Bill:
these points are all quite logical and well thought-out. Making me think some
more about my notion of heavy LSR bike wheels (at least w/ resp. to the front).
Do you know of a published engineering study of speed-wobble causes/ effects/
remediation? Also, I didn't receive Jon's response to your original. Is in not
for public consumption?
Another problem w/heavy wheels (for suspended vehicles) is the slower suspension
response due to the inertia of the unsprung weight. Everything in design is
compromise. Still trying to sort out those compromises before I decide what to
build.
Russ Mack
ardunbill@webtv.net wrote:
> Hi Folks, last week one or two of us kicked this around a little bit,
> since someone theorized that heavier-than-normal wheels would be
> beneficial to the stability of a LSR bike.
>
> Unfortunately, no-one among the 200 mph bike riders has yet commented,
> so the point is moot so far.
>
> >From my observation, most if not all the fast LSR bikes use production
> wheels or custom replacements of about the same weight, and since they
> have been satisfactory for many decades, people see no reason to change
> them.
>
> >From reading, I gather that traditional speed-wobble(front wheel and
> fork oscillation, perhaps from lock to lock), which can easily cause a
> wreck, is still a threat to LSR bikes today, as it has been from time
> immemorial. The best answer is still an effective steering damper.
>
> In 45 years of motorcycling I can tell you what I've learned about
> speed-wobble. It seems clear to me that the heavier the front wheel,
> the more serious the threat of wobble. I attribute this to the pendulum
> effect of the oscillating wheel, and if the fork and fender, headlight
> assy., etc. are also heavy, they aggravate the wobble, once it has
> started from any little bump on the road that strikes the tire off
> center, when the tire, as it is supposed to do, tries to center itself
> again.
>
> Another design feature that seems to give the inclination to wobble is
> heavy drum or disc brake assys. on only one side of the front wheel.
> When this is present, every bump the wheel goes over makes it "kick" to
> the side a little from the inertia of the brake parts. When this is
> combined with the other features mentioned before, you have a wobble
> always lying in wait. Many years ago I had such a bike, made by a
> famous Japanese company. I made it manageable (the bike HAD many
> virtues) by the addition of an aftermarket hydraulic steering damper.
>
> The BEST bike I ever rode for freedom from speed-wobble is the one I
> have now, my 250 Kawasaki Ninja. Careful examination of it for the
> reasons WHY reveals:
>
> 1.The cast aluminum front wheel is made strong but as light as is
> possible for fatigue-resistance, the metal is where it's needed, but not
> where it isn't. It runs true and has no cracks after 70K road miles.
> The 16" tire on it is small and light, but lasts 20K miles or more.
>
> 2. The joint between wheel and fork ends is strong and rigid.
>
> 3. The forks themselves are strong, rigid, but light, and are separate
> from the headlight or any other unnecessary bits that increase their
> pendulum effect.
>
> 4. The single disc brake is, of course, mounted on one side, but is made
> as light as possible, yet is very powerful for the 300 lb weight of the
> bike, so it wears very little.
>
> This bike has the most ideal steering feel of any I ever rode, except
> the lovely treat I once had of riding a Manx Norton on an airport at
> high speed. This Ninja seems to tell the rider "I will NEVER do
> anything BAD with my front fork; no matter what surfaces you ride over,
> you can ALWAYS trust my stability, Pal!" And, it neither has nor needs
> any steering damper.
>
> The LSR point I am getting to is that after pondering the question of
> any benefit of heavy wheels on stability of a fast bike, I have
> concluded that when speed-wobble is under review, heavier wheels would
> be more dangerous than light ones, because of their greater pendulum
> effect, which might easily outweigh any benefit of stand-up,
> straight-ahead gyroscopic effect.
>
> My two cents. Cheers Ardun Bill
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