Nerd nerd nerd.... Powertap stuff

[DanielS]

As some of you have seen, I got myself a Powertap! Its totally nerdtastic.

If you don't know what a Powertap is - its a rear hub powermeter. The hub has a bunch of sensors in it that send data to the 'head unit' (i.e. the computer bit on your stem), and you can see how many Watts you are producing at any given moment. The head unit also stores all of the data so that you can upload it to your computer and do all sorts of other things.

Why measure power? Simply, power is equal to torque * pedalling speed. It is a measure of how quickly you are putting energy into your bike. While tactics are still the most important thing for winning a bike race, at some point the amount of power you can produce over some period of time will decide the race - be it in a sprint, up a hill, in a breakaway, etc...

Why bother? Like a heart rate, power is way of quantifying your effort level. However, a powermeter also gives you a very objective way of measuring performance. Some of the things a powermeter are useful for:

*Training in 'zones', like you would with a HRM
*Measuring your average power over different time intervals - e.g. 5s, 1m, 5m, 20m - and using that to get an accurate, objective measure of your strengths and weaknesses (which you can use to train your weaknesses, race to your strengths)
*Measure training load over time, to give a measure of your fitness/fatigue/form.

Should you get one? I would say get a powermeter if (a) you are willing to analyse data or (b) you have a coach who is willing to analyse data :) Even if you just want to train in zones, like you might with a HRM, some basic data analysis is still required.

There some good software out there to help you do the data analysis. The most popular is WKO+. Powertaps come with a program called 'PowerAgent' but it is very limited. I am using an open source program called Golden Cheetah, which seems to work very well (and works on Mac/Linux/Windows, whereas WKO+ is Windows only).

A good overview of everything to do with training by power can be found here: http://home.trainingpeaks.com/power411.aspx

I'd also highly recommend the book 'Training and Racing with a Powermeter' by Allen & Coggan. The book basically expands on the info on the Training Peaks website.

I bought my Powertap from Excel Sports. They are doing a special which is the Powertap, built into a 32 spoke DT RR 1.1, for $659 USD, shipping was about $120 USD to Adelaide. Expensive compared with a HRM, but cheap compared with the amount we spend on many other things in this sport!

Here is my data from today's C-grade crit:



If anyone is interested, average speed was 36.7 km/h and average power 248 W. Each 'bump' in the graph is pretty much one lap (low power, high speed on the front straight, and high power, low speed on the back straight into the wind). I was dropped hard on the last lap so no massive Ws at the end, sorry.

I'm still learning, but if anyone is considering getting one of these contraptions and wants to know anything, ask away...
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What would Jens do?

[steve]

By the way dan from what i hear you can order a separate HRM strap that works with the Powertap comp. Im getting one in from Bicycle Express

[DanielS]

Yep good point, I should have mentioned that the power tap head unit is also a fully fledged HRM as well. I don't have a HR strap, hence why I appear to be dead in the graph...

I'm not sure if I'll get a strap yet, as everything you can do with HR can be done with power instead, but it might be nice to see out of curiosity.
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What would Jens do?

[Alasdair]

There's still a lot you can do with HRM, particularly with regards to increasing your aerobic threshold or staying below it (think TT). Wattage doesn't tell you how hard you're working, it tells you what the results of that effort are.
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Two wheels good, four wheels bad...

[Dr Matt]