Opel/Vauxhall’s 155mph Astra VXR/OPC hot hatch excellent handling is attributed mostly to the German-built Drexler limited-slip differential that’s the first of its kind to be used in a production front-wheel-drive road car. The differential uses circular plates that lock to prevent the 276bhp VXR from spinning away power in corners and over cambers when the car is being driven hard.
Since the 1960s, the plate-type diffs have been used in motorsport in front-drive cars. But typically, they work with an aggressive action and are challenging to drive. But then, Vauxhall said that the Drexler Motorsport unit is incredibly easy to drive.
VXR boss Volker Strycek, a former touring car racer, said that there’s “very little snatching of the wheel” and that it has been tuned so that the operation wouldn’t be felt. In addition, Strycek has driven front-drive cars that utilize torque-sensing front diffs like the Ford Focus RS. He also said that the VXR has much better steering. The VXR’s HiPerStrut front suspension, which decouples the front wheels from the steering axis, aids in reducing torque steer.
Next month, Strycek will personally be driving the VXR around the Nürburgring as Vauxhall enters the final development phase of the Astra VXR project before its launch this summer.
Project chief Uli Pfeffer said that the new VXR is a major improvement over the outgoing car with more power and performance, and with an enhanced ride and better grip. This new bodyshell is 40% torsionally stiffer, which means that it’s a better platform for the suspension. Furthermore, the FlexRide active dampers have a wider operating range that improves the daily ride quality but with a track performance that’s much improved.
The Opel Astra OPC’s braking system was tailored to fit the vehicle’s high performance requirements, even under maximum load. Engineers working on OPC, together with Italian specialist Brembo, have designed an 18-inch brake booster solution featuring larger ventilated, cooled and cross-drilled 355 x 32 millimeter discs as well as four-piston callipers in the front. The Opel Astra OPC can also be used as special high-performance brake pads.
These discs, called the "co-cast floating brake discs," are made of two different materials and together make up a special system. The cast iron brake rotor is mounted on a disc bell made of aluminum, therefore combining the heat resistant property of the cast iron and the lightweight quality of the aluminum. The Brembo brakes’ overall advantage is the improved temperature resistance in case of repeated braking as well as performance feedback during a temporary long brake.
Additionally, the OPC front calliper weighs 5.1 kg, which is 2.8 kg lighter compared to the standard unit being used. Moreover, the front’s light-weight brake discs are up to 4.2 kg lighter per disc compared to their conventional counterparts. This lighter weight reduces unsprung mass while increasing steering, agility, and handling precision.
Engineers likewise altered the rear axle’s torsion tube in terms of its stiffness and its weld-on angle. This ensures that the rear axle provides more support to the front axle. Also, the entire chassis, together with the brakes, has been tested on public roads, as well as in tough environments such as Germany’s Contidrom and Nürburgring race tracks, Scandinavia’s ice and snow, and Idiada’s Spanish heat. After this intensive testing, the engineers from Opel’s Performance Center in Rüsselsheim picked 245/40 RZ-sized tires, which have been fitted for flow-formed 19-inch alloy wheels.
However, those customers who prefer Opel's cutting-edge forged wheels can choose the lightweight 20-inch alloy version, which weighs 1.86 kg or 14% less than the Astra GTC’s 5-star spoke 20-inch version. The forging process used in making the lightweight alloy produces a tougher material so that it can be thinner than the material in a flow-formed wheel.