[Fwd: [MC-CHASSIS-DESIGN] Fwd: Steering dampers - a warning.]

Randy Grein randygrein at comcast.net
Tue Sep 7 23:01:55 PDT 2010


While Tony is correct in a technical sense, most motorcycles seem to  
benefit from a damper. Getting it tuned is a bit of a trick, but it  
seems to be a matter of MINIMAL damping - just enough to allow the  
rider to catch the oscillation, and no more. A subject worthy of some  
thought and discussion.

Like most of the 'experienced' crowd I have ridden many a bucking  
bronc, and have first hand experience in the difference between a  
wobble and a weave. My 1100 was a great example of this when I first  
got it - once the rear tire got the tiniest bit of profile from wear  
it would start to weave at speed. Cutting back from full to half  
throttle would stop it, increased damping did little, but I could  
exert enough force on the bars to get another 20 mph before it became  
unmanageable. Replacing the stock leading link forks with GS1000 forks  
and a huge set of clipons took care of the problem nicely, and it  
became a well behaved beast that responded well to a heavy hand.

I can see a point where dampers are no longer needed for any bike.  
Cycle World, IIRC had an article a year ago about a reverse spinning  
brake rotor that seemed to eliminate wobble and nervousness associated  
with insanely shallow rake angles. Even if that doesn't pan out other  
technical advances are likely to solve the entire problem, and we are  
stuck with a rulebook that requires a safety device that doesn't  
increase safety - and could make it worse.

Randy Grein, WMRRA #141

On Sep 7, 2010, at 9:12 PM, Jim Stewart wrote:

> From the MC Chassis Design list. Tony Foale is an internationally  
> renowned motorcycle chassis handling authority. Knows his stuff...
>
> -js
>
>
>
> -------- Original Message --------
> Subject: [MC-CHASSIS-DESIGN] Fwd: Steering dampers - a warning.
> Date: Tue, 7 Sep 2010 20:02:37 -0400
> From: Tony Foale <info at tonyfoale.com>
> Reply-To: MC-CHASSIS-DESIGN Mailing List <mc-chassis-design at micapeak.com 
> >
> To: mc-chassis-design at micapeak.com
> References: <AANLkTimfxDYMUkhpbma85gBGXa_hZ-okoHUpHsTrg+Wx at mail.gmail.com 
> >
>
> There has recently been some discussion on the USCRA list about  
> steering
> dampers.  The following is a post that I have just made on this  
> subject,
> which is also appropriate for this list.
>
> Regards
>
> Tony Foale
> info at tonyfoale.com
> www.tonyfoale.com
>
>
> ---------- Forwarded message ----------
> From: Tony Foale <info at tonyfoale.com>
> Date: 7 September 2010 13:25
> Subject: Steering dampers - a warning.
> To: USCRA at yahoogroups.com
>
>
> Although hydraulic steering dampers can be useful in reducing the  
> steering
> kick back caused by bumps and dropping a misaligned front wheel on  
> the deck
> after a wheelie, they also have a dark side which is little known  
> about nor
> understood by the average rider.  There are no free lunches.
>
> This is not a suitable forum in which to go into great technical  
> detail, and
> this is a very technical subject, so I shall try to keep it as  
> simple as
> possible.
> There are two oscillatory modes of instability inherent in all  
> inline two
> wheelers.  Viz: Wobble and weave.
>
> Wobble is a relatively low speed problem which shows itself as an
> oscillation of the handlebars at around 30 to 40 mph.  Some bikes  
> are more
> prone to it than others.  e.g. The old 1960s BMWs with the Earles  
> forks were
> well known for this.  In general this is more an annoyance or  
> curiousity
> rather than a real danger and it can be easily reduced by the use of  
> an
> hydraulic steering damper.
>
> Weave, on the other hand occurs at higher speed and has often  
> resulted in
> serious injury and many fatalities.  This form of oscillation  
> involves the
> whole machine not just the steering.  The bike will roll and yaw  
> side to
> side as well as the steering.  Whilst some bikes are known to  
> exhibit this
> behaviour it usually remains hidden until a particular set of  
> conditions
> sets it off, but ALL bikes have the potential for it to occur.
> Unfortunately, a HYDRAULIC STEERING DAMPER INCREASES THE PROBLEM.   
> In simple
> terms, the steering forces provided by the damper occur at a time that
> reinforces the weave oscillation.  The forces are out of phase with  
> that
> required.
>
> For those who are unfamiliar with just what a weave means I offer  
> this link
> to a dramatic video from the IoM.
> http://www.youtube.com/watch?v=XiKmPFo6xNA
>
> Here is a layman's description wobble and weave
> http://docs.google.com/viewer?a=v&q=cache:uVwYj-iOW0YJ:metrohog.com/images/20020215_NYTimes_Motorcycles.pdf+bray+hill+motorcycle+weave&hl=en&gl=us&pid=bl&srcid=ADGEESiddJprAM8XY0R6Pfok2riB0rggv1NxhkeKPPK8XrhgxyGdE2jw9jEnZJOHHi06X2N0v0GBenMR4NaPwISdnRqeuzNswRV8mEox4vN0pMh1lHVwYhqSI0Dp0CPpfsjTEWAFlxDY&sig=AHIEtbRVqHhMX2FdFqdqHhk7wEpjrqeWOQ
>
> Here is a technical paper on the subject (not suitable viewing for  
> maths
> phobes - parental guidance advised)
> http://eprints.imperial.ac.uk/retrieve/3175/license.txt
>
> If WERA have mandated the use of steering dampers, then they are  
> seriously
> misguided if they believe it to be a general safety enhancement.  As I
> stated at the beginning, it can be very useful to reduce the effects  
> of
> kickback and that can improve safety.  However, the characteristics  
> of such
> dampers is that they make a bike more prone to the very dangerous
> possibility of weave.
>
> This is a plea to the USCRA rules committee, to reject any future  
> proposal
> to mandate steering dampers under the misguided assumption that they  
> are
> always a safety feature.
> If a bike shows no sign of kick back problems at a particular  
> circuit then
> you are better off to not fit a damper.  On the other hand, if the
> handlebars try to fly out of your hands at times then a damper may  
> be the
> lessor of two evils.  Not all bikes need them, even on circuits like  
> the
> IoM.  I rode there for 5 years and never had one fitted.
>
> Footnote.
> There is some hope that in the future devices will be available to  
> reduce
> kick back, wobble AND weave.  Micro-computer controlled active  
> systems could
> do it, but there is a passive device which analysis has shown to have
> positive effects with regard to damping out weave etc.  It has been  
> called
> an "inerta",  an hydraulic damper produces a force which is a  
> function of
> its compression or extension velocity, an inerta produces a force  
> which is a
> function of its compression or extension acceleration, which is 90  
> deg out
> of phase with the velocity.
> The reason that your neighbourhood MC shop doesn't stock them is two  
> fold:
> 1.  It is only recently that their effect has been studied.
> 2. They are more difficult to impliment in metal than hydraulic  
> dampers.  In
> the past we had friction dampers because hydraulic items were too  
> expensive,
> so maybe in time we can hope that inertas may become common place.
>
> As regards to dampeners, these were quite common in the days before  
> tearoffs
> to clean one's goggles.  They usually took the form of half a tennis  
> ball
> clamped to the handlebars, this contained a tethered sponge which  
> had been
> dampened before the race.  Their effect on wobble and weave was said  
> to be
> minimal, but they worked wonders removing the remains of insects  
> impaled at
> high speed.
>
> Regards
>
> Tony Foale
> info at tonyfoale.com
> www.tonyfoale.com
>



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