POWER METERS: Crank, Hub or Pedal-based?

[Spinnekop]

Few random thoughts

I have had the opportunity to ride the SRM, Powertap and the Quarq.

 

First I have to mention that all are tools to try and figure out what your body can do, might do and refuses to do.

That said, I have been cycling competitively for almost 17 years. So I basically know what I can do....might can do and should not do.

 

Fact of the matter is you have good days and you have bad days. No reason for you to 'limit' your good days by looking down on the computer and mind screwing yourself saying......"hey.....I can't do that....slow down".

 

Well.

Basically I use the powermeter to measure where I am and where I want to go fitness wise. Improving or slacking.

That is it.

Comparisons have been thrown left and right and % out and and etc. Only engineers can understand and I have sort off cast a blind eye towards all that. If a PM is inaccurate, so be it. As long as it is consistent!!! And that is important for me.

 

Powertap:

• Cheaper of the options
  
• Limited to one wheel. If you want racing data (Assuming it's built into your training wheels) you have to race with a heavy wheel
  
• I have no idea of battery life and how easy it is to replace.
  
• With the right software it uses ANT+ which opens up some choices.
  
• Chain ware, bearings might influence the readings.
  

SRM

• My favourite. BUT
  
• Very expensive
  
• Battery needs to be replaced in Germany. R2-R4k
  
• If you want you can replace at home but it has strange batteries. I have friends that source from the East
  
• Very tidy/neat
  
• You have to use a crank set where the arm is not one unit with the spider as the SRM replaces the spider
  
• No issues with changing wheels
  

Quarq

I have owned a quarg for nearly 2 years now.

• Initially the battery caps broke. Quarq replaced mine with an alu one.
  
• I replace the battery (Buy at Dischem) every 3 months or so. Twist cap, battery, back on. Easy and R20 later sorted
  
• I have not had issues with calibrating but I know of one or two of the earlier models that gave issues. Basically what I found was that if you do not torque your chain ring bolts, it will give you issues. Interesting
  
• Neat and tidy
  
• Limits you to crank choice
  

 

Thus far I have only been happy with my quarq. No bad readings and always consistent with what I expect the reading should be.

 

I think it helps a LOT in the way where your HR will vary from day to day depending on how much sleep you got. How good your diet was. Alcohol. Water consumption. Sick. Tired. Stressed.

City boys will know what I talk a bout.

With power it is constant. A watt is a watt is a watt. And referring to W/kg will always put things in perspective.

I will climb on the scale and have a HUGE scare but push out bigger numbers than usual. Working back to W/kg gives me my ave and the argument there will be that it is status quo in terms of fitness. Muscle gained.

Stuff like that.

 

Pedal based arriving soon in SA

• You will be limited to pedal use....
  
• Crashing and bike falling over, that is usually the first thing to scratch and break. Scrathing a R2000 pedal vs. R10 000 pedal....mmmmmm....I will be PISSED!! :-D
  
• I think acuracy should be fine.....again....as long as it is consistant. We don't really compare each others watts on a regular basis........
  
• Price point will be important. I heard rumors of $1000 RRP for the Garmin. If that is still the case, this is going to be a good option!
  
• You will be able to swing to the MTB to figure out stats for long tours on the gravel.
  

All said and done, everything is toys. Add ons. You should enjoy your ride. If number crunching is your thing, go for it!! If you just ride your bike to get out, do that.

Buying a pm won't make you any faster. It will just help measuring and give you NUMBERS wise an idea of where your fitness are.......

 

Long story.

Sorry.

['Dale]

Cool post, Spinnekop.

 

"What you cannot measure, you cannot control..."

 

HR is a so-so measure.

 

During 2010/2012, I raced and checked out my HR on a long false flat.

It read 91 % effort level and I was physically feeling much better than how I interpreted the 91%.

It did not feel like an accurate reflection of my output or strength.

And my interpretation messed with my confidence during the race.

 

The PM will give me greater accuracy of my output, I believe.

And to use that information well.

That is the value I want to buy.

 

Lots more to be written about this.

[MTB_Roadie]

I am also looking at going into this route.

 

Dale, what quotes have you received so far? Please PM me prices as I dont want the hub, I would prefer the crank, not sure on brand though.

['Dale]

I am also looking at going into this route.

 

Dale, what quotes have you received so far? Please PM me prices as I dont want the hub, I would prefer the crank, not sure on brand though.

 

Not at the quotation phase yet.

Just early research.

 

Aiming for a after-season 2011/2012 purchase.

[Minion]

Powertap:

• I have no idea of battery life and how easy it is to replace.
  

