A Gentleman & The Size Of His Wattage

A wise man once said…….

“In polite company, a gentleman will never discuss the size of his wattage”

For those who use power meters, there’s a danger you may be becoming what is known as a ‘powerbore’, such is your excitement at the numbers you’re generating that you can’t help telling everybody all about them, all the time! But it’s probably best to keep that kind of information to yourself (and your coach if you have one) otherwise you’re going to become a pain in the SRM.

Going back a few years, and even now, you would often hear heart rate monitor users exclaim how hard a ride was, not by a percentage effort, but by an absolute number. “I was riding at 160bpm!!”, may sound close to your maximum for some, but to others, it’s a zone 2 effort. So what you’re really telling people is that you know nothing about how heart rate varies across different riders for the same effort, which also implies you know nothing about how it affects you, or even worse, you were using 220 minus your age to calculate maximum heart rate. The same thing can now be heard on the subject of power, so let’s get a few things sorted before you make a fool of yourself, or if you need some help on deciding whether or not you really need a power meter at all.

Things To Consider….

In simplistic terms, a smaller rider produces less watts than a larger rider.

This is the first thing to consider when you’re hearing somebody else’s wattage & trying to compare yourself to it. Watts per kg is the most touted number out there, it can give an indication, but it’s doesn’t solely define how fast a rider you are.

  • If you’re looking at your ability on the hills then the main limiter is your power to weight ratio (watts/kg).
  • If you’re looking at your ability on the flat, then your main limiter is power to aerodynamic drag.

This means that unless you’re on an incredibly steep hill with no wind, then aerodynamic drag will also play a part in your hill climbing ability. To add to the mix, sometimes a larger rider can create less aerodynamic drag than a smaller rider, they may be able to get into a better position while maintaining their watts, or their body shape may be more aerodynamic. As Nasa tell us, “long thin rockets have less drag than short thick rockets”. Imagine 2 riders, both with same length of legs, but one taller by virtue of having a longer back. The larger rider will likely have a more efficient aerodynamic position & produce less drag than the smaller rider, due to basic aerodynamics.

Not all power meters will give you the same numbers, for exactly the same effort, but does it matter?

Every power meter has an accuracy that it operates within, most are in the region of +/- 1.5%. So if you’re riding at exactly 300W, the powermeter should display (if everything is set up & calibrated correctly) between 295.5W & 304.5W, a band of 9 watts. Now, that’s for the exact same make & model of powermeter, which is brand-new & calibrated before it left the factory. If we start looking at different manufacturers, the effect of wear & methods of power measurement, then we’re undoubtably going to be looking at larger differences.

For example, if you’re measuring power at the rear hub, the manufacturers introduce an allowance to account for power loss through the chain & drivetrain, as an absolute recorded number would not accurately reflect the power delivered at the pedals. A bicycles drivetrain efficiency can vary between 93% to 98% normally, but as power increases the efficiency becomes greater due to frictional losses being a lower percentage of total losses (see the Cycling Power Lab link for more details). So we know that frictional losses vary depending on power output & that all drivetrains are different (components, wear etc), therefore it’s unlikely a power meter measuring power accurately at different points will ever return the same number.

Combining variations in accuracy, manufacturing procedures, method & position of measurement, drivetrain wear, calibration, etc, I don’t really consider precise comparisons from one make of powermeter to the other as valid. We can take it as a rough guideline, but that’s really all we can safely use as a scientific comparison. Now, that’s not to say that one type is better than the other, as long as you’re measuring power by the same method, then you’re going to see improvements taking place, which is what it’s really all about. In some ways Obree’s method of measuring performance was the equivalent of an isolated power meter, without watts, but where he was able to determine exactly how he was performing. I’ll not go into it in detail, buy his book & see how far ahead of the game he really was.

Power numbers can be much more closely correlated between riders than heart rate can be, but don’t dwell too much on comparisons to your buddies, for all you know somebody’s got an error or some other issue that affects their numbers. Use your own data, ignore everybody else’s. It makes me a little wary when we see Chris Froome’s predicted numbers versus his measured numbers, neither are probably correct, especially when he’s measuring power from just one crank. But that shows what’s important here, measuring from one crank will still show any improvements (and is good enough for data hungry pro teams), it’s getting a good reliable recording method for you, then comparing yourself to that, it’s only your power that matters.

Numbers without analysis or meaning, are just numbers.

Many people buy a power meter because it’s seen as the latest thing to do, another technical cycling accessory to show you’re a proper cyclist. For people who use power correctly, then it’s likely that if you’re not fully aware of what the numbers mean, or how to use them & spout off about watts, you’ll not look like the smartest guy on the chaingang (again, if you’ve a power friendly coach who analyses your data, you’re off the hook here).

So to avoid this, either get yourself a coach with some knowledge on the matter, or educate yourself. The place to start on this is with a book called ‘Training And Racing With A Power Meter’ by Hunter Allen & Andrew Coggan. There’s a lot of information in there, so spend your Christmas money on that if you’ve got a power meter, no coach & lots of numbers you don’t know what to do with.

Alongside that, you’ve probably spent a silly amount of money on your gadget, so you’re probably looking for a reliable & affordable method of analysing it. I’ve tried a few, TrainingPeaks, GoldenCheetah, even the premium Strava analysis is reasonably good.

I’m now using Golden Cheetah, it’s an open source programme for Macs, Windows & Linux with lots of interesting features, plus most of those found on Training Peaks, but it’s free. Training Peaks will cost you around £75 for a 12 month subscription (If you’re a British Cycling member, you can get a 20% or 40% reduction depending on your Gold/Silver/Bronze membership type). Strava Premium will cost you around £30 per year. A coach will vary massively depending on the service & contact you require.

The Gist Of It

You may have read this & realised that just having a power meter, without the additional work is going to be pointless for you, if so I’ve saved you a bit of cash you spend on something shiny. Hopefully there’s some pointers on how to go about analysing your data if you have absolutely no idea what to do with it.

Above all, your number are entirely relative to yourself, so telling everybody how hard a ride was in absolute terms is pointless, percent of FTP, perhaps more relevant, but still boring. Those are conversations that should stay inside your head, the only place they’re relevant.

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