Measuring the Effect of Transmitted Road Vibration on Cycling Performance
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Measuring the Effect of Transmitted Road Vibration on Cycling Performance A. Z. Hastings, K. B. Blair, and K. F. Culligan Center for Sports Innovation Massachusetts Institute of Technology Cambridge, MA, USA D. M. Pober Department of Exercise Science University of Massachusetts Amherst, MA, USA Introduction Road racing bikes designed for specific functions ¾ Optimized for aerodynamics, stiffness, weight Ride Quality = Vibration transmission ¾ Frame geometry ¾ Frame materials ¾ Viscoelastic frame inserts ¾ Components (wheels, tires, handlebars, etc.) Literature Review Davis & Hull (1981), Hull & Bolourchi (1987), Stone & Hull, (1995) ¾ Strength, stress and fatigue in road bicycle frame design DIN, JIS, IS0, and ASTM ¾ Frame strength, fatigue, static stability, rigidity, and safety Thibault & Champoux (2000) ¾ Modal characteristics of bicycles without a rider ¾ Relation between components and vibration transmission Wojtowicki, Champoux & Thibault (2001) ¾ Front wheel bump impact test Highest response ~50 Hz ¾ Testing on a floor with 1 m bump spacing Inconclusive at distinguishing response between bicycles ¾ Recommended using a stationary road test simulator No method/standard exists for quantifying ride quality Study Objectives Develop a system to characterize the effect of transmitted road vibration in road bikes ¾ Quantify vibration response ¾ Rider performance Demonstrate the ability of the test method ¾ Tested three different bicycle frames Variables of interest ¾ Independent Bicycle frame material ¾ Dependent Vibration response of the frame Cyclist performance Methods Spirometry Test Subject Acceleration Bike Frame Treadmill Power Output w/ Bump Treadmill w/ Bump Extra-wide treadmill ¾ U Mass - Amherst ¾ 5% grade ¾ Speed 19.3 km/h 0.64 cm ¾ 0.99 sec/rev ¾ Pedaling cadence of 77 rpm Bump 3.8 cm dia ¾ Created to induce wide spectrum vibration ¾ Cast using 75 Shore A polyurethane (poly 74/75) Polytek, Easton, PA) Bicycles Supplier: Cervélo Cycles Inc. ¾ Toronto, Ontario 3 Frames tested ¾ Steel (ST), aluminum, (AL) and carbon fiber (CF) All frames built in the same geometry ¾ Equipped with an identical set components Same wheel/tire set ¾ Tire pressure was set to 7.6 bar Identical riding position for all bikes ¾ Matched subject’s own bike Test Subject Single subject used ¾ Eliminate bicycle size adjustment variables ¾ Mass and stiffness of rider the same for all trials Professional cyclist ¾ Kevin Monohan 2002, 2003 USPro Crit Champ ¾ Able to ride the treadmill ¾ Smooth pedal stroke ¾ Comfort and experience with V02 testing ¾ Height = 182.9 cm, Weight = 79.5 kg Completed 3 treadmill habituation sessions ¾ Total 1.75 hours Instrumentation Spriometry ¾ Rider energy expenditure, V02 ¾ Measures inspired/expired gas ¾ Data complied every 30 s SRM Powermeter Crankset ¾ Power, cadence, and heart rate ¾ Schoberer Rad Meßtechnik Julich, Germany Accelerometers ¾ Vibration response ¾ Mounted at seat post Orthogonal with gravity ¾ CXL04LP3 3-axis, 100 Hz roll off ¾ Crossbow Technology, Inc. San Jose, CA ¾ Data logging at 512 Hz Test Protocol Results Vibration Data ¾ Is the rider experiencing something different between the frames? Steel (ST), Aluminum (AL), Carbon Fiber (CF) ¾ Analyze accelerometer data Rider Parameters ¾ If there is a difference, does it effect the rider? ¾ Analyze rider power output, heart rate and energy cost (V02) Results – Vibration Accelerometer output for one treadmill revolution 3 Bump - Front Bump - Front Wheel Impact Wheel Impact 2 1 Acceleration, g 0 Treadmill Seam Impact -1 0.0 0.2 0.4 0.6 0.8 1.0 Time, s Results – Vibration 30 Sequential Rear Wheel – Bump Impacts 3 3.0 Maximum maximum 2 2.5 1 Acceleration, g 2.0 AL CF ST range Acceleration, g 0 3.5 Range -1 0.5 0.6 0.7 3.0 Time, s Z-Test Acceleration, g 2.5 AL-ST AL-CF ST-CF AL CF ST Max, g 5.85 5.47 1.06 Range, g 4.62 4.93 0.28 Frame Type Results – Vibration Power Spectral Density ¾ 16 - 2 sec time samples Calculate 16 PSD’s, then average 3 AL Frame CF Frame ST Frame 2 /Hz 2 1 PSD, g 0 025507510002550751000 255075100 Frequency, Hz Frequency, Hz Frequency, Hz ¾ AL - maximum values ¾ CF - broad band around 60 Hz ¾ CF - Damping in 30-35 Hz range Results – Rider Parameters Power, Heart Rate, Energy (VO2) ¾ Data averaged over 200 s Power, W Heart Rate, BPM VO2, ml/kg-min 250 170 45 225 160 40 200 150 35 AL CF ST AL CF ST AL CF ST ¾ Trend of stiffer bike requiring less effort ¾ Single subject design precludes generalization of this result Discussion Vibration ¾ Magnitude of vibration transmission matches manufacturer’s design intent ¾ PSD signatures of each bike frame may illustrate ride quality Cyclist Performance ¾ No significant difference in rider performance results Short-term test (5 minutes) ¾ Longer test sessions needed Hypothesize there is an energy cost of stiff bikes Conclusion Developed a system to characterize the effect of transmitted road vibration ¾ Bike response characteristics ¾ Rider performance Demonstrated the ability of the test method ¾ Distinguish between different bicycle frames Future Work ¾ Understanding rider performance issues will require longer/more test sessions ¾ Test program easily extendable to bike components such as forks, wheels, tires, etc. Instrumentation SRM Powermeter Crankset ¾ Schoberer Rad Meßtechnik, Julich, Germany ¾ Rider power output, cadence, and heart rate, 0.5% ¾ Data logging via the Powermeter computer Accelerometers ¾ mounted to the bicycle at the seat post using a specially fabricated clamping system ¾ Set to be orthogonal with gravity while on the treadmill ¾ Crossbow Technology, Inc., San Jose, CA ¾ CXL04LP3 3-axis accelerometer High frequency roll-off of 100 Hz Data logging 512 Hz ¾ Valitech ReadyDAQ AD2000, Dayton, OH Spirometry Equipment Rubber mouthpiece ¾ High velocity two-way non-rebreathing valve (dead space 95ml) Hans-Rudolph, model 2700, Kansas City, MO Inspired volume ¾ Electronic pneumotacho-graph Fitness Instrument Technologies, Quogue, NY Expired gasses ¾ Directed into a 3.0 liter mixing chamber and ¾ Continuously sampled (250 Hz) ¾ Analyzed for oxygen and carbon dioxide concentration ¾ Ametek oxygen and carbon dioxide analyzers AEI, Pittsburgh, PA Test Protocol Single Run ¾ Subject mounted bike, holding hand rail ¾ Subject fitted with spirometry equipment ¾ Treadmill slowly brought to target speed ¾ Subject releases handrail and begins riding ¾ Once settled in, data acquisition runs for 5 minutes Transition ¾ Wheels and instrumentation moved to next bike Test Matrix ¾ Single run on each bike in one afternoon Test order: ST, AL, CF.