TECHNICAL JOURNAL OF THE IHPVA
NUMBER 52 SUMMER 2001
Summaries of articles in this issue; mast ...... 2 Contributions to Human Power ...... 2 Articles The mechanical efficiency of bicycle derailleur and hub-gear transmissions Chester Kyle and Frank Berto...... 3 Technical notes Bicycle stability after front-tire deflation Dave Wilson ...... 11 There is a better way than rolling Detlev Tschentscher...... 12 Tire-rim compatability, John Stegmann ...... 13 Control of hydrofoils using dynamic water pressure Alastair Taig ...... 14 Project review CHicK-2000 Project Team “Active Gals” Reviewed by Mark Drela ...... 16 Book review Richard’s 21st Century Bicycle book(s), by Richard Ballantine, reviewed by Dave Wilson ...... 19 Letters Battle Mountain crank arms, Matt Weaver ...... 19 Response to Matt Weaver, Danny Too...... 20 Crank-arm length and leg length/proportions? John Stegmann ...... 21 Response to John Stegmann, Danny Too ...... 21 Editorials Number 52 A bit of history viewed from Eastern Europe Marek Utkin ...... 23 Summer 2001 $5.50 The future of Human Power, Dave Wilson ...... 23 The mechanical efficiency of HUMAN POWER bicycle derailleur and hub-gear transmissions Number 52 Summer 2001 $5.50/IHPVA members, $4.50 Chester R. Kyle, Ph.D. Frank Berto IN THIS ISSUE Al Taig has developed a lower-drag and HUMAN POWER cleaner alternative: using the impact (pitot) competition [3, 4]. Previous published reports The mechanical efficiency of bicycle INTRODUCTION pressure picked up on the leading edge of is the technical journal of the derailleur and hub-gear transmissions Since human power provides the For example, suppose Christopher There have been many published International Human Powered Vehicle the strut supporting the foil from the hull Chet Kyle and Frank Berto have given us propulsion for a bicycle, losses in Boardman, the present holder of the reports on the mechanical efficiency of Association and controlling the attack angle from, e.g., a long-awaited and very valuable report mechanical energy are far more impor- bicycle world hour record (56.375 km; bicycle transmissions during the past Number 52 Summer 2001 a bellows. on a precise study of the efficiencies of a tant than if purely mechanical or elec- Manchester, England, 1996), were to century; however, only a few have Editor wide range of bicycle transmissions. It is PROJECT REVIEW trical power is used. use a bicycle with a drive that lost 2% measured the efficiency using accurate David Gordon Wilson both quantitative and well discussed. One CHicK-2000 project team “Active Gals” The mechanical efficiency of a drive more energy than his record machine. mechanical means [1, 2, 5, 6, 7, 8, 9, 21 Winthrop Street intriguing conclusion is that, in general, system is defined as the ratio of the Boardman would travel almost 0.5 km 10, 11]. These studies found that bicy- Winchester, MA 01890-2851 USA Mark Drela reviews the report and hub gears have efficiencies about a couple power output to the power input in per- less in one hour [3]. The hour record cle drive efficiency depends upon many
2 Number 52 Summer 2001 Human Power Human Power Number 52 Summer 2001 3 all drive-train components such as today in Europe where they are used electronically. The output shaft of the efficiency, the ergometer drive losses ing for the losses would raise the and a 19-tooth rear cog. The three hub the bearings, chains, sprockets, gears, mainly on city commuter bikes. Hub- motor was connected to a bicycle would have to be determined, and this reported efficiencies by 2 to 2.5%. gears are: (1) Ratio = 0.75); (2) 1.00; and derailleurs are usually included in gear transmissions have the advantage crank through a flexible coupling. was done only at 75 rpm. However, • The test fixture was then used to and (3) 1.33. the efficiencies. However, some studies of being nearly weatherproof, with low Knowing the torque and the rpm, the for determining the rank order between test the efficiency of eleven transmis- 3-speed: Shimano report the efficiency only of isolated maintenance—and they permit a chain input power to the crank could be transmissions, since they were all test- sions. Weights were chosen to produce A rear hub with a 40-tooth front components [6, 7, 9]. Thom [6] mea- guard that completely shields the chain, calculated. The dynamometer was fur- ed under identical conditions, no cor- 80 watts, 150 watts and 200 watts out- chainring and a 19-tooth rear cog. The sured the efficiency of three-speed hub and allow bicycle commuting without nished by the U.S. Olympic Committee rection is necessary. The efficiencies put power at 75 crank rpm. All chains three hub gears are: (1) 0.74; (2) 1.00; gears and bearings without including worrying about soiling good clothes on (USOC) Sports Sciences Division. reported in this article include ergom- were well oiled with light machine oil. and (3) 1.36. sprocket losses. Dell’Oro [7] isolated a greasy chain. However, they have The power input to the bicycle crank eter-wheel drive losses, so the actual Hub gears were usually left with their 3-speed: Sturmey Archer derailleur losses from the rest of the never been popular with serious rec- was given by: transmission efficiencies would be original grease lubricant, but this was A rear hub with a 40-tooth front drive system. Cameron [9] measured reational cyclists or racers since the Pi = kτω where Pi is the power, k higher by 2 to 2.5%. replaced in two hubs with light oil. chainring and a 19-tooth rear cog. The the required static force to lift a known range of gears has been limited. Also, is a proportionality constant, τ is the 4. Data-acquisition system The transmissions that were tested three hub gears are: (1) 0.75; (2) 1.00; weight with a bicycle chain draped they are heavier than a derailleur-type torque and ω is the angular velocity of A portable computer was adapted by had the following gears. and (3) 1.33. over a single sprocket. He assumed transmission and they have had the the crank. Peter Kauffman of Browning to receive Derailleur-type transmissions 4-speed: Shimano Auto D losses were constant with rpm, and reputation of being mechanically inef- 2. Bicycle-drive-train fixture signals from the load cells and revolu- 4-speed automatic: Browning A rear hub with a 31-tooth front estimated fixed-gear efficiencies under ficient. Recently, however, there has A special test fixture was built to tion counters. The computer sampled This transmission has a gear layout chainring and a 23-tooth rear cog. The various loads. The remaining studies been a revival of interest in the hub mount a bicycle bottom bracket, crank the transducers and averaged the read- similar to a standard derailleur system four hub gears are: (1) 1.00); (2) 1.24; measured the overall efficiency of the gear for several reasons. They are now and chainrings, plus a rear hub without ings over a selected time interval. except electronically actuated hinged (3) 1.5; and (4) 1.84. bicycle drive system [1, 2, 5, 8, 10, 11]. available with an increasing number of spokes or wheel. On the non-drive side The software automatically calculated gear segments in the rear cluster shift Indirect methods such as repetitive gears (as many as 14), they lend them- 7-speed: Sachs of the hub, a sprocket was attached to ergometer power along with the the chain up or down either automati- A rear hub with a 40-tooth front field time trials, field or laboratory oxy- selves to fully automatic operation, and the hub which drove a Monarch bicycle mechanical efficiency of the bicycle cally or manually. The Browning chain chainring and a 19-tooth rear cog. The gen-consumption studies, crank-power- they can easily be adapted to bikes ergometer wheel. The adjustable fix- drive including the ergometer drive. All guide and tensioner, with its two jock- transmission shifter was damaged and meter field trials, or crank-power-meter with an electric-motor boost. Regarding ture was built by Jim Merz for Brown- of the data and calculations were dis- ey pulleys, has a similar appearance to could be shifted to only two gears: studies on stationary trainers, lack the the hub gear’s reputation for mechani- ing Research, and it allowed rapid played in tabular form on the computer a derailleur, and probably has nearly (1) 0.59 and (4) 1.00. necessary precision to give reliable cally inefficiency, this paper will pres- changing of front sprockets, chains and screen, and the data were stored for identical friction characteristics. It is results. Usually such methods have an ent information that shows this is not rear hubs. later analysis. 