Powermeters 101 - The lowdown

Triathlon Forum
1

Okay so i am going to try and keep this clear and simple
I think we all agree that a powermeter is the best tool a triathlete and cyclist can buy
Currently as far as i know there are 6 powermeter options. I will try and give a quick run down on each
Each of them has their pro’s and cons and depending on what you want should help you make your decision on buying one
plus then everyone can say their opinion to help aswell.

First up is the Grandfarther of powermeters - SRM (strain gauges in the crank set)
The SRM power meter is the oldest and first commercially available power meter for mass market coming from Germany. The SRM measures power output with strain gauges in the crank set and has become the standard by which all power meters are measured. Depending on the level of purchase (Amateur, Pro and Lab) it tends to be one of the most reliable of the power meters. The SRM measures wattage in the spider of the crank. The downside to SRM is the cost. It is the most expensive of the power meters. Another downside is the battery inside the power meter itself must be replaced by the factory when it is dead, and this requires some downtime for the user while you mail it in and wait for it to be returned.

Next up is Powertap (strain gauges in rear wheel hub)
The PowerTap is a complete rear hub for the back wheel of a bicycle that houses a power meter. The hub contains a “torque tube” with strain gauges similar to those used by the SRM. These strain gauges measure the torsion inside the hub as it twists from the load that is applied to the pedals by the rider. The bicycle chain wraps around the cogs on the hub and, as it moves, causes small twists in the hub itself. This torque is measured and then converted into wattage at the PowerTap computer. The wattage that is measured in the PowerTap is the wattage that is actually getting to the road, as it has to “go through” the drivetrain from the crank. This causes the wattage to be about 5–10 watts lower than what would be measured by the SRM at the crank. A major disadvantage to the PowerTap is that you are stuck into the wheel that the hub is built to. If you want to use your super trick wheels for racing, you’ll need to get an additional hub for racing and then keep your standard wheel for training which increases cost significantly.

Next Up is the Ergomo - (measures the torsion, or twisting, of the bottom bracket spindle)
Ergomo, also made in Germany. The Ergomo measures power differently from the units reviewed above in that it measures the torsion, or twisting, of the bottom bracket spindle. Every time you pedal, there is a small amount of twisting that occurs on the spindle, similar to the twisting that might occur with a wet towel if you twisted it into a whip. The Ergomo contains an optical sensor that allows it to measure the distance the axle twists, and from this distance it calculates the torque and the corresponding watts that are being applied in order to make that caliber of a twist. A complete Ergomo consists of the Ergomo bottom bracket and crankset.
The downside of an Ergomo is the sensor measures power at the bottom bracket spindle, resulting in a measurement of the side that twists—the left side. The right side of the spindle is attached to the crankset so there is no real twist on the right side. The Ergomo can only measure the rider’s left leg power accurately. Ergomo takes the power output from that left leg and doubles it in order to get your wattage. This may seem to be a problem, but in reality it has not proven to be one for a majority of the users. Only cyclists with a big discrepancy in the strength of their legs would have inaccurate reading. Every rider has a small discrepancy in leg strength, but this discrepancy is usually less than 5 percent.

Number 4 on the list is Polar (tension in the chain)
The Polar power meter features a unique measuring system to measure power. The Polar systems measure chain tension via a chain stay mounted sensor that detects vibration in the chain; similar to how a guitar string “hums”, a chain vibrates faster as its tension increases. This translates into an amount of force, which is then multiplied by chain speed, as measured by a sensor mounted on the rear derailleur, to come up with power output: Power (in watts, or W) = chain tension (N) times chain velocity (in meters per second, or m/s). If installed correctly, the Polar can be an accurate beginner power meter.

Number 5 is the ibike
The iBike Pro power meter needs no special wheels, hubs or cranks making it easy to transfer to any bike. The lightest power meter weighing in at 62 grams. The iBike Pro power meter delivers precision and innovation at a fraction of the cost of the competition and is a great beginner power meter with a simple user friendly screen and easy to navigate programming. Not as robust as the competition.

And the newest to the market is Quarq (strain guages in from the crank spindle)

A new power meter, the Quarq CinQo, shows tremendous amount of promise in function, build quality, and simplicity. The Quarq powermeter system is comprised of two distinct products, the cinqo - which is the power measurement device and the Qranium - handlebar mounted computer. At this time only the CinQo has been produced and it integrates wirelessly with the Garmin 705 computer.
The Quarq was introduced at Interbike September 2007 and the first production models of the cinqo were shipped to customers in June of this year. CinQo is a crank based system that measures power output with strain gauges in the crank spyder. As I understand it, SRM’s patent expired this year and Quarq is using simliar technology with their system. While the CinQo is still in limited supply. The CinQo replaces the crank spyder and is currenly available for FSA team issue and SRAM S900 cranksets. Quarq is planning on introducing units compatible with more cranks in the near future.

