Though I've been critical of Grant Peterson's effort to revive centerpull brakes, I have to admit
that the latest Rivendell Reader (#30) gave me reasons to pause.
First of all, in the letters section, a reader (Thomas Papetti) points out that dual-pivot sidepulls
won't track an out-of-true rim the way all other brake types will. I'm not sure how much that counts
in favor of centerpulls (Papetti doesn't discuss them at all). Even though most riders would
probably use long-reach dual pivots in lieu of centerpulls, long-reach single-pivot sidepulls and
cantilevers are still available if tracking is a significant worry.
Then in an article, Jan Heine makes several claims for the superiority of sidepulls.
He says, "The long lever on the cable side [above the pivot, if I understand him correctly] and the
short lever on the pad side [below the pivot] gives centerpulls a huge mechanical advantage over
sidepulls. Just like a bolt-cutter, where long arms and short jaws allow you to cut through thick
steel bolts." Later on, he adds that only with the advent of dual-pivot brakes did sidepulls catch
up to centerpulls in this respect.
That doesn't seem to jibe with Jobst's discussion in the FAQ, which seems to suggest that
single-pivot sidepulls and centerpulls had the same mechanical advantage.
He argues that only the part of the arm below the pivot needs to be beefy, because that's the only
place where flex matters. "As a result, the arms above the pivots can be incredibly skinny, as they
don't need to resist flex. That is where the weight savings of a centerpull originate." He doesn't
say what the weight savings is.
He writes, "And since the pivot on centerpull brakes is on the fork leg, adding reach does not
increase the flex or change the mechanical advantage. So there is not incentive to go to short-reach
brakes." I think he means that since the distance between the pad and the pivot point always remains
the same, adding lever length above the pivot doesn't effect the mechanical advantage. That sounds
dubious to me -- doesn't changing the length of a cantilever brake's straddle cable effect
mechanical advantage even if all else remains the same? Furthermore, from the photos of old
centerpulls in the Reader, it doesn't seem as if the distance from pivot to pad was always kept
constant (some long-reach brakes seem to achieve that reach in part by increasing the lever below
the pivot).
He notes that centerpulls don't stick out to the side like centerpulls. It seems to me that that
problem can be cured by using v-brakes, though that introduces problems of its own (e.g., mating
them to road levers).
He says that even the standard-reach (what would be called long-reach by most) dual-pivot brakes
offered by Shimano don't leave much room for fenders. Is that true? Just how big a tire would you
have to run before you would crowd out the dual pivots? (Elsewhere in the Reader, Grant says that
centerpulls will clear a 40mm tire or a 38mm tire with fenders; what's the limit with the current
long-reach dual pivots?) Furthermore, why not long-reach single-pivots, which are still available?
Probably his most controversial claim is that single-pivot sidepulls "offered inferior performance"
and became widespread mostly because of Campagnolo's advertising and gruppo packaging. Contrast that
with Jobst's claim in the FAQ that, "The centerpull brake of the 1950's, was popular for nearly a
decade, in spite of being entirely without merit, being worse in all respects than the side pull
brake with which it competed."
In the past, I've been pretty fed up with Grant's talk of reviving centerpulls, because it so often
appeared side-by-side with complaints about Rivendell's financial straits and lack of popularity. I
do notice a more refreshing tone in this issue: he mentions a bike planned for next year that will
have braze-on pivots for centerpulls and adds, "But we don't expect anybody to follow that lead.,
and we fully expect to sell fewer bikes because of it. Centerpulls, for as much sense as they make,
will still scare off most customers."