Verve Cycling is a relatively new Australian company and their first product is the InfoCrank powermeter. Rather than emulate strategies adopted by other companies, the InfoCrank was conceived as an integrated powermeter purpose-built to provide accurate power measurements without the need for ongoing calibration. In this review, CTech editor Matt Wikstrom takes a closer look at the InfoCrank.
There has been enormous growth in the number of powermeters on the market in recent years. Part of the reason for the growth can be attributed to society’s growing fascination with data; another has been a clear demonstration of the effectiveness of power-based training; yet another was the expiry of the patent held by SRM for the design of a crank-based powermeter.
The majority of powermeters utilise strain gauges to determine a rider’s power output. SRM ushered in crank-based powermeters in 1987 with its design for a spider fitted with a series of strain gauges, while Saris installed gauges in the hub for its Powertap design. More recently, Garmin’s vector pedals have strain gauges located on each pedal shaft, while Quarq and Power2Max have essentially emulated SRM’s spider strategy. In contrast, Stages and Pioneer have developed discrete units that attach to the spider and/or crank arm to measure torque.
At face value, Verve Cycling’s InfoCrank resembles any other crank-based powermeter, however it is unique in that the strain gauges are integrated into each crank arm. According to Bryan Taylor, Verve’s president, the idea behind the InfoCrank was a very simple one: “We want to stop with the use of zip ties on bikes, and we want to integrate the technology into the bike.”
A pragmatic powermeter design
Work on the InfoCrank began in 2008 with a request from the Australian Institute of Sport to design a powermeter to suit their test jig. Five years later, Verve Cycling was formed to build a crankset around the technology (which was dubbed the KIP module at the time). Richard McAinsh, a former technical director at 3T and motorsport engineer, designed the crankset, electing to use alloy so that a niche could be machined in each arm to house the load cells.
Measuring 35 x 20 x 5mm, each niche essentially positions the strain gauge within the crank arm while serving as a battery compartment. The niche design allows the strain gauges to be positioned so as to exclude competing forces, thereby improving the overall accuracy of all torque measurements. Working with precision-machined crank arms also affords enormous reproducibility when comparing one arm with the other, as well as one crank with another.
Verve claims that the InfoCrank has an accuracy of ±1% for loads up to 3,000W. Independent testing with static loads reported a maximum error of 0.11Nm for loads below 17Nm and 0.57% for all loads above that, as shown in the extract below:
Verve also performed comparative testing against an SRM crank and found that the InfoCrank matched or bettered it, both in static load testing and track tests. While these results do not automatically extend to every set of InfoCranks, they provide a clear demonstration for the capabilities of the design.
Verve claims that the power measurements made by the InfoCrank are insensitive to temperature. In the first instance, the strain gauges are compensated against the thermal expansion of the alloy crank arms; and in the second, four strain gauges are arranged in each crank arm in a Wheatstone bridge that automatically removes the influence of temperature. As a consequence, there is no need to zero the InfoCrank before use, or indeed, at any point in the life of the crank.
During the course of developing the InfoCrank, it became apparent that reliable cadence data was as crucial to the accuracy of the powermeter as a high quality load cell. While some manufacturers are utilising accelerometers to indirectly measure cadence, Verve installed a Reed switch in each crank arm to directly measure cadence, and thus two magnets must be installed on the bike (one on each side of the bottom bracket) to trigger the switches.
An equally important consideration relates to data sampling. Each load cell generates an analogue signal that must be digitised for processing, wireless transfer and display. Thus, the accuracy of the powermeter depends, in part, upon the frequency of sampling. How many data points are required to accurately measure the torque signal?
Verve settled on a rate of 256Hz (samples per second) so that every pedal stroke is sampled more than 50 times, even at very high cadences (>200rpm), to provide a clean measure of torque. To put that sample rate into perspective, SRM’s powermeter (that has historically served as the gold standard) samples at a rate of 200Hz, while Power2Max, Quarq and PowerTap all have a sample rate of 60Hz.