Claimed life is about 400hrs of riding, but I found mine didn't last much more than 250hrs.

 

There's a special tool to take off the end cap, but you could probably also use a large shifting spanner to do it. Once the cap's off it's easy to replace the batteries and they're fairly easy to find.

[Spinnekop]

I would LOVE to get my tenticles on one of these:

 

http://www.power2max.de/shop_details.php?artikelid=7

 

Will fit the 'Dale.

Price wise looking at €990 which is not bad for a crank based system and you get the cranks with!!!

[DangerDave]

Which do you recommend and why??

 

Money is but one consideration.

Overall value and accuracy is very important.

 

Thanx for the feedback, in anticipation, Fellow Riders!

 

B)

 

easy, it does not matter how high or low the systems read as long as they are accurate, you do not want a system that is not accurate, accuracy at the moment is as follows:

 

SRM Science @ +/-0.5%

Power Tap @ +/- 1.5%

SRM Pro @ +/- 2%

QuarQ @ +/- 2% think may even be a little less

Garmin, unknown

I bike ???????

Polar ???????

 

a little note to go with all this, Power Meters do go wrong, SO make sure you buy a unit this is supported locally and has a track record for being able to support the product, i.e. SRM and Power Tap. Power Tap can fix your system with in a day!!!

[DangerDave]

Claimed life is about 400hrs of riding, but I found mine didn't last much more than 250hrs.

 

There's a special tool to take off the end cap, but you could probably also use a large shifting spanner to do it. Once the cap's off it's easy to replace the batteries and they're fairly easy to find.

 

the Guys at CycleOps do NOT suggest you use a shifting spanner, buy the tool for R75.00 if lost, but all new hubs bought though Bicycle Power Trading should come with the hub wrench!! battery cost is R20.00 per battery (x2) and should last between 3-6months!!! great value for R20.00!!!!

[DangerDave]

Hope I'm not hijacking 'dale's thread too much by asking this. What is the most 'cost effective' (OK cheap) way to measure power for comparison purposes for improvement that is rather than against others?

 

Hopefully that make sense? I do have a Garmin 500 ....

 

if you have a gamin 500 you are half way there, go for a Power Tap it IS the Cheapest ar R8 895.00 for a Pro+ built into a Mavic Open Pro wheel for free!!!

[Zac.A]

I would LOVE to get my tenticles on one of these:

 

http://www.power2max...php?artikelid=7

 

Will fit the 'Dale.

Price wise looking at €990 which is not bad for a crank based system and you get the cranks with!!!

 

 

I'm getting mine in sometime this month, will answer all questions fielded when it arrives

[DangerDave]

Not quite a power measure, some say the CycleOps PowerCal is more of a Training Impulse measurement:

 

http://www.cycleops....g-powercal.html

http://velonews.comp...wheelset_178521

 

And then the DC Rainmaker take on it: http://www.dcrainmak...-joule-and.html

 

well done HEman!!! finally a Power Meter for someone who wants to put value to training, i am sure we all want to!!! there are 4 Power Cals in South Africa along with a Joule GPS and Joule 1.0 the guys at Bicycle Power (www.bicyclepower.co.za) have them and are putting them through final testing. the PowerCal is an interesting toy and requires a 20min test made up of a 5min warm up and 5 x 3min efforts each harder than the previous! pricing is expected to be under R2000.00 pricing on the New Joule is expected around the R1900.00 mark.

 

more details on the web page listed above!!!

[Agteros]

well done HEman!!! finally a Power Meter for someone who wants to put value to training, i am sure we all want to!!! there are 4 Power Cals in South Africa along with a Joule GPS and Joule 1.0 the guys at Bicycle Power (www.bicyclepower.co.za) have them and are putting them through final testing. the PowerCal is an interesting toy and requires a 20min test made up of a 5min warm up and 5 x 3min efforts each harder than the previous! pricing is expected to be under R2000.00 pricing on the New Joule is expected around the R1900.00 mark.

 

more details on the web page listed above!!!

 

A few questions on the PowerCal still to be answered:

• From what I've read you'll need access to a power meter to set this up? Or how will the test work?
  
• What about the effect of a lowered heart rate for a specific output due to training? How often would this need to be re-calibrated?
  
• Will BicyclePowerTrading assist with tests? How much will these cost?
  

[DangerDave]

 

 

A few questions on the PowerCal still to be answered:

• From what I've read you'll need access to a power meter to set this up? Or how will the test work?
  
• What about the effect of a lowered heart rate for a specific output due to training? How often would this need to be re-calibrated?
  
• Will BicyclePowerTrading assist with tests? How much will these cost?
  

