What’s the most accurate system? Is accuracy the be all and end all? Which is the easiest to live with?
Go on any group ride these days and training talk usually ends up being about numbers or – more specifically – watts.
Keen riders will be saying how they have sessions where they ride to a certain number of watts or how they were on the limit at X watts or “did you see the professional on that ride averaging blah blah blah watts?”
How do you measure watts? With a power meter.
What is a power meter?
Power meters are relatively small devices that measure the force of output a rider produces whilst pedalling. This power is measured in watts which are displayed on some sort of display unit (usually on the stem or bars) to let the rider know how well, or otherwise, they are performing.
Power meters may be expensive but the information they provide is invaluable if you know how to use it.
Why is measuring power so good?
Training with power is the most reliable and consistent way to train. It reduces the variables. It provides the most accurate results.
Heart rate is still a good way to train but can be influenced by certain outside factors. Power is consistent. Power output is basic and honest. If you aren’t trying hard enough you won’t deliver the required watts.
How do power meters work?
Power meters are strain gauges. Strain gauges in the meters measure force produced by assessing small deflections in material (eg. crank arms) and transmit the numbers produced to the display unit.
There are several types of power meter which measure either from the bottom bracket area or the rear hub. Depending on the system they can either take one reading from either the hub, the left hand crank, the more accurate left and right crank combo readings, the pedals or the chainset spider..
Currently there are five main power meter manufacturers each with a unique method of measuring power. They all come with their own pros and cons.
Chainset spider based systems
From Quarq, SRM and Rotor. These are very reliable but they are also the most expensive. As the gauges are in the crank spider arms the system is restricted to one bike (unless you fancy changing the chainset when switching between bikes every time).
Pros – the most reliable and consistent method of measuring power as it measures each side to give a correct figure.
Cons – very expensive, restricted to whichever bike you have the system’s chainset fitted to.
Non-driveside crank arm system
Stages’ design is probably the simplest system in that a strain gauge sits in a specially adapted left hand crank arm. The crank looks identical to current systems and doesn’t need any special tools to fit apart from the usual left hand crank tools.
Pros – easy to fit, less expensive.
Cons – only available for newest Shimano, SRAM and FSA chainsets (Campagnolo ones are due in 2016), only measures left hand power output and doubles it – still better than nothing though!
Garmin Vector pedals are the only pedal based system available at the moment and they have the strain gauges built into the pedal body making them very easy to use and switch between bikes which is handy if you have several bikes.
Pros – reliable information as takes readings from both pedals, easy to fit and good if you switch between bikes regularly.
Cons – expensive, only available in LOOK style pedals, still needs setting up when switching between bikes.
Powertap measures power through strain gauges in the rear hub. This makes it very easy to switch between bikes as long as they are all similar groupset and gear numbers.
Pros – less expensive, very easy to switch between bikes.
Cons – do you build it into a race or training wheel?
Do you have to be a professional to get the most from a power meter?
No, ironically those who have the least time available who will benefit just as much from using one as the professionals.
If you only have a certain amount of time each week – say 1 hour per day – then using a power meter can make your training sessions really specific and rewarding. Riders with more time can also benefit by having a constant performance indicator and again create specific or varied rides.
Should you buy one?
Anyone who wants to take their training more seriously will benefit from using a power meter providing they know how to best to use the figures. Get a coach to set you a program and the numbers will let you know how you are progressing. Remember to review your training regularly and adjust levels and sessions accordingly.
The downside is the cost as they are expensive, currently starting around the £600 mark right up to over £2,000. They can also be tricky to set up and some need servicing by specialists so bear that in mind if you are going for an expensive system. You will also need a head unit to display figures if you are using pedal, hub, left hand crank or certain BB crank systems, usually via ANT+ wireless transmission, so bear that in mind.
Saying that, training with power really is a great way to train (especially on turbo trainers) and certainly makes sessions more structured and tracking progress or form much easier.
At the moment the best power meter for the vast majority of people is a Stages system. Although plagued by software and hardware issues when they first came out they are now fully on top of the game and leading the pack.