As I’ve said before, my powermeter holy grail is a product that:
- doesn’t add significant weight
- measures left and right leg power so that pedalling efficiency can be analysed and improved
- is easily swappable between different bikes, and
- is affordable.
Stages brings an innovative solution to satisfy three of those four requirements (which aren’t equally weighted and aren’t necessarily complementary).
Let’s quickly talk about each of these with regards to Stages:
1) It doesn’t add significant weight
In fact, the Stages unit only adds a mere 20g to the overall crankarm weight. In comparison, Garmin Vector adds ~55g, Powertap adds ~100-200g, Quark adds ~200g and SRM adds 150-200g.
2) It measures left and right leg power
Actually, most powermeters measure force, but I’ll refer to it as power for the sake of simplicity from now on. Stages doesn’t measure power from both legs. It measures the left side only. Is this a deal breaker? Not to me.
In fact, most people will probably get no real benefit out of having L/R power measurements. All this does is add complexity, cost and weight to the overall system for something that very few people in the market will benefit from.
3) It’s easily swappable between different bikes
Swapping a crank arm is as easy as swapping a set of pedals or a wheel. That said, when I look at all five of my bikes, none of them have the same cranksets, so the Stages may not be as transferable as you’d imagine. But if you have a road and TT bike both with Shimano cranksets for example, swapping is a piece of cake. For true swap-ability between bikes, I don’t think you can beat the pedal-based Garmin Vector.
4) It’s affordable
The highest priced Stages model is the Dura Ace 9000 crankarm which retails for AUD$999 and the price falls to $799 for Shimano 105 or SRAM Rival.
Design and compatibility
The entire design of the Stages powermeter is elegant and simple on the outside. The basic premise is this: a regular left-side crankarm is fitted with a unit which contains a strain gauge and the other necessary circuitry to measure and transmit power to an ANT+ or Bluetooth-compatible device.
The Stages unit transmits 64 force and position measurements per second to the head unit. The powermeter itself is specially bonded on to the crankarm at the Stages facility in Boulder, Colorado where it is calibrated and quality tested.
It’s one of those solutions that is so simple you wonder why it wasn’t thought of earlier. To be fair, miniature electronics such as accelerometers and temperature sensors that cram into such a small unit, along with low power consumption, have only been around for a short while. However simple Stages appears on the outside, the more you learn about the technology packed into the tiny unit the more you realise how complex and ingenious the engineering is.
Here are a couple things to take note of before purchasing a Stages powermeter. This isn’t meant to show pessimism, but rather to state the realities that you might not think of:
- Unfortunately aluminium crankarms are only available at this time. This is because the flex of aluminium is predictable and therefore the strain (and thus force) being exerted is accurately measurable. Carbon cranks do not flex in a uniform and predictable pattern. This could be a dealbreaker for carbon crank SRAM or Campy owners.
- There are a few bikes that Stages won’t fit on. The Trek Madone 5 series (and up), for example, has the rear brake situated underneath the seatstays which gets in the way of the Stages unit (I can’t see a workaround for this — sorry Madone owners). Also, some bikes with the Di2 battery placed on the non-drive side chainstay (such as the Giant Propel or TCR) may may need some fiddling around with to get the necessary clearance. Check here for a full list of compatible frames.
- In case you’re wondering, you cannot send your existing crankarm to Stages to be fitted
- If you don’t have a crankset that’s compatible with one of the models that Stages offers, you may need a whole new crankset (and possibly bottom bracket) to be able to use the system. Check here for a full list of compatible cranks.
Stages comes in the following road models:
- Shimano Dura Ace (multiple versions)
- Shimano Ultegra (multiple versions)
- Shimano 105 (multiple versions)
- SRAM Rival
- Cannondale Hollowgram SI
- FSA MegaEXO or BB30 (available early 2014)
There are also a number of MTB and BMX options available.
Accuracy
The first question many people ask is “is Stages accurate”? I firmly believe that a powermeter only needs to be consistent and accurate in itself in order to do the job it’s intended to do. In the end, power is just a number that you use as a tool to train towards.
Most powermeters state their accuracy as +/-2% and Stages is in line with this, however Stages defines this further. Accuracy is +/-2% when measured at 100 watts at 90rpm (this is done because a 2% accuracy is a much different error at 100w versus 1500w.)
That said, there have been a number of independent tests, including this comprehensive piece by DC Rainmaker in which he independently compares Stages with other existing powermeters. As you can see, a direct comparison of powermeter accuracy isn’t as simple as you might think.
