Chain Testing: Full Load Test Method
The Full Load Test Method (FLT) uses a variable speed drive motor, simulating a rider pedalling a front chain ring. A torque load (DC generator) is applied to the rear axle to simulate the load at the rear wheel. The chain follows a path in a similar manner to a bicycle drivetrain—around the front chain ring, through two derailleur pulleys, then around the rear cog. To measure the friction losses of the chain, two rotational torque transducers are used; one transducer on the front drive shaft and one on the rear load shaft. During operation, both sensors measure the torque on their respective shafts. In a simplified explanation, the difference between the power measured at the rear axle and the power measured at the front axle is the friction losses that occur within the chain. For example, if the rear sensor is measuring 250 watts and the front sensor is measuring 265 watts, then the chain is consuming 15 watts of energy in order to transfer the 250 watts of power. In this example, the chain’s friction losses would be stated as “15watts@250Watts,” or the chain is “94% efficient.” It must be noted—the chain does not actually consume all of the 15 watts.
The equipment’s ceramic bearings holding the shaft and the derailleur pulleys consume a fractional wattage. The chain might consume 14.75 watts; the bearings 0.25 watts. This is detailed further below.
The Full Load Test Method is not novel. It has been used in several previously published papers. Possibly the most popular and commonly referenced paper published on the subject of bicycle chain efficiency is “Effect of Frictional Losses...”, by Spicer et al. Spicer uses a very similar test method to the FLT.
- The front ring cadence can be varied from 0 to 125 RPM. Friction Facts by CeramicSpeed typically performs tests at 95RPM.
- The load generator can be varied from 50 to 350 watts.
- The hub on the front axle is a 130mm BCD, which can accommodate large and small front rings of various tooth sizes. Friction Facts by CeramicSpeed typically uses a 53T ring.
- The rear hub is a machined 1.275” diameter drum which can accommodate individual cogs from a common cassette.
- The front hub can be laterally adjusted outward up to 2” to simulate front ring-rear cog offset, for non-coplanar testing.
- Calibration of both torque transducers is by static beam method. Norbar static beam calibration example
- The accuracy of the FLT is +/- 0.25W.
- Equipment system losses due to the four ceramic bearings and two derailleur pulleys are 0.28 watts for the FLT. The Test Results typically have the system losses already removed from the final data, unless noted otherwise.
- The electronics path is as follows—two strain gauge rotary torque transducers connected to two strain gauge conditioners, outputting two analogue signals to a single Analog-to-Digital data acquisition device, then connected to a PC running data acquisition (DAQ) software. The DAQ software performs all calculations converting the torque signals into usable watt measurements. The DAQ software typically averages the data over 1-minute intervals, with a 25 samples/second sampling rate.