Both SRM and the Quarq CinQo consist of a power meter that is located within the crank region. In the SRM, the measuring unit is located in the center of the crank and uses strain gage strips to deflect the force that is applied to the pedals. The deflection registers force (torque) and cadence (angular velocity). These units are then converted to a signal, which is sent through ANT+ to the power control. The Quarq CinQo uses the same technology, but the power meter is located in the crank spider.
Power Tap places its power meter within the rear wheel hub, measuring the torque of the hub multiplied by the speed or angular velocity of it. Like the SRM or Quarq, the hub has strain gauges that deflect these measurements, converting them through a signal sent via ANT+ to the power control.
By having the power meter located within the crank, both the SRM and Quarq are great options for those who want to train and race with different wheels. On the opposite side of the argument, the Powertap wheel is easier to swap between multiple bikes. Thus, as the consumer, you have to decide how you want to train and or race with power.
Accuracy between the instruments is a moot point. As seen in the comparison charts below, each model has an error ratio of greater or less than 2%. It may appear as though the SRM offers more crank options that are compatible with both Shimano and SRAM components. The Quarq offers fewer options because Shimano cranks do not contain an interchangeable spider. However with a 110 bolt pattern, Dura-Ace and Ultegra chain rings can be placed on the SRAM S975 crank. Thus, both the Quarq and SRM can run seamlessly from that aspect. There does happen to be a weight difference between the two available crank power meters. SRM’s power system is on average over 100 g heavier than the comparable Quarq model when compared to the weight of a standard Shimano 7800 crank with a length of 172.5mm. Additionally, service is less convenient with the SRM unit. When the battery does die, the unit has to be shipped back to SRM’s Colorado Springs location for battery replacement and calibration because it is soldered into the power meter. This is a fairly seamless process costing $100 (shipping not included) with a turn-around time of 2 days once received. With the Quarq, battery life is lower but user replaceable.
If race wheels or racing with power is not a concern, the Powertap is the most affordable option. As hub weight decreases, cost will increase with this option. Battery life is equal to that of the Quarq and is user replaceable. Head unit options are abundant across the board, with each power meter running off of ANT+ technology. The Joule 2.0 is arguably the greatest head unit, allowing the rider to customize the dashboard with 18 different metrics. Twenty hours of memory is available and 8 analysis reports can be performed while riding without any uploading. If route mapping or directions are important features, the Garmin head units are the route to take.
This is meant to be a summary comparing the three power meter options that we carry. Please call or visit us at the shop for more details and allow us to set you up with the appropriate power meter and computer unit