Toyota GR Yaris Technical Analysis

Unveiled at the 2020 Tokyo Auto Salon, the Toyota GR Yaris has changed the landscape in the hot hatchback segment, bringing with it a number of engineering firsts.

Toyota GR Yaris Circuit Pack

Above: Toyota GR Yaris with optional Circuit Pack

Originally designed to serve as the homologation car for Toyota's 2021 WRC challenger, the GR Yaris is the first true homologation car for rally use since the Subaru Impreza 22B STi debuted in 1998 - a car to rival Toyota's existing Celica GT-Four ST205. With COVID-19 putting a hold Toyota's WRC car development, the plan to use the new GA-B chassis was eventually shelved in favour of retaining the previous year's competitor - based on the previous generation Yaris - until an overhaul to the top-class Rally1 regulations in 2022. 

Chassis & Bodywork

Built in Japan at Toyota's specialised Motomachi plant - previously host to the Lexus LFA production line - the GR Yaris bodyshell differs significantly from the GA-B chassis used in the standard cooking model.

 

For the GR Yaris, the GA-B platform from the standard Yaris is retained at the front, but with the 4WD-compatible GA-C platform used in Toyota's C-HR employed at the rear of the car. Furthermore, to improve chassis stiffness, the bespoke chassis relinquishes its rear doors and gains 6.6% more spot welds and 70% more structural adhesive over the standard car.

The  body-in-white, whilst predominantly steel, has undergone strict light-weighting, with a thinner gauge of steel being used in the wings and side members, and substituted for aluminium in the bonnet, boot and doors. 

Toyota GR Yaris body shell carbon roof

Above: Body-in-white with aluminium doors, bonnet, boot and CFSMC roof

A first for a hatchback, the GR Yaris has a carbon fibre roof skin, saving 3.5kg and lowering the car's centre of gravity height by 2.5mm. Unique to the GR Yaris, the carbon roof skin is not made from bidirectional carbon fibre typically used in high performance cars (e.g. BMW M3), but with a carbon fibre sheet moulding compound (CFSMC), often called 'forged carbon'. This carbon fibre manufacturing process is not only cheaper and faster than the resin transfer moulding (RTM) method traditionally used, but also gives the carbon a marbled appearance from its use of short, chopped carbon fibres.

Toyota GR Yaris smc carbon roof

Above: Toyota GR Yaris 1st Edition with exposed CFSMC roof

Toyota has continued its light-weighting exercise on the exterior bodywork making the rear bumper from Toyota Super Olefin Polymer (TSOP), its own high-performance composition of Polypropylene, allowing for a 38% weight reduction.

Aerodynamics

With the help of Tommi Mäkinen Racing (TMR) who run Toyota's WRC programme, the GR Yaris received extensive development to its aerodynamic profile, despite not looking much like another bewinged überhatch. The most significant of these aerodynamic developments is the lower roofline, afforded by having a bespoke body-in-white for the GR. This lowered roofline, totalling a 95mm drop against the standard car at the rear of the roof serves to increase the volume of clean airflow reaching the rear wing. With current Rally1 regulations mandating a maximum rear wing height relative to the height of the car, Toyota's lowered rear roofline gains them c.950cm² frontal area for air to flow to its rear wing.

Toyota GR Yaris roofline

Above: -95mm lowered roofline bespoke to the GR Yaris bodyshell

To improve the airflow along the side of the GR Yaris, TMR's engineers added aerodynamic features to the side skirts and front wing behind the wheel arch. The front wing features a mild cutaway to its trailing edge, following the recent motorsport design trend for opening up this area to evacuate air from the wheel arch, reducing lift and drag created by turbulent air flow inside the arch. Once evacuated, much of this airflow can be controlled by the side skirt, which serves two purposes; firstly, the flat step along the length of the skirt creates a vortex to seal the airflow underneath the car, secondly, the trailing end of the skirt rises up towards the rear wheel arch, promoting airflow over rather than into the turbulent wheel arch.

Toyota Yaris GR
Toyota GR Yaris side skirt
Toyota Yaris GR
Toyota Yaris GR wheel arch

Above left: stepped side skirt feature. Above right: wheel arch cutaway for drag reduction

At the front of the GR Yaris, a lot of aerodynamic features have been incorporated into the front bumper design in order to aid cooling and effectively manage airflow around the car. The main grill opening has a large frontal area to feed air to the radiator and the smaller intercooler positioned in front of it. Flanking the intercooler are symmetrical ducts to feed air into the front wheel arch, directed at the brake assembly to aid cooling.

Above: Radiator, intercooler, brake cooling ducts, transmission cooling ductair intake

At the front of the GR Yaris, a lot of aerodynamic features have been incorporated into the front bumper design in order to aid cooling and effectively manage airflow around the car. The main grill opening has a large frontal area to feed air to the radiator and the smaller intercooler positioned in front of it. Flanking the intercooler are symmetrical ducts to feed air into the front wheel arch, directed at the brake assembly to aid cooling.

Performance-orientated design features at the front of the GR Yaris comprise a redesigned front lip and canard-inspired lips at the sides; the redesigned front lip has a turned-up centre section between the front wheels to promote airflow underneath the car, where it runs along a relatively flat floor. This design has been seen notably on the Ferrari 488 GT3 as it not only increases the underbody flow, but also reduces pitch sensitivity allowing for a larger performance envelope. Far less noticeable are the flicks that have been incorporated onto the bumpers corners, only a slight upward angle can be seen - more of a nod to the car's WRC bloodline than a performance feature.

Below: Up-turned centre section profile for improved underbody flow

Toyota GR Yaris front aerodynamics

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