What’s in the box?
Verve’s InfoCrank comprises a crankset with chainrings and magnets for the cadence sensors. An ANT+ USB stick is also supplied for firmware upgrades along with a pair of batteries for each crank arm, all for a revised asking price of $1,949 (effective December 1). Buyers can obtain InfoCranks from Verve Cycling online and through its network of local bike shops and affiliates (in Australia as well as the US and throughout Europe).
The InfoCrank crankset is available with a choice of two axles (24mm or 30mm) with regular or compact five-bolt chainrings, two five-bolt spiders and six arm lengths (155, 160, 165, 170, 172.5 and 175mm). Buyers electing the compact crankset get a choice of three chainring combinations (Praxis 50/34T, Praxis 52/36T, or TA 53/39T) while the 130bcd crank is limited to one (Praxis 53/39T).
Buyers will need to supply their own bottom bracket if they choose a crankset with a 24mm axle, however the design is compatible with any of Shimano’s Hollowtech II bottom brackets (or similarly formatted aftermarket brands). Put another way, the InfoCrank will be an easy fit for any bike that has a Hollowtech II crank. In contrast, Verve supplies a Praxis bottom bracket with the 30mm option because the axle has an exclusive design with differential drive- and non-drive-side diameters. There is one proviso though: bottom bracket compatibility is limited to BSA, BB30, PF30, Specialized OSBB, and BB86.
The load cell in each crank arm requires a pair of 303 batteries (aka SR44) that can be easily installed and replaced by the owner. While these batteries are identical in size to the more common alkaline LR44 battery, the 303 is a silver oxide battery that has a much greater lifespan and is better suited to the power demands of the InfoCrank than LR44 batteries (however the latter will serve in an emergency). Verve expects a run time of around 500 hours for each pair of 303 batteries.
InfoCranks broadcast their data using ANT+, so any capable device can be paired with the cranks, though many devices won’t be able to display data on separate left and right pedal measurements. O’Synce’s Navi2Coach is one device that will display this data, otherwise it can be analysed with post-ride software.
The 175mm crankset sent for review weighed 854g with an alloy 30mm axle and a set of Praxis sub-compact (52/36) chainrings installed. The InfoCrank is therefore heavy by current standards, where the penalty is in the order of 200-300g.
Another, less important, consideration is the aesthetics of the InfoCrank, which are bold, industrial-like, and perhaps best suited to an off-road bike. Regardless, the crankset integrates well with the rest of the bike; however, the magnets ruin the effect a little. More work is required to achieve the same level of integration for the magnets, so while there are no zip ties in sight, it’s still obvious that the InfoCrank is an instrument rather than a component.
The InfoCrank crankset has a two-piece design, where the axle is integrated into the right crank arm, while the left arm has a single bolt with a built-in extractor. As such, installation is straightforward, especially for cranks with a 24mm axle. As noted above, Verve’s 30mm axle utilises a proprietary bearing design, so a new bottom bracket will have to be installed in the frame, which is best left in the hands of an experienced mechanic.
The cranks sent for review had a 30mm axle and I was supplied with two Praxis bottom brackets, one for a BSA-threaded frame, and the other for BB86. The former was easily installed, requiring only Praxis’s purpose-built tool to tighten the cups in the frame. The BB86 bottom bracket was more demanding in terms of tolerance, with Verve warning that the cups may not fit all frames. In this instance, the frame satisfied the required tolerance and I was able to install the bearings with a conventional bearing press.
While the crankset was easy to install, I came across two complications, both of which were related to the cadence sensors. In the first instance, the domes that cover the sensors are quite tall with a risk of hitting the chainstays of some bikes (e.g. Cervelo P5). There is no work around for this problem but Verve will be switching to lower profile domes early in 2016, so that will improve the compatibility of the cranks.
The other instance related to the installation of the magnets. Verve offers a couple of different magnet designs for the InfoCrank: one has the magnet attached to a plastic ring that fits over of the external cups of the bottom bracket and is easy to use but flimsy; the other employs adhesive backing that quickly failed on the matte-painted bike I was testing.
