Go Back  Bike Forums > Bike Forums > Road Cycling
Reload this Page >

An $8 Power Meter?!

Notices
Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

An $8 Power Meter?!

Old 02-13-14, 02:26 PM
  #26  
JTGraphics
Senior Member
 
JTGraphics's Avatar
 
Join Date: Dec 2006
Location: So Cal
Posts: 2,678
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
I think everyone has answered your question. A real power meter works in a range of +/- 1.5% accuracy +/- 15% not useful information and how do you use that when you are actually riding?
If you just want to see some #'s use something like Strava it will give that to you free.
Go spend that $8 on something else.
__________________
It may not be fancy but it gets me were I need to go.
https://www.jtgraphics.net/cyclist_bicycles.htm
JTGraphics is offline  
Old 02-13-14, 02:46 PM
  #27  
save10
Arrogant Roadie Punk
 
save10's Avatar
 
Join Date: Oct 2005
Location: California
Posts: 2,353
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by elcruxio View Post
Ya'll taking this thing way too seriously. It's a curiosity for those who don't have the interest or money for a power meter. Like me

I mean you don't really do anything with watts if you're not going to train with them. However it's always nice to now your ballpark average fitness. Average speed is worth practically nothing if not done in a velodrome. The calculators you find on the internet are possibly as useful as this app but the good thing in the app is that you can access it mid ride and be surprised about how well you are doing.

It's for fun people! Don't you know that fun means?
it would be more fun and worthwhile to spend 7.99 on scrap wood, dousing it with gasoline then lighting it on fire.
save10 is offline  
Old 02-13-14, 02:49 PM
  #28  
wphamilton
Senior Member
 
wphamilton's Avatar
 
Join Date: Apr 2011
Location: Alpharetta, GA
Posts: 15,280

Bikes: Nashbar Road

Mentioned: 71 Post(s)
Tagged: 0 Thread(s)
Quoted: 2932 Post(s)
Liked 333 Times in 223 Posts
Originally Posted by Homebrew01 View Post
And when they fall out of your ears while riding, you can spend another $200
You don't think that developers will race against time to integrate the $8 app that doesn't work into the $200 earbuds that nobody wants?
wphamilton is offline  
Old 02-13-14, 02:52 PM
  #29  
canam73
Senior Member
 
Join Date: Jun 2007
Location: Haunchyville
Posts: 6,400
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 11 Post(s)
Liked 5 Times in 2 Posts
Originally Posted by elcruxio View Post
Ya'll taking this thing way too seriously. It's a curiosity for those who don't have the interest or money for a power meter. Like me

I mean you don't really do anything with watts if you're not going to train with them. However it's always nice to now your ballpark average fitness. Average speed is worth practically nothing if not done in a velodrome. The calculators you find on the internet are possibly as useful as this app but the good thing in the app is that you can access it mid ride and be surprised about how well you are doing.

It's for fun people! Don't you know that fun means?
I believe the posters are doing what they consider fun.
canam73 is offline  
Old 02-13-14, 03:51 PM
  #30  
rpenmanparker 
Senior Member
 
rpenmanparker's Avatar
 
Join Date: Dec 2009
Location: Houston, TX
Posts: 28,682

Bikes: 1990 Romic Reynolds 531 custom build, Merlin Works CR Ti custom build, super light Workswell 066 custom build

Mentioned: 106 Post(s)
Tagged: 1 Thread(s)
Quoted: 6554 Post(s)
Likes: 0
Liked 51 Times in 33 Posts
It's not clear from OP's initial post whether the +/- 15% is the accuracy or the precision. Actually I suspect it is the accuracy. I imagine it doesn't move around a lot during use, but the approximations evident in entering your weight and "type" of bike as well as your personal drag coefficient could easily cause a relatively FIXED 15% error. Yes that would be a problem the first time you used it. But if you could possibly calibrate your output under standard conditions to a power meter as compared to the app (more or less), you could transfer that calibration to the app and determine the fixed error you are dealing with. Then just make the necessary correction to the results.
__________________
Robert

Originally Posted by LAJ View Post
No matter where I go, here I am...
rpenmanparker is offline  
Old 02-13-14, 04:28 PM
  #31  
halfspeed
Senior Member
 
halfspeed's Avatar
 
Join Date: Nov 2003
Location: SE Minnesota
Posts: 12,275

Bikes: are better than yours.

