On 30 Mar 2007 19:51:55 GMT,
[email protected] wrote:
>Carl Fogel writes:
>
>>>>>> I thought I'd share something I just happened across -- an
>>>>>> account of how Germans made their own bicycle tires during the
>>>>>> post-WWII shortages:
>
>>>>> The description reminds me of an older picture I chanced across
>>>>> some time ago:
>
> http://woment.mur.at/images/GrazerDamenBicycleClub.jpg
>
>>>>> The picture shows an interesting transition between the solid
>>>>> rubber tyres of Fräulein Sorg and the ultra-fat pneumatics of
>>>>> Louise Albl. Mitzi has what looks like a string of squash balls
>>>>> attached to her rims.
>
>>>>> It's also interesting to note that the older young ladies have
>>>>> foot pegs, and are therefore presumably riding fixed, while the
>>>>> young Albls have none.
>
>>>> My ignorance never ceases to amaze me...
>
>>>> Do you know what those huge levers (or whatever) near the riders'
>>>> right hands are?
>
>>>> I'm guessing that they're handles for adjusting the tension of
>>>> some kind of suspension, judging by faintly similar things in
>>>> side-view diagrams in Sharpe's "Bicycles & Tricycles" (figures 272
>>>> and 276), but Sharpe doesn't seem to think that the huge lever on
>>>> one side of the handlebars needs any explanation.
>
>>> I assumed they were brake levers.
>
>> Here's a diagram from Sharp with a similar right-hand monster lever:
>
>> http://i14.tinypic.com/3zs1od1.jpg
>
>> And here's James's picture again:
>
> http://woment.mur.at/images/GrazerDamenBicycleClub.jpg
>
>> Whatever they are, those damn levers are almost big enough to serve
>> as the handle for a car jack.
>
>> Maybe they push a spoon brake down directly onto the front tire,
>> like a plunger?
>
>> I skimmed Sharp's text again, but he seems to think that the purpose
>> of the odd levers must be obvious to the meanest intelligence and
>> not worth mentioning.
>
>I've seen these things and find that they are not for descending
>hills, there being no place to dissipate heat in the skid pad that is
>pressed against the tire. The tire rubber melts and leaves a skid
>mark on the pad and if the brake is used for descending, the pad, if
>metal, gets red hot.
>
>As you see, bicycle tech has not been subjected to much engineering
>even then.
>
>Jobst Brandt
Dear Jobst,
Hunting around in Sharp, I see even more support for your views about
the inadequacy of very old brakes.
After considerable calculations (probably limited by the design and
materials of 1896), Sharp arrived at this conclusion:
"That is, no brake, however powerful, can stop the machine on a
gradient of 121 in 1,000, about 1 in 8."
--Chapter XXXII
Even if Sharp's calculations are mistaken, it sounds as if back in the
spoon-brake era it was assumed that a sustained 12% grade was simply
suicidal.
Sharp mentions pneumatic (!) spoon brakes:
"In the pneumatic brake the movment of the brake block on the tire is
produced by means of compressed air, pumped by a rubber collapsible
ball placed on the handle-bar, and led through a small india-rubber
tube to an air chamber, which can be fastened to any convenient part
of the frame. With this simple apparatus the brake can be as easily
applied to the rear as to the front wheel."
Sharp was also dubious about the new-fangled band-brakes, which were
applied to not only the hubs, but to the crank axle (presumably on a
fixie). After more calculations, he concluded that the crank-axle
brake was a bad idea:
"This example shows the ineffectiveness of a crank-axle band brake,
since the elasticity of the gear is such that the brake lever would be
close up against the handle-bar long before the required pull was
exerted by the band."
"If oil gets in between the band and the drum, the coefficient of
friction will be much less, and a much greater pull will be required,
than in the above examples."
Cheers,
Carl Fogel
