Captain
27-11-2008, 02:27 PM
You've heard of vicious "tank-slappers", but what are they and how do we control them? With steering dampers, of course.
http://upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Steeringdamper.JPG/800px-
Steering dampers have moved in and out of fashion over the years. Back in the 1970s, they were regularly fitted to ill-handling bikes in an attempt to shore up the basic inadequacies of chassis design. The likes of Kawasaki's H1 two-stroke triple wore a damper to help counteract the frenzied flexing of the under-engineered frame and running gear during cornering.
But by the mid 1980s, the Japanese had managed to make bikes handle reasonably well on their own, and machines like Kawasaki's GPZ900R were stable and still steered pretty well for big heavy bikes. There wasn't much need for dampers, so they became exotic, mystical items generally found only on intensely prepared track bikes and one-off specials.
Fast forward to the present day and the sheer power, short wheelbases and sharp steering geometries of most liter bikes means a steering damper was fitted at the factory-again to calm the bikes down.
But what exactly is a steering damper? And why does a bike need one? Essentially, a steering damper is a device that absorbs rotating kinetic energy from the steering components of the bike-the front wheel, forks, handlebars and anything else that moves when you turn the bars. When something tries to turn the handlebars, the damper makes it harder by resisting the force and absorbing some of the energy.
There can be a few things trying to turn the handlebars, too. The obvious one is the rider who tries to make the bike turn into a corner-and we generally prefer this to require less effort, not more. Making the steering harder for the rider to turn makes a bike steer more slowly, harder to control in a bend, and more physically fatiguing to ride. Obviously, you don't want a damper working against your efforts.
But bumps in the road can also make the steering want to turn. Hit a bump at speed, and it can deflect the wheel and tire to one side. The self-centering "caster effect" of a bike's steering makes the wheel want to return to the midpoint-and fast. If it moves back too quickly, it can travel past the center point until it's actually pointing the other way. The caster effect makes the wheel come back towards the center point once more, and the same thing can continue to happen until the steering enters an unstable back-and-forth oscillation-the classic "tank-slapper."
Many characteristics of the bike and riding conditions can make a tank-slapper more or less likely. If the bike is accelerating hard when it hits a bump, there is less weight on the front wheel and the tire is more likely to skip off the ground-gripping and centering at random points-inducing steering instability that can develop into a serious tank-slapper. A short wheelbased bike, one with lots of power or one with a very sharp steering-head angle will be more susceptible to steering instability.
http://images.superstreetbike.com/howtos/0809_sbkp_03_z+electric_dampers+hydraulic_unit.jpg
A steering damper mechanism is aimed at preventing the dangerous, unstable steering motions induced by a tank-slapper, while allowing normal steering movement. Luckily, there is a damping mechanism that's eminently suited to this-hydraulic damping. A hydraulic damper offers much more resistance to movement as speed increases, so if you attach one to a bike's steering and turn the bars slowly (like when you're turning into a corner), there isn't much resistance. But try and turn the bars quickly and violently (as in a tank-slapper), and the damping effect increases sharply.
Most linear-type hydraulic steering dampers use a cylinder of hydraulic oil with a piston inside it. When the steering moves, the piston is pushed back and forth inside the oil, and carefully engineered holes allow the oil to pass through in a controlled fashion. Adjustable dampers allow the user to increase or reduce the damping effect by altering the orifices the oil passes through-generally, making them larger reduces the damping effect.
Apart from linear-type dampers, the other main type of unit is a rotary damper. This uses an oil-filled chamber that has a series of vanes inside it that are attached to an input shaft. As the handlebars are turned, the shaft moves the vanes through the oil, pushing it through carefully designed orifices. Again, the orifices can be adjusted to provide more or less damping effect.
The traditional "push/pull" style damper has been used for years by race teams and is tried and true. This particular example is a nonadjustable unit from a Suzuki GSX-R600, but aftermarket dampers allow for easy adjustments as well as color options. Mounting options are numerous but almost always 8include one end attached to either fork leg, while the other end is typically fixed to the frame.
Rotary dampers gained popularity with off-road bikes before crossing over into sportbike applications. Many top-level race teams have been using the rotary style dampers, and they're popular with the stunt crowd as well to control high-speed rolling stoppies.