Fortunately, there are a variety of workarounds for this problem, such as double-sided tape, putty, and other adhesives (where possible, I’d recommend fixing the magnets within the chainstays for a clean, integrated finish). Verve is continuing to work on designs for the magnets, recently adding a bolt-on version that might be better suited to some bikes. They are also working on a firmware upgrade for 2016 that will allow the InfoCrank to measure cadence without magnets (by deducing it from the torque signal).
While the magnets seemed like an afterthought, I was impressed with the battery compartments in each crank arm. Each compartment has an LED that provides immediate feedback on whether the batteries have been installed correctly, the device is working, and the cadence magnets are detectable (the LED lights up with each revolution of the cranks if the magnet is within range of the cadence sensor). Another nice touch is that the small bolt is secured to the lid of the battery compartment with a clip, so there is no danger in losing it when changing out the batteries.
Out on the road
Putting the Infocrank to use is very simple, just turn on the data unit and start pedalling. Since there is no need to zero the powermeter, the only delay is waiting for the data unit to initialise and acquire GPS satellites. In this regard, the Navi2Coach device that was supplied with the InfoCranks was noticeably slow compared to any Garmin device, but in the space of a couple of minutes the unit was alive with the data I had programmed for each display page.
InfoCrank provides all of the expected power measures (average and maximum power for various intervals; normalised power; intensity factor; and training stress score) as well as data on power balance, pedal smoothness and torque effectiveness. The latter two are relatively new metrics: pedal smoothness provides a measure on how much of each pedal stroke is spent producing the average power output; torque effectiveness compares the power produced on the downstroke with the upstroke. At present, it’s not clear if these pedalling metrics have any value to a cyclist in training, but owners can marvel at them nonetheless.
The InfoCrank is rated for use in all weather conditions. I’ve already noted that the load cells are not susceptible to fluctuations in temperature. The crank arms have an IPX7 rating, so they can be submerged, but Verve warns they may not resist a blast from a high-pressure hose. On balance, I expect there is a greater risk of the cadence magnets coming off the frame or bottom bracket cups than there is of weather damaging the cranks.
Reviewing the data
The InfoCrank generates an enormous amount of data that is best handled with a sophisticated analysis program. Sure, you will be able to view basic ride data using Strava, but you won’t be to mine the data to any great extent. I found that Cycling Analytics provided an easy way to have a look at the power balance, torque effectiveness, and pedal smoothness data provided by the InfoCrank, but a paid subscription is required to make full use of the application.
Ultimately, power data is best used in conjunction with a formal training regimen. The InfoCrank is a tool, and while it will quickly satisfy the curiosity of most riders, it will not improve their cycling until they use it to guide their workouts. Thus, one worthwhile prerequisite is experience training with a heart-rate monitor.
Summary and final thoughts
Verve’s InfoCrank is an impressive product. There is enormous appeal in the company’s approach to the design of the crankset, where the position of the load cell within the crank arm is intuitively sound. I’ll leave it to the engineers (and Internet experts) to debate the approach, but Verve’s lab and track testing demonstrates that it allows for gold-standard levels of accuracy.
While the crankset has a robust design with some thoughtful touches, Verve needs to do more work to improve cadence measurement. In this regard, collaboration with manufacturers to integrate magnets into the chainstays would provide the ideal level of integration for the InfoCrank and any other crank-based powermeter.
This last point may seem improbable but there are signs that the powermeter market will continue to grow. For example, both Shimano and Campagnolo recently lodged patents for their own crank-based powermeter designs. Thus, there may come a time when powermeters are no longer considered niche aftermarket items as technology further infuses the bicycle to provide a steady stream of data for the rider.
- Pragmatic design achieves high accuracy
- Easy to install, use, and maintain
- Compatible with a variety of bottom bracket designs
- Promises long-term reliability
- Pragmatic aesthetics won’t suit all tastes
- Adhesive magnets can fall off