Steering Damper

Steering damper is a damping device designed to inhibit an undesirable, uncontrolled movement or oscillation of a vehicle steering mechanism.

Alternative terms: Steering stabiliser, sprint damper

This phenomenon known in motorcycling as wobble, or in extreme cases, a tank-slapper. Modern motorbikes are unlikely to exhibit this behaviour in daily use thanks in part to better dampers and due to their very stiff front ends and other general improvements in design and tyre technology.

Sport bikes have a short wheelbase and an aggressive steering geometry to provide the ability to make very quick changes in direction. This has the harmful side-effect of making the bike less stable, more prone to feedback from uneven road surfaces, and more difficult to control. In addition, their light weight and powerful engine can cause frequent wheelies. If the front wheel significantly deviates from the direction of travel when it touches down, it may cause an unwanted wobble. Steering dampers are factory installed on some high-end sport motorcycles and fitted to most contemporary racing bikes to counter these behaviours. Steering dampers are also mounted to off-road motorcycles such as motocross bikes. A damper helps keep the bike tracking straight over difficult terrain such as ruts, rocks, and sand, and also smooths out jolts through the handlebars at the end of jumps. They also reduce arm fatigue by reducing the effort to control the handlebars.

On motorcycles, one end of the damper is mounted to the steering yoke or triple tree, the other to the frame. Two main types are linear and rotary. Linear dampers resemble a telescoping shock absorber and operate in a similar manner. They can be aligned either longitudinally and to one side of the steering, or transversely across the bike. Rotary dampers resemble small boxes and operate via a rotating pivot. They are mounted coaxially with the steering axis and are typically located on top of the steering head. An electronically variable damper uses a rotary damper with hydraulic fluid that flows freely at low speeds, allowing easy turning, while restricting flow at higher speeds when more damping is necessary, as determined by the engine control unit.

For motorcycles with sidecars, especially for motorcycles which have been retrofitted with a sidecar and where the front wheel geometry, or trail, has not been adjusted for use with a sidecar, a steering damper is beneficial. This prevents low speed wobble which may occur in the lower speed range of about 13 to 20 mph. In older motorcycles adjustable friction dampers had been routinely installed. Hydraulically operated steering dampers may be retrofitted. In some jurisdictions, the installation and operation of a steering damper must be

inspected by an expert or examiner and must be entered in the vehicle papers.

Alternative description

Ever had that heart-stopping moment when the ’bars oscillate nervously, or even flap uncontrollably out of your hands?

What you have experienced - or probably will experience sooner or later - is the problem known as a tankslapper, which, if it becomes violent enough (as it easily can), often leads to an accident.

Tankslappers happen when a bike’s front wheel leaves the road surface momentarily (or for longer if the bike is wheelieing) and moves from the straight-ahead position whilst airborne (this almost always happens if the rider touches the front brake which stops it rotating and thus loses its gyroscopic resistance to turning).

When the wheel lands, the trail (or castor) self-straightening effect of the steering, causes the wheel to snap back towards the straight-ahead position, but does it so rapidly that it passes through the straight-ahead point again and goes towards the opposite lock. At this point, the effect pushes the wheel straight-back again and if the movement is too fast, the oscillation can become so violent that the handlebars can become impossible to hold on to.

Even if control is regained, if the steering has gone from lock-to-lock, the tankslapper often causes the front brake caliper pistons and pads to retract, leading to reduced braking - or braking at all - being available at the next corner!

If you’ve never experienced a tankslapper – but ride a modern Sportsbike - you can be pretty sure that one day you will probably experience one, as it’s generally found that as a rider becomes more and more familiar with their bike, they gradually gain the confidence to ride it more aggressively, until the front wheel is going light, or skimming the road without them knowing.

It can be something as small as a cat’s eye in the road, which under such conditions, has been known to send the bike and rider into the hedge!

Sources: Wikipedia, Bike hps