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A bicycle power meter is a serious training tool.

"Training with a bicycle power meter will greatly improve your results." According to Wikipedia, a power meter is "a device on a bicycle that allows measuring of the power output of the rider." While this may seem like a pretty simple explanation, the physics and engineering behind the power meter is not so simple.

I'll take you through an overview of the different types of power meters as well as give some pros and cons from those that I have experience using.

Where or how the power is measured:  Link will take you to section of article.

Hub Type Bicycle Power Meter

The hub type bicycle power meter uses strain gauges in the rear wheel hub andbicycle power meter, powertap SL measure the power after the drive chain.   These meters work well because they are directly measuring the power going to the rear wheel.

The most common of these is the Power Tap SL.  This hub has been around for many years and is well known in the bicycle power meter community. These are made with both a Shimano compatible hub body and a Campy compatible hub body.

A less expensive version, the Power Tap Pro, offers the ability to measure power but weighs a little more.

Available in both a wired and wireless model the PowerTap is simple to interchange between bikes as long as the drive trains are compatible.  Here is what a built up wheel looks like with the Power Tap hub installed.
bicycle power meter, powertap

The strain gauges in the rear hub transmit the data to the head unit where it is viewed by the cyclist as well as stored for downloading to any number of software products.  You can even upload your data to coaching software for self-analysis or review by a coach.  

The data gets to the head unit via either a wired or wireless connection. Each type of connection has its ups and downs.  The upside of a wired connection is that it is less prone to interference than a wireless connection.  Traditionally a wired connection will also use less battery than a wireless connection because the radio transmitter is not present. Both models of the PowerTap bicycle power meter have the same type of head unit (seen right).bicycle power meter

The Saris company offers the head unit as a bicycle computer alone that can later be upgraded to a bicycle power meter with the purchase of just the hub.  

The Power Tap bicycle power meter works very well.  It gives you a great deal of data including:

  • Power (current, average and max)
  • Cadence (current and average)
  • Speed (current, average, and max)
  • Energy Expenditure (total kjoules)
  • Ride Distance (miles or km)
  • Ride Time
  • Programmable Odometer
I rode one of these for a while and I found it quite good.  It takes a second or two to get your power readings.  This could be due to the fact taht you have to get the power through the cranks, the chain and to the rear hub before it begins measuring.  You get used to it and don't really notice the lag after a few rides.

The battery in the computer and the hub both last a long time.  The manual says 400 hours of riding time and I can say that is pretty accurate.  The use of the Power Tap in the really cold weather will sap the batteries faster than riding in warm weather.
Check out eBay if you are interested in a good used Power Tap bicycle power meter.

Chain Measured Power

There is currently only one chain measured power meter on the market. This is the Polar power system.  I got this when it first came out in 2005-2006.  When I first saw this system I really didn't know much about power meters other than I wanted one.  I really wasn't in the market to spend $3500 on an SRM at the time and the Polar seemed like a viable option for me.  

I purchased the S710 Heart rate monitor and the Polar power output sensor kit as an add-on.bicycle power meter, polar 725x, polar power kit

The Polar power output sensor kit use chain vibration to measure power.  It works with the Polar S710, S720i,S725X , S625X, and CS600
You can buy the power meter kit with these or as an add on.

How does it do it?  Think of it like an electric guitar. When you strum the strings of an electric guitar you are putting energy into the string.  The frequency of the vibration has an equivalent energy signature.  The power kit for the polar works in very much the same way.  There are some  parts placed on different areas of the bike.  Take a look at the picture below to get an idea of what I am talking about.