7-speed: Shimano Nexus however a passive follower. In this A rear hub with a 40-tooth front error band of several percent. necessarily so. 3. Monarch ergometer wheel TEST PROCEDURE paper, the two Browning transmissions chainring and a 19-tooth rear cog. The Purpose of current tests NEW TESTS To measure power output, a Mon- • The load cells were calibrated and the 27-speed derailleur transmis- seven hub gears are: (1) 0.63); (2) 0.74; The purpose of the current tests was During 9–13 October 2000, in the arch aluminum ergometer wheel was using weights. The load cells agreed sion will often be referred to as “derail- (3) 0.84; (4) 0.99; (5) 1.15; (6) 1.34; and to compare the mechanical efficiency Laboratory of the Browning Research driven by a chain from the drive-train with the weights within ±0.2%. The leur-type” transmissions. The Browning (7) 1.55. of the most common types of bicycle Facility on Bainbridge Island, Wash- fixture through two 36-tooth sprockets, accuracy of the angular-velocity trans- 4-speed was tested with a 42-tooth drives under identical conditions. Since 7-speed: Sturmey Archer ington, the authors and Peter Kauff- one on the ergometer wheel, and one ducers of both the crank and the front chainring and a 12-, 17-, 23-, and limited time was available, the test A rear hub with a 40-tooth front man, technical consultant to Browning on the non-drive side of the bicycle ergometer wheels were checked by two 32-tooth rear cluster. apparatus had to handle all of the chainring and a 19-tooth rear cog. The Research, used a specially-devised hub. A nylon cord, approximately 3 mm methods. The crank rpm was verified 12-speed automatic: Browning most common types of bicycle trans- seven hub gears are: (1) 0.60; (2) 0.69; dynamometer system to measure the in diameter, was wrapped twice around with a stop watch. The rpms of both An automatic transmission similar missions and to rapidly measure effi- (3) 0.80; (4) 1.00; (5) 1.24); (6) 1.45; and mechanical efficiency of eleven bicycle the ergometer wheel with one end the crank and the ergometer wheel, as to the Browning 4-speed, except with ciency. Since power input to a bicycle (7) 1.68. transmissions. The transmissions were attached to a transducer and the other indicated by the transducers, were then three front chainrings 48/38/30, and the crank is typically between 50 and 400 14-speed: Rohloff two Browning automatic bicycle trans- hanging downward with a suspended used to compute the gear ratio which same 4-speed rear cluster 12/17/23/32. watts [4], and since losses can be as A rear hub with a 40-tooth front missions (a 4-speed, and a 12-speed), weight. The direction of rotation of was compared with the known ratio. The gears are (1) 30/32; (2) 38/32; low as one to two percent, the trans- chainring and a 16-tooth rear cog. a Shimano 27-speed mountain-bike the wheel was away from the hanging The calculated gear ratio agreed with (3) 30/23; (4) 48/32; (5) 38/23; (6) 30/17; mission test system had be sensitive The fourteen hub gears are: (1) 0.279; derailleur transmission and eight inter- weight so the tension in the load-cell the known ratio normally within three (7) 48/23; (8) 38/17), (9) 30/12); enough to determine power differences (2) 0.316; (3) 0.360; (4) 0.409; (5) 0.464; nal hub-gear transmissions (Shimano cord (slack side) was a small fraction significant figures (one part in 1000). (10) 48/17; (11) 38/12; and (12) 48/12. of just a few watts (less than 5). of the applied hanging weight (load (6) 0.528; (7) 0.600; (8) 0.682; (9) 0.774; 3-, 4- and 7-speed, Sachs 3- and 7-speed, • The first test series was with the 27-speed: Shimano side). The ergometer load and thus (10) 0.881; (11) 1.000; (12) 1.135; Sturmey Archer 3- and 7-speed, and a TEST EQUIPMENT crank dynamometer directly connected A Shimano Ultegra 27-speed moun- the power output could be adjusted by (13) 1.292; and (14) 1.467. Rohloff 14-speed. The test system consisted of four main to the ergometer wheel through two tain-bike transmission with three front hanging various weights on the nylon Most of the previous bicycle-trans- elements (see photo on page 3). 36-tooth gears. The purpose was to chainrings (44/32/22 teeth) and a RESULTS AND DISCUSSION cord. Knowing the difference in tension mission tests were done on derailleur- estimate the power losses of the ergom- 9-speed rear cluster (12, 14, 16, 18, We tested each transmission at 1. Bicycle crank dynamometer between the two cords and the rpm, type chain drives [1, 7, 8, 9] and these To measure input power, a dyna- eter wheel drive. Since chain tension 20, 23, 26, 30, and 34 teeth). Because three loads: 80 watts, 150 watts, and the output power from the bicycle efficiency tests were limited to only mometer fed power to a bicycle crank is probably the most important factor of time constraints, only 15 of the 200 watts (power output at the ergom- hub could be calculated. The rpm of a few gears. As far as the authors by means of a 2-horsepower variable- in gear friction [8] the ergometer wheel 27 gears were tested: (1) 22/34; eter wheel)—all at 75 rpm. The crank the ergometer wheel was measured know, the wide-ranging 27-speed trans- speed DC motor, mounted on gimbals weights were the same as those used (3) 22/26; (4) 32/34; (7) 22/20; (9) 32/26; speed of 75 rpm was chosen as being electronically. missions available today have not been so that the motor case could rotate in normal testing—from 1.8 kilos to 16 (10) 44/34; (11) 22/16; (15) 32/20; typical of recreational cyclists. There The power output of the system was: tested, or at least the tests have not freely. The motor case was restrained kilos. The speed of the crank and wheel (16) 44/26; (18) 22/12; (20) 32/16; was insufficient time available to test P = kω (Τ1−T2), where P is the out- been published. No doubt manufactur- by a torque arm attached to an elec- o o o were constant at 75 rpm. This test did (21) 44/20; (24) 32/12; (25) 44/16; and each transmission at both variable load put power, k is a proportionality con- ers have tested their transmissions for tronic load cell that measured the not directly measure ergometer-wheel (27) 44/12. and variable rpm. The power outputs stant, ω is the ergometer wheel angu- efficiency, but if so, the results of their torque force. Oscillations in the load o drive losses since the wheel rpm did of 80, 150 and 200 watts, represent lar velocity, T1 is the weight, and T2 is Planetary-geared rear hubs tests are unpublished. were smoothed by connecting the not vary (as when testing transmis- the typical energy requirements of com- the slack-side tension. 3-speed: Sachs Prior to the 1970s, before derailleur- torque arm to the load cell through a sions). Also, the bottom-bracket bear- muting or recreational cyclists in good A disadvantage of this method was An internal planetary-geared rear equipped bikes became really popular, thin nylon cord that transmitted force ings were in the loop, making an extra physical condition, traveling at speeds that the friction losses in the ergometer hub with a 40-tooth front chainring there were some efficiency tests per- through a flywheel-type inertial damp- set of bearings. The friction losses were from 24–35 kph (15–22 mph), on a wheel drive were unknown. In order formed on planetary hub gears [5, er. The rpm of the motor shaft was small (from 1 to 6 watts; see fig. 13*), level, smooth road with no wind [1, 3]. to find the corrected transmission 6]. Hub gears are still quite popular measured by timing each revolution but as previously mentioned, account- *See pages 8–11 for figures and tables. Bicycle racers can produce steady