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Originally Posted by elcruxio View Post
Ya'll taking this thing way too seriously. It's a curiosity for those who don't have the interest or money for a power meter. Like me

I mean you don't really do anything with watts if you're not going to train with them. However it's always nice to now your ballpark average fitness. Average speed is worth practically nothing if not done in a velodrome. The calculators you find on the internet are possibly as useful as this app but the good thing in the app is that you can access it mid ride and be surprised about how well you are doing.

It's for fun people! Don't you know that fun means?
Self delusion?
__________________
Telemachus has, indeed, sneezed.
halfspeed is offline  
Old 02-13-14, 04:36 PM
  #32  
Homebrew01
Super Moderator
 
Homebrew01's Avatar
 
Join Date: Jul 2004
Location: Ffld Cnty Connecticut
Posts: 21,652

Bikes: Old Steelies I made, Old Cannondales

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 1066 Post(s)
Liked 496 Times in 359 Posts
Originally Posted by wphamilton View Post
You don't think that developers will race against time to integrate the $8 app that doesn't work into the $200 earbuds that nobody wants?
Lots of people donated
__________________
Bikes: Old steel race bikes, old Cannondale race bikes, less old Cannondale race bike, crappy old mtn bike.

FYI: https://www.bikeforums.net/forum-sugg...ad-please.html
Homebrew01 is offline  
Old 02-13-14, 05:00 PM
  #33  
spectastic
commu*ist spy
 
spectastic's Avatar
 
Join Date: Aug 2012
Location: inside my body
Posts: 4,450

Bikes: a few

Mentioned: 17 Post(s)
Tagged: 0 Thread(s)
Quoted: 649 Post(s)
Liked 3 Times in 3 Posts
It may not be accurate for instantaneous readings, but I think if the errors average out over a long ride, then it shouldn't be completely worthless.
spectastic is offline  
Old 02-13-14, 05:10 PM
  #34  
rpenmanparker 
Senior Member
 
rpenmanparker's Avatar
 
Join Date: Dec 2009
Location: Houston, TX
Posts: 28,682

Bikes: 1990 Romic Reynolds 531 custom build, Merlin Works CR Ti custom build, super light Workswell 066 custom build

Mentioned: 106 Post(s)
Tagged: 1 Thread(s)
Quoted: 6554 Post(s)
Likes: 0
Liked 51 Times in 33 Posts
Originally Posted by spectastic View Post
It may not be accurate for instantaneous readings, but I think if the errors average out over a long ride, then it shouldn't be completely worthless.
Just assuming, I admit , but I don't think that is how it works. It is not precision error that averages out. It is accuracy. It gives the wrong answer. Besides power is an instantaneous measurement. What is the point of averaging it over time?
__________________
Robert

Originally Posted by LAJ View Post
No matter where I go, here I am...
rpenmanparker is offline  
Old 02-13-14, 05:19 PM
  #35  
Phantoj
Certifiable Bike "Expert"
 
Join Date: May 2005
Posts: 5,647
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Are they selling the ibike for $8 now?
Phantoj is offline  
Old 02-13-14, 05:22 PM
  #36  
cthenn
Senior Member
 
Join Date: Jan 2010
Location: Walnut Creek, CA
Posts: 2,567

Bikes: 2015 Trek Emonda SLR, 2002 Litespeed Classic, 2005 Bianchi Pista, 2016 Devinci Hatchet, Some BikesDirect MTB I never ride.