bicycle power meterPower Kit

The parts are starting from top left:
  1. Chain link counter - This mounts on your derailuer and keeps track of how many links are going by and feeds this data to your computer on the handlebars.  
  2. The vibration pickup - This mounts on your chainstay and measures the vibration of the chain much like an electric guitar pickup.  It also houses the candence pickup.  There is a thin line on the top which you can't see that lets you align it with the cadence pickup.
  3. The head unit mount - Here is where you put your 710 or S725X watch.  It has a battery in it to power the additional requirements of the power pickup kit.  There are two little brass interfaces that hook into your watch when you mount it.  This is how the data gets from the power kit to your watch.  Battery lasts a really long time.  I also noticed my watch battery seemed to last a long time also.
  4. Speed sensor pickup.  This mounts on the chainstay opposite the vibration pickup.  Your speed is taken from your rear wheel.  This is nice if you are riding your bike on an indoor trainer rather than rollers.  Your power will work on an indoor trainer this way.
Here's a picture of all of the parts mounted on the bike.  I had to use a stock photo because I never took any pictures of the setup on my bike. Never really thought about sharing it with anyone until now.
bicycle power meter, polar power kit
The setup looks pretty complicated but it really isn't that bad.  You will spend about 30 minutes setting the power meter up; i.e. running wires, aligning power sensor on chainstay and just getting everything right.  The setup on the software really is just turning on the "power" option on the heart rate monitor.  After that you merely decide on what recording interval you want to use.  The more closely spaced the interval, the more accurate the output file will be.  If you are riding very flat, unchanging terrian you might be able to get away with even the 60 second interval.  That will record for a really long time.  I only ever used the 5 second interval during races.  Most of the time it was the 15 second interval.

One big thing I learned about using this bicycle power meter is it helped me train at a consistent power output rather than a consistent heart rate, which is really tough and  both are way better than a perceived exertion style of training.
After some initial fiddling with the meter, I got it on the bike and it worked, sort of.  I noticed that when the chain was in the big ring on the front and first gear in the back (yes, I know you shouldn't cross like this but I was using a compact crank), the power readings were not very accurate. However, in the rest of the gears, this thing was really accurate.  I even tested it against my Computrainer Pro and it was within 1-2% all the time.

Take a look at these on eBay if you don't want to buy a new bicycle power meter.  I sold mine on eBay.  There wasn't anything wrong with it, I just wanted to try something different.

Bottom bracket bicycle power meter

There is only one bottom bracket bicycle power meter out there currently and it is discontinued due to durability problems.  It was from Ergomo.  
Rumors abound about another manufacturer bringing out a bottom bracket power meter and I'll try to find out about it and post it here.

One of the riders in my club has gone through three of them.  They kept failing.  He is buying them pretty cheaply on eBay now.
If you are brave, you could try one.  Here is a listing of the current Ergomo bottom bracket bicycle power meters on eBay:

Crank based bicycle power meter

There are two crank based bicycle power meter systems on the market. One is by SRM Training Systems and the other is from a relative newcomer to the scene, Quarq.  Both measure power at the crank, but each utilizes a slightly different method.

SRM Training Systems is very well known throughout the cycling community.  Among cyclists, it is a well respected power measuringbicycle power meter, srm training systems device that is used by many, many pros in both training and races.  If you watch stages of the Giro d'Italia or the Tour de France, you can see SRM power meters on many of them.  
The three main component suppliers, Shimano, Campagnolo and SRAM have versions available to work with virtually anyone's bike.

The system is comprised of the following pieces:

  • Head unit
  • Crank
  • Wiring Pickup (for wired units) (power and speed)

Inside the crank spider, there is a strain gauge.  This measures the power applied to the crank arm and calculates the wattage the rider is generating from the force applied.  Along with power, these systems measure altitude, heart rate, distance, cadence.

SRM released a full wireless system in 2008 that uses the ANT+ standard bicycle power meterfor wireless data transmission.  Now you can have wireless power, speed and heartrate pickup with the SRM system.

One of the biggest drawbacks to putting any bicycle power meter system on a bike is the running of wires.  Now that more and more manufacturers are getting on-board with the ANT+ standard, I don't think it will be long before we see everyone release a wireless version of their bicycle power meter.