So there are the 6 and by the way these words are taken from online sources and there are other reviews if looking for more info. This is just to help distinguish the difference to help you cut down the list. For me Powertap is not an option because of the number of wheels i have. The power and ibike are just to hard to set up and not reliable enough.

To me it comes down to SRM, Ergomo and Quarq.
SRM is proven to be the king but the king comes at a hefty price
Ergomo only tells you what the left leg is putting out and seems not to be as easy to set up as the SRM and Quarq
Quarq is well priced but hasn’t even been out for 14months yet as it came out near end of 2007.
To me buying a powermeter is a very important buy and should be bought with the knowledge of the product
I am looking for the same as everyone else
I powermeter that i can afford, like the design,is reliable, functional, is avaqilable, easy to use, easy to set and has a warrenty if any problems arise.

So which to go with… What do you think?

2

I think that I’d strike Ergomo. They are bankrupt, and my personal experience is that I’m on my 3rd headunit and 5th bottom bracket (between 2 bikes). That said, you can get the final US stock really cheaply on ebay now.

3

Are you putting it on just one bike? If so then SRM or Quarq would have to be at the top of the list.

Kevin

4

If you have multiple bikes and money is an option get a PT. If you have one bike and can afford it get an SRM.

You say you cant use a PT cause you have multiple wheels. Well you can always train with a PT. For races you can make the decision if you want to use a PT or not.

For road races and crits PTs are only useful to analyze the data afterwards. They are good for establishing FTPs and peak power outputs. I enjoy using it but you could use your other wheels if you wanted.

For TTs and triathlons I suggest always using the PT. If it’s a flattish course you can add a wheel cover and get about the same aero benefit as a disc (so says john cobb).

Even if its a hill TT the general consensus on the google wattage group is that you will save more time pacing on a PT than the weight you will save by having a climbing wheel.

But again, if you only have one bike or can afford two SRMs get that.

-Nate

5

+1 on striking ergomo.

I’d also add that there are wireless SRM, PT, and Quark PMs that speak ANT+ Sport. (iAero speaks ANT+ Sport, but as a receiver) And a long as you start talking about ANT+ Sport PMs, then you need to bring up the various CPU options and their relative compatability…but maybe that belongs in Powermeters 201.

6

If you have a 9 speed road bike and 10 speed tri bike, do you have options beyond 2 powertap set ups? Is the SRM able to be switched back and forth without too many complications?
Walter

7

How does ibike work? Looks like you just put a marketing blurb on the post for that unit

8

If you have a 9 speed road bike and 10 speed tri bike, do you have options beyond 2 powertap set ups? Is the SRM able to be switched back and forth without too many complications?
Walter

A single PT hub can run both a 9-speed and a 10-speed cassette (at least my shimano compatible PT hubs can). No need for 2 separate wheels. BTW- you can also purchase a wheel cover in order to convert your training wheel to a disc and back as the situation dictates.

Switching a SRM between bikes takes a bit more time than changing PT wheels and involves some potential wear over time. That said, I know of riders than routinely switch their SRM between bikes, while mine stays only on my TT bike (soon to be replaced by a Quark).

9

Ok so all I would need to do would be to swap cassettes? between which bike I have? I also have a set of Jet 60’s. Is the powertap built around a wheel or can I use the existing Jet 60 I already own. One more ?, use the Jet 60 or use my Mavic Ksyrium? Advantages/Disadvantages…discuss.
Walter

10

How does ibike work? Looks like you just put a marketing blurb on the post for that unit
Stand-alone, it calculates power based on variables entered by the rider during calibration and detected by the PM during the ride. The validity of the power data is dependent on careful calibration/set-up by the rider and acceptable riding conditions, such as relatively low cross winds and solo, non-drafting riding. As a stand-alone, it is not a direct force power meter, as are SRM, PT, and Quark. However, the iAero can double as a CPU for these ANT+ Sport DFPMs, offering both DFPM recording and reporting, along with CdA estimations.