4 Number 52 Summer 2001 Human Power Human Power Number 52 Spring 2001 5 power outputs that are much higher rected efficiency increased from about efficiency tends to decrease for all cessive gears are reached by pulling on reason is not clear. 46:5–7. than this for periods of more than 91% to over 97% as the output power transmission types. the single shift cable in one direction Had more time been available, it 10. Wilson, D.G. Transmission efficien- one hour—from 300 to 450 watts [3]. increased from 50 watts to 370 watts at This is illustrated by the trend lines or the other. No attempt will be made would have been interesting to mea- cies. 1999. Human Power, 48:20. Although the occasional recreational 75 rpm. in figures 6, 8, 10, and 11. Even though to explain this mechanism. It is obvious sure the effect of such things as rpm, 11. Kyle, C.R. 1998 (September 15). cyclist may produce over 200 watts, By assuming that ergometer-wheel the greatest efficiencies are sometimes from the diagrammatic illustration (fig. all gears in the 27-speed, a wider range The mechanical efficiency of bicycle it is doubtful that cyclists using hub rpm has no effect on the drive losses near the highest gear ratios, the aver- 15) that it cannot easily be explained. of power inputs, and various chain and transmissions. Report to Browning gears would frequently put out more (fig. 13), a rough estimate of the abso- age efficiency decreases with higher Derailleur gears hub-gear lubricants. As usual, there are Research. than 150 watts unless being chased by lute system efficiency can be made. ratios, (the high efficiencies were: On the other hand, factors affecting more questions than answers. 12. Berto, F., R. Shepherd and R. Henry. rabid dogs. The results of the tests are Spicer shows that drive-train losses Shimano 4 = gear 1, Rohloff = gear 9, 2000. The dancing chain. San the efficiency of derailleur gears CREDITS shown in figures 1–14. are a function of the crank rpm [8]; Browning = gear 2, and Shimano 27 = Francisco: Van der Plas Publications, become clear by examining the curves The authors wish to thank Browning however, as previously explained, this gear 21). in figures 10 and 11. For example, a pp 23, 48–52. PLOTTING EFFICIENCY Research for making available the facil- effect was not measured. When correct- 4. With modern transmissions, where 12-tooth sprocket seems to cause ineffi- In figures 1–12 the efficiency is plot- ities of their laboratory for this project THE AUTHORS ed for ergometer-drive losses, the trans- multiple gears are available, there is ted in three ways. ciency. In the Shimano 27-speed, gears and for supporting this study. Chester Kyle, adjunct professor of mission efficiency increases from 1% to often a difference of 1% to 3% in effi- 4, 9, 15, 18, and 24 have the lowest Thanks also to the Sports Sciences mechanical engineering at California 1. Efficiency vs. power output 3% (see fig. 14). Efficiency is over 98% ciency between adjacent gears. efficiency. The two gears with the low- Division of the United States Olympic State University at Long Beach, is a Here all of the individual power at the highest load. The corrected effi- This applies to both hub gears and to est efficiency of the 15 tested, both Committee for loaning us the bicycle- consultant on the science of sports and efficiency data points were plotted ciencies are in good agreement with derailleur gears. See figs. 2, 6, 8, 10, and use a 12-tooth sprocket. The gears with crank dynamometer. equipment and has worked with several for each gear. These curves give the Spicer [8] who found that efficiency 11 (especially figures 8, 10 and 11). 12-tooth sprockets (18, 24 and 27) have teams and organizations: US Postal Ser- detailed performance of each transmis- was over 98% with 52/15-tooth sprock- In figure 11, in the Shimano 27-speed, REFERENCES an average efficiency of 91.2%, while vice 2001 Tour de France team, design sion under varying load. As examples, ets at 200 watts. there is a 4% difference in efficiency 1. Kyle, C.R. and V.J. Caiozzo. 1986 those involving 16-tooth sprockets (11, teams for USA 1984 and 1996 Olympics see figures 1, 4 or 5. All transmissions 2. Hub gears are generally about 2% between gears 21 and 24 and between (May). Experiments in human 20 and 25) have an average efficiency cycling teams’ bicycles and clothing, were not plotted but they could be, lower in efficiency than derailleur-type gears 24 and 25. In figure 8, for the ergometry as applied to the design of of 93.5%. and Nike, as well as others, for aerody- using the data in tables 1 and 2. gears. But there are exceptions. Rohloff 14, there is a 3% difference human-powered vehicles. Int. Jl. Other gears namic sports clothing. 2. Average efficiency vs. gear number This is illustrated by figures 3, 6, 7, between gears 7 and 8. Sport Biomech. 2:6–19. In the Browning, the 12-tooth sprock- Co-organizer of the first International Here, efficiencies for all test loads and 12. Figure 12 shows that the effi- An average 2% difference in efficien- 2. Marks, L.P. 1979. Mark’s standard ets averaged 92.1% efficiency, while Human Powered Speed Championships were averaged for each gear and the ciencies of the Shimano 4, Sachs 7, cy is thus easily possible if the wrong handbook for mechanical engineers, the gears involving a 17-tooth sprocket at Irwindale, California, in 1975, Kyle averages were plotted against the gear Shimano 7, Sturmey 7 and the Rohloff gears are chosen. 8th ed. NY: McGraw Hill. p3–29, 11–7. averaged 92.9%. The two lowest effi- and eleven others founded the Interna- number. This curve shows the effect of 14 all cluster about two percent lower If racers, or even commuting or tour- 3. Bassett, D.R., C.R. Kyle, L. Passfield, ciencies of the 12 gears tested had tional Human Powered Vehicle Associa- gear ratio on efficiency under varying than the Browning 4, Browning 12, or ing cyclists, could choose optimum J.P. Broker and E.R. Burke. 1999. 12-tooth sprockets (gears 9 and 12). tion (IHPVA) the following year. Kyle load conditions. For examples see fig- the Shimano 27. gears they would be hundreds of Comparing the world hour record in Apparently the sharp angle of chain is past president and secretary of the ures 2, 6, 8, 10, or 11. However, two of the 3-speed hub meters ahead at the end of 60 km cycling, 1967–1996: Modeling with link bend in the 12 causes increased IHPVA, as well as the de facto historian 3. Average efficiency vs. load gears did not follow this trend. (37 mi). For example, if Lance Arm- empirical data. Medicine and Science friction compared to larger sprockets. of the organization. Editor and publish- Here, transmission efficiencies for The grease in the Sachs 3 and the strong, in the Tour de France 58.5-km in Sports and Exercise, 31:11, So it appears that larger gears than 12 er of Cycling Science (1989–1991) and each load were averaged for all gears. Sturmey Archer 3-speeds was replaced time trial (36.4 mi) were to choose 1665–1676. are necessary for efficient operation. science editor of Bicycling Magazine This curve is a measure of the per- with light oil, and unlike the other hub the wrong gear, a drop of 2% in efficien- 4. Broker, J.P., C.R. Kyle, and E.R. When there is a choice of gear ratios (1984–1989), Kyle is a frequent contrib- formance of each transmission under gear transmissions, the efficiencies of cy would cause him to be 410 meters Burke. 