Power meters for training – are they worth it?

A heavy focus of VeloNomad is on Etape du Tour (with an increasing focus on Haute Route and Marmotte) and am important part of Etape du Tour is training for Etape.

Most people can effectively train for cycling or a sportif like Etape du Tour using a heart rate targeting plan, but the most benefit will be using power. Whilst the VeloNomad Training programs don’t use power (yet), power meters are still worth mentioning. Power meters are an expensive investment and come in a variety of guises, and sifting through the pros and cons of each type of meter can be overwhelming.

In this guest article, Damian Ruse from SemiProCycling talks about his research and thoughts on power in the quest to answer the question: Power meters for training – are they worth it? 

Power meters for training: are they worth It?

By Damian Ruse, Semiprocycling.com
Of all the things to spend money on to improve your cycling and in particular your training, a power meter is probably one of the most impactful (along with investing in the training itself).

Traditionally though, if you didn’t have $2000 to spend, you would be left without one.

I’ve been training without one for a long time because I could never afford to buy one.

With the recent announcement of the StageOne power meter [Ed: more info here], there are signs that power data is becoming more affordable for the Semi-Pro cyclist. This coincides with my hunt for a complete data solution for my new training regime.

My show, Semi-Pro Cycling, is a podcast that analyses and addresses cycling issues from the riders’ perspective. As part of the show, I revisited the idea of buying a power meter for my training. This post is a summary of those findings. For a full analysis and recommendations on the ultimate data setup for your bike, check out Episode #17 – Is it time to buy a power meter?

What’s changed recently?

Like the evolution of our phones, bike computers are increasingly getting smarter. This not only means that more effort is involved in interpreting rider’s data, but data collection from the bike has also become more complex than ever with data able to be recorded in a variety of ways.

Sifting through things like proprietary wireless sensor network technology and wireless radio technology is rather overwhelming, let alone intuitively knowing how to combine them with head units, power meters and the like.

Before we get started with the investigation, let me share with you why I’m revisiting power meters in the first place.

The last time I had a coach, I turned down the option of training with power and instead bought a Garmin Edge 305 for $300, which I thought was expensive enough.

I thought that the 305, when combined with SportTracks, would give me sufficient data for my training.

I was with that coach and under her system for two years. At times, I contemplated my decision not to use a power meter in my training because if I couldn’t hit the magic number in my training – for example 170bpm for 5-minute intervals – I felt like a lot of my sessions were wasted.

Something inside me believed that following an absolute measure of output, say averaging 250W for a 5-minute interval, would’ve been a better target to aim for. [Ed this is essentially right as power is less subjective than heart rate.]

Therefore I’m now re-investigating the whole idea of power. Let’s take a look at the questions I asked myself in my investigation.

How is power measured on a bike?

Each power meter measures forces differently and at different places on the drive-train:

• PowerTap measures at the rear hub
• Quarq/SRAM, SRM, StageOne and Power2Max measure at the left or right crank
• Look/Polar and Garmin Vector (unreleased) measure at the pedal spindle
• Brim Brothers (unreleased) measures at the shoe cleat

Measuring power at various points along the drivetrain results in varying output but that does not necessarily affect accuracy (it becomes an exercise in careful calibration).

For example, a PowerTap will usually read lower than a SRM because it is further away from where the power is generated. This difference has no bearing on the accuracy of the power meter as long as the reading is consistent.

The PowerTap, Quarq, Power2Max, StageOne and SRM use strain gauges. These are small thin foil strips whose electrical conductance and resistance varies as they are deformed.

Strain gauges are used in lots of applications and their properties are well-understood.

In general, strain gauges are combined in a “rosette” or “Wheatstone bridge” [Ed: an electrical circuit – Wiki page] in order to produce more accuracy and precision, and more strain gauges usually produce better results.

When operating properly the PowerTap, Quarq, and SRM are usually accurate to within 1-2 percent.

This has been verified both statically using known weights hung from the crank and also dynamically using a large powered rolling drum in a lab.

The forces are then combined with a measurement of angular velocity or speed to get power.

A virtue of strain gauges is that the change in resistance can be measured even when the device is stationary.

So the cyclist can measure the accuracy of the strain-gauge-based power meters at home by hanging weights of a known mass from the crank. Something of note is that the new Power2Max uses fewer strain gauges than the current PowerTap, Quarq/SRAM, or SRM models.

A common problem with the strain gauge approach, however, is that they can be sensitive to changes in temperature and so need to be “re-zeroed” prior to and sometimes during rides.

The StageOne power meter is calibrated for temperature by using an active temperature compensation that measures both outside temperature as well as the electronic’s temperature and continually zeroing out the calibration to keep it spot on.

To set it up initially, you only need to drop the left crank to 6 o’clock and use your cycling computer to zero it. For absolute accuracy, you should do that before each ride, but it’s not super critical since the unit is constantly self-calibrating for temperature anyway.

Rumour has it that the unreleased Garmin Vector pedal meter and Brim Brothers pedal cleat power meter use piezoelectric sensors and solid-state accelerometers instead of foil strain gauges. The accuracy of measuring forces this way is yet to be proven.

On the other hand, the Look/Polar power meter uses a more traditional approach, and is based on strain gauges arranged along the pedal spindle. This provides its own challenges though since each pedal must be carefully installed so the pedals know which direction the forces are being applied.