11

Ok so all I would need to do would be to swap cassettes? between which bike I have? I also have a set of Jet 60’s. Is the powertap built around a wheel or can I use the existing Jet 60 I already own. One more ?, use the Jet 60 or use my Mavic Ksyrium? Advantages/Disadvantages…discuss.
Walter

12

Are you putting it on just one bike? If so then SRM or Quarq would have to be at the top of the list.

Kevin

From personal experience, after mounting a spare GXP BB on a second bike, swapping the CinQo from one bike to the other is LITERALLY a single bolt, 2 minute operation.

edit: Therefore, saying it’s better suited for a “one bike” use is really not accurate. IME it’s actually less of a hassle than swapping my PT wheel between the same 2 bikes, since one is 9-speed and the other is 10-speed. I’d much rather swap the cranks over than swap cassettes.

13

First: Powertap in weight is heavier.
Second: with having different wheels (Mavis Ksyrium SL’s, Zipp 404’s, Disk)
i will go with SRM, Quarq or Ergomo
plus the reason i believe for a triathlete to have a powermeter is to help with racing
if you know you sit on 250watts for a 90km TT and your pushing 260watts in a half ironman
you know you going to die out in the run

So.
SRM. If i can get it at a good price
Quarq. if i can get it at a even better price
Ergomo. If it beats better value then the other 2

I live in Australia. I know that SRM is available hear. not so sure about the other 2 yet

14

A major disadvantage to the PowerTap is that you are stuck into the wheel that the hub is built to. If you want to use your super trick wheels for racing, you’ll need to get an additional hub for racing and then keep your standard wheel for training which increases cost significantly.

Full PT training wheel including computer = $1700 (prices 2008 retail)
Extra PT hub w/o computer = $1200
labor + spokes to put the PT hub into your race wheel = $100
Total = $3000

SRM = $3500

Still cheaper to go PT and get it built into a race wheel. Use a $100 wheelbuilder.com wheel cover and have a “disk” too.

15

That is a good breakdown. Just for reference, a Quarq is about $2050 ready to roll (Quarq, eBay’d crank, Garmin 705) and you do not need to rebuild any wheels. The Powertap model you listed no longer holds if you use separate wheels for training, road racing, and time trialing. At that point a crank-based powermeter makes more sense.

16

Sure.

For me, I use a deep dish for road racing, and use the same setup with a disk cover for TTing. I split time on my road and TT bikes 70-30 (or less if you add my CX, SS MTB and XC MTB that don’t have power meters), so for me it’s better to swap wheels than crankarms/spiders.

This is why there are more than one of these gizmos on the market–each is good in it’s own right. What works for you is the question.

17

Sure.

For me, I use a deep dish for road racing, and use the same setup with a disk cover for TTing. I split time on my road and TT bikes 70-30 (or less if you add my CX, SS MTB and XC MTB that don’t have power meters), so for me **it’s better to swap wheels than crankarms/spiders. **

Trust me…I actually find it easier to swap the CinQo crank than to swap wheels between bikes…especially if they take different cassettes…

18

I agree with npearson99, if you have one bike, and $$ is no option, SRM is the gold standard. I run a PT SL 2.4 laced into my Zipp 808 and that is a true race wheel that I would not want to trade for anything. $3k for the SRM is not an option for me, but if you look at the stats, PT and SRM are very close in lab accuracy. Training peaks works with both, so there you go.

Todd

19

A nice summary all in all.

I would advocate Ergomo as it turns out to be the most cost effective right now. Also, keep in mind that the powermeter market is likely oversupplied and in the slowing economy the small may not make it.

Lastly, I have done a lot of research, including to speaking to some of the engineers behind the different units, and I am reasonably convinced we will see something from Shimino in the reasonably near future. Expect them, if they do something to use the Ergomo approach, including possibly trying to acquire the Ergomo patents. I am told they tried once before to obtain them. To see a company like this enter the market could be a real game changer in economics, features, availability and support.

20

A nice summary all in all.

I would advocate Ergomo as it turns out to be the most cost effective right now. Also, keep in mind that the powermeter market is likely oversupplied and in the slowing economy the small may not make it.

Unless it doesn’t work properly/reliably, which has been the case for each of my clients who have/have used ergomos. And the inability to validate calibration without reference to another power meter. They are bankrupt, no-one is providing any effective after sales service/support. So make sure you factor that into your value equation.

In terms of Pros & Cons, one item that is often overlooked is “idiot-proofness” (or maybe that should be “ease of use” :smiley: ). Some meters simply don’t suit certain people’s abilities to use them / set them up properly / keep them working reliably. The PT is probably the most idiot proof PM.