The damper mounts on top of the triple tree and is easily adjustable on the fly.
The main wing (vane) exchanges oil from one side of the body to the other as the bars are turned. In the exchange process, the oil has to pass through three sets of valving circuits, all of which are externally adjustable by the user, to ensure a perfect match between what you are asking the stabilizer to do.
The base valve controls the general flow of oil from one chamber to the other and is what the user feels initially. The sweep controls, located on each side, determine the amount of damping from the straight-ahead position outward, releasing where the user chooses. This allows for easy turning at lower speeds. The high-speed valce is a separate circuit altogether and absorbs any hits greater than what the base valve is capable of handling, it's also adjustable to suit specific rider input.
http://images.superstreetbike.com/howtos/0809_sbkp_05_z+damper+top.jpg
The main wing (vane) exchanges oil from one side of the body to the other as the bars are turned. In the exchange process, the oil has to pass through three sets of valving circuits, all of which are externally adjustable by the user, to ensure a perfect match between what you are asking the stabilizer to do.
The base valve controls the general flow of oil from one chamber to the other and is what the user feels initially. The sweep controls, located on each side, determine the amount of damping from the straight-ahead position outward, releasing where the user chooses. This allows for easy turning at lower speeds. The high-speed valve is a separate circuit altogether and absorbs any hits greater than what the base valve is capable of handling, it's also adjustable to suit specific rider input.
ELECTRIC DAMPERS
Honda and Suzuki have both recently used dampers with electronically variable damping circuits in them. The idea here is that with a bit of clever computing power, an electronic control unit can assess the risk of a tank-slapper happening and alter the damping to suit the situation. At low speeds with small throttle openings, there's no chance of a tank-slapper, so the ECU reduces the amount of damping in the hydraulic unit. Conversely, at higher throttle openings and higher speeds, the ECU stiffens up the damping effect to deal with a much more likely slapper.
The benefits are clear: lighter steering for slow-speed maneuvering together with effective tank-slapper suppression when needed.
http://images.superstreetbike.com/howtos/0809_sbkp_01_z+honda_cbr1000rr+steering_dampers.jp g
http://upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Steeringdamper.JPG/800px-
Steering dampers have moved in and out of fashion over the years. Back in the 1970s, they were regularly fitted to ill-handling bikes in an attempt to shore up the basic inadequacies of chassis design. The likes of Kawasaki's H1 two-stroke triple wore a damper to help counteract the frenzied flexing of the under-engineered frame and running gear during cornering.
But by the mid 1980s, the Japanese had managed to make bikes handle reasonably well on their own, and machines like Kawasaki's GPZ900R were stable and still steered pretty well for big heavy bikes. There wasn't much need for dampers, so they became exotic, mystical items generally found only on intensely prepared track bikes and one-off specials.
Fast forward to the present day and the sheer power, short wheelbases and sharp steering geometries of most liter bikes means a steering damper was fitted at the factory-again to calm the bikes down.
But what exactly is a steering damper? And why does a bike need one? Essentially, a steering damper is a device that absorbs rotating kinetic energy from the steering components of the bike-the front wheel, forks, handlebars and anything else that moves when you turn the bars. When something tries to turn the handlebars, the damper makes it harder by resisting the force and absorbing some of the energy.
There can be a few things trying to turn the handlebars, too. The obvious one is the rider who tries to make the bike turn into a corner-and we generally prefer this to require less effort, not more. Making the steering harder for the rider to turn makes a bike steer more slowly, harder to control in a bend, and more physically fatiguing to ride. Obviously, you don't want a damper working against your efforts.
But bumps in the road can also make the steering want to turn. Hit a bump at speed, and it can deflect the wheel and tire to one side. The self-centering "caster effect" of a bike's steering makes the wheel want to return to the midpoint-and fast. If it moves back too quickly, it can travel past the center point until it's actually pointing the other way. The caster effect makes the wheel come back towards the center point once more, and the same thing can continue to happen until the steering enters an unstable back-and-forth oscillation-the classic "tank-slapper."
