Re: [CR]Why normal reach calipers on short reach frames?

(Example: Racing)

Date: Fri, 11 Jan 2002 23:18:52 -0800
From: "Brian Baylis" <rocklube@adnc.com>
To: Sheldon Brown <CaptBike@sheldonbrown.com>
Cc: classicrendezvous@bikelist.org
Subject: Re: [CR]Why normal reach calipers on short reach frames?
References: <14.20b673b1.2970d595@aol.com> <001a01c19b04$573e9c20$6e615cd1@YOUNGC> <v04210107b86564aa3898@[10.0.1.13]>


Sheldon,

I was refering to the concept of minimum clearance and shorter lengths resulting in stiffer parts/frames or what-have-you. My understanding of the purpose of designing a frame to give minimum brake drop was to give the brakes the least amount of flex in the caliper. Shorter tubes also gives the same results in the frame. I suppose I should have explained the concept I was focusing on which is not brakes per se, but shorter is stiffer. Comming from a racing background and a racing frame heritage it is something I am aware of as a framebuilder. I guess I should also have mentioned that I just don't see the point of track bikes built with road clearances or with road fork blades for that matter; assuming we are talking about track bikes for racing as opposed to some perversion thereof. Make sense, or no?

Regarless, you ARE a fountain of knowledge.

Brian Baylis La Mesa, CA
>
> I wrote:
>
> > > 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.
>
> Brian Baylis wrote:
> >
> >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.
>
> Huh? How does this apply to track frames? They aren't made for brakes.
>
> Charles T. Young wrote:
>
> >As long as the brake pads are the same distance from the pivot point (and
> >the arms have equal amounts of flex), it shouldn't matter. The braking force
> >will be solely a function of the length of a straight line from the pivot to
> >the pad.
>
> That's a bit of an oversimplification. With a single-pivot sidepull,
> it's a function of that line _and_ of the distance from the pivot to
> the cable. The ratio between these two distances is the mechanical
> advantage of the caliper. Calipers with longer lower arms generally
> have longer upper arms to maintain the desired mechanical advantage.
>
> The _system_ mechanical advantage is the product of the caliper's
> M.A. and that of the lever.
>
> The mechanical advantage or "power" of a caliper has nothing to do
> with it's quality or cost, you can make a caliper with any desired
> mechanical advantage for the same cost. Making them both light and
> stiff does cost money, but stiffness is mainly a matter of "feel" not
> function.
>
> Douglas R. Brooks wrote:
>
> >I understand Sheldon's point entirely but my question is that
> >given the power of contemporary brakes, such that long reach brakes
> >like RX100s have stopping power comparable to, say, Dura Ace brakes,
> >are the vast majority of modern brakes made short reach to create
> >_that much more mechanical advantage_? Alas, I see no advantage
> >to the short reachers now that brakes are so much better!
> >I guess race bikes don't need clearances, is that it?
>
> I believe that's it. This is sort of like the disappearance of
> fender eyelets. Although it doesn't make the bike a jot faster, it
> says "this is a pure racing machine, useless for any practical
> purpose." It's basically a fashion statement.
>
> >Classic content: Is there any reason why classic centerpulls have
> >not made a comeback?
>
> I've long thought that they were due onacountta the cyclical nature
> of bicycle technology.
>
> >They have many advantages as I see it: easy
> >set up, pulling from the center is mechanically simple and distributes
> >the power efficiently, lots of clearance for fenders, so much so that
> >on my Rivendell it is the fork crown, not the brakes that create the limits.
>
> Centerpulls, like dual pivots, are a way of getting the pivot closer
> to the rim and thus shortening the lower arm, increasing mechanical
> advantage while allowing plenty of tire clearance.
>
> >With Mathauser pads, even the low end Mafacs work as well as any
> >modern brake I use (DA, Record, Mavic, etc.)
>
> That's true. The much superior design of modern brake levers also
> helps. My '61 Paramount still has the original Weinmann centerpulls,
> but with low-end Ergo brifters they work great, in fact better than
> any single-pivot Campagnolo setup I've ever tried.
>
> Sheldon "Freins" Brown
> Newtonville, Massachusetts
> +------------------------------------+
> | Experience is a hard teacher, |
> | because she gives the test first, |
> | the lesson after. -- Vernon Law |
> +------------------------------------+
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