Stages Power Meter – First Ride

“Good things come to those who wait,” goes the old saying and, by and large, this is true. Carbon frames were once five-figure price tags, if you could even find someone high enough up the food chain for access to them. Shifters moved from the downtube to the brake levers, and finally to the extensions on our aerobars. Not just a single company, but a host of them now produce UCI-Illegal frames that even the average triathlete can afford. Even the much-vaunted power meter, once the purview of only the deepest of pockets, have finally come down into a price range that is attainable by mere mortals. And one of the companies pushing the envelope on affordable power, Stages Cycling, has made power not just affordable, but accessible, too.

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Where most companies require serious surgery to fit a power meter—replacing the crankset or lacing a new hub into your rear wheel—Stages has a far less invasive solution: replace your non-drive side crank arm. That’s it; that’s the entire process. It takes about five minutes with a set of Allen wrenches and a torque wrench. We know, because we timed Devon as he did the swap, and he even stopped to find his Loctite in the middle. So we’re confident that this isn’t just minimally invasive, but is easily swappable without requiring a trip to the local pro shop! For those of us who are our own mechanics, this is a welcome move towards less complexity on modern race bikes.

The way that Stages deals with being only on the crank arm is by using something called a strain gauge. What a strain gauge does is actually pretty neat. As a rider applies power to the pedal, the crank arm flexes, if only slightly, and this deflection is not only measurable, but by understanding the material composition of the crank arm, can provide a measurement of how much power a rider is putting down. More power means more deflection, less power means less deflection. Stages claims that their strain gauge is accurate to +/-2% of actual power, which is in line with what the rest of the industry is providing at this time.

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The trade-off is that Stages only reads power from the left leg, and then (effectively, the math is a little more complicated than this) doubles it to account for the right. Now, since Stages only measures one leg, it is possible that it is measuring the non-dominant leg and reporting a (marginally) lower total wattage than is actually being produced. On the other hand, you could be part of the 25% or so that are left-leg dominant and be reading a marginally higher number. We’ve brought this up to make one very important point—it doesn’t matter in the slightest.

We feel this is important to reiterate: there is almost no reason to care about this left-leg-only business. The reason we don’t care, and neither should you, is that there are only two things that you should care about in a power meter – that it is reasonably accurate (that +/-2% number from before) and that it is, most importantly, consistent. Consistency matters more than accuracy for the simple fact that, all things being equal, your power number is a personal reference point and nothing else. At 30mph, it does not matter if your power figure is 200w or 203w, so long as your reported wattage is the same number each lap at the same speed, windage, gearing, etc. When you go harder, the number goes up in an arc that can be described through a non-piecewise function. The same for when you ease off the gas. Power is a quantifiable, recordable measure of effort. Everything else is noise.

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That said, this “quantifiable, recordable measure of effort” is a big deal. It lets a rider build a training plan around wattage targets. You can dial in an interval set and see progress as the same wattage gets easier, week over week. We can build a race profile and then understand that when the wind kicks up we need to stay at our wattage, not at our speed, if we wish to save our legs for the run. Power is important for a triathlete in so many ways that it is hard to overstate how much use we can derive from training and racing with data.

As some of our readers know, our Technical Editor, Devon, broke his wrist earlier this year while snowboarding. Part of his lesson on why he should stick to just three sports was a doctor-mandated abstention from riding for the better part of three months… at least, riding in the road. Nobody said anything about riding on the trainer, however. And so, armed with a Stages power meter, he has been riding for the past few months on the trainer and thinks that Stages has this consistency problem licked, and the left leg “problem?” Well, “What problem,” he says.

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The Stages meter hooked up to both computers he was using without incident. It is also recommended that a “Zero Reset” calibration be performed before each ride, which involves pointing the crank arm straight down and waiting thirty seconds before each ride. We did not notice any significant problems with not doing a calibration pre-ride, but minor variations in power did occur once or twice, which were fixed with a Zero Reset, and off we went again. We do recommend doing a pre-ride calibration before every ride as Stages says to. Besides, it’s less time than we spend chatting waiting on our training buddies to be ready to go, so just do it. Unless you’re the last one ready, you’ll have plenty of time (we’re looking at you, Devon).

Once on the bike, we noticed that the Stages power meter does best with either a five or ten second average. The instantaneous power figure tends to update too fast to read at a glance, and even the three second average seems to have a problem with fluctuation faster than we can read without devoting actual attention to it. To our eyes, five second rolling averages scale in step with our perceived effort transitions and show us a figure that is both legible and intelligible from a feedback perspective while riding and racing, even if it takes a fraction of a second longer to get to our desired wattage thresholds when doing interval workouts.

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The most impressive thing about Stages power meter has been how uneventfully transformative it has been to our rides. Its provided feedback on everything from, “Are we really going this fast, or is there a headwind?” to “We’re way above our threshold. This is going to hurt in a mile or two.” What Stages, and riding with power, does is provide another point of referential data that can be used to inform your riding and, ultimately, make you a better rider. We can’t think of anything better than that.

 

One response to “Stages Power Meter – First Ride

  1. Pingback: 3-16-2014 WiR | AeroGeeks·

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