Speeding in the wet

Europe's first independent wet handling circuit, an automotive test facility run by the Motor Industry Research Association, is attracting much interest in Britain.

The circuit, built at a cost of about $3 million, will help shape future development of safer vehicles and technically advanced components.

It was built to study tyres, braking systems, traction control, vehicle handling, suspension and stability under wet road-surface conditions.

Five of Mira's member companies - Dunlop Tyres, Honda Research and Development (Europe), Jaguar Cars, Nissan European Technology Centre and the Rover Group - played key roles in the planning and provision of the facility through financial support and co-sponsorship.

More than 600 specially designed low-arc swivelling water sprays, together with some long-reach water cannons, can completely soak the entire 1.6km circuit in minutes, irrespective of weather conditions except severe frost or snow.

The Mira-designed spray system minimises the use of wind-screen wipers which distract test drivers. Water is drained and recycled through a nine million-litre reservoir.

Graham Townsend, Mira's engineering director, said: "As a provider of engineering consultancy to the automotive industry, our vehicle dynamics department is involved daily with evaluation and development of components and systems that affect the adhesion of the vehicle to the road, especially in wet conditions."

Some 6.1km of pipes have been installed to serve the new circuit. In all, more than 8.6km of supply and drainage pipes are employed.

High-power pumps can deliver 10,200 litres a minute, more than four modern fire engines pumping at full speed.

Circuit wetting is divided into seven individual sections for which the sprays may be controlled independently to allow different tests and reduce water and power usage.

To prevent sprays being left on needlessly, the pumps are switched off after a pre-set time unless re-selected. But water is sprayed even when it is raining to ensure repeatability of tests and comparability of results. Analysis has shown that different results are obtained from reservoir water which contains different minerals from `pure' rain water.

A special asphalt surface includes a mixture of crushed and rounded gravel. This gives a more slippery surface than typical roads.

The circuit is not designed to be run dry. But immediately after its completion it was subjected to intensive dry running to rapidly condition the surface by removing excess bitumen and polishing the small stones to provide a constant coefficient of friction, called the `mu value.'

The circuit layout is carefully designed so that its characteristics vary according to the direction of
travel.

Each of the 11 main corners has a different radius
ranging from 22m to 85m. For most of the circuit the width is six metres but it includes a 300m straight, used for wet lane-change manoeuvres, that is 8m wide.

A sophisticated Formula One-style timing system helps test drivers in the development of vehicles and components. By measuring the speed of the vehicle driven on the limit on a wet, low-friction surface, engineers will be able to develop vehicles that can be driven more safely by the ordinary driver in typical everyday conditions.

The timing system records vehicles over various sections for instant comparison, and details are displayed in the test vehicle.

Mira's new wet handling circuit is the latest in a long line of highly successful co-sponsored research and development facilities. It is also the fourth handling circuit in which Dunlop has collaborated with Mira to create special tracks and friction surfaces.

The industry describes such an arrangement as an industrial `timeshare' system, where co-sponsors share research and development costs.