Sheldon,
Pin a silver star on Mr. Sheldon Brown! That is exactly the reason for minimizing the brake reach on a racing bike. The same principal applies to track frames and tire clearance between the fork crown and the seat stay bridge.
That Sheldon, such a fountain of information!
Brian Baylis
>
> Lee Berg wrote:
> >I have noticed a number of '70s bikes, whose frames appear to have been
> >made for short reach calipers, sporting normal reach calipers with pad
> >holders in the tops of the slots. Were normal reach calipers installed
> >due to some desired mechanical property of this arrangement?... or due
> >to a some extended shortage of short reach calipers?... or was it just a
> >fashion of the time?... Or...???
>
> Short reach calipers generally have a reach range of 39-49. Long
> reach is usually 47-57. (Talk of "normal" reach is likely to be
> confusing, and I'd urge everybody to purge this ambiguous term from
> their vocabulary.)
>
> A caliper brake has its greatest mechanical advantage when the pads
> are high up the arms, close to the pivot. Back when long reach was
> the "norm" a conscientious frame builder building a high performance
> bike would locate the bridge and crown to maximize the braking
> mechanical advantage. Especially, the old Campag single pivots had
> such poor braking that this was a very nice touch.
>
> You may also see this on bikes made to work with both 630 mm (27
> inch) clinchers and 622 (700c) tubulars. When the larger wheels were
> installed, the shoes should be near the tops of the slots.
>
> Sheldon "Stop!" Brown
> Newtonville, Massachusetts
> +----------------------------------------------------------------+
> | The thing about the cold is that you can never tell how cold |
> | it is from looking out a kitchen window. You have to dress |
> | up, get out training and when you come back, you then know |
> | how cold it is. -Sean Kelly |
> +----------------------------------------------------------------+
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