1999. Racing cyclist power that are close, cyclists should choose utor to scientific and popular publica- varying conditions. For example, see the Sachs 3 and Sturmey 3, compare behind (27 seconds) at the end of the requirements in the 4000-m individual the gearing combination with larger tions. figures 3, 7, 9, or 12. These curves pro- well with the best of the derailleur time trial, easily enough to lose the and team pursuits. Medicine and diameters [8]. Chet Kyle and his wife, Joyce, live on vide probably the simplest way to com- transmissions (figs. 7, 9, and 12). stage [3]. Incidentally, Armstrong aver- Science in Sports and Exercise, Cross-chain gears make little differ- ten acres of rural pasture and forest in pare transmissions. Also, these transmissions were worn aged about 54 kph (33.6 mph) for the 31:11, 1677–1685. ence. In the Shimano 27, the cross a home they and their four, now-grown in, whereas many of the others were time trial (58.5 km long = 36.4 mi). 5. Whitt, F.R. and D.G. Wilson. 1982. CONCLUSIONS chain between the two big gears on the children built near Weed, California. new. Manufacturers would do well to With commuting riders who travel Bicycling science. Cambridge: MIT By viewing the curves, several general Shimano has a higher-than-average effi- Frank Berto, author of more than 150 replace heavy grease in their hub gears 24 kph (15 mph), instead of 54 kph Press. Figure 11.16, p. 296. observations and conclusions can be ciency (gear 10, 44/34), while the cross articles and several books on cycling with light oil. Although oil wouldn’t (33.6 mph), it only gets worse. A 2% 6. Thom, A.P., G. Lund and J.D. Todd. made. chain between the two small sprockets technology, was engineering and West last as long as grease, the energy drop in efficiency would lead to an 1956 (July 1). Efficiency of three- 1. Efficiency generally increases with involves a 12-tooth sprocket (gear 18, Coast editor of Bicycling Magazine savings would be significant. Unfor- 800-meter gap (about 2 minutes). The speed bicycle gears. Engineering, the load—for all transmissions. 22/12; see fig. 11). In the Browning, (1986–1990). Berto is a consultant tunately commuters have a tendency reason for the increasing gap is that the 180:78–79. Figures 1, 3, 4, 5, 7, 9, 12, or 14 the large cross-chain gears (gear 4, on oil field gauging and instrumenta- to ignore maintenance until something slower cyclist spends much more time 7. Dell’Oro and M. Malone. 1995. Bicycle all show this trend. Although friction 48/32), have a higher-than-average effi- tion, cycling equipment and technology breaks, so light oil probably wouldn’t on the course [3]. The point is, why derailleur losses. Melbourne: increases with chain load, rpm, and ciency, while the small-gear cross (especially gearing), as well as a fre- be a popular choice. waste energy when it is unnecessary. University of Melbourne, Department other factors [8], obviously the residual chain involves a 12-tooth sprocket (see quent expert witness on cycling litiga- Also, with the Shimano 4, the first 5. The tests show that some gears of Mechanical and Manufacturing friction in a gear train becomes less fig. 10). tion. He is also a historic aircraft and gear (a 1.0 ratio) had a higher efficien- are inefficient. Engineering. important as the input power increases, For some reason that is not appar- machinery enthusiast. cy than the derailleur transmissions, 8. Spicer, J.B., M.J. Ehrlich, J.R. while the friction factors that increase Hub gears ent, the mid-chainrings on both the Frank and Connie Berto live in San even though gears 2, 3, and 4 had a Bernstein and C.J.K. Richardson with load go up less rapidly than the In hub gears, such as the Rohloff Browning 12 and the Shimano 27 did Anselmo, California, on a large plot of lower efficiency (see fig. 6). In a plan- (Johns Hopkins University); M. load. 14, the efficiency no doubt depends on not have high efficiencies. On the land affectionately called “Sleepy Hol- etary transmission (also called epicy- Masahiko Fukuda and M. Terada The clearest example of this is how many elements of the gear train Browning 12, gears using the 30-tooth low”. clic), even when the hub ratio is 1.0, (Shimano Inc.) 1999 (June) . shown in figure 14. This was the only are in motion as each gear is selected chainring (1, 3, 6, and 9) had a lower- Berto’s latest book, The Dancing the planet gears are still in motion [12]; Efficiency and energy-loss location in case where we tested a transmission (see fig. 15). In the Rohloff, gears 3, 5, than-average efficiency. On the Shima- Chain, was reviewed in Human Power however, all of the planetary transmis- bicycle chain drives. Journal of at over 200 watts and under 80 watts. 7, 12, and 14 have the lowest efficiency. no 27, gears using the 32-tooth chain- 51, Fall 2000. sions we tested had high efficiency at More tests were planned, but a shear This superb but complex transmission ring (4, 9, 15, 20 and 24), all had a low- Mechanical Design. 1.0 gear ratios. pin parted in the drive train and this has roller bearings and uses light oil as er-than-average efficiency. This does 9. Cameron, A. Measuring drive-train 3. As the gear ratio increases, the experiment was aborted. The uncor- a lubricant. Shifting is quite simple: suc- not appear to be a coincidence, but the efficiency. 1998–99. Human Power,
6 Number 52 Summer 2001 Human Power Human Power Number 52 Summer 2001 7 96 93 96 96 95 94 92 94 94
93
y 91 92 y 92 92
90 Efficienc 90 Efficienc 91 90 90 Sachs 88 89 Efficiency (percent)
Efficiency (percent} Shimano 89 Rohloff 14 Sturmey Browning 4 Gear 1 = 0.75 88 Trend 86 88 Shimano 4 Gear 2 = 1.0 88 1 2 3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Gear 3 = 1.36 84 Gear number 86 Gear number 50 100 150 200 250 50 100 150 200 250 Output (watts) Figure 2. Sachs 3, Shimano 3, Sturmey 3 (average efficiency vs. gear) Output (watts) Figure 8. Rohloff 14 (average efficiency vs. gear) Figure 1. Shimano 3-speed (efficiency vs. load) Figure 7. Browning 4-speed, Shimano 4-speed (average efficiency vs. load)
96 96 96 95
94 94 94 94 92 y 93 92 Shimano 7
90 92 Efficienc 92 Sturmey 7 90 Sachs 7 Browning 12 88 Gear 1 Rohloff 14 91
Efficiency (percent) Trend Efficiency (percent) Efficiency (percent) Gear 2 Sachs 3 90 Shimano 4 Gear 3 Shimano 3 88 Sachs 3 Gear 4 90 86 Sturmey 3 Shimano 3 1 2 3 4 5 6 7 8 9 10 11 12 Sturmey 3 Gear number 84 88 86 50 100 150 200 250 50 100 150 200 250 50 100 150 200 250 Figure 10. Browning 12 (average efficiency vs. gear) Output (watts) Output (watts) Output (watts) Figure 4. Browning 4-speed (efficiency vs. load) Figure 3. Sachs 3, Shimano 3, Sturmey 3 (average efficiency vs. Figure 9. Hub gear bicycle transmissions (average efficiency vs. load) load) 96
95 96 96 94 94 95 94 93 94 92 92 92 y y 91 93
90 Shimano 4 90 92 90
Efficienc Sachs 7 Efficienc
Efficiency (percent) Shimano 7 88 89
Efficiency (percent) 91 Sturmey 7 Gear 1 88 Rohloff 14 Gear 2 88 86 Shimano 27 Browning 4 Gear 3 Shimano 4 90 87 Trend Browning 12 Gear 4 Browning 4 Shimano 27 84 89 86 86 50 100 150 200 250 1 3 5 7 9 11 13 15 17 19 21 23 25 27 1 2 3 4 50 100 150 200 250 Output (watts) Gear number Gear number Output (watts) Figure 5. Shimano 4-speed (efficiency vs. load) Figure 6. Browning 4, Shimano 4 (average efficiency vs. gear) Figure 11. Shimano 27 (average efficiency vs. gear) Figure 12. Derailleur-type transmissions compared with hub gears (average efficiency vs. load)
8 Number 52 Summer 2001 Human Power Human Power Number 52 Summer 2001 9 Table 2. Derailleur-type transmisions: mechanical efficiency vs. load y = -3.60886E-12x3 + 8.73374E-08x2 - 1.98405E-04x + 1.88475E+00 99 R2 = 9.97064E-01 8 98 Gear = 1 2 3 4 5 6 7 8 9 10 11 12 15 16 Maker/Speeds Power Effi ciency Percent 7 97 Browning 4 80 93.0 93.3 93.3 90.3 Automatic 150 95.3 95.0 94.8 93.8 6 96 200 95.3 95.0 94.9 93.3
