Technical Report:
Accuracy Testing of 4iiii Innovations PRECISION
Powermeter Technology
Scott Cooper, Ph.D, 4iiii Innovations Inc.
Wouter Hoogkramer, Ph.D and Rodger Kram, Ph.D, University of Colorado Boulder
University of Colorado BoulderLocomotion Lab
September 14, 2018
Executive Summary
The Locomotion Lab at the University of Colorado, Boulder is a world class facility
renowned for independent analysis of biometric performance systems. Rodger Kram,
Ph.D. and his team at the Locomotion Lab have developed an objective testing protocol
to confidently determine the accuracy of power meters used on bicycles.
4iiii Innovations Inc. requested a study to independently test the accuracy of thePRECISION Powermeter technology at the Locomotion Lab.
Tests included multiple PRECISION PRO and Podiiiium Pro PRECISION Powermeterson alloy and carbon cranks being compared to power calculated by a bike treadmill for
outputs ranging from 150-350W. Results showed an average error in power reading of1.58​% for PRECISION PRO Powermeters and ​0.84​% for Podiiiium Pro PRECISION
Powermeters on carbon cranks.
These third-party test results prove the accuracy of PRECISION and Podiiiium
PRECISION Powermeters.
The sports technology industry is driven by advancements such as higher accuracy andreliability, however, these are seldom verified by independent testing. By encouraging
studies such as these, verification of power meter performance can help consumers
make more informed product decisions and strengthen the validity of the sports
technology market.

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Introduction
Currently in the sports technology industry, there is little independent data to support
product claims to device accuracy and reliability. Dr. Rodger Kram at the Locomotion
Lab at the University of Colorado, Boulder has developed a quantitative and unbiased
protocol to determine the accuracy of bike powermeters. Using a bicycle treadmill in acontrolled environment allows accurate determination of theoretical power to compare
to powermeters installed on the bike of test riders following a defined power profile.
Methods
Theoretical Power Determination
Test riders were weighed before and after testing and the total weight of the bike andrider noted. The bike’s rolling resistance (C​RR​) was determined using a simple force
balance as demonstrated in Figure 1.

Figure 1: Schematic diagram of force balance used to determine C​RRBriefly, the amount of mass required to keep a freewheeling rider stationary in this setup
allowed for the determination of the force, F​N​, of the rider + bicycle normal to thetreadmill when the treadmill was set to a 4.1​o​ incline and 3.13 m/sec velocity. This result
was used in Equation 1 to determine C​RR​:
C​RR​= Force​Pull​/ F​N(1)The mechanical power (Power​Mech​) and rolling resistance power (Power​RR​) werecalculated using Equations 2 and 3:Power​Mech​= (Total Rider + Equipment Mass) * g * V​treadmill​ sin(4.1​o​)September 14, 2018

V1.0.0(2)2/7Power​RR​= (Total Rider + Equipment Mass) * g * cos(4.1​o​) * C​RR​ * V​treadmill(3)With the total theoretical power being calculated using Equation 4:
Power= Power​Mech​+Power​RR(4)Powermeter Test Protocol
A test rider rode for 2min at each 150, 200, 250, 300 and 350W on the treadmill set to a
4.1​o​ incline. It should be noted that there was a certain response time of changing thetreadmill speed and slight variation in physiological output of the rider. Therefore
recorded power was taken during the 2nd minute of each power step. The rider
remained in the same gear ratio for the duration of the protocol.
During testing, 10 second average power was used and a data point was sampled
every 10 seconds for 1 minute. These 6 values were then averaged to calculate thedata points at each power output and are referred to as “Powermeter Power”. The
theoretical power output calculated using the treadmill data are referred to as“Calculated Power”.
Table 1: Variables used to calculate theoretical power
Variable

Value

Treadmill Incline

4.14​oRider Weight75.60kg

Bike Weight

8.55kgC​RR

0.0041

Tire Pressure

100psiDrivetrain Losses

2.4%

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Results
Three PRECISION PRO Powermeters were put through the testing protocol, Table 2.
These cranks were “off-the-shelf”, being shipped directly from the 4iiii factory toincrease objectivity of the study.
Table 2: Cranks used for testing protocol
Crank Number

