On Thu, 29 Jun 2006 19:26:15 GMT, Call me Bob
<
[email protected]> wrote:
>On Thu, 29 Jun 2006 11:35:11 -0600, [email protected] wrote:
>
>>>The R&M Birdy City folding bike uses a coaster brake with a chain tensioner:
>>>
>>>http://www.kinetics.org.uk/html/city2.shtml
>>>
>>>My initial reaction is that this shouldn't work:
>>>What have I missed?
>
>>Dear James
>>Motorcycles.
>
>Perhaps I'm being thick (I frequently am), but I don't see the
>correlation. Motorbikes don't routinely have chain tensioners and
>coaster brakes, so how do they give a clue to the way the Birdy copes
>with that set up?
>
>"Bob"
Dear Bob,
No, you're not being thick.
Trials motorcycles have used trailing-arm chain tensioners since 1972.
Rod and naked-wire actuated rear hub brakes even longer.
Floating rear brake arms ditto.
Increasing rear suspension travel.
And so on.
Bicycles do have lighter, thinner, flimsier chains that are more prone
to de-railing, but the pitch and tooth height are the same as 428h
motorcycle chain.
Many bicyclists remain unaware of the history and design of the other
two-wheeled vehicles. For example, experienced bike mechanics have
asked on RBT whether motorcycles freewheel, as opposed to behaving
like fixed-gear bikes.
To be fair, I've met motorcycle mechanics who were initially skeptical
of my description of a bicycle derailleur and insisted that it would
ruin the sprocket teeth after a few shifts. (We at RBT have trouble
believing that there are people as unfamiliar with bicycles as some of
our posters are with motorcycles, but they really do exist. I have a
fairly athletic brother-in-law from Maryland who somehow never learned
to ride a bicycle.)
It's a little like doctors and veterinarians, who are often unaware of
each other's worlds.
My father, a surgeon, was puzzled when I described the crude
veterinary treatment for canine sebaceous gland cysts (marble-sized
hair-root pimples from hell), which often consists of sticking a
large-bore needle into the swelling and "manually expressing the
matter," as my vet delicately put it just before he squeezed the lump
and the stuff literally hit the ceiling. Then a bit of digging around
with a sharp needle and removal of some shreds of the oil gland in
hopes that the destruction of the gland would prevent re-infection.
For human sebaceous gland cysts, my father explained, treatment
involves a small incision under local anaesthetic and the neat removal
of the entire distended oil gland, which prevents it from ever
becoming re-infected.
My father's technique for humans was unquestionably better than the
common veterinary approach, but my father's patients were willing to
pay much more than Fido's owners.
They also submitted gracefully to local anaesthetic without being
muzzled. (It's odd, but many dogs will stoically let a vet gouge them
with a needle, but climb the walls hysterically if they see a
hypodermic barrel attached to it. Similarly, lots of dogs shriek and
cry pitifully when the cruel rubber tourniquet is lightly tightened on
their foreleg, but then ignore the actual drawing of blood.)
My father's patients also did not require shaving their thick fur off,
rarely tried to nibble their stitches out after surgery, and scarcely
ever rolled naked on their wounds on a lawn that they used as a toilet
(although insane patients from the state hospital sometimes posed
unusual challenges). They also didn't grow new sebaceous gland cysts
every month from head to toe.
Cheers,
Carl Fogel
