Meet the Polo R WRC

Developing a competitive car for the FIA World Rally
Championship (WRC) is an extremely complex task. One minute it is crouched low on
smooth asphalt, the next it is travelling sideways on ice and snow, then it is tearing over
rough gravel on tiptoes – then you have searing heat at one event and icy cold at the next.
No other type of international motorsport offers such a wide range of climatic conditions
and different surfaces. The cars in the World Rally Championship must overcome all these
obstacles. Take this fine example of the flexibility that must be demonstrated by the car’s
concept: there is a difference of about 100 mm between the ground clearance for gravel
and asphalt. The chassis and engine must be as efficient as physically possible in the
multitude of different conditions. Strong enough to take the strain, light enough to
guarantee the necessary performance.

Step by step: the continuous and systematic development of the Polo R WRC

The Volkswagen engineers applied a minimalist approach during the 17-month
development of the Polo R WRC, which was based on the production Polo, from which the
basic chassis was used. Every single component was subjected to numerous tests to
determine the dimensions and weight, and was continuously improved over the course of
the one and a half year development period. A strict schedule was adhered to, in order to
ensure the homologated Polo R WRC was ready to be launched in time for the 2013
season: after the launch of the concept car in May 2011, Volkswagen initially tested a socalled 0 car as a component carrier, which completed its roll-out in the vineyards around
Trier in autumn 2011. At the wheel of the concept car were Dr. Ulrich Hackenberg,
Member of the Board of Management responsible for development, and rally legend
Carlos Sainz.

The computer-assisted simulation of the first concept for the actual Polo R WRC began at
the same time. The Volkswagen engineers then produced their own very special
Christmas present: the first Polo R WRC was delivered to the foyer at Volkswagen
Motorsport on Christmas Eve 2011. The roll-out followed at the Volkswagen test track in
Ehra-Lessien in January 2012. Initial tests were also performed in Sweden and Spain.
From March onwards, the technicians performed constant modifications to the Polo R
WRC. This included work on issues such as chassis kinematics and the lightweight
construction of the car. The assembly of this improved version of the Polo R WRC, which
will line up at the 2013 Rally Monte Carlo,ultimately began in September 2012.

A love of detail: development steps “powered by Wolfsburg”

Every single component on the Polo R WRC underwent a series of fundamental processes
on its way to attaining the “ready to race” status. First up was the theory: the parametric
design process on CAD (computer aided design) systems is verified by computer-aided
simulations (e.g. CFD – computer fluid dynamics) and tested in practice in wind tunnels
and the Volkswagen Group’s altitude environmental test chamber. Only then did the
extensive test drives follow. The resources available in Wolfsburg play a key role in
designing and testing the chassis. Volkswagen’s Design department made a significant
contribution with valuable development work focussing on crash tests and safety. Tests on
the car in wet conditions were also made possible by the engineers at the headquarters in
Wolfsburg.

“Experience plays a major role when developing the chassis,” said François-Xavier
Demaison, Technical Project Manager WRC. “The know-how acquired in previous years
allows you to take short cuts without going through a long simulation and test phase that
would otherwise be necessary. This is the case, for example, when it comes to ground
clearance, kinematics, suspension or the configuration of the differential. For example, you
can spend many kilometres slowly adjusting the dimensions of the undercarriage until you
find the optimal configuration. It saves an awful lot of time if you already know how strong
you need to make a part.”

The result, under the guidance of Volkswagen Motorsport, is a high-tech jigsaw consisting
of about 3,000 pieces, of which 1,360 were designed from scratch for use in motorsport –
not including the engine and gearbox.

Nothing left to chance: state-of-the-art engine development

When designing the Polo R WRC’s engine, which consists of around 300 individual parts,
Volkswagen took a completely different approach to that used in the development of the
chassis. The result is the 315-hp, 1.6-litre engine. The automated interplay between CAD
design and simultaneous simulation using CFD processes led, among other things, to the
optimal design of the intake ports. Volkswagen took a strictly analytical approach to
decisions for or against various concepts within the strict regulations of the World Rally
Championship.

Over the course of the development process, the Engine Development department at
Volkswagen Motorsport tested all the options permitted by the regulations and simulated
their dependence on each other. “To a very large degree, the engine for the World Rally
Championship has been designed using electronically-aided development methods, in
order to ensure that the right decisions were made,” said Dr. Donatus Wichelhaus, Head of
Engine Development at Volkswagen Motorsport. “The cooperation of our colleagues in
Volkswagen’s Production and Research departments was invaluable here. They were of
great assistance, particularly in the automated development steps during the design phase
– such as those used for the intake geometry.”

Throughout the entire process, Dr. Wichelhaus’s team of engineers checked a wide range
of different solutions. Two different stroke/bore ratios, three different cylinder head
concepts, nine different intake port geometries, countless injector variants, and two
different valve diameters were checked, with the best solutions selected for the final
engine. This general approach resulted in a largely problem-free engine development,
which produced impressive test results right from the outset. The so-called anti-lag system
to reduce turbo lag received particular praise from the Volkswagen drivers during testing.

Volkswagen Polo R WRC

Engine

Type: Straight-four engine with turbocharger and intercooling, transversally mounted in front of the front axle
Displacement: 1,600 cc
Power output: 232 kW (315 hp) at 6,250 rpm
Torque: 425 Nm at 5,000 rpm
Air restrictor: 33 mm (FIA regulation)
Engine control unit: Bosch

Power transmission

Gearbox: Sequential, six-speed racing gear box, transversally mounted
Final drive: Permanent four-wheel drive with fixed drive between the front and rear axles, multi-plate limited-slip differentials, front and rear
Clutch: Hydraulically actuated double-disk sintered metal clutch

Chassis/suspension

Front/rear: McPherson struts, dampers from ZF
Suspension travel: approx. 180 mm on tarmac, approx. 275 mm on gravel
Steering: Servo-assisted rack and pinion steering
Braking system: Ventilated disc brakes (front Ø 355 mm on tarmac; front and rear Ø 300 mm on gravel) aluminium brake callipers (four callipers, front and rear)
Wheels: Size 8 x 18 inch for tarmac, 7 x 15 inch for gravel
Tyres: Michelin competition tyres

Chassis/bodywork

Build: FIA-conformant reinforced steel body

Dimensions and weight

Length/width/height: 3,976/1,820/1,356 mm
Track width: 1,610 mm
Wheelbase: 2,480 mm
Minimum weight: 1,200 kg

Performance

Acceleration: 0–100 km/h in approx. 3.9 seconds
Top speed: Up to approx. 200 km/h (depending on gear ratio)