95 Browning 12 80 91.1 92.5 91.3 91.6 92.5 91.2 91.9 90.7 90.9 91.1 89.8 89.8 5 Automatic 150 93.8 93.9 92.5 94.5 93.3 92.9 93.8 93.5 92.2 93.7 93.4 91.8 200 92.7 95.2 92.8 94.2 94.3 92.7 94.0 94.4 93.4 94.1 93.2 93.5 4 94 Uncorrected Eff. Shimano 27 80 93.1 — 92.8 89.4 — — 92.6 — 90.0 92.1 91.7 — 89.5 91.0 93 Corrected Eff. Ultegra Mtn. Grupo 150 94.6 — 94.6 92.9 — — 94.5 — 92.5 93.9 93.8 — 93.0 93.6
3 Efficiency (percent)
Power loss (watts) Uncorr. Eff. 200 95.0 — 94.5 93.6 — — 94.2 — 93.1 94.2 93.9 — 93.6 93.9 92 2 Corrected Eff. Shimano 27 18 20 21 24 25 27 91 (continued) 54 — — — — 90.6 1 80 90.7 90.9 94.3 86.9 93.8 91.1 90 150 91.8 93.0 95.0 91.0 94.8 93.3 0 50 100 150 200 250 300 350 400 200 91.9 93.8 95.9 91.4 95.5 93.7 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 307 — — — — 97.1 Net ergometer load (grams) Output (watts) 370 — — — — 97.2 Figure 13. Power loss vs. net ergometer load Figure 14. Shimano 27-speed, gear 25 (44/16) uncorrected and corrected (efficiency vs. load; 75 crank rpm; correction is used fiberglass tape and polyester resin estimated) (Oury had used layers of masking tape, which gave a soft seat of low strength). She found, as did Oury, a steady improvement in behavior as Table 1. Hub gear transmisions: mechanical efficiency vs. load the bead-seat diameter was increased. Subsequently I continued the build-up (the fit between the tire and rim was Gear = 1 2 3 4 5 6 7 8 9 10 11 12 13 14 exceedingly loose) until the diameter Maker/Speeds Power ciencyEffi Percent** Sachs 3 80 95.0 92.9 93.6 was too large for the tire, and then 150 94.2 95.6 94.8 machined it down (using a profiled 200 94.1 94.9 94.1 router) until a smoothly shaped round- ed-edge bead seat was produced that Shimano 3 80 90.5 93.5 87.2 allowed the tire bead to snap into posi- 150 93.0 93.9 88.6 tion only after the tube was inflated to 200 93.2 95.0 87.2 about half final pressure. Sturmey 3 80 92.3 95.4 91.8 When this final step was taken the 150 93.3 95.3 91.8 difference in performance changed dra- 200 93.0 95.6 91.8 matically. Flopping disappeared entire- Shimano 4 80 93.6 90.1 87.1 85.8 ly, and the tire could provide safe Automatic 150 95.6 90.9 88.9 87.0 and stable bicycle direction during the 200 95.3 92.8 90.0 88.0 deceleration after deflation. Figure 15. Diagrammatic view of the Rohloff hub Sachs 7 80 88.7 — — 89.2 These results therefore add to the previous somewhat tentative recom- 150 89.9 — — 92.3 TECHNICAL NOTES deflated tires to “flop” from side to side. 200* 91.0* — — 93.0* This past academic year another MIT mendation: that wheel and tire manu- facturers and standards organizations Shimano 7 80 90.8 90.7 87.4 89.0 83.6 90.9 88.2 Bicycle stability after undergraduate student, Soohyun Park, should arrive at standards for the sizes 150 91.8 92.9 89.9 89.0 85.6 92.8 90.4 chose to do her BSME thesis2 on a 200 92.8 94.5 90.3 91.8 86.4 93.7 91.4 front-tire deflation continuation of this study. She first and profiles of rims and of tire beads so that a fit tight enough to produce stable Dave Wilson (reporting partly for researched an improved bicycle model, Sturmey 7 80 87.3 88.7 88.4 93.0 89.3 86.0 83.0 steering under deflated conditions is Soohyun Park) resulting in the use of a BMX bicycle 150 89.1 89.0 91.1 93.3 90.4 88.5 85.4 achieved. There seems little doubt that 200 89.7 90.3 91.3 94.7 91.0 88.6 85.3 We reported in Human Power, 51 with a weight mounted on it represent- ing approximately a rider’s weight and many deaths and injuries would thereby Rohloff 14 80 89.1 90.3 87.8 90.3 87.5 87.8 86.1 89.7 90.8 87.7 89.7 87.1 87.8 86.1 (pp. 16–18) on experiments to provide be prevented. steering stability after a front tire center of mass. She found that over a 150 90.6 92.5 89.9 92.2 89.6 91.0 89.9 92.6 92.7 90.4 92.3 90.4 89.7 89.1 wide range of weight values and posi- —Dave Wilson 200 91.3 92.5 90.9 93.4 90.5 90.9 90.2 92.8 92.7 91.1 93.5 90.0 91.1 90.4 has deflated, there having been many
10 Number 52 Summer 2001 Human Power Human Power Number 52 Summer 2001 11 There is a better way lyze where and how the human way of usable walking device. It combined the the internet on my homepage (see refer- money?” (Bike Tech 2:5), I talked to learn to ride it! To our surprise, the running needs to be supported. One of use of artificial legs with a spring pack ence 4). a South African aluminium producer/ rims proved to be quite satisfactory the main weak points in human running on the back of the runner (see fig. 1). extruder and decided that their 6063 and were never heat treated. Although than rolling REFERENCES is, that (because of our leg design) we Although the Springwalker was report- aluminium alloy would be soft enough heat treating after rolling is definitely by Detlev Tschentscher 1. Homepage of the DARPA: http:// use only little energy for the forward ed in all news media it was never to roll easily, would be strong enough the preferred procedure, a certain www.darpa.mil/dso/thrust/md/ Human-powered vehicles on land movement. If we would divide a normal improved to become a functioning after heat treatment, and would then be amount of hardening does take place exoskeletons/index.html usually have wheels. But there are step into separate actions, only the part device for the market. Today inventors suitable for anodizing if required. during rolling, as well as during use and 2. A good example of “kangaroo” boots attractive alternatives. where we jump up to move forward is focus on servo-powered versions of the Chris Juden’s article, “The aluminium with age. are made by Powerskip. See useful in gaining ground. The rest of Springwalker for military use. But a rim: Design and function,” (Bike Tech The next rim was made to suit a pop- WALKING AND RUNNING AIDS http://www.powerskip.com the movement is wasted for our fight few other attempts have gone into pro- 3:2), was the great inspiration. It pro- ular 25-622 fold-up high-pressure tire. Humans are just ordinary mammals 3. Link to walking machine catalog: against gravity.1 Another approach for duction. Several kangaroo-boots have vided a wealth of information on rims, We had it heat treated and anodized except for two differences: http://www.fzi.de/ids/WMC/ support is to focus on increasing the appeared on the market recently.2 tires and wheels. I chose to make a rim in dark bronze, and built a beautiful • we walk on two legs; and walking_machines_katalog/ distance covered with just one step. Most of these are aimed at fitness with an inside width of 16 mm which wheel with stainless-steel spokes and • we consider ourselves to be intel- walking_machines_katalog.html Research in bionics shows that kan- enthusiasts and are based on several would suit tires from the then-popular a red powder-coated hub. I had made ligent. 4. Homepage: http://www.kenguru.de garoos for example can run long dis- spring-systems attached to ski-boot-like 22-mm high-pressure tires to the more an appointment in the morning with my This should mean that we have the Detlev Tschentscher is a production tances at very high speed with very low boots. With these boots it is possible practical 38 mm. My new IZIZI profile bank manager to apply for a loan to ability to improve our lives. It is surpris- engineer who has been working on energy consumption. They can jump up to jump up to four meters at two should result in a mass of 280 gms/ start manufacture. I pumped the tire to ing therefore that we do not use this designs for human-powered legged to a length of six meters and store the meters high. Two technicians, Atanow meter and suit the stock 4-mm alumini- 6.9 bar (100 psi) and set it aside. We intelligence to improve our natural way vehicles for four years. energy that would normally be wasted and Gordejew, of the Lufthansa-univer- um rod that would be used to pin the were excited at the success and by the of movement: walking on two legs. —Detlev Tschentscher by a kind of spring-mechanism, using sity of Ufa, even created a boot pow- joint. I based it on the successful Rigida prospects. Little did we know that our John Dick (one of the designers of the Neusser Landstrasse 352 their tail as a kind of spring. Several ered by a fuel engine. With this device 1622 which is similar to the Moulton. problems were about to begin. Springwalker, member of the DARPA* Germany 50769 Cologne approaches have been made to make it is possible to take a one-hour walk (IZIZI was the name I chose because I was still busy in my workshop five team) describes the situation as follows: Tel: +49 (0) 221-978622 this simple phenomenon available for using only a matchbox full of petrol it reads the same when viewed from hours later when the tube exploded! “We have had 150 years of engineering Fax: +49 (0) 40 360 306 4005 humans. (gasoline). But these efforts cover only either side of the wheel.) Why? Was the tire defective? Had the now, and still there is no powered exo- E-mail:
12 Number 52 Summer 2001 Human Power Human Power Number 52 Summer 2001 13 trous. Tie a string around a beer and mountain bikes arrived. IZIZI rims the foils, mounted on the tip floats, density, = 1000kg/m 3 SAMPLE CALCULATION can and you will easily slip a match- were fitted to the recumbents used by have a variable angle of incidence, they S is area of foil (sq. m) Step 1. stick between them. Similarly, if the Lloyd Wright for two of his winning may be adjusted to provide variable lift, V is speed (m/sec) Craft weight, W = 118 kg (260 lbf) bead-seat circumference was 1952 mm rides in the 105 km Argus Cycle Tour, independently. Cl is lift coefficient of the foil Foil lift, L = 59 kg = 579N (130 lbf) 2 instead of 1954 mm, there would be suf- and to Wimpie van der Merwe’s recum- This could be by manual control, And p = 500V (2) Lift-off speed,Vl = 4.9m/sec (16 ft/sec) ficient slack for the tire to blow off the bent when he set the course record requiring a skilled “pilot”, or by an auto- p is dynamic pressure, N/sq. m L = 500V2SCl (0.97V2SCl) eq. (1) rim. This also is the reason why rims (which still stands) and three IHPVA matic system which maintains each foil Also F = pA (3) S = 0.0603 sq m (0.654 sq ft) at work fine with quite a shallow well. world records, one of which still at a constant depth below the water A is actuator piston area, sq. m.; Cl = 0.8 2. Given that the air pressure is stands. Despite these achievements and surface. But L.b = pSCl b and F.h = p.Ah p = 12005 N/sq m (248 lbf/sq ft) equal, the stress in the casing of a nar- the fact that we exported rims (King- Existing, state-of-the-art foil boats Hence SClb = Ah (p cancels on both Step 2. row tire will be less than that of a fat cycle), local dealers avoided us saying (such as the sailboats, Rave and Hobie sides of the equation) Assume speed when foils start lifting, tire since the force is a function of the that buyers wanted a big-name rim. The Trifoiler) use devices that follow the Or Cl = Ah/Sb = constant depending V0 = 3 m/sec (10 ft/sec) cross-sectional diameter. Therefore, if expected (hoped-for!) swing to recum- surface (a kind of water ski on the Tri- on the dimensions. p0 = 4500 N/sq m (97 lbf/sq ft) there is a little slack in the rim/tire fit, bents never happened. None of these foiler) connected by a mechanical link- This implies that the foil lift P = 4500A N (97A lbf) at some point around the wheel the tire factors was good for business. We did age to the adjacent foil. These surface coefficient will remain constant until Step 3. will lift a little. That lifting increases not make enough money to afford to followers provide increased water drag, the pitot tube reaches the surface Using dimensions the cross-sectional diameter and con- re-tool to make aero or mountain-bike and are vulnerable to damage. (when p decreases). Figure 3. Diagram showing dimensions used in h = 0.61 m (24 in); b = 0.0127 m sequently also raises the stress in the rims. In retrospect, that is probably The following diagram illustrates the the equations The system performance can be mod- (0.5 in) tire fabric slightly more than elsewhere. what we ought to have done to save proposed pressure-controlled system, ified by a return spring, which holds P.h = pA.h−pSCl.b This increased tension slowly draws to the business. in which dynamic water pressure is uti- change of the foil angle, hence the sen- the foil at its minimum angle until the 4500A × 0.61 = 12005A×0.61−12005 × that region whatever other slack there —John Stegmann lized to adjust the angles of the lifting sitivity to waves. Static water pressure, speed is sufficient to pressurize the 0.0603 × 0.8x0.0127 might be. This may take time, but can
14 Number 52 Summer 2001 Human Power Human Power Number 52 Summer 2001 15 (from a communication from Toshiaki from Yoshikawa)communication a (from Japan HPAin ActiveGals team of achievement Remarkable TeamGals” “Active Project CHicK-2000 P 16 ROJECT
powered flight in Japan in 1992. in Japan in flight powered human- FAIclass first I-C the made successfully who Hori, Kotono pilot the including members, team the of some and itself plane the show photographs The drawing. the note. this follow team the of achievements remarkable the of Drela’sMark review 2001). March 26 Toshiakileader Yoshikawa (letter, team’sthe by sent and Japan, in “ActiveGals” team the by built KoToNo“HYPER-Chick Limited” aircraft human-powered the of REVIEW On 4 and 5 November 2000, the 2000, November 5 and 4 On in shown are data technical The details some gives note This
method is by twisting the flexible the twisting by is method circling new “The thusly: described method,” circling new a realize to “working is team the that also wrote He skin.” on paper styrene GFRPed and spar on CFRP structure, posite HPA.an for minimum world a pedals, the to input power of watts 160 only needing meters) 2 of height a (at fly could that craft air-an was fiber.result carbon The with reinforced la’swere review Dre- Mark in mentioned paper rene construction. stressed-skin with HPAan of flight first the made team Number 52 Summer 2001 Summer 52 Number Opposite: Working on one of one Workingon Opposite: Toshiakileader Project Right: pilot with above, flight, In to found been has This wing. left the of that of direction opposite the in applied is aeroelasticity.applied by banking during wings Yoshikawa wrote, “It has a com- a has Yoshikawa“It wrote, sty- the and spars I-beam the Both the technical chart. technical the craft—and the of wings the Yoshikawa (left). Hori Kotono “The twist of the right wing right the of twist “The
Kakamigahara Aerospace Museum. Aerospace Kakamigahara losses. namic aerody- the reducing further 43.7, ratio, aspect high very a of use the permits and deflection wing reduces greatly also It turn. the during directions) opposite (in warping wing- of use the allows struction con- Stressed-skin lift.) lose to tends and wing outer the than slower much goes wing “inside” (The turns. the in difficulty control the and es loss- power increased greatly the of turn.” HPA’sthe during loss power reduce The aircraft is on display at the at display on is aircraft The because difficult is flight Circling —Dave Wilson Human Power Human
Photos and chart, CHicK-2000 team Human Power Human Drela Mark by Review stiffness. The I-beam spar is a far more far a is spar I-beam The stiffness. bending the provide to spar I-beam full-depth a of use the allows instead shape. airfoil the providing skin wing Mylar thin a and sheeting foam secondary with stiffness, torsional and bending the all provide to spar tubular a on rely to been has approach common contour.most The airfoil the forming of duties usual its to addition in stiffness torsional sary neces- the provides which skin stressed features. notable of number a has group ActiveGals the by craft Using the stressed skin for torsion for skin stressed the Using a employs structure wing The air-human-powered CHicK-2000 The {no e-mail address provided] address e-mail {no Japan city,664-0882, Itami Hyogo Suzuhara-cho 6-36-11 TeamGals” “Active Project CHicK-2000
