04 Jun 09
2 - The spring
"Springs provide force. And the more you compress them, the more force they give. On a World Rally Car we run two springs per strut. The first supports the weight of the car while the second - known as the helper - is placed on top to take up any free-play and stop it rattling around.
The main spring sits on an adjustable platform which we can move up and down the strut to adjust the car's ride height.
If we were to rely purely on the springs for our suspension the car would have a bouncy ride, as energy stored in the springs was transferred directly to the chassis. Springs are not shock absorbers because they do not dissipate or absorb energy."
3 - The damper
"The third component is the damper itself. On Petter's car we use an off road unit made by Reiger racing. The main body of the damper is oil filled and contains a piston which can move up and down through the fluid. A series of shims and ports on the piston determine how quickly the oil can pass through, and so how fast it can move up and down. Energy is absorbed as heat by the oil in the dampers and as a result the units get extremely hot.
A second cylinder, connected to the main damper, acts as a reservoir for more oil and helps absorb more heat. The second cylinder also contains pressurised gas (usually nitrogen) to pressurise the oil and stop it 'cavitating' - or frothing up like a cappuccino. Foaming oil would temporarily reduce the damping ability of the unit."
Listen to the stage end interviews on World Rally Radio and you'll often hear drivers talking about the need to alter their damper 'clicks'. This relates to the adjusters fitted to each damper, which allow the units to be fine tuned to suit different terrains and driver preferences.
"The damping characteristics of our Reiger units, like most in the WRC, can be altered by the drivers," explains Hodge. "There are two adjustment wheels on each unit. The first - known as the bump adjuster - alters the speed at which the damper compresses. The second - known as rebound - changes the speed at which it extends. Turning the adjustment wheels is a bit like opening and closing a tap. There are numbers on the wheels to show how open or closed the tap is, and an audible 'click' as the wheel is turned."