Friction Steering Damper

[BMCMOTO]

Yes the originals like this are friction.  https://www.mgcycle.com/index.php?main_page=product_info&products_id=556   They may not look like it but they are. I put a new one on my MILLE GT and it squeaked all the time. I gave the shaft a tiny squirt of brake clean and it loosened up till the brake clean evaporated, works silently now.

Brian

[moto]

Crusty calls its seemingly identical unit non-adjustable hydraulic.

A hydraulic damper gives more resistance as the rate increases.
A friction damper should be the opposite. My vague recollection
is that the Crusty item acts like it is hydraulic.

Whatever the original was, it seems hydraulic is better here.

Thanks for your answer, though.

[BMCMOTO]

Simple to test per my post!

Brian

[Gusable]

Anyone put an aftermarket damper on a Guzzi that did NOT come with one?  I’d like one on my cal2. Didn’t come with one and I don’t see any tabs or brackets on frame. Need to fab something up I guess.

[moto]

Simple to test per my post!

Brian

What test do you propose, exactly?

[BMCMOTO]

A simple squirt of brake clean on the shaft. If it then moves more easily, it indicates that it is a mechanical device and not hydraulic. Usually, friction dampers of this type are actually packed with rubber rings around the shaft and then compressed into the tube for resistance. A drop of fluid will make the rubber slide along the shaft easier. I suggest brake clean because it evaporates quickly and leaves no lubricant behind, unlike WD40 or carb cleaner. I believe Crusty's description is mistaken, just my opinion, and I am willing to be proven wrong. In fact, I would welcome it as I would like to have one if it really is hydraulic!!

Brian

[BMCMOTO]

So Moto, what is the verdict, is the damper hydraulic, or friction, enquiring minds want to know???

Brian

[moto]

So Moto, what is the verdict, is the damper hydraulic, or friction, enquiring minds want to know???

Brian

It's friction. I'd already decided I had been wrong about this, which seemed to de-motivated me to look.
But on removing one end of the damper it is completely obvious that is friction because it resists movement
constantly at any speed of movement. By the way, your suggested test was excellent, though I didn't need to use it.

While I was procrastinating I thought more about the issue of friction vs. hydraulic, and wondered whether
Guzzi had a reason to choose friction. After all it could easily have whipped up a hydraulic unit since it
was making its own fork hydraulics on site.

I decided that friction might be better sometimes. When I was being hammered by that tremendous side wind
I think bike would have been better off not yielding at all to the blows rather than deflecting and then
damping the resulting weave.

I opened my copy of the engineering text, Motorcycle Dynamics, 2nd English ed., by V. Cossalter.
It turns out that he analyzed the effect of a hydraulic steering damper among
many other factors in a complex mathematical model describing both wobble and weave.
Weave is the more dangerous mode in which both the fork and the body of the bike rotate
around the steering head. In wobble it's just the fork.

The equation he used to describe the damper's force is Nm = c (Radians/Sec). Radians/sec is a rate of
movement like mph, where a radian is about 57 degrees of rotation around the steering head,
and c is the damping constant. The formula says the force of resistance in Newton meters
is a linear function of the speed of rotation. This describes a hydraulic, not a friction, damper.

The author concludes that "increasing the the damping constant ot the steering damper
is a very easy way to increase the damping ratio for the wobble mode, although it has the
undesired effect of slightly reducing the weave mode damping" (p.272). This is in a
complex mathematical model being run through many simulations changing parameter
values.

I'm left wondering what is best: no damper, a friction damper, or a hydrualic damper. But the
one I bought from Crusty is clearly friction, not the advertised hydraulic type.

[BMCMOTO]

Thank you for checking it out! If it had been hydraulic I really did want one! They mount very easily that's for sure, most of the hydraulics are harder to mount and if mounted on the right like many Guzzi's harder to adjust on the fly. A non adjustable hydraulic would be perfect in that location.

Brian

[wirespokes]

The hydraulic damper resists motion in both directions. So in that respect it's the same as the stock friction unit.

