"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.
The hub type bicycle power meter uses strain gauges in the rear wheel hub and 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.
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).
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.
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.
Power
Kit
The parts are
starting from top left:
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.
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.
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.
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.
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
measuring
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
for 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. 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 Velonews 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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measure the power after the drive chain.
These meters work well because they are directly measuring
the power going to the rear wheel. 
hub body and
a Campy
compatible
hub body.
, offers the
ability to
measure power but weighs a little more.
as an add-on.
,S725X
, S625X
, and CS600
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.
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. 
to work with
virtually anyone's bike.
for wireless data transmission.
Now you can have wireless
power, speed and heartrate pickup with the SRM system.
They are offering the Cinqo power system.
or and 
news for the 
. 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." 