 

The powercal will require a power meter or an indoor cycle or a power beam ( the a frame trainer with power) and as mentioned the calibration takes 20min, once calibrated the power meter will not be needed till the next recalibration that may be with in 4-6 weeks, as you would do if you were training on power and required your FTP to be assessed.

 

As for heart rate drift due to a multi stage event like the epic, CycleOps have made it clear that the powercal is an entry level system and if you want 1,5% accuracy then buy a power tap, this system is ideal for the average cyclist who wants to improve their time and wants to be able to track their performance though systems such as the fit track and performance management charts in WKO systems.

 

The idea of a PowerCal assessment has raised its head with the guys from BPT and I am sure they will offer such a facility as for pricing this has not been finalised.

[capeofstorms]

If you looking to upgrade your groupset them SRAM would be a no brainer with a PM thrown in the mix. Review of the SRAM/Quarq PM here

 

http://pelotonmagazine.com/Goods/content/11/1238/Quarqs-New-RED-Power-Meter

[Shebeen]

outsider's question here.

 

power in = loss of power in drivetrain + power used to combat rolling resistance + power used to combat wind resistance + power used in altitude gained/lost

 

how accurate would a gps based power meter calculator be? couple it with a cadence sensor and you could probably work out which gears you're in too using the speed reading. obviously wind resistance would be an unknown, but there could be ways to approximate that. at worst a differential pressure sensor on your handle bar could give a decent reading. if a software solution could come anywhere close to these rather expensive items i think it could be handy.

 

is this being looked at in skunklabs anywhere, or is the powermarket quite happy with their current price offerings?

[Minion]

how accurate would a gps based power meter calculator be? couple it with a cadence sensor and you could probably work out which gears you're in too using the speed reading. obviously wind resistance would be an unknown, but there could be ways to approximate that. at worst a differential pressure sensor on your handle bar could give a decent reading. if a software solution could come anywhere close to these rather expensive items i think it could be handy.

An accurate estimate would first require you to have good estimates of your weight on the day, coefficient of rolling resistance (Crr), coefficient of drag (Cd) and drag area (A).

 

Weight is easy to measure and shouldn't vary by more than 3-4% during the ride (and that much only if you drop something or become dehydrated). You could make your estimate more accurate by modelling a linear (or some other relation) decrease in weight from start to finish value.

 

It is possible to get a good estimate of Crr and CdA using a power meter (and also without a power meter under some conditions) with the Virtual Elevation method.

The Crr value would change with pressure so you would need to make sure you pump your tyres to the same value every time. It would also vary with road surface conditions. As a thumb-suck, I reckon it could vary as much as 5% during a ride. The variation would be unpredictable and you wouldn't easily be able to account for it.

The CdA value would vary with position on the bike and equipment and kit used. It will also vary with wind direction to some extent. If you could measure wind direction, you'd still be left with the problem of cheaply measuring CdA variation with wind direction).

You could eliminate variation due to equipment by riding the same bike and wearing the same kit for each ride. You could measure CdA for each position, but you'd still have the problem of monitoring which position you're in as you ride. I think CdA values could vary by 10% or more.

 

You would then need to have accurate values for speed, elevation change and wind conditions around your bike.

 

Speed can be accurately and consistently measured using a GPS-calibrated wheel sensor. Elevation change could also be fairly accurately measured using a barometric altimeter (a pure GPS altimeter would add extra innacuracy).

 

Wind conditions (particularly direction) around your bike are the biggest source of variance. A differential pressure sensor would give a rough estimate of wind speed, but not direction. You can get weather station data for your ride that will give global wind speed and direction, but will not account for local effects such as environment shielding or local turbulence.

There is currently some development being done on a commercial bike wind sensor (that may even work with ANT+) - Google 'Chung-on-stick'/Aerolab.

 

Measuring values eliminating as many sources of variation as possible, I think it might be possible to get accuracy of around +-20% for post-ride analysis and perhaps better for rides done in one position on a calm day.

 

The Strava website estimates power based on speed and weight and there is a plugin for Sporttracks that also estimates power using more parameters. I haven't compared either estimate to actual power values (it's on my to-do list).

 

Real-time power measurement would be a more difficult problem:

 

The iBike Aero 'power meter' measures front wind speed, speed and gradient in real time and is reported to give average values for rides over 20min that are within 15% of conventional power meters. For shorter durations, it's accuracy is, apparently, worse.

 

I feel that these power estimates are OK for rough comparisons and comparing long-term training effect, but they're not much better than using a HR monitor for this purpose and they aren't currently practical for measuring and controlling short intervals which is where the PM is most useful.

Edited February 7, 2012 by Edman