I can adjust mine on the fly by reaching over the tank with my left hand. It's not clumsy or at all difficult.

I can't help thinking the friction damper was the cheapest solution and the reason Guzzis came with them.

[moto]

...
I can't help thinking the friction damper was the cheapest solution and the reason Guzzis came with them.

I will push back on this a little. 1970s Guzzis were not cheapest-component bikes. They were instead
carefully designed and mostly built in-house.

For example, the little hydraulic dampers in the forks were a Guzzi design, the first cartridge forks. That
was no off-the-shelf solution.

I think the designs reflected the engineers working on them. In particular, Eng. Umberto Todero
was head of the racing department from 1951 and remained heavily involved in design of non-racing
bikes after the closing of the department. He was part of the design of the MGS-01 of 2004, and
had been the lead developer of the Tonti/Brembo integral braking system in the early seventies.
Having had chief responsibility for the inherently unstable dustbin-fairing racers of the 1950s,
he would have known his steering dampers. His input on the choice of dampers for the V7 Sport
and later Tonti-frame bikes seems almost certain since he was working there and had the experience.

Because top-speed performance was a big seller of motorcycles in the seventies, good top speed
stability was needed. The top speeds of some early Tonti frame bikes were about 115 to 130 mph.

I think Todero and the other designers chose a friction damper because the type had worked on
the 1950s racers. They knew about hydraulic dampers (in the cartridge fork) and could have
designed one. But Cossalter's analyses finding weave instability induced by hydraulic dampers
could have been directly experienced by the Guzzi engineers if they had tested some.

Friction dampers may have been better at high speeds than simple hydraulic dampers,
and therefore may have been specified particularly on the high speed models like the V7 Sport
and the Le Mans. Later on the hydraulic dampers got better, but even the adjustable ones like
John mounted are not immune to increasing weave instability with increased damping settings,
according to Cossalter.

[wirespokes]

Since both friction and hydraulic dampers work in both directions, I don't get how there's any difference in their effects. They're both damping front end oscillation.

As for the reason Guzzi went with friction, it's all conjecture at this point. I had thought the early dampers, like for the Ambo, were hydraulic and wondered why the change to friction. Now I find that there were no hydraulics, so evidently they hadn't been created yet. Maybe they didn't even consider hydraulic early on - like nobody even had the idea to go that route?

[Antietam Classic Cycle]

None of the Loopframe Guzzis came from the factory with a steering damper until the last of the disk-brake Eldos. Then it was the damper in question, which had been previously fitted to the V7 Sport.

[moto]

Since both friction and hydraulic dampers work in both directions, I don't get how there's any difference in their effects. They're both damping front end oscillation.
...

They both work in both directions, but they work differently. The friction damper offers maximum resistance immediately, while the hydraulic type ramps up its resistance as the speed of the shaft increases. This difference could mean the friction damper would be inferior as a shock absorber where some initial travel is important when the wheel hits a bump. Maximum rigidity at the first impulse is desirable for the steering damper because it keeps the bike from deflecting in its path and starting to weave. That's what I think.

[wirespokes]

I think it's the other way around, moto. If a side wind gust hits you, it forces the front end away from the wind which then leans the bike against the wind. It's a self-correcting action. If the steering won't deflect, the bike would weave rather than lean to correct. 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.

[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]

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.

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]

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 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]

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?)

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.

[moto]

Well, I needed something during that wind event. I thought I was gonna fall off the bike for almost 100 miles. The friction damper seems to stiffen things up, but I can't repeat that particular wind event at will.

Why you think Guzzi wouldn't give the damper issue much thought on their 170 mph racer with stability problems is beyond me.

[Tusayan]

Why you think Guzzi wouldn't give the damper issue much thought on their 170 mph racer with stability problems is beyond me.

