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 Fifty Plus (50+) Share the victories, challenges, successes and special concerns of bicyclists 50 and older. Especially useful for those entering or reentering bicycling.

 09-18-07, 07:54 PM #1 George Senior Member Thread Starter     Join Date: Jul 2006 Location: Katy Texas Bikes: Specialized Roubaix Posts: 5,456 Mentioned: 3 Post(s) Tagged: 0 Thread(s) Quoted: 28 Post(s) Gearing I don't know if I'm having a senior moment or not. I'm trying to figure speed out in gear inches. I'm in the middle ring 36 and the 18 on the cog with a 27" wheel, that gives me 48.84422. How or where, do I go with this figure to figure my speed. __________________ George
 09-18-07, 08:05 PM #2 John E feros ferio     Join Date: Jul 2000 Location: www.ci.encinitas.ca.us Bikes: 1959 Capo; 1980 Peugeot PKN-10; 1981 Bianchi; 1988 Schwinn KOM-10; Posts: 18,274 Mentioned: 15 Post(s) Tagged: 0 Thread(s) Quoted: 410 Post(s) Actually, 36/18 = 2.0, and 2.0 * 27" = 54", meaning that every time you turn the cranks one full revolution, you advance 54 * pi inches along the pavement. If you turn the cranks at 90 RPM, that's 1.5 revolutions per second, and you are traveling 1.5 * 54 * pi = 81 * pi inches per second, or about 21 ft/sec = 14.5 mph. speed (mph) = (cadence in rev./min.) * (1 min / 60 sec) * (60 mph / 88 ft/sec) * (gear inches = wheel diameter * chainring teeth / cog teeth) * pi * (ft/12 in) Simplifying, we get: speed (MPH) = cadence (RPM) * gearing (gear-inches) * 0.003. Thus, if you can spin the cranks at 120 RPM in a 96-inch gear (50/14 on a road bike, 48/13 on a mountain bike), you can hit a speed of just over 34 mph. An easy calibration point is 100 RPM in a 100-inch gear = 30mph. __________________ "Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt Capo: 1959 Modell Campagnolo, S/N 40324 Capo: 1960 Sieger, S/N 42624 Peugeot: 1970 UO-8, S/N 0010468 Bianchi: 1981 Campione d'Italia, S/N 1.M9914 Schwinn: 1988 Project KOM-10, S/N F804069 Last edited by John E; 09-18-07 at 08:24 PM.
 09-18-07, 08:09 PM #3 SaiKaiTai Senior Member     Join Date: Nov 2006 Bikes: Posts: 2,990 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) That's about as nice an explanation of how gear inches work as I've ever seen. And I've looked a LOT
 09-18-07, 08:15 PM #4 George Senior Member Thread Starter     Join Date: Jul 2006 Location: Katy Texas Bikes: Specialized Roubaix Posts: 5,456 Mentioned: 3 Post(s) Tagged: 0 Thread(s) Quoted: 28 Post(s) Thanks John, that's great, I was wondering what was/is happening to my average. It must be slowing down for turns and stop signs, but I sure don't average that much and I can't understand why. __________________ George
 09-18-07, 08:23 PM #5 George Senior Member Thread Starter     Join Date: Jul 2006 Location: Katy Texas Bikes: Specialized Roubaix Posts: 5,456 Mentioned: 3 Post(s) Tagged: 0 Thread(s) Quoted: 28 Post(s) One more question, John, what do you mean by pi? thanks. __________________ George
09-18-07, 08:26 PM   #6
John E
feros ferio

Join Date: Jul 2000
Location: www.ci.encinitas.ca.us
Bikes: 1959 Capo; 1980 Peugeot PKN-10; 1981 Bianchi; 1988 Schwinn KOM-10;
Posts: 18,274
Mentioned: 15 Post(s)
Quoted: 410 Post(s)
Quote:
 Originally Posted by George One more question, John, what do you mean by pi? thanks.
Pi, the transcendental ratio of the circumference of a circle to its diameter, is approximately 3.1416. To understand pie (with the silent "e"), you need to read elsewhere in this forum.
__________________
"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324
Capo: 1960 Sieger, S/N 42624
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1981 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069

