Now surpassed, but still important to know about.

Rub Me All Over

  In the last section, we mentioned how the friction between leaves in a leaf spring provides a damping effect. A friction damper works in exactly the same way, with plates rubbing against each other to slow the motion of the suspension. The picture on the left is actually of a damper used to help reduce engine vibration on a Rolls Royce, but the design is identical to the kind most commonly used for suspension.

  Generally these consist of alternating disks of friction material and metal, with the two end disks extended to form levers. If you attach the damper across the suspension system, any suspension movement acts through these levers to twist the disks against each other, and them rubbing together provides the damping.

  The amount of damping effect is governed by the size of the disks, their number, the materials used, and how tightly they are clamped together. This means that you can adjust the damping by tightening or slackening the bolt that usually runs through the centre of the disk pack.

  The downsides of this kind of damper are numerous. For starters, the rubbing wears out the disks, and a LOT of heat is generated when the dampers are asked to work hard - a fast set of laps on a bumpy track will soon see them protesting. Also, they are neither the lightest nor most compact bits of kit (especially when designed for a heavy car), so getting them on the vehicle in the first place may involve a lot of compromises in other areas.

  On the whole, friction dampers are just too limited to have survived as a design, and their use petered out well before the middle of the 20th century - but you will almost certainly encounter them if you ever get involved with classic cars from this period and earlier. After this, the motor industry as a whole progressed to hydraulics for its damping needs, as we shall see.

Back to Suspension Basics 10 - Undamped Suspension

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