Recordholder... Than the a Bicycle with Its Wheels -And "Pro6l": Looks at How Changing the Wheel Can Sheathed in Plastic Fairings
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Materials o Mechanics o Physiology . Engineering . Artodynamics Bicycling Magazine's Newsletter for the Technical Enthusiast August 1984 Volume 3, Number 4 $2.50 In an article published more than four AERODY]IAMICS years ago, "Aerodynamics or Light IN ilHIS Weight"t I estirnated that if Eddy Merckx had been riding a Renault-Gtane "Profl" bi- 'SSUE cycle, he could have ridden 51.470 krn in an hour, instead of 49.431 km, with the same AERODYNAMICS 1 energy expenditure. My htpothesis, based Hour Record Holder on data plovided by the manuhcturer, was In "The True that tlis bicycle would have reduced by 70 . Is Bracke," Claude Genzling watts the energy needed to ovelcome air re- compares the effects of air drag of The True Hour sistance. Francesco Moser caried out his record three hmous hour-record rides. attempt on a bicycle even more aerodynarnic in "Spoke Drag," Glen Brown RecordHolder... than the a bicycle with its wheels -And "Pro6l": looks at how changing the wheel can sheathed in plastic fairings. It is interesting Is Bracke! tllat Moser's record distarce (51.151 km) is decrease wind resistance. slightly less than the distance I had calcu- lated for Merclo< on the "Profl" (51.470 Claude Genzling km) , It seemed that the question oI the aero- 6 dynamic bicycle called for further evaluation. MATEilALS I had aleady collected additional data, nota- Lunas concludes his discussion bly on the Gitane "Delta e" bicycle,'?This -Les of Imron in "Painting with lrnron, new data now permits us to calculate tle im- Ed;tol's hote: Of coarse, the true ho / rec- portance of reduced air resistance in Mo- Part II," while Harvey Sachs details ord hoder is Frøncesco Moser, bat ø liælt de- ser's record-breaking ride. the precautions necessuy when bate is u deruø! as to uløhat engineer gor using this wonder paint in "Using dthletic the gftater role in Mo- tlouess flated Pdnciple of the Caldations sel's stt rnirrg victory. Claude Genzling ex- Imron Safely." llores this question b! {sittg tha fu darrrental eqøtion that relates bictcle sfued to øir drag The power which a cyclist expends m given bo )er loss, cornbihed t;th a few ury Pløu- overcoming air resistance is by the for- DE$AN 8 sible, thoøgh ,tot cornlleteb tested, øssumr- mula: CRIIERIA tians. Genzling cakalates th. tlworetical Oer- p Pipkin's "An Analysis of of Moser, Eddl Merch, qøur rccor- = p. CD.A.(V/3.6),/2 -Raymond lornance Front Fork Flexibility" looks at how dman beforc Moser), Bernard Hina and t, (watts) Ferdirattd Brache (hour recordman in 1967) where P : power the front fork affects ride comfort of air density ftg/m')^ on ø oøiety of biqcles øld at borh high awt = touring and racing frames. lou altitulzs. The resulh are tral! suriisiøg! cD = &ag coefficient (dimension- Unlortufidtelj, sorne oI the assumtlions less) (m) øeeded for this calrulalioh are uhtestable. ifi a A = ftontal area sense. Praetical lechniqucs fol t teasuing = sæed (km/hr) sHoP tAu( 14 ufuel air d.rag and tire rolling resistørce, 3.6 = factor for converting km/hr to for your perfectly erafille, are still undel fuuelotnerrt. This m/s (See footnote 3.) -You can tune spokes daes not dztroct frorn the tulue of Genzlittg's if you follow "A Musical Test for stud!, but it does out the arcas øfure ,oint Conect Spoke Tension" by John S. øore uorh is needed. 'See Le Cyde, na. 51 , Nooen ber 1979. 'zSu LE Cycle, tu. 95, Noneflbet 1 3. Allen. 'E&lot s nol2: Th, orisinal Frefth anicb s )es all sfue(k in fieteE second (nt/s), Oø hansl$" Retrinted Le Cycle (no. 99), Malch fur lron tion gioes sbeedt ifl h;lomate/s rer lønr (hfi/hr), be- 1984, Pais, Frørce. Tronslation assistarrce cause this number telk itlrhediatal! hou lar the rider IDEAS & OPINIONS 16 bf lohn S- Allen- Thabks to Eic Hjertberg for uouw bat)el ir, one hour if he fiai toir.s corrsta biøging this øtficle to ou.r øtten ion. sryed. -ATB's and HPV's This equation can be rearranged to solve for the rider's speed in terms of the power he expends against at lesistance: Table 1. Bemard Hinault riding at Sea Level' 3\/2flG v = 3.6 CDIA) From this second equatiin, we ian compute exactly how much the rider's speed OI) will increase iI either the air density (p) or the effective frontal area (CD A) are made smaller.