Materials o Mechanics o Physiology o Engineering o 4.rodynamics Bicycling Magazine's Newsletter for the Technical Enthusiast Winter 1985 Volume 4, Number 5 $3.00 meant by the phrase, "good brakes can III THE LAB make you go faster." Of course, brakes still IN THIS need to perform their basic function: stop- ping the bike as efficiently as possible. Espe, 'SSUE cially on commuting and touring bikes, IN THE UB Mechanics of brales are needed for panic stops and for Shimano's New Dura-Ace maneuvering through Iraffic. And ATB ridhg brakes are designed on the theory Braking is always more fun if unlimited bmking force Performance is available. that yu can go faster with good brakes. Engineer Shinpei Oka- Part 1: Desigr of tk jima expLains here why low fric- tion means better control. Shimano New Dura-Ace SAFETY Braking System Bike lights today seem lretty crude compared to most other cy- Shinpei0kajma cling components. It's not be- eause the laws of optics and. elec- Auto racing drivers always demand good ticity are a mystery. In this test brakes on their cars, but not because they o/ 29 pofular headlights, the Ro- plan to come to a screeching halt duling the dale Product Test Lab a race. Rather, tley need tle precise zalr?,l- found Lving abilitJ that a fine-tuned braking sys- glaring 300-to-1 diffcrenrc in tem can deliver. For this reason, improve brightness betueen brands. ments in cai brakes have kept pace witl other automotive developmeDts, such as greater engine horsepower and better sus- TDEAS & oPtNtoNS 13 pensions. As a result, the millions of drivers on tJle road today all take lbr granted that tleir brakes will perform flawlessly. DESIGN 14 But in bicycle racirg, the role of brakes The adhesiae-bonding method has been uadervalued fo! a long time. And tle primitive state of many bike brake sys- used to build the VITUS 979 tems today is a reflection of this. alwninum frames was patented The situation is about to change, however last Here is the background Now that mces are becoming faster, and fall. dders of more nearly equal ability are com- of that frocess, told by it's inaen- peting, high-performance bike brakes can be tors. a real competilive advantage. This is what is NEWSLINE 16 Mt Ohajina is Assistant Matøger of the Det;elofment Section in Shimano's Technical Ed Seott's new Superbrake puts Figure 1: The "geomelric" mechanical Dll*ioa in Osake, He has ptaled a toian. advantage a stop to limp brake calipers. najor mle in deoeloping Shimano's "Neø of brak8 lovors and Galiperc is determined let distances DuPont weaues its Dura-,4ce" lifie of conNrone h, ikcluding the by oFarm as Company brabing sJstem descibed in this article, akd lollows: way into the structural com\os- the SIS ixdzxed shiftiag slstern, diseussed ;n M.A. ol lever = L1lL2 ites business. And other deuelof- his anile in APil 1985 Bike'fech. Mr. Oka- M.A. ol caliper = C1/C2 jima ments of interest. ako races as an ameteur ir, the lalanese M.A. ol cables = 1 e4uiLolerrt of Category 2 eoekts. M.A. ol syslem = (tl/12) x (G1/G2) Our brake research project at Shimano rs New Dura-Ace design. In Part II, scheduled aimed, therefore, not or y at increasing the for the next issue, we will report on a thor- braking force delivered by the system, but ough stopping-distance comparison of both also seeks to refine the degree of braking new Shimano systems against Campagnolo. control a\ailable to the ider. How is this achieved? ln four words: "lcss " Mecharucal Advantage friction, less flex." Specifically, our tests "Geometric found that conventional brake designs suffer from large friction losses, a problem we One variable the designer cannot adi)sl ar- found easy to correct, in part by use of bitrarily is the mechanical advantage of the lubricarlt filled nylon inserts. Once this was bmking system. Mechanical advantage is the done, we conce[tnted on increasing the multiplying factor by which the rider's force stiffness of the caliper arms (through on lhe hand-lever is ampLfied al the point computer-aided design) and cable housings where the brake blocks compress the wheel (by using flat-wound steel casings). rim. The two components which generate The end result is the New Dura Ace brake mechanical advantage are the hand-levers set, on the market for nearly a year, and the and the caliper arms. If everl'thing in the new Shimano 600 brake package, scheduled system were PeiectlJ igid ald had zo losses for release in early 1986. By actual on-road due to intemal friction, then mechanical ad- tests, we have demonstnted that these new vantage would be simply a geo%etic factori be ralculated measuring Shimano systems show as much as 14 per- Fiqure 2: Test setup t0 measure