General Category > General Discussion
Friction Steering Damper
moto:
A weave starts when the bike folds around the steering stem, with the front wheel and the rear moving around it in opposite directions. I think that's what was going on in my big wind event. It's best not to let that get started, rather than having the bike begin that motion in the first place.
EDIT: With both tire contact patches firmly on the road, the motorcycle main frame with the rider is like a sail attached to two spars, and in effect billows out when the wind hits, leaving the spars unmoved (at first).
wirespokes:
You lost me there. What are the two spars you mention? True, a cross wind hitting the bike pushes it like a sail. But I don't see how it can cause a rotational motion without the tires skidding. It will try to turn the bike away from the wind, which in turn acts like a counter-steer pointing the bike back into the wind. A self-correcting action.
I believe the most important factor is rake and trail - something I don't have a complete grasp of. Tony Foale did some interesting experiments along that line. It's been shown that loading the rear of the bike increases the likelihood of front end instability.
Tusayan:
--- Quote from: wirespokes on September 03, 2026, 07:19:46 PM ---I've noticed that since I've mounted the hydraulic steering damper and set it to medium strength, the bike has the unpleasant tendency to wander at lower speeds.
--- End quote ---
If you set it to a lighter setting, the weave effect will mostly go away but it will still work when a tank-slapper wobble induces rapid oscillation - which is what a steering damper is for. A hydraulic unit's damping force increases as the square of displacement speed, and therefore the energy absorption as the cube. By comparison a friction damper creates much more low speed weave for the same anti-oscillation effect.
Cars and motorcycle went to hydraulic suspension damping from friction damping for the same basic reason in the 1920s or so - friction damping works too well at zero displacement speed (often termed 'stiction'), and not well enough at high displacement speed.
Some hydraulic steering dampers (for example those used on some production BMWs) have no effect at all lower displacement speeds, and then 'click-in' and assume normal hydraulic damper behavior when the motion speeds up a bit. This eliminates the weave effect on normal low speed steering while still damping tank-slappers effectively. That's the best solution if you must have a steering damper although the on/off behavior may be noticeable at parking lot speeds if you're sawing away at the handlebars.
moto:
--- Quote from: wirespokes on September 04, 2026, 12:11:37 PM ---You lost me there. What are the two spars you mention? True, a cross wind hitting the bike pushes it like a sail. But I don't see how it can cause a rotational motion without the tires skidding. It will try to turn the bike away from the wind, which in turn acts like a counter-steer pointing the bike back into the wind. A self-correcting action.
...
--- End quote ---
I mean the contact patches will restrict the two wheels from moving sideways in the gust, so that wind pressure on the body of the bike causes it to move away from the patches, folding up along the steering axis. A weave, as described by Cossalter, involves rotation of the front wheel and the body of the bike in opposite directions while the bike moves forward. He says this is initiated by an impulse or force to the side, often a quick movement of the torso of the rider. In my case, the rider's torso and the bike's frame were moving because of wind impulses.
I guess I was getting too metaphorical with "spars". What I mean is the the contact patches anchor the system just as spars (e.g. the gaff and the boom) on a boat would do. Hence a billowing or bowing outward around the lines drawn up from the two contact patches, as the gust hits.
High speed weaves are more dangerous than wobbles, as Cossalter emphasized. I believe the immediate resistance of a friction damper would be better than the initial give of a hydraulic damper. When a hydraulic damper in a shock absorber yields immediately to a road shock, the wheel absorbs a bump or pothole more easily. There is no effect on the steering in principle. But when a hydraulic damper fitted as a steering damper yields immediately to a shock, the bike goes immediately off course as the fork turns. Better not to do that.
Tank-slappers are an extreme form of wobble, not of a weave.
A report from an AI (Claude, but not definitive) says the 1953 Guzzi four racer used a friction-type damper mounted on top of the steering stem, like a 1960's Triumph twin. It says it has photos showing this. Guzzi could have used a hydraulic damper, but didn't. (Why?)
EDIT: Maybe this is a waste of bandwidth.
EDIT 2: Here is a view showing what I believe is the friction steering damper on a 1957 Moto Guzzi V8:
Tusayan:
--- Quote from: moto on September 04, 2026, 02:39:02 PM ---A report from an AI (Claude, but not definitive) says the 1953 Guzzi four racer used a friction-type damper mounted on top of the steering stem, like a 1960's Triumph twin. It says it has photos showing this. Guzzi could have used a hydraulic damper, but didn't. (Why?)
--- End quote ---
BMW claims to have introduced the first production hydraulic steering damper on the 1960 R69S, God knows they needed it given the huge rotational moment of inertia of their leading link fork and its susceptibility to wobble. I suspect Guzzi didn't have them available in 1953 or 1957 and that the friction damper was just something they routinely installed, not the subject of much thought.
https://www.bmwmotorcycles.com/en/engineering/innovation-overview/innovation/milestones.html
I’m not sure steering dampers of any type have a huge effect on high speed weave behavior, just a little.
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