stressed-skin HPA structure is that HPAis stressed-skin structure HPAs.lightly-loaded more than ditions con- windier handle to ability the gives also and range, large for potential the gives speed high with coupled power Low m/s. 8 about of speed cruising fast rather a gives which Pa 46 of loading wing high fairly a despite mass, pilot W/kg 3.6 of power flight specific est mod- the to contributes obviously ratio aspect high The 44. of ratio aspect wing immense its and kg 31 of weight empty low its considering small amazingly is load under CHicK-2000 the of tion weight. given a for wing stronger and stiffer a provides spar,hence and tube the than member bending efficient One practical disadvantage of a of disadvantage practical One deflec- surprisingly,wing-tip Not the Number 52 Summer 2001 Summer 52 Number ulus for the task. the for ulus mod- shear cient suffi- a have not do foam styrene poly- as such als materi- struction con- common
how the wings are twisted in practice. in twisted are wings the how clear not is it although aircraft, the of control three-axis full have to appears pilot the yoke, control of type the from Judging control. roll for wings the twist to effects aeroelastic of use the craftsmanship. meticulous reveal photos Construction sound. structurally clearly is aircraft the as surmounted been have to appear lems prob- these Again, failure. or buckling local preclude to quality struction con- and details design of demanding paper.styrene glass-reinforced fiber-their with problem this solved have to appears group ActiveGals The (principal designer and constructor of Massachusetts Institute of Technology Other reported innovations include innovations reported Other very also is skin stressed The professor of aeronautics several MIT HPAs). —Mark Drela, MIT and astronautics,
17 BOOK REVIEW Richard has been more dedicated and LETTERS more successful. RICHARD’S 21st CENTURY BICYCLE The books differ mainly in the use, Danny Too responds to two letters BOOK(S) by Richard Ballantine. about his article (with Chris Williams), respectively, of American English and reviewed by Dave Wilson “Determination of the crank-arm length to British English, including some transla- This book is two books, or one book maximize power production in recumbent tions of slang. Some examples slipped cycle ergometry” (Human Power 51, Fall in two versions. One is for non-North- through. For instance, how many Amer- 2000). American readers; and was published ican readers would know what to Battle Mountain crank arms by Pan Books (Macmillan) in Britain at expect if an HPV were classed as the end of 2000. Earlier editions came “dodgy”? (Roughly it means that it Matt Weaver out in 1972, 1975 and 1989. It is a very wouldn’t be a good bet.) In light of crank-arm length, I have a successful book: one of the messages The British version of the book has, few observations on the recent article on the cover states “…the best-selling as the sole representative of cycling on on bicycle cranks [by Danny Too and bike book of all time, with over one- the front cover, Richard’s daughter in a Chris Williams]. It took me a moment million copies sold!” As I wrote this I carbon Windcheetah tricycle HPV with to deduce what was actually tested, but was about to leave for Norwalk, CT, for a lot of advanced components. We must if cranks are of any interest to you, I the June first launching of the North- give Richard some of the credit for the find it important to note and relay the American version with the author him- publisher’s belief that a bike book with following. self. an HPV on the cover was not going 1. The test was a variable-rpm, Before I wax too enthusiastic about to put people off buying it. The U.S. “fixed-torque” test: relatively light pedal the book(s) I should publisher, The Overlook force, proportionately lighter for longer confess my biases. Press (Woodstock and cranks; riders “gave their all” (maxi- I first met Richard New York), apparently mum exertion) for 30 seconds. Cadenc- Ballantine in 1980 in felt that doing this in es reached high rates (>170 rpm) Bremen, Germany, at North America would for the shortest cranks, and modest a bicycling confer- be too risky, and I think rates (135 rpm) for the longest cranks; ence called “Velo- that many of us would cadences dropped to the low 80 rpm City”. I had brought agree, with some sad- range for short cranks, and low 90 rpm along one of the first ness. for longest cranks in the final five Avatar 2000s, which Inside the books have seconds. Calculated power output was received a great deal many similarities: there proportional to cadence: the faster of favorable publici- are 22 chapters having you can spin, the more power you ty. (We hadn’t patent- the same titles, starting get (fixed torque, and flywheel inertia ed it in Europe, and with “Get a bike!” to ignored). several rather faith- “Done!” All the chapters 2. The torque decided upon was ful copies were sub- are written with a referred to as the “appropriate load” or sequently manufac- breezy enthusiasm cou- “85 g/kg of subject body mass” (appar- tured by some new U.S. version of Richard Ballantine’s pled with a deep knowl- ently total mass, not lean or leg-muscle enterprises that did book. edge of the field and mass). well with them.) an instinct for telling 3. I’m not sure what “appropriate Above: A closer view of the cockpit and propeller of the Richard had already CHicK-2000 aircraft. Right, Takashi Hattori, right-wing run- people, from raw begin- load” is, but it can be deduced. The ner; below, Kouta Sata, left-wing runner. bought an Avatar, and put it (with a ners to seasoned enthusiasts, what they apparatus was as follows: a 52/14 sin- rather wild British female model) on want to know. gle-chain drive to a flywheel with a the cover of “BICYCLE”, the British Of particular interest to HPVA mem- 1.615-meter circumference, with a fric- magazine he published and edited, as bers is chapter 5: “Zzzwwaaaammo!”, tion belt of known net tension wrapped “the bicycle of the future.” He felt that 27 pages devoted entirely to extolling about it. That’s roughly a 0.5-meter it could also be fast, formed the Nosey HPVs, and, on a quick scan, having diameter (20-inch) flywheel, (mass/ Ferrett Racing Team, recruited Derek more illustrations than any other chap- inertia not given)—comparable to mov- Henden, who made several full fairings ter. That alone sets Richard’s book well ing the belt tension force a distance of for it, and named it the “Bluebell”. This apart, (i.e., well ahead) of all competi- 6.0 meters for every revolution of the went on to win the IHPVA World Speed tors. cranks: effectively a fixed-mean crank Championship in the US and many You will enjoy this book. The British torque = 0.8 N.m per kg total rider body races in Europe over several years. version has the ISBN number 0 330 mass. (0.27 ft.lbf per pound total rider Therefore I start by being biased in 37717 5; it costs UK£16.99. The North weight) (ignoring flywheel inertia). favor of Richard Ballantine. He did a American version has ISBN 1 58567 112 For example, for me (“85g/kg” belt great deal for the Fomac-made Avatars, 6; I bought my copy from the Overlook tension mass, and 80kg rider body and for recumbents and HPVs in Britain Press, Lewis Hollow Road, Woodstock, mass, 175 mm cranks): belt tension = and Europe. NY 12498, for US$28.50 including P&P; 6.8 Kg×9.81m.s−2 = 67 N (15 lbf); pedal We are an “odd couple”. Richard is the bookstore price should be about tangential force = 364 N (82 lbf); or an American who has lived in Britain US$18.00. roughly 1/2 to 1/3 my mean pedal force for decades; I am an ex-Brit who has —David Gordon (Dave) Wilson normally developed during a sprint (30, lived in the US for decades. We both
