Another modification introduced by Toyota was the introduction of a second dive plane. Apart from generating a (small) additional downforce, a second plane is a backup in case of damage of one of them, something Toyota drivers experience quite often….especially during tests.

tanak mc 2018picture by Honza Froněk –

O.Tänak/M.Järveoja, Toyota Yaris WRC, Rallye Monte-Carlo 2018, 2nd

Finally, lights were integrated inside the bumper (with a cover when not in use) to reduce drag. It is a big improvement versus original configuration, in which they were fitted externally when required (as shown in the picture below), in a very poor design, from an aerodynamic point of view.

yaris 2017.jpgpicture by DR /

JM.Latvala/M.Anttila, Toyota Yaris WRC, Rallye Monte-Carlo 2017, 2nd

Citroën only detected change has been a reinforcement of rear diffuser strakes, which do not ‘flap’ anymore. Initial design included flexible diffuser strakes, in anticipation of them being damaged by the road surface. But surprisingly they were hardly damaged in normal use, so they have gone with solid strakes. Obviously, having something flexible and uncontrolled was not very effective for the aerodynamic performance of the diffuser.

rear diffuser c3.jpgpictures by Honza Froněk and Craig Coomans –

K.Meeke/P.Nagle, Citroën C3 WRC, Tour de Corse 2018, 9th

C.Breen/M.Scott, Citroën C3 WRC, Rally of Australia 2017, ret.

Citroën main problem in 2017 was the lack of grip and stability at the rear of the car, so they concentrated most of their tests in improving the suspension of the car, as well as the transmission split, which is now adapted to each surface. Results in 2018 seem to confirm the problem may be solved. With a reduced budget for 2018, it seems the team would be already working on the 2020 car, rather than in the current C3 WRC. Also, the team has changed twice his Technical manager in this period (C3 WRC designer Laurent Fregosi and Christian Besse since July 2017), as well as his Team principal (Pierre Budar replacing Yves Matton), which probably has had an impact on the team performance.

Ford used a joker on the side skirt, with a layup change for durability purposes. But the modification also allowed reducing the thickness of the front edge of the side skirt, as shown in pictures below.

side skirts comparative.jpgpictures by Grzegorz Roslon and Tomasz Kalinski

T.Suninen/M.Markkula, Ford Fiesta WRC, Rally of Sweden 2018, 8th (top)

O.Tänak/M.Järveoja, Ford Fiesta WRC, Rally of Sweden 2017, 2nd (bottom)

M-Sport saw his technical capacities increased with the added support of Ford Performance for 2018 season. First collaboration has been the evaluation of the Fiesta WRC in the wind tunnel of Windshear (Charlotte), after Rally of Mexico. The goal of such evaluation was the verification of the original design, as well as some short and long-term car improvements. Short term modifications are expected to be introduced in the next rallies. Hats off to a team who entirely designed the car with CFD, that is, with no wind tunnel support and with very short time for road tests in 2016. But even so, they managed to win both titles in 2017.

Suninen MX 18.jpgpicture by David Williamson –

T.Suninen/M.Markkula, Ford Fiesta WRC, Rally of Mexico 2018, 12th

Only modification seen on the Fiesta WRC tests is the introduction of new design side mirrors, with a similar purpose of Hyundai. However, after being used in Mexico shakedown, the team returned to the original design and still has not been used in competition.

July 22nd, 2018 update: M-Sport has confirmed the use of a new joker in the Rally of Finland devoted to a new rear aero package (bumper and diffuser), which we reviewed here.

This post includes opinions of the author, which are certainly not always right. If you detect any error or you disagree, do not hesitate to contact us, by sending an email to We love to learn!

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