Communication between head units and the meter can be imperfect (packets can be lost, transmission rates may be different etc). Even pairing two Garmin head units to the same power meter can result in slightly different results due to variations such as temperature calibration.
As stated before, Stages only measures left side power. Total power is simply calculated by multiplying by two. Is this accurate? The guys from Stages tell me that most L/R differences are less that 5% (unless you have serious imbalance or injury) and when you combine that with a +/-2% accuracy rating, this difference is basically absorbed into the margin of error. For most people, I cannot see the real-world practicalities of worrying about the fact that only left side power is being measured.
Features
You might wonder what features a small power measurement unit on the back of a crankarm could possibly have. It just measures force and calculates power, right? There’s more.
A wonderful design feature of Stages is that it incorporates a temperature sensor so that it can dynamically compensate for heat changes in its calibration settings. This means you rarely need to zero your head unit. It’s recommended that you do this once per week or so, but there’s no real urgency for this unless you think your readings are off.
The built-in accelerometer means no magnets need to be affixed to the bike. Why is a magnet needed normally? All the strain gauges measure is the deflection of the crankarm, thus the force being put down by the rider. Power is a function of force and rotation, so a magnet or accelerometer is required to measure the rotation of the crank. Thanks to Apple, accelerometers are now small and affordable and can be of great benefit in applications such as this.
A feature that I would have skimmed over on the spec sheet turns out to be one of the most profound features on the unit: Bluetooth Smart. Bluetooth 4.0 devices (such as your iPhone) can communicate with Bluetooth Smart devices as well as legacy Bluetooth versions. For users who choose to do so, this means that an iPhone can be used as the head unit if purchasing a Garmin or the like isn’t an option.
Screenshots from the Stages Power iOS app.
Why is this significant? Because it allows connectivity to your iPhone in a meaningful way and Bluetooth 4.0 doesn’t drain your battery which was a downfall of legacy Bluetooth standards.
Bluetooth Smart also allows you to connect your Stages powermeter directly to apps such as Strava, Wahoo Fitness or Training Peaks and directly upload the data without the need to plug your head unit into your computer. Yes, you can do this with ANT+, but you need an adaptor for your phone.
Bluetooth Smart also allows you to update the firmware on the crankarm directly from your iPhone without plugging anything in. It’s worth nothing that not all phones have Bluetooth 4.0 and the app is only available for iOS devices at this time.
Last but not least, Stages doesn’t just leave novice powermeter users with a piece of technology and no guidance on how to use it. Stages has partnered with Training Peaks to provide you with resources on how to interpret your power numbers and how to train properly using power.
Reliability
I’ve used almost every powermeter on the market and you won’t go without hearing about some problems here and there for every unit. To Stages’ advantage, it’s a simple and elegant solution where there is very little to go wrong, aside from the entire unit failing.
That said, it’s worth going through some of the early problems that Stages went through since I’m sure someone will bring them up:
- I’ve heard of some early issues where the Stages power unit has broken away from its bonding and the battery door has failed. I asked the guys from Stages about this and they assured me that these issues have been identified, fixed, and no failures have been seen since the changes.
- In terms of water resistance, Stages says that the units can withstand downpours and can be fully submerged in a stream crossing. If something were to go wrong, simply removing the battery and letting it dry out will solve the problem.
- In terms of battery life, the CR2032 battery is reported to last for 200 hours of riding, does not need to be sent in for replacement, and is easily found at any supermarket for a couple dollars.
If there is a issue, the 12 month warranty will come in handy.
The Bottom Line
I’ve only done a week of testing but so far I can’t speak highly enough about the Stages powermeter. It has absolutely everything I need from a powermeter at a price that I can afford. In terms of everyday operation and usability, it’s the most practical powermeter on the market. I’ll definitely be buying one.
Image: Stages.
Image: Stages.
Crank comparison showing the Stages powermeter attached to the non-drive side crank (left).
Two of the men behind Stages: Left: Doug Crawford, Vice President. Right Pat Warner, Senior Vice president (big titles for two guys who are very down to earth and love to ride their bikes)
WRAP-UP
- Very affordable
- Available in all sizes and bottom bracket standards in aluminum cranks
- Accurate power measurements
- Easily transferable to other bikes (if you have same crankset)
- No external hardware required (magnets, wires, etc.)
- Bluetooth Smart to connect directly to social apps and allows smartphone to be used as head unit
- Temperature sensor eliminates the need for calibration
- Available for aluminium cranks only
- If your existing crankset isn’t compatible, you’ll need to purchase one that is.
- Some bikes may have brakes or Di2 batteries that get in the way