 09-18-07, 08:50 PM #7 cccorlew Erect member since 1953     Join Date: Dec 2006 Location: Antioch, CA (SF Bay Area) Bikes: Roubaix Expert, Motobecane Ti Century Elite turned commuter, Cannondale F500 Mtn bike, Some old French thing gone fixie Posts: 6,861 Mentioned: 3 Post(s) Tagged: 0 Thread(s) Quoted: 34 Post(s) Pi is roughly 3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706 7982148086513282306647093844609550582231725359408128481117450284102701938521105559644622948954930381 9644288109756659334461284756482337867831652712019091456485669234603486104543266482133936072602491412 7372458700660631558817488152092096282925409171536436789259036001133053054882046652138414695194151160 9433057270365759591953092186117381932611793105118548074462379962749567351885752724891227938183011949 1298336733624406566430860213949463952247371907021798609437027705392171762931767523846748184676694051 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2691041407928862150784245167090870006992821206604183718065355672525325675328612910424877618258297651 5795984703562226293486003415872298053498965022629174878820273420922224533985626476691490556284250391 2757710284027998066365825488926488025456610172967026640765590429099456815065265305371829412703369313 7851786090407086671149655834343476933857817113864558736781230145876871266034891390956200993936103102 9161615288138437909904231747336394804575931493140529763475748119356709110137751721008031559024853090 6692037671922033229094334676851422144773793937517034436619910403375111735471918550464490263655128162 2882446257591633303910722538374218214088350865739177150968288747826569959957449066175834413752239709 6834080053559849175417381883999446974867626551658276584835884531427756879002909517028352971634456212 9640435231176006651012412006597558512761785838292041974844236080071930457618932349229279650198751872 1272675079812554709589045563579212210333466974992356302549478024901141952123828153091140790738602515 2274299581807247162591668545133312394804947079119153267343028244186041426363954800044800267049624820 1792896476697583183271314251702969234889627668440323260927524960357996469256504936818360900323809293 4595889706953653494060340216654437558900456328822505452556405644824651518754711962184439658253375438 8569094113031509526179378002974120766514793942590298969594699556576121865619673378623625612521632086 2869222103274889218654364802296780705765615144632046927906821207388377814233562823608963208068222468 0122482611771858963814091839036736722208883215137556003727983940041529700287830766709444745601345564 1725437090697939612257142989467154357846878861444581231459357198492252847160504922124247014121478057 3455105008019086996033027634787081081754501193071412233908663938339529425786905076431006383519834389 3415961318543475464955697810382930971646514384070070736041123735998434522516105070270562352660127648 4830840761183013052793205427462865403603674532865105706587488225698157936789766974220575059683440869 7350201410206723585020072452256326513410559240190274216248439140359989535394590944070469120914093870 0126456001623742880210927645793106579229552498872758461012648369998922569596881592056001016552563756
 09-18-07, 09:20 PM #8 turtleguy54 Senior Member     Join Date: Nov 2005 Location: Lubbock, Tx Bikes: 1971 Motobecane Grand Record (frame), 1983 Vitus 979 (Bought new and built up. My son still rides it), 1978 Raliegh Roadster (complete but totally torn down right now. 28" wheels, Surly Cross Check ( my love. What a bike) Posts: 130 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) George, gear inches relate back to the early 1900's ordinary bikes, those with the huge front wheel and no gears. 54 gear inches means you are riding your modern bike just like someone then with a front wheel of 54" diameter. So, one rotation of your pedals turns the 54" wheel one rotation or approximately 170". From there you can extrapolate how fast or far you are traveling by minute or hour. I do this all the time on rides over 2 hours by myself (I quit using a bike computer in the 80's). It keeps my mind busy on looooong West Texas roads.
 09-18-07, 09:23 PM #9 Tom Bombadil His Brain is Gone!     Join Date: Sep 2006 Location: Paoli, Wisconsin Bikes: RANS Stratus, Bridgestone CB-1, Trek 7600, Sun EZ-Rider AX, Fuji Absolute 1.0, Cayne Rambler 3 Posts: 9,980 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) Pi? Did someone mention Pi?
 09-19-07, 05:11 AM #10 stonecrd OnTheRoad or AtTheBeach     Join Date: Aug 2005 Location: Weston, FL Bikes: Ridley Noah RS, Scott CR1 Pro Posts: 2,170 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) Or you can do it the easy way with http://www.analyticcycling.com/GearChart_Page.html or http://www.kreuzotter.de/english/ecadence.htm __________________ The problem with the gene pool is that there is no lifeguard and the shallow end is much too large 2013 Noah RS
 09-19-07, 06:42 AM #11 George Senior Member Thread Starter     Join Date: Jul 2006 Location: Katy Texas Bikes: Specialized Roubaix Posts: 5,456 Mentioned: 3 Post(s) Tagged: 0 Thread(s) Quoted: 28 Post(s) cccorlew, I tried to work out your answer and I'm sorry you're wrong. Thanks everybody! __________________ George
09-19-07, 08:35 AM   #12
Small Member

Join Date: Nov 2003
Bikes: Diamondback Clarity II frame homebuilt.
Posts: 7,149
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Quote:
 Originally Posted by cccorlew Pi is roughly 3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706 7982148086513282306647093844609550582231725359408128481117450284102701938521105559644622948954930381 9644288109756659334461284756482337867831652712019091456485669234603486104543266482133936072602491412 7372458700660631558817488152092096282925409171536436789259036001133053054882046652138414695194151160 9433057270365759591953092186117381932611793105118548074462379962749567351885752724891227938183011949 1298336733624406566430860213949463952247371907021798609437027705392171762931767523846748184676694051 3200056812714526356082778577134275778960917363717872146844090122495343014654958537105079227968925892 3542019956112129021960864034418159813629774771309960518707211349999998372978049951059731732816096318 5950244594553469083026425223082533446850352619311881710100031378387528865875332083814206171776691473 0359825349042875546873115956286388235378759375195778185778053217122680661300192787661119590921642019 8938095257201065485863278865936153381827968230301952035301852968995773622599413891249721775283479131 5155748572424541506959508295331168617278558890750983817546374649393192550604009277016711390098488240 1285836160356370766010471018194295559619894676783744944825537977472684710404753464620804668425906949 1293313677028989152104752162056966024058038150193511253382430035587640247496473263914199272604269922 7967823547816360093417216412199245863150302861829745557067498385054945885869269956909272107975093029 5532116534498720275596023648066549911988183479775356636980742654252786255181841757467289097777279380 0081647060016145249192173217214772350141441973568548161361157352552133475741849468438523323907394143 3345477624168625189835694855620992192221842725502542568876717904946016534668049886272327917860857843 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Its generalities like this that lead to crashed mars landers!..