Many characteristics of the bike and riding conditions can make a tank-slapper more or less likely. If the bike is accelerating hard when it hits a bump, there is less weight on the front wheel and the tire is more likely to skip off the ground-gripping and centering at random points-inducing steering instability that can develop into a serious tank-slapper. A short wheelbased bike, one with lots of power or one with a very sharp steering-head angle will be more susceptible to steering instability.
http://images.superstreetbike.com/howtos/0809_sbkp_03_z+electric_dampers+hydraulic_unit.jpg
A steering damper mechanism is aimed at preventing the dangerous, unstable steering motions induced by a tank-slapper, while allowing normal steering movement. Luckily, there is a damping mechanism that's eminently suited to this-hydraulic damping. A hydraulic damper offers much more resistance to movement as speed increases, so if you attach one to a bike's steering and turn the bars slowly (like when you're turning into a corner), there isn't much resistance. But try and turn the bars quickly and violently (as in a tank-slapper), and the damping effect increases sharply.
Most linear-type hydraulic steering dampers use a cylinder of hydraulic oil with a piston inside it. When the steering moves, the piston is pushed back and forth inside the oil, and carefully engineered holes allow the oil to pass through in a controlled fashion. Adjustable dampers allow the user to increase or reduce the damping effect by altering the orifices the oil passes through-generally, making them larger reduces the damping effect.
Apart from linear-type dampers, the other main type of unit is a rotary damper. This uses an oil-filled chamber that has a series of vanes inside it that are attached to an input shaft. As the handlebars are turned, the shaft moves the vanes through the oil, pushing it through carefully designed orifices. Again, the orifices can be adjusted to provide more or less damping effect.
The traditional "push/pull" style damper has been used for years by race teams and is tried and true. This particular example is a nonadjustable unit from a Suzuki GSX-R600, but aftermarket dampers allow for easy adjustments as well as color options. Mounting options are numerous but almost always 8include one end attached to either fork leg, while the other end is typically fixed to the frame.
Rotary dampers gained popularity with off-road bikes before crossing over into sportbike applications. Many top-level race teams have been using the rotary style dampers, and they're popular with the stunt crowd as well to control high-speed rolling stoppies.
The damper mounts on top of the triple tree and is easily adjustable on the fly.
The main wing (vane) exchanges oil from one side of the body to the other as the bars are turned. In the exchange process, the oil has to pass through three sets of valving circuits, all of which are externally adjustable by the user, to ensure a perfect match between what you are asking the stabilizer to do.
The base valve controls the general flow of oil from one chamber to the other and is what the user feels initially. The sweep controls, located on each side, determine the amount of damping from the straight-ahead position outward, releasing where the user chooses. This allows for easy turning at lower speeds. The high-speed valce is a separate circuit altogether and absorbs any hits greater than what the base valve is capable of handling, it's also adjustable to suit specific rider input.
http://images.superstreetbike.com/howtos/0809_sbkp_05_z+damper+top.jpg
The main wing (vane) exchanges oil from one side of the body to the other as the bars are turned. In the exchange process, the oil has to pass through three sets of valving circuits, all of which are externally adjustable by the user, to ensure a perfect match between what you are asking the stabilizer to do.
The base valve controls the general flow of oil from one chamber to the other and is what the user feels initially. The sweep controls, located on each side, determine the amount of damping from the straight-ahead position outward, releasing where the user chooses. This allows for easy turning at lower speeds. The high-speed valve is a separate circuit altogether and absorbs any hits greater than what the base valve is capable of handling, it's also adjustable to suit specific rider input.
ELECTRIC DAMPERS
Honda and Suzuki have both recently used dampers with electronically variable damping circuits in them. The idea here is that with a bit of clever computing power, an electronic control unit can assess the risk of a tank-slapper happening and alter the damping to suit the situation. At low speeds with small throttle openings, there's no chance of a tank-slapper, so the ECU reduces the amount of damping in the hydraulic unit. Conversely, at higher throttle openings and higher speeds, the ECU stiffens up the damping effect to deal with a much more likely slapper.
The benefits are clear: lighter steering for slow-speed maneuvering together with effective tank-slapper suppression when needed.
http://images.superstreetbike.com/howtos/0809_sbkp_01_z+honda_cbr1000rr+steering_dampers.jp g