One pedal is the “master” and the other is the “slave”; the slave pedal transmits information to the master, which then bundles data from both pedals and forwards it to the head unit.

Another unique factor to consider with the Look/Polar pedal is the use of its own transmission protocol, which no other manufacturer has yet committed to provide compatible head units.

Whereas the ANT+ protocol, which is owned by Garmin’s parent company, has been widely adopted and different brands can easily “talk” to each other.

This means you’ll have to buy a complete Look/Polar systems, rather than being able to, for example interchangeably use a Garmin Edge 500 with Ant+ combined with a Powertap or Quarq meter.

When newly-adjusted and allowed to perform under ideal conditions, all of the commercially released power meters produce accurate readings.

However, conditions are not always ideal and certain parts can get damaged, dirty, and deteriorate.

So the important factor in choosing a power meter is not the design but rather the ability to remain accurate under adverse conditions and that it can be easily verified by when its accuracy has drifted.

Equally as importantly, an ability to easily recalibrate a unit is very important to avoid having to take the meter to a specialist for recalibration.

Best Place to Measure Power?

Honestly, there is no best place to measure power (cost and practicalities aside).

As long as they have been tested to produce an accurate reading, then there are more important factors to consider than where the power is measured.

These include the type of bike you own, how many bikes you have (Quarq/StageOne are on the crank, so if you have multiple bikes you need a Quarq crankset or StageOne crank arm on each bike, or swap parts across bikes), whether you have race wheels (Powertap is installed in a wheel hub, so if you have multiple wheels, you need multiple a meters on each hub) and so on.

All of these factors affect the cost and is why something like the Garmin Vector pedal system or Brim Bros cleat system is so ideal. Changing pedals is easy and most of us can easily change cleats or only have one pair of shoes.

Why is Power Data So Expensive?

Of all the available data, be it speed, cadence, heart rate or GPS, power is the most expensive.

It’s expensive because, as mentioned earlier, power meters use highly-sensitive strain gauges and require careful calibration.

A lot of design has to go into working out how to overcome external factors like temperature changes while at the same time producing a light and weather proof system (obviously something Garmin haven’t worked out yet).

The Best Options according to SPC: PowerTap or StageOne

StageOne is a game changer. At $699-$899 USD, the cost is an appealing attribute. By adding a $300 head unit to a StageOne breaks the mythical $1000 price point (unless you already own one).

A small strain gauge and accelerometer measure direct force by being bonded onto a metal left crank arm and then send the data to the head unit. The crank arm is purchased with the unit already attached to it. Then all you need to do is attach the crank arm and calibrate it with your head unit.

StageOne claims that accuracy is the same as the big players. It’s also quite light, only adding 20g to your crankarm weight.

StageOne’s price is low. However, when compared to the cheapest PowerTap, there is not much difference in the price.

The real advantage of StageOne over PowerTap is that for riders who have multiple wheelsets, StageOne allows them to choose whatever wheels they want without worrying about the rear hub (if you have multiple bikes, you’ll need to be able to switch the StageOne crank arm between bikes, meaning you need the same crankset size across all your bikes).

The big question is, will the StageOne live up to its promise? The fact that it has not been used and abused by riders on the road in real situations for any length of time is a risk in itself, as with any first generation gadget.

Relying on the announced release date is also a gamble until it is actually available in the market. Since they are new in the power meter game, it’s likely that the StageOne will have bugs that need to be worked out.

Look at Garmin’s Vector product as an example. Despite being a smart and large company, Garmin are still failing to meet their originally planned, and subsequent, release dates (to the extent the product now has no release date).

If you opt to buy a proven product today, the closest rival to the StageOne is Cyclops’ PowerTap.

It has been around for over 10 years and has a solid reputation. Something to note here is that all models except the G3 will soon be phased out, which is important because, at the time of writing, there is $350 difference between the PRO and the G3 models.

Will I be buying a power meter?

Not yet! It’s clear that prices have come down but the cost is still relatively high. I just sold a bike for $1500, turning around and spending this on a power meter sounds crazy to me.

It’s interesting that even with the introduction of the StageOne power meter, power data is still not cheap.

I would only save $300 by buying StageOne over the PowerTap.

This doesn’t even take into account the risk, I mentioned earlier, of buying a product that is unproven in real riding environments.

I’m actually still unconvinced. Sure the price is half of what it was the last time I looked into it back in 2008. For now, I’m going to hold off until the StageOne has been road tested, work out the bike I’m going to buy, then figure if I can squeeze it into my total budget.

I’ve talked about some of the options available, and now I’d love to hear from you. Are you going to buy a power meter? If so, what makes you justify the cost? If no, is it because of the price?

Damian Ruse is the host of Semi-Pro Cycling, the podcast for semi-pro cyclists. We research, analyse and address cycling issues from the riders perspective. We inspire all cyclists to become better and more knowledgeable. It’s cycling talk for cyclists every Tuesday at 8am (GMT+10).

Tim's comments

I’m with Damian on this. Until power meters (excluding the head unit) are around $500, I will wait. I think they will reach that point eventually, as volumes increase and production costs decrease and the initial research/investment costs are recouped; i.e. when power becomes a commodity.

In most cases, a large percentage of riders can gain immense benefit from training with heart rate monitors. Until your HR-based training is providing marginal return and you have spare cash, perhaps a HR monitor and training regime will suffice.