Crank Model

Crank MaterialPowermeter1

Shimano Dura-Ace
FC-9100

Alloy

PRECISION PRO2

Shimano Dura-Ace
FC-9100

Alloy

PRECISION PRO

3

Shimano Dura-Ace
FC-9100

Alloy

PRECISION PRO

The collected data for each crank can be found in Tables 3-5.
Table 3: Results of testing for Crank 1
Cadence(RPM)

Calculated
Power (W)Powermeter
Power (W)

Absolute
Difference (W)Absolute %
Error

49

149.8

147.6

-2.17

-1.45%

65

200.4

193.1

-7.31

-3.65%

73

250.2

240.9

-9.25

-3.70%

80

300.1

295.1

-4.98

-1.66%

85

350.4

358.2

7.84

2.24%

Table 4: Results of testing for Crank 2
Cadence(RPM)

CalculatedPower (W)Powermeter
Power (W)

Absolute
Difference (W)Absolute %
Error

49

150.0

149.2

-0.75

-0.50%

65200.2

198.3

-1.93

-0.96%

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73

250.2

246.9

-3.25

-1.30%

80

300.1

298.1

-1.98

-0.66%

85

350.2

350.0

-0.18

0.05%

Table 5: Results of testing for Crank 3
Cadence(RPM)

Calculated
Power (W)Powermeter
Power (W)

Absolute
Difference (W)Absolute %
Error

49

150.1

152.7

2.57

1.71%

65

200.2

201.3

1.07

0.53%

73

250.3

254.5

4.17

1.66%

80

300.3

304.74.441.48%

85350.5

358.7

8.16

2.33%

The collected data is summarized in ​Table 6​.
Table 6: Compiled results for PRECISION PRO Powermeters
CrankAbsolute % Error

12.50%

20.70%

31.54%

Average

1.58%

Based on this data, 4iiii is confident to claim an accuracy of 1.58​%​ on PRECISION PROPowermeters.
Conclusions
4iiii endeavoured to use third-party testing to determine an objective measure of theaccuracy of PRECISION Powermeter technology. Dr. Roger Kram at the University ofColorado Boulder, previously developed a protocol to accurately measure power output

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using a bicycle treadmill. 4iiii sent multiple off-the-shelf cranks from their factory which
had PRECISION PRO dual powermeters installed on them. Following the testing, anaverage absolute error of +/-1.58% was observed.
Within these tests, the top performing powermeter had a calculated error of +/-0.70%
demonstrating the accuracy the technology is capable of. These measurements wereobserved on alloy cranks but similar results have also been seen from previous testingon this apparatus with Podiiiium Pro PRECISION Powermeters on carbon cranks, Table
7.
Table 7: Results for SRAM XX1 cranks with Podiiiium Pro PRECISION Powermeters
installed (early 2018)
Crank

Absolute % Error

11.01%

20.61%

30.81%

40.93%

Average

0.84%

It is evident that the 4iiii PRECISION Powermeter Technology is capable of achieving
within +/-1% error. 4iiii endeavours to ensure this level of accuracy on its entire productline which includes a variety of alloy and carbon crank options.
Limitations
Within this study, calculated power required knowledge of both drivetrain losses as wellas rolling resistance, C​RR​. The margin of error on C​RR​ calculation is relatively small withrespect to the order of magnitude of power calculations. Currently, the Locomotion Lab
is developing a method of accurately measuring drivetrain losses but for now, the value
used was an estimate. Previous work has identified drivetrain losses to be on the orderof 2-3% giving confidence in the 2.4% estimate. However, both of these errors
compound the results of this study and the Locomotion Lab will continue to refine theirprotocols to decrease this error.

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Disclosures
This testing was commissioned by 4iiii Innovations. Cranks were provided to theUniversity off-the-shelf from general inventory from the 4iiii Alberta Factory. No 4iiii
employee was involved in the testing protocol or collection of data.

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