{ It is precisely these two factors which were crucial in Moser's record- breaking ride: -air density, which decreased ftom 1.225 kg/m3 at sea level to 0.961 kg/m3 at the altitude of about 2,000 meters in Mexico where Moser achieved the record, assum- ing equal temperahfe; 'Air density p = 1225 kqh3 -effective frontal area, wluch was !e- t&ditor's note: The terrn "efrecthe hor.tnl orca" lelers to the ftoduct ol drag coelfubnt (C hnas hontal alea (A) . In thh aniale, the ølvas qu.ottd lor alfectbe l/onbl ana ,ertain b AE corhb;aation of imFoving position physiological question biclcle rid.r. Effectil,e funtal area b ,ethols duced by the of the below, after 6rst dis- ride! on the bicycle and by aerodlramic cussing the purely mechanical effects of ai! th" rwst'tus ustul siryb iunn$ lot sPrilying the b ). clc's aelod} amir qualitbs, h/ hoo reasons. strean ining of the bicycle and its wheels. dmg and altitude. Fi/st, it accounts lor both the shaw of the bic>ub/ The actual values o{ effective ftonta.l area t;dn conbination hmql tt+ CDt rrn) and * six" (Ce.A) for typical mar/machirc combirta- (lhtotsh lhz A terrt). Se.ohd, erl?rimfiløÅ .an tions are well-klown today, thanks to the Hinault Baseline Qeti!! fiets n elfecti& arpa uith simpb in- as Experimental hontat work of the Aerotechric Institute of Saint- slru,,,ants, but haae grsal dilfit1/lt, il naatuiflg ei. Cyr-l'Ecole, directed by Maurice Menard.s tfur drcg coaficbnt ol fmr.tal area selaratab. The provided precise lhls,aal^units ol ellediw funtal alea arp søøn me- He has measured data on Since 1979, the Aerotechnic Irstitute of t?ts tt') ifi 1? SI ststeri, and square leet ifi the this subject. For example, we lnow tllat Saint-Cyr-l'Ecole has been testing a yariallt English sfsttn . Eddy Merckx on a taditional bicycle h the of the "Pro6l" bicycle intended for a possi- recotd-seeker's low dding position exhibits ble future houl record attempt by Bernard an effective tontal area of 0,39 m2. I have Himult. This bicycle, with a 600 mm front used this and other test data6 to derive rca- wheel and 700 mm rear wheel, is virtually sonable assumptions about the effective identical to the one which Francesco Mos€r TECH frontal areas of Fralcesco Moser and Fer- used in Meico, except that it lacks failings dinand Bracke (an exceptioMl but often for- on the spokes.T We know that Bernard Hi- gotten hour-record holder) riding various bi- nault would have to develop 550 watts at seå Exeoltive Editor Chairm.n Robei G. Floøel RoM Rodttb cycles. level to overcome air resistånce at a speed of We are now in a position to calculate the 50 km/hr on a "Profl" bicycle. We also President Technical Ediior distance which these three champioos would know the differences in effective frontal area lin Redeq RoM Teulel have traveled on differert bicycles and at dif- between the traditional bicycle, the "Profl" . Publisher Manåging Edjtor ferent altitudes, given only that their power bicycle, Hinault's "hour record" bicycle Jdfies C. McC,r agh output rvodd be the same in our fctional rec- (which later became the "Delta e") and Mo. Assistat Editor Contributing Editors ord attempts as it was in their real ones. ser's bicycle with its faied wheels. Conse- Fred DeLong Actualy, there's one additional problem quently, we can calculate the power con- Gary Klein Aft Dnector we must fuce in tryirl8 to compare record at- sumed by air &ag with Hinault riding each of Daoid Gordol l{/ilson tempts in Mexico against others in Rome or these cycles: Editor Emeritus Assistånt Art Director Milan: altitude reduces the cyclist's orygen Ctisr,, Mount MiÅer Calheiw L, Schuarh consrmptio[ and so reduces his maximum P = 1.225(50.000/3.6f(CD.A) i 2 CnolationManåger Ilustrator possible povrer output. We wil deå.I with this P:1,641(Cp.A) Patoilfith Georye Retseck BIKE TECH (ISSN 0734-5992) is published bi- 5&e From this, we have delived Table 1, which Ir Cycle, ,',. 52, D.cenbel 1979. ntontt'ly by Rodale Press, lnc-, 3i] E. Minor St., Em- GEditor's applies to Bernard Hinault ridiry at 50 ktrL/hr inaus, PA 18,(}19. Subscription rates: United States, note: For lhos, wha work with Englbh ,t ittstead of SI units: tha afectit)e lnl at sea level. The faLed wheels alone achieve one year $14.97; two years $æ.94; Canadiah add tih fu alea ol a savings of approximately 18 \r,atts, reduc- S.00 per year, payable in Canadiar irnds; other for- the least st/eofilineil bicwle/idel combination (0.3g power eiSn add $6.00 per year for sea mail, $10 for air rnail, $otct in rhis anirte # lor Mercht on o tlodi- ing by haf the consumed by "aero" payable iD U.S. tunds. Single copy pricer $2.50. In- tional bicrrle) equals 4.20 f in E"gtish ,,its.