The excellent team results obtained by Toyota in recent Rallye Deutschland, where they finished first, second and third) confirms the excellent design of the Yaris WRC, as probably the best car of the lot. And one of the reasons behind such supremacy is the constant development work the Japanese team, Finland based, continues to develop all over the year.
The results of such development work periodically translate into new modifications that contribute to keeping the car at the forefront of the competition. And this is what has happened again in Germany, where Toyota has introduced some modifications to improve the Yaris performance, as well as an additional modification (rear wing) in order to adapt the car to the latest clarifications on this issue distributed by FIA, following the recent controversy on rear wings in Rally Finland. The aim of the present post is to review these modifications and to evaluate their impact on the aero performance. Other teams have also introduced modifications in Germany (such an engine joker by Citroën), but none related to the aero, as far as we know.
J.M.Latvala/M.Anttila, Toyota Yaris WRC, Rallye Deutschland 2019, 3rd – picture by Hervé Tusoli
The main modification of the Yaris was a new design of the air intakes for rear brake cooling. This solution had been previously evaluated in some of the Toyota pre-event tests this year (Mexico, Portugal, Finland and Germany). Such design is very similar to the design Hyundai included in the i20 WRC since its original version in 2017, and it consists in a NACA air intake located on top of the rear side panel (while previous was located ahead of the rear fender).
O.Tänak/M.Jarveojä, Toyota Yaris WRC, Rallye Deutschland 2019, 1st – picture extracted from WRCplus images
A NACA design of an air intake is included in those applications where it is important to minimize air pressure loss, in order to ensure optimal performance (better cooling of rear brakes in this case).
The advantage of this modification is to improve rear brake cooling, by sending a higher airflow into the brakes due to a better location of the intake, and an optimize intake shape (NACA duct). The new intake location, on top of the side rear panel, is an area with significant airflow, channeled from front fenders and A-pillar towards the rear wing side winglets. Some of this airflow is now deviated towards rear brakes, ensuring a better cooling, which is crucial in those events where brakes are highly demanded (such as in Germany) or the ambient temperature is high (such as Turkey) for what the introduction of this modification now makes full sense.
J.M.Latvala/M.Anttila, Toyota Yaris WRC, Rallye Deutschland 2019, 3rd – picture by Michelin
There are three main differences between the new Yaris intake and that of the Hyundai i20 WRC Coupé. On one side, while both are located on the upper side of the rear panel, this surface is flat in the Yaris and inclined in the Hyundai.
A.Mikkelsen/A.Jaeger, Hyundai i20 WRC Coupé, Rallye Monte Carlo 2019, ret.
On the other side, the Yaris air intakes are located in a more delayed position, with respect to that of the Hyundai. The third difference is in size: the Yaris includes a smaller intake than the Hyundai, as shown in pictures below.
Upper picture – A.Mikkelsen/A.Jaeger, Hyundai i20 WRC Coupé, Rallye Monte Carlo 2019, ret. – picture by llluis555
Lower picture: J.M.Latvala/J.Hanninen, Toyota Yaris WRC, Rally Deutschland 2019 pre-event test, July 2019 – picture extracted from this video by Mk2 Racing Videos
The second modification Toyota introduced in Germany are new rims for the Yaris WRC, in order to solve the problem of frequent punctures they had suffered in the last events.
The new rims are the result of the combined effort between OZ and Toyota to create a stronger rim, preventing the wheel damage that was behind the frequent punctures the team suffered. With this objective in mind, the spokes (radius) of the new wheels have changed: now they are thicker and shorter, while the central part of the rim has been strengthened.
Toyota Yaris WRC OZ rims – old (left) vs new (right) picture by Toyota Gazoo Racing WRC
The modification has been really successful, as Toyota did not suffer any puncture during Rally Deutschland. However, the thicker strokes may reduce air/heat removal through the rim, due to the reduction of free open area. Also, the rim is less prominent, but with a deeper hole in the center, which might cause a small increase in drag.
Left picture: J.M.Latvala/M.Anttila, Toyota Yaris WRC, Rallye Deutschland 2018, ret, – Right picture: K.Mekke/S.Marshall, Toyota Yaris WRC, Rallye Deutschland 2019, 2nd – both pictures by Toyota Gazoo Racing WRC
The drag increase could be minimized with the inclusion of a cover in the central part of the rim, which would be also protection for bolts and an obstacle for dust entrance.
The third modification Toyota included in the Yaris WRC in Germany consisted in the replacement of the rear wing, as we already analyzed in our previous post. This is the first consequence of the controversy generated during Rally Finland on rear wings. As Tommi Mäkinen and a Toyota spokesperson confirmed in this article from Autosport, the aerodynamic profile was the same that it had always been, but in order to meet tolerance in clarifications there had been positional adjustments. The clarifications they referred to were detailed in a letter from FIA that had recently been sent to all teams, according to the British magazine.
The rear wing used in Germany is a temporary solution, prepared in the short time available between Finland and Germany (just three weeks), as Mäkinen declarations seem to corroborate. There will be a new rear wing in Turkey, according to Finnish rally website rallit.fi.
The result of the modification is a replacement of the rear wing, which has been moved 30 mm ahead, to fulfill with homologation and regulation requirements. The picture below shows the different location between 2018 (upper picture) and 2019 (lower picture) from Rally Deutschland. Also, the relative position of the wing end with respect to the rear bumper has changed, after the modification.
Upper picture: J.M.Latvala/M.Anttila, Toyota Yaris WRC, Rallye Deutschland 2018, ret, – Lower picture: K.Mekke/S.Marshall, Toyota Yaris WRC, Rallye Deutschland 2019, 2nd – both pictures by Toyota Gazoo Racing WRC
The excellent result obtained by the three Toyota cars in Germany confirms that this modification has little or negligible effect on the car performance. Toyota drivers dominance in the timesheets was even higher than last year, when the original wing was used.
In terms of downforce, the reduction in length of 30 mm of the lower plate of the rear wing (which probably measures between 500 and 600 mm long and 1100 to 1200 wide) represents a reduction in the surface around 5-6%. Assuming that lower plate may generate a 50% of total rear wing downforce, and that rear wing may generate a 30-40% of total car downforce, the impact of the modification would be, at maximum, around a 1% reduction of the total downforce generated by the car. Although it is not negligible, it is small enough not to have a significant impact in car performance, as results confirm.
The combination of a great car design and the multiple modifications Toyota has been introduced has allowed them to lead the current Driver’s Championship, as well as to significantly reduce the difference to Hyundai in the Manufacturer’s title chase. But, for sure, new modifications will arrive to still improve the excellent performance of the Japanese car. And from the rest of the teams, as the battles for titles are still really open.