A Gentleman & The Size Of His Wattage

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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.

Power Struggles

Possibly not the blog you thought it was from reading the title, but really some down to earth answers to questions on a piece of kit you may be considering as a tool to help your training. Before you read on, please be aware that purchasing a power-meter & sticking to a power based training programme will put a huge dent in any ‘social cycling’ you currently do. It may also turn you into a number crazed power nerd, if you read on & decide to purchase one, make sure you decide on a suitable power/life balance beforehand, otherwise you’ll end up with as much social ability as a ’50’ TT specialist.

What is a Power-Meter

It’s a device that is attached to your bike which directly measures your how hard you are working. We’ve gone through era’s of coaching ‘perceived exertion’, moving onto heart rate monitoring, now we have another better way to monitor your cycling, power, measured in Watts. The benefit power has over heart rate as a measurement is that power is a direct measurement of what you are doing right now. Heart rate is a historic measurement of your exertion levels & is also affected by lots of other factors & will rise (cardio-drift) during a sustained effort. Power measures what you are doing right now, heart rate measures what you were doing a minute ago, including the accumulated stress of what you did before that time. As a simile, you know that annoying delay you get on an internet stream of a race, where you see the result on Twitter a minute before you see it in pictures? That poor quality delayed coverage is heart rate, the up to date HD Eurosport coverage is power.

Power-meters come in two major types, hub & crank.

  • Hub based power-meters are generally the cheapest power measuring option. The cheaper versions are less accurate on the power reading & weigh quite a bit. Powertap hubs can be bought separately & built on a rim yourself, or by a local shop. So you can ride them on different bikes, but if you’re buying one, get one that you’ll be riding in your training & can race to gather data if need be. A race only Powertap wheel (i.e. with a tub on it) isn’t going to get you the desired benefits unless it’s a 2nd wheel, you need to be using it for most of your training.
  • Crank based power-meters are currently much more expensive, accuracy is very good, but you’ll have to do a bit more fiddling with calibration. SRM’s are the standard for crank based power-meters, but lots more coming out slowly over time, at what looks like much cheaper pricing. You’ll be using this on the bike you use for training & racing, but possibly not put it on a winter bike, which could be useful.

Do I Need One?

Nobody ‘needs’ one, but if you’re struggling for time, it may help you go faster. It’s a great tool for removing ‘junk miles’ from your bike riding & helps you monitor progress, you can squeeze your training into a much smaller time-space. Power-meters are yet another expensive bike part, so I’d suggest that it’s going to make a much bigger difference to your performance than a frame upgrade or a set of ‘fast’ wheels, for a much smaller outlay. The only thing is that new frames & wheels look ‘bling’, power-meters look a bit drab & clumsy sometimes, so if your thing is posing & not going fast, a power-meter is not for you. You can probably buy a professional bike-fit, a power-meter for racing, a power-meter for training & individual coaching for the same money you’d spend on a new carbon race frame or a pair of top branded carbon wheels. It kind of makes sense, a new frame might not make you any faster, a properly used power-meter certainly will.

I’ll emphasise again, that a power-meter without analysis is just a toy, with the occasional, “I did the (insert local climb) at (insert respectable number) Watts last week”, which means nothing to you or anybody else. There are a large number of ‘power users’ doing this kind of thing, so just having one is going to make zero difference to your performance, but spending the time to work out what it’s for is required.

You need this book, “Training & Racing With a Power Meter” by Andrew Coggan & Hunter Allen, it has all the information you need to make use of a power meter. It might be wise to buy it first if you’re really serious & you are coaching yourself, then if it’s too much for you, sell the book on & you’ll only lose £3 or £4 on it, people want this book, it’s well used. If you’re using a coach, check they know about power, can analyse your files & tell you what you want to know, many can’t, but they’ll tell you.

There’s an argument too that riders who have incredible amounts of available time won’t benefit as much from a power-meter, if you have all the time in the world, to ride your bike during the day, ride chaingangs, race a bit during the week & weekends. It’s probably likely you’re getting all the training you need, plus it would ruin your enjoyment of the bike over long periods sticking to a set power output. I’d advice those people to stick at what you’re doing, how you’ve managed to get kind of lifestyle I don’t know, but you are living the dream, don’t ruin it with a power-meter.

What will it tell me?

The first thing you do is build a ‘power profile’, this is basically how well you perform over various times. These are 5 seconds, 1 minute, 5 minutes & Functional Threshold (FT). So an average power over the first three, then the functional threshold is what you can produce for an hour, but an hours testing is a bit of a drag, so it’s often taken as 95% of your 20 minute output, which is enough of a drag in itself. I tend to extrapolate it from a ramp test, but you’ll need the technology to do that, which many don’t have at home, so the 20 minute test should work for most. You also have to look at your events & see what timeframes are important. Simplistically, if you’re a road racer, then 5 minute & FT are very important, you can read a chart (in the book) which will show you where you stand on an international scale in each timeframe, be prepared to be humbled.

Once you have a profile, you can see if your abilities match in any way the events you’re trying to perform at, maybe you decided you were a kilo riders, but your 1 minute power turns out to be naturally rubbish, but you FT is great, could be you’re doing the wrong events for your natural talent.

One of the best tests is to actually run a power meter in a race, especially useful to look at data where you were struggling, or even better where you were dropped. This will tell you, in no uncertain terms, exactly what was going on, especially as your heart rate is likely shown too, so you can see how well you recover between efforts & which a particular efforts cause you big problems. We call these demanding efforts ‘matches’, you only have so many ‘matches’ you can burn in a race before you are totally spent, so identifying what your own matches are (different for everybody), then training that area specifically will help you perform. Then after some training, you can theoretically increase the number of matches you take into a race, the efforts of others will have less of an effect on you, then you can survive & perform to a higher level. This kind of thing is impossible to identify with just a heart rate monitor.

So imagine a rider who trains by heart rate, he does lots of 5 minute intervals, but keeps getting dropped in races when it goes ballistic for short periods of time. The initial power profiling would likely show a poorly developed 1 minute output, resulting in tha rider starting to do shorter intervals & performing better. So you can help pinpoint things like the length of interval sessions you could be doing. This is assuming you’ve not digested the entire book, it gets quite technical, so I’m demonstrating what you can do before you’ve really grasped the mechanics of it, which you will be capable of if you’ve read this far & not given up.


Power measurement is going to become almost standard, prices will drop massively for measuring devices & knowledge will grow regarding how exactly to use them, but that’ll all take some time. If your club has a ‘power-nerd’, see if they’d be willing to help you find out about it, maybe borrow theirs, or get your club to think about purchasing a Powertap wheel (you’ll get problems with Shimano & Campagnolo cassette wars though, so be aware, but it’s easy to change if you buy both freewheels, which just ‘push-in’). A club power-meter could be a valuable device, I can see that becoming more normal, something that will actually make a difference to riders, but you need somebody who knows how to use the data to tell you something useful.

That’s the jist of it, power is useless without knowledge, the same as has been displayed for centuries by many, many people.