"Do I really need a power meter?" – an often asked question, with a clear answer. No, you do not need a power meter. Norman Stadler became a two-time Kona champ pacing himself by just "going all out." Eddy Merckx managed to win approximately every bike race he ever entered without one, and set an hour record that stood for 28 years. However, when that hour record finally was broken by Chris Boardman, it was done with extensive use of a power meter to guide his training. A power meter is not absolutely necessary for success, but it can be a fun and useful tool.
What is a power meter anyway? How do they work?
What are power meters good for?
- Pacing Workouts
Bike workouts are often prescribed in terms of zones or power targets. While heart rate can be used to pace longer intervals, short intervals are problematic since heart rate does not change instantaneously. With a power meter, if a coach or training program prescribes "4x5 minutes @ zone 5 or 300 watts" you will know exactly what to do. You will also know whether you hit your training plan goals and can analyze the power file later or send it to your coach.
- Pacing Races
By doing practice runs, you can figure out exactly how hard you can ride to finish a triathlon bike leg and still have enough gas to run, or how hard to push during a time trial so that you have nothing left at the line. Using a power meter to pace a race can be especially helpful when the route has climbs or a lot of wind. A cyclist's natural reaction to a hill or headwind is to push much, much harder. While you should push a little harder on uphills, using a power meter to pace allows you to make sure you don't burn too many matches. Late in any race with significant hills or headwinds, you'll find yourself passing people who blew themselves up early on. Compared to time trial efforts, for mass start bike racing a power meter is not as useful for pacing, but you may find it beneficial to gauge your effort in breakaway attempts. However, after the race you can often review your data and identify places where you wasted energy, or didn't attack hard enough, etc.
- Monitoring Progress
Once you hit a decent level of fitness, gains start to come rather slowly. Over the course of a year you might expect to only gain 10 or 20 watts of power on the bike. Without a power meter it can be hard to tell if you're making progress. For example, you may do a monthly time trial event and think you're getting slower only because each month it gets a little windier. With a power meter, you can accurately chart your progress over time. You'll also be able to see your best power efforts over various durations, which can guide your training. For example, you may find that your 30-minute power has been improving, but your 15-second sprints are declining.
- Evaluating Your Talents
By testing your best power at short, medium, and long durations, you can put together a profile of your strengths and weaknesses on the bike. This is mostly relevant in bike racing, a sport in which both aerobic talent and sprinting talent play a role. Using a chart developed by Andrew Coggan, you can get an idea of whether you are currently more suited to sprinting or breakaways or are more of an all arounder. You can also identify weaknesses and address them. See Andy's article on power profiling for more details. Triathletes who plan to experiment with or transition to bike racing can also get an idea of how they may stack up by referring to the chart.
- Field Testing
One of the most fascinating applications of a power meter is to use it as a poor man's wind tunnel. This isn't easy to do, as finding the proper location can be difficult and the procedure requires patience and care. For those willing to put in the time, however, a power meter can be used to test equipment and position choices out on the road. With a good location and methodology, you can detect small changes in aerodynamic drag, as was demonstrated by Andy Coggan in his Aerodynamicists Challenge. In short, you need to find a stretch of road where you can do multiple loops without using your brakes and that is relatively low on wind. Velodromes or out-and-back routes with little traffic are good choices. You also need to know the elevation profile of your route. You can then use the Chung method to estimate your coefficient of drag. The aerolab tool in the free power meter software Golden Cheetah lets you do this without a degree in math.
- Sweet Race Reports
Everyone loves a good race report, and with a power meter you don't have to say "I attacked the peleton with a big surge!"; you'll know exactly how many thousands of watts you attacked with. You can also post annotated charts of the race for extra fun. Most importantly, you can track your latest power records and brag about them on the internet.
Which one should I get?
There are currently three main players in the market, with a few others on the horizon:
- Quarq - Crank Based
Quarq is currently ATC's best-selling power meter. It is built into the crank, which means you are free to use any wheels you want and still record your power. It is available with many models and sizes of crank, including Shimano, SRAM, and FSA. Chain rings can be swapped but will require re-calibration at the factory, which usually is a quick and inexpensive process. Quarq has been around a long time, and they have a reputation for good customer service and reliable operation. The downside with the crank-based system is that it is sometimes harder to swap the crank from one bike to another. However, if your bikes share the same bottom bracket type, this can be a fairly quick change.
- CycleOps Powertap - Rear Wheel
Another popular type of power meter, and the most affordable, is the Powertap. The power meter is built into the rear hub of your wheel. You can purchase a powertap prebuilt into a wheel or as a hub and build your own. As with the Quarq, the Powertap is available on many models of wheel, from the basic Mavic Open Pro training wheel to a HED or Zipp race wheel. Different Powertap models are available, with the only difference being less weight. Now on their third generation of hubs, Powertap also has a reputation for painless, reliable operation and good customer service. Swapping your power meter between bikes is simple. The downside of a Powertap is that if you want to train and race with power, you either have to train and race on the same rear wheel or get two of them. One solution to this problem is to get a Powertap with a basic training wheel and put a disc cover on it for races.
- SRM - Crank Based
SRM is considered by many to be the best of the best, but you pay for it. Like the Quarq, these power meters are built into the crankset and are available with many models and sizes of crank. SRM has a reputation for being the most reliable and accurate, with examples in the field that continue to operate after many years of service.
- Garmin Vector - Pedal Based
Many people are excited about this upcoming product, which integrates the power meter into both pedals. This promises to offer the advantage of easily moving the power meter from bike to bike, as well as freeing up race wheel selection. Some consumers are also excited to get left vs. right leg power data, which the Vector will provide to supporting head units. Sports physiologists are dubious as to whether the information is useful, but having the data available will at least let some people confirm or deny that for themselves. Garmin expects to have this pedal, currently in development, ready in a few months. But buyers beware: even the best power meter models tend to have a few issues in their first run.
Where can I buy one?
Power meters are not generally kept in stock at your local bike shop, as wheel and crank preferences are so personal and varied. However Austin Tri-Cyclist is offering 10% off and free installation on all power meters for the next month. Stop by the shop and ask for Adam Stroobandt, and he'll help you select and order your power meter.
How do I get started?
A good place to start is the book Training and Racing with a Power Meter. This book is full of useful information about training and racing for both triathletes and cyclists.