The other player in the crank based power meter is newcomer Quarq.bicycle power meter They are offering the Cinqo power system.
The Cinqo power system replaces the spider on your existing crank, if it is one of these listed below:
  • Rotor Agilis
  • FSA Team Issue
  • Pinarello MOST (with a removable spider)
  • SRAM S900
  • Bontrager Race X Lite
  • Truvativ Rouleur Carbon

They are working on bringing more options to market, just give them a little time.  This will be the next power system on my bike.  I like the idea of using your existing cranks and keeping a more "stock" look to the bike.
Here's an overview of how their system works:

A torque sensor and candence sensor measure how much strain, through 10 gauges on the spider, and how fast the cranks are turning.  Through this information, power in wattage can be computed.  This information is sent via a 2.4ghz link to any ANT+ power enabled device.  You could used an SRM head unit, an Edge 705 or and iBike Pro to get data from this bicycle power meter.

Opposing Forces Bicycle Power Meter

I started using this type of power meter in 2007 when I saw the ad in Velobicycle power meternews for the iBike power meter. I thought: "Now here is a great idea. A power meter that you can just put on your bars without all of the complicated setup, wiring and special do-dads that the other types of power meters required."

For the most part I was right. The iBike has outstanding customer support. I spent a good amount of time on the phone with the developer and owner of the company. He was very helpful in getting many of my problems solved. I have even visited the factory.  Made in the USA is a plus.

I had a problem on a trip in Italy and one of the designers spent 40 minutes on the phone with me to help me solve the problem. I can't say I have had service like that (with no fee mind you) from anything other than a small local company. These guys know their customers and how to treat them.

Now on to how it works:

The iBike goes on your handlebars. If you get the wireless version you only have to put the wireless mount on your bars and do the calibration to set it up for your bike. Calibration is three different choices.  Fast Setup, Advanced (called USER) and Racer setup. The fast setup will work for about 95% of the riders out there.  The User and Racer setups just get you that last little bit closer to perfect.

Before every ride the system will auto calibrate the wind speed sensor. This gives you a zero line for wind hitting the power meter

During the fast setup, you will have to do this one time:

  • Set up the tilt (to make it level itself on your bars), rider weight, tire size etc so you can get everything set up. Instructions are pretty clear on this and I can't see putting the entire manual in here. Figure about 5 minutes to get all of this stuff done including getting the sensors paired with the head unit.
  • Do a two mile calibration ride.  Now you are done.  Should you wish to get more you'll have to do some additional steps:
  • Do an acceleration calibration. This consists of riding from about 2 mph to around 20 mph. The screen will tell you to accelerate then coast. These are called "coast downs". The idea is to do about 10 of them and you can do more. It gives an average to the accelerometer in the powermeter.
  • Do a 4 mile ride right after on a fairly flat course in the position you would normally ride in. This will calibrate the meter.

I have been using this for several years.  The firmware updates that come out make these units more and more advanced.  For the money, I feel they are a great deal!

The data I have seen is very accurate. There is even data from racers using several power meters at once to compare back and forth. I used the iBike with a Power Tap and I can say the data was very close.

The only downside I have found to this bicycle power meter is that it eats batteries in the cold weather.  The latest version of the firmware, 4.0 is supposed to have changed this quite a bit.  It hasn't been cold yet so I'll have to report back later.  I find it necessary to replace one every month in the cold months. The good thing is they are still good to put in during the summer they recover when they warm up.

Here are some iBikes currently available on eBay:


Direct Applied Force Meter

There is a new product out now from a company called Metrigear.  They have a power meter that is integrated into the hollow shaft of a standard bicycle pedal.  It will be available the first quarter of 2010 from the company.  After the release I will do a review of the product.

You can get more information here from their website.


An in development project is also in the works from is from an Irish company called Brim Brothers. They don't have a product on the market yet. It is still in development and they aren't saying much about it. You can see their site here if you would like.

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