2018 WRC winter tests: time for side mirrors review

The tests the WRC teams have been developing during the 2018 winter, for the preparation of the first three rallies of the year, have not shown significant modifications of the aero package, and only minor fine tuning has been done. If there is one area teams have been working with, this is side mirrors. Although small, they are located in a complex area, where different air flows converge, and their influence on aerodynamic performance can’t be neglected.

The picture below shows the design of the side mirrors included in 2017 cars, for comparison with modifications detailed below. Side mirrors have a small but non-negligible contribution to the overall aerodynamic drag of a vehicle. Typically for passenger cars is in the range of 2.5–5%.

side mirrors signed

Hyundai i20 Coupé WRC/Toyota Yaris WRC/Ford Fiesta WRC/Citroën C3 WRC side mirrors, Rally Catalunya 2017

The picture shows how all side mirrors are located in the channel where the air coming from dive planes and fenders flows towards the rear wing, thus perturbing such flow and generating drag. Only Yaris mirror support design leaves a significant space for this air stream to flow, with minimal perturbation. Hyundai reduced such perturbation by including a very thin support, while Citroën and Ford’s rounded mirrors are clearly obstructing airflow in this area.

The first modification was introduced by Hyundai, by testing a new side mirror design during the tests they carried out in January in France. The new design was very similar to that of the Yaris WRC, with an inverted L –shape support, in order to allow more airflow to the car rear. Such flow is especially important for Hyundai, as their rear brake air intakes are located behind the side mirror, under the shape of a NACA duct. The higher the perturbation generated by the side mirror, the lower the amount of air for brake cooling.

hyundai mikkelsen december 2017 test.jpg

A.Mikkelsen/A.Jaeger, Hyundai i20 Coupé WRC, Preseason tests in France, January 2018 – picture by Julien Pixelrallye

Surprisingly, they did not include this new design in the Hyundai i20 Coupé WRC which took part in Monte-Carlo 2018, although they keep using it in Sweden and México pre-event tests….until Hyundai announcement (March 8th) that they will be using the new design since México (see note at the end of the post on side mirror homologation and regulation).

hyundai new side mirror.jpg

Ford also started to test a new design in the pre-event test of Rally Sweden, in February 2018. It consists of an inverted C shape support, but the philosophy is the same: to maximise free flow of air coming from fenders into the rear wing.


L.Bertelli/S.Scattolin, Rally Sweden pre-event test, February 2018

Although they did not use such side mirrors in the Rally Sweden, pictures from Evans/Barritt and Ogier/Ingrassia México pre-event tests confirm that they keep testing the new design.

evans front view

E.Evans/D.Barritt, Ford Fiesta WRC, Rally México pre-event test in Spain, February 2018

The picture from Evans’s car shows how the vertical support is located away from the fender edge line, to let as much space as possible for airflow to the rear of the car, between the mirror and the side windows.

Ford also decided to use the new design in México shakedown (see note at the end of the post on side mirror homologation and regulation).

AUTOMOBILE: WRC Mexico- WRC -08/03/2018

E.Evans/D.Barritt, Ford Fiesta WRC, Rally México 2018, shakedown – picture by Michelin

But the poor reliability of the new design, as it is more exposed to damage in case of a side collision with any obstacle, forced them to start the rally with the old side mirrors.

broken side mirror.jpg

E.Evans/D.Barritt, Ford Fiesta WRC, Rally México 2018, shakedown – picture by Michelin

The final goal of Hyundai and Ford new designs’ is to reduce drag and increase rear wing efficiency, that is, generating higher downforce at the car rear. In the case of Hyundai, it also helps to rear brake cooling, which is especially required in rallies run under hot temperatures, such as in México.

An alternative improvement has been proposed by Toyota in their 2018 evolution of the Yaris WRC: they left the side mirrors unchanged, but incorporated a small wing on top of the fender, to prevent airflow coming from dive planes to interact with airflow coming from front wheels. As a result, airflow coming from the fender bypasses the side mirror, which still faces the air coming from the wheel arches.

new toyota 2018 side

E.Lappi/J.Ferm, Toyota Yaris WRC, Rally Monte-Carlo 2018, 7th – picture by Rallyrinki.kuvat.fi.net

In addition to the mirror and support design, teams have opted for different longitudinal locations for their side mirrors, as shown in the picture below.

longitudinal comparative signed

Toyota Yaris WRC/Hyundai i20 Coupé WRC/Citroën C3 WRC/Ford Fiesta WRC, Rally Catalunya 2017

Note the different longitudinal locations of the side mirror. Taking as a reference the sticker of the RACC (placed ideally at the same location), the side mirror goes from the most advanced position (above the car number) in the Yaris (top picture) to the center of the sticker (Hyundai, 2nd picture), and close to the end of the sticker in Citroën and Ford (lower Fiesta).

In their location, side mirrors receive also the impact of airflow coming from the bonnet and windshield, part of which is forced to turn around the front pillar and flow onto the car side. Mixing of such airflow with air coming from fenders generates a full 3D flow impacting on the mirror, and the result is a very complex wake, which can easily generate noise, vibrations and, what is worse for a rally car, drag.

To minimise these effects, some of the designers have opted for replacing the side mirror as back as possible (in spite of reducing drivers’ vision through them), in order to minimise the interaction with the above described complex flow. This is what Ford and, to a lesser extent, Hyundai and Citroen have done, as the above picture confirms.

The longitudinal location of the rear mirror also has an impact on the overall aero balance of the car, due to their downforce generation effect. For this reason, it is important to evaluate the balance of the car and to locate the side mirror accordingly, so the balance is not disturbed or even improved.

No changes in the longitudinal location of the side mirrors have been observed in the new designs Hyundai and Ford have been evaluating in 2018 winter tests.

Finally, it is important to remember that was Toyota who showed the way with their original design of the Yaris WRC, presented in December 2016, which included a wider, two-plane side mirror.

original Toyota-Yaris-WRC-2017.jpg

The design included a double plane to act as a very small double wing, to try to generate additional downforce in the center of the car, but, surprisingly, the car they presented at the Rallye Monte-Carlo 2017 did not include such an original design. They removed one of the planes, while the remaining was flattened, and this is the configuration they are still using in 2018.

Side mirrors regulations and homologation.

Side mirrors are regulated by Article 253 of Appendix J, which sets the following requirements:

Rearward visibility must be ensured by two external rear‐view mirrors (one on the right and one on the left). These rear‐view mirrors may be as standard.
Each rear‐view mirror must have a reflecting surface of at least 90 cm².
An inside rear‐view mirror is optional.

They are not part of any level of homologation, so no joker is required for their modification.

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 wrcwings@gmail.com. We love to learn!


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2 thoughts on “2018 WRC winter tests: time for side mirrors review

  • 2018-09-21 at 13:39

    another reason for adjusting longitudinal location of rear mirror is to change the overall aero balance

    • 2018-09-21 at 21:47

      You’re completely right, thanks! A good complement to the post, so we have included it.


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