elliciency lhat is, it could b, lengths of the mechanical lever arms of cent sroLl stopping distance, compared to and "elastic recovery" of brake levers. The the In the brake handles and calipers (see Figure Campagnolo Super Record components. air cylinder, under control ol an automatic (Part focus 1). This geometric definition of mechanical this Bihe Tech article I), we pr0grammer, applies lincar ramp displace- mainly on the R&D evaluations leading to the advantage is not the whole story, but it is ments allernating directions, correspond- in useful as a starting point for the designer. phases ing t0 lhe "apply" and "release" 0l Ideally, the brake system should provide lull is 10 brake operation. Time lor a cycle as large a mechanical advantage as possible, seconds. Load-cell dala versus time ale so that large braking forces could be pro- recorded digitally: typical data ale shown in duced with minimal hand effort. But in prac- Fioure 3 below. The 15 kg dead weighl tical designs, a mechanical advantage of corresponds t0 a hand-level lorce (load about 5 is the highest that can be achieved. 1) lbs. The same load-cell "law of ExecutiveEditor Chairman Gell 0I about I The major constraint here is the lev- Rabert C. Flotuer Robert Rodak equipmenl is also used l0 measure etficiency eragei" rhjs sals, cssentially, lhal to in- and recovery 0l brake cables and calipers. crease a system's mechanical advantage you TechnicalEditors President Teulet Hat lelrel Dads Robelt Figure 3: Typical t0rce-versus-time data lrom brake lever elliciency tesl. Point A is lhe stalt 0l "pull" slroke, point C is the end ol "release" slroke, and point I is the instant when Managins Ediror Publisher pulling slops and release starts (i.e., when air cylinder reverses direclion approrimalely 4 Ed Paulka James C. Mccullash seconds aller the start ol the cycle). Point D is the relatively constanl output lorce reading on load cell 2. (Note that outpul l0rce becomes somewhat ermlic du ng the r8lease stroke.) ContributirgEditors CopyEditor/Proofreader Fnd Delons ChaD'l E- Ki,nba Load.cell data lrom points A, B, C, and D are used t0 calculate brakeleuel elliciency and Ga/! ltlein recovery as lollows: elliciency = D / (B mechanical advantage) Da'id Ca,dan WiL A15:sra-l Arr Dire.ror recovely =C/A Atdvth A- Cabe Crculåtlon Manaper Pat GÅlrtth Bihe Tech-Bnlclinæ Magazjne's Newsletter for the Technical Enthusiase GSSN 0?34-5992) is published qtrarterly by Rodale Press, lnc. , 33 E. Minor St. , Em- naus, PA 18M9. Subscription rates: United States, one year $11.97; two years $23.94i Canadian add $5.00 per year, payable in Canadian tunds; other for eign add ff.00 p€r year (inciudes air mail poståge) payable in U.S. tunds. Single copy pricei $3.00. In" quire about bulk rates. Coplaight 1985 by Rodale Press, Irc. A.l rishts resereed. POSTMASTER: Send address chanse to 8r,, Ircr, 33 E. Minor St., Ern- maus, PA 18049. Second-Clåss Postage Paid at Em- ma,rs, PA 78M9. Bike Tech may not be reploduced in any form without the writteo permission of the pub- lisher. Editorial contributions are welcome. Send inquty or write for suidelines. Include a stamped, self- addressed envelope for relurn of unuscd m crial. This publication is available in micmlorm fmm U versity MicrolilEs Internatiotral. aill lolljree am s21.3044. Ormaiinouirv lo umv€rsrlv l4crolins lhterna tiona l, 3&r No.th zÆb Roaa. Am A.bo., i,fl 43106. '(Nøle: in this gnph, inpul aMl ouloal toftes aæ plolled with dillerc verllcal scele leclots.) Figurc 4: Results 0l brake elliciency tests. Mechanical advantage is Galculated direclly trom Figure 4 shows the results of these lm- provements. efficiency of the Cam- dimensional measulemenls Ll, t2, C1, and C2. Elliciency and ]ecovery ale measured by Overall pagnolo SR system is about 40 percent, l0ad cell selup sh0wn in Figurc 2 above. while for the New Dura-Ace system, it is about 63 percent, an improvement by a fac tor of more than 11/r. Another way to say Shimano Campagnolo this is: with a hand-lever input of 10 kg l,lew SUPeI (about 22 lb), the force pressing the brake Dura-Ace Rccord pads against the rim' in the Campagnolo sys- tem is about 20 kg (10kg X 5.04 M.A. X Lever mechanical advanlage 4.2 4.2 40Va), rcrsus about 32 kg (10kg X Lever elticiency 950/o 900/o 5-04 M.A. x 63%) t,lith Ne$ Dura-Ace. Lever recovery 950/o 850/o Cable mechanical advantage 1.0 1.0 Instruments 0n-Board Cable €lliciency 700/o 550/0' For a better understanding of the dy- Caliper mcchanical advantage 1.2 '1.2 namics of bike bmking, moment-by-moment Caliper elliciency 950/o 800/o recordings of lhe impor!ant variables, during Overall mechanical advantage 5.04 5.04 reål on-road performance, are needed.