Motorcycle chassis design was nowhere near advanced in the 1950s and whatever thoughts they had were built on very limited understanding.  They knew a friction steering would help prevent wobble, that's all they had and most of what they knew.  So that's what they did.  Stability and control development was done mainly by experiment at that time, I don't think anybody knew anything about weave except perhaps that rear suspension and tires were involved, with various theories about how.   All of the above remained true until the 1970s and 80s.  Companies like Bimota started building advanced chassis based on mid-late 1970s racing technology that showed what worked experimentally, and the Japanese realized chassis design needed more analysis after horrible handling bikes made it into production.

[moto]

It's hard to credit your amazingly deep knowledge about what designers knew and did way back then.

I expect they well knew that their friction dampers were helpful at high speed, from long experience. I think I see why. I don't know what they considered, but I don't think my ideas would have escaped them. No matter.

[wirespokes]

Consider this, moto: Guzzi invented the cartridge forks, but it took the Japanese, what, 20 or 30 years later to make it work?

I think you're right - that's a friction steering damper on the V8.

[moto]

Here's a great V8 photo showing the friction steering damper and the front hydraulic suspension damper -- it looks like there is only one of the latter, EDIT but another view shows there is one on the other side. (The rears were spindly looking hydraulics on each side, reminiscent of Girlings):





You can see the separate lever arm fastened to a sturdy post in front of the damper. The post and longer arm give more leverage than the usual stem-top design, probably because greater forces had to be applied to stabilize those faired bikes. Unfaired single-cylinder racers seem to have gotten by with regular friction dampers.

The friction steering dampers (both types) were adjustable. Putting non-adjustable cylindrical friction dampers on the Le Mans, etc., was a compromise.

[Tusayan]

Consider this, moto: Guzzi invented the cartridge forks, but it took the Japanese, what, 20 or 30 years later to make it work?

I think you're right - that's a friction steering damper on the V8.

Guzzi made their own forks in house and instead of making the expensive and precise internals they bought a bolt-in damper cartridge starting with the V7 Sport.  Easy and cheap, although wear prone and life limited.  It was a trend - my late 60s European airplane has the same design in the nose gear. A kit was available (Cosmopolitan distributed it) to replace Guzzi LM forks with Marzocchi Stradas so you didn’t have to change the damper cartridges regularly any more. 

A lot of old bikes had a friction damper on the steering head, even bevel drive Ducatis that had no need for them, and Guzzis were no exception. Hydraulic steering dampers slowly replaced them starting in the 60s and 70s, and perhaps even more so chassis design improved to the point that they weren’t necessary to preclude wobble on most production bikes.  The spine frame Guzzis of the 90s were one exception, they have a 40 mph decel wobble that’s addressed by a Bitubo hydraulic damper.

[moto]

Wobble is mostly a nuisance. Weave at high speed is what the friction damper fought.

[Tusayan]

The motion of the front wheel/fork assembly around the steering head is small and relatively slow in a weave situation, so no steering damper of any kind can absorb much energy even if it were extremely stiff.  Therefore they can’t damp out weave oscillation very effectively.  Also, if a friction damper specifically had so much stiction that it prevented steering motion entirely, it would make the bike uncontrollable by the rider - the forces involved in weave are high.

The way weave is prevented is to stiffen the frame or otherwise reduce the energy being fed into the oscillation, typically meaning to use effective rear shock absorbers.  If the frame is relatively flexible, a narrower rear tire helps and a wider rear tire is problematic. 

All steering dampers are intended to absorb the energy associated with a wobble.  Hydraulic dampers are better in doing this, which is why you won’t see a friction damper on any bike built in decades.

[moto]

Tusayan convinces me he knows what he's talking about.

I put too much faith in Cossalter's model. Its specification of a linear instead of quadratic response to velocity was probably intended as a first-order approximation and may have been responsible for the "surprising" increase in weave he found with increases in the damping factor.

The presence of both the friction steering damper and the hydraulic suspension dampers on the V8 may only reflect a preference for adjustability over response curve.

I should keep reminding myself that all models are wrong, even if some are useful. George Box said that. Tusayan, thanks for talking me down.

[ridingron]

I can't believe this thread is still going!

Almost like an oil thread.