18 Number 52, Summer 2001 Human Power Human Power Number 52 Summer 2001 19 4. Test starting rpm (at t=0) is not power; I would not conclude in any a loose wire shorted and destroyed the accuracy) with the heaviest subject needs to be done under an environment Response to John Stegmann given, except that it said the ergometer way long cranks are better for longer power-electronics circuit. Other than tested. Based on the literature available where all conditions and variables are Stegmann: “Their research into the flywheel was accelerated until “inertial events (especially based on a brief logging a few torque profiles and dis- with upright ergometers, there is an very carefully controlled and accounted effects of crank-arm length on power resistance had been overcome.” 30-second maximal and large cadence covering that my left (dominant, but interaction between pedaling cadence, for (while the experimental variable is production has left me wishing to know 5. Inertia still exists, and cadence variation anaerobic bout). I would knee-operated) leg is hopelessly weak- load, and power output. With the addi- manipulated and tested), and is not why there was no discussion on the varied between start rpm, 174 rpm and suspect that if a sufficiently high er than my right, I ended up resuming tion of another variable (crank-arm always going to be “specific to the relationship between crank-arm length 82 rpm during 30-second test. Power “appropriate-load” torque were chosen, crank-power testing by utilizing hill- length), one would expect that there nature/durations of interest”. However, and leg-length/proportions?” sink/source from flywheel during rpm the experiment observations would climb tests, because of limited time. will be an interaction between crank- research does produce empirical data First, we do have the data on leg changes may or may not have been sig- reverse, with the longer cranks supe- More recently, I found something arm length, pedaling rate, load, and that provide information and direction lengths and leg-length/proportions (as nificant depending on flywheel inertia rior for peak power. My primary con- interesting about cadence. I was invited power output. Therefore, Mr. Weaver regarding how performance may be well as other anthropometric data) on (not given, except for the ergometer clusion, honestly, is simply that a group to test my output on an ergometer at is correct in stating “that if a sufficient- enhanced in the real world. all subjects tested. Second, we did not model number). of maximally-exerting healthy guys can the home of John Howard. I had time ly high appropriate load torque were —Danny Too
20 Number 52 Summer 2001 Human Power Human Power Number 52 Summer 2001 21 optimal joint angles to maximize 1,88 m, and there must surely be the bution to the total joint moments to EDITORIALS tain, I can reveal that the designer of beginning of the 1990s in Poland it cycling performance? This has not been possibility of greater variation in their affect the joint-moment cost-function this bike was working as an aircraft seemed that HPVs would find their determined yet because of the difficulty leg configurations?” minimum. The reference for the paper A bit of history viewed from armament engineer, a really top-secret niche, but after the “opening to the in manipulating, reproducing and then It is very possible that there is great- is: Too, D. & Landwer, G.E. (2000). Eastern Europe occupation. I got in touch with him West,” cars became much more afford- testing various combinations of joint er variation in their leg configurations. The effect of pedal crank-arm length by Marek Utkin M.A., Poland when he retired in 1987, and he was able, and the mountain bike appears to But again, it is probably not the actual angles with subjects of different leg on joint angle and power production In what must now be considered still trying to develop a new kind of be the only bike on the market. The leg configurations that is as important lengths and leg-lengths proportions. in upright-cycle ergometry (Journal of historical, a bicycle-design contest was bike drive-train. The prototype of Stani- popularity of practical HPVs is inverse- as the leg configurations that will result Even if the optimum joint angles were Sports Sciences 18:153-161). organized by Dave Wilson in the mag- slaw Garbien’s bike was in use for a ly related to the availability of cars. in the hip, knee, and ankle angle that determined, to obtain these optimum Stegmann: Plotting the Too & azine Engineering over 33 years ago. long time, but in about 1980 it was con- This can be confirmed by looking at will maximize power production when joint angles may result in crank-arm Williams MAXPED and MINPED figures Two successful Polish entries became verted into an upright bicycle with con- France and Britain in the 1920s, Swe- interacting with some given crank-arm lengths that are similar (or different) from Table 1 on the graph in Figure 2 (p. known through publicity in the techni- ventional drive and with the front beam den during and shortly after WW II, or length. And there are probably as many 4), using a scale of 1000 W=145 rpm, for subjects of the same leg length with cal HPV and cycle literature (e.g., in serving as a luggage carrier. This con- Poland and Russia in the 1980s, when different leg configurations with crank- the Power and rpm curves are an different leg-length proportions, or of Bicycling Science). version from recumbent to upright is in all sorts of pedal cars and HPVs were arm-length combinations that would almost perfect match. There should be different leg lengths with the same leg- One of the entrants, Kazimierz some way significant. Eastern Europe made by amateurs and also by small result in the optimal joint angles to a very close match between MAXPED length proportions. This would imply Borkowski, creator of the sliding-seat (including Poland) is very fashion-sen- manufacturers. maximize power production as there and MINPED from Table 1 with Peak (and possibly conclude) that the opti- rowing-action bicycle, claimed that “it’s sitive. It’s not easy to be a trendsetter It is difficult to fight the car, but are cyclists. Hypothetically, if a study and Minimum Power from the graph in mal crank-arm length is very individ- just for sports and recreation”. He was there: if the item is not of Western ori- there is another medium that helps HPV was conducted with very tall people Figure 2, since MAXPED and MINPED ualized, and dependent on, both the an engineer in the biggest Polish bicy- gin, it is usually ignored or laughed at. enthusiasts to communicate and not to (long-legged cyclists) versus very short were determined from the flywheel revo- leg length and leg length-proportions of cle plant, Romet, and never developed A young engineer, Jacek Ziolkowski, feel alone: the world wide web. May people (short-legged cyclists), I would lutions for a 5-sec interval, as was Peak the cyclist (in addition to other factors his concept further. Nowadays Rowing- who made his three-wheeled HPV human power be with you! suspect that similar curvilinear trends and Minimum Power (which was then such as pedaling rate and load). This used to generate a regression equation bikes, very sophisticated (and practi- from a MiG-17 auxiliary fuel tank —Marek Utkin for both groups would be found for would not be a very satisfying answer for Peak and Minimum Power). cal) machines, are made by Derk Thijs (HPV News, Sept. 1987), died after
22 Number 52 Summer 2001 Human Power Human Power Number 52 Summer 2001 23 International Human Powered Vehicle Association IHPVA PO Box 1307 San Luis Obispo, CA 93406 USA http://www.ihpva.org