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 602 Post(s)
Liked 97 Times in 60 Posts
I'm trying to figure out why this thread is still going. I mean, from the point you read "$8" and "app", I was done. Completely useless.
cthenn is offline  
Old 02-13-14, 05:52 PM
  #37  
spectastic
commu*ist spy
 
spectastic's Avatar
 
Join Date: Aug 2012
Location: inside my body
Posts: 4,450

Bikes: a few

Mentioned: 17 Post(s)
Tagged: 0 Thread(s)
Quoted: 649 Post(s)
Liked 3 Times in 3 Posts
oh wait it's an app? I missed that part. nevermind, it's s**t.
spectastic is offline  
Old 02-13-14, 06:19 PM
  #38  
WhyFi
Senior Member
 
WhyFi's Avatar
 
Join Date: Jan 2010
Location: TC, MN
Posts: 35,525

Bikes: R3 Disc, Haanjo

Mentioned: 346 Post(s)
Tagged: 1 Thread(s)
Quoted: 17405 Post(s)
Liked 6,130 Times in 3,159 Posts
Originally Posted by spectastic View Post
It may not be accurate for instantaneous readings, but I think if the errors average out over a long ride, then it shouldn't be completely worthless.
The description states that it's typically within 15% *over a given ride* - so, no, it's not averaging out errors over a long ride. Even if it did, frankly, I still don't see what value that would provide.
WhyFi is offline  
Old 02-13-14, 06:44 PM
  #39  
Homebrew01
Super Moderator
 
Homebrew01's Avatar
 
Join Date: Jul 2004
Location: Ffld Cnty Connecticut
Posts: 21,652

Bikes: Old Steelies I made, Old Cannondales

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 1066 Post(s)
Liked 496 Times in 359 Posts
Originally Posted by phantoj View Post
are they selling the ibike for $8 now?
__________________
Bikes: Old steel race bikes, old Cannondale race bikes, less old Cannondale race bike, crappy old mtn bike.

FYI: https://www.bikeforums.net/forum-sugg...ad-please.html
Homebrew01 is offline  
Old 02-13-14, 06:56 PM
  #40  
Pirkaus
Coffin Dodger
 
Pirkaus's Avatar
 
Join Date: Mar 2013
Location: New Hampshire
Posts: 2,136

Bikes: Motobecane Vent Noir, Lynskey R345, Serotta Nova Special X

Mentioned: 11 Post(s)
Tagged: 1 Thread(s)
Quoted: 794 Post(s)
Liked 292 Times in 143 Posts
Originally Posted by canam73 View Post
I can guess your ftp +/- 15% by looking at a picture of your bike and knowing your favorite flavor of ice cream. For free.


I just pee'd myself a little bit!
Pirk
Pirkaus is offline  
Old 02-13-14, 07:07 PM
  #41  
halfspeed
Senior Member
 
halfspeed's Avatar
 
Join Date: Nov 2003
Location: SE Minnesota
Posts: 12,275

Bikes: are better than yours.

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Originally Posted by Phantoj View Post
Are they selling the ibike for $8 now?
I don't think it's even that good. Heck, it's not even as good as that PowerCal thing.
__________________
Telemachus has, indeed, sneezed.
halfspeed is offline  
Old 02-13-14, 07:39 PM
  #42  
canam73
Senior Member
 
Join Date: Jun 2007
Location: Haunchyville
Posts: 6,400
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 11 Post(s)
Liked 5 Times in 2 Posts
Originally Posted by Pirkaus View Post


I just pee'd myself a little bit!
Pirk
Mind you, only the first one is free. If you think you have a training increase the retest will cost you.
canam73 is offline  
Old 02-13-14, 10:16 PM
  #43  
Falchoon
Senior Member
 
Falchoon's Avatar
 
Join Date: Oct 2002
Location: Oz
Posts: 981
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 27 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Originally Posted by Drew Eckhardt View Post
Of course it's not accurate - it doesn't know what the local wind conditions are, your personal aerodynamics, coefficient of rolling resistance which can vary by a factor of 2 between best and worst slick tires, etc.
Neither does an SRM/Quarq/Powertap/Stages etc...
Falchoon is offline  
Old 02-13-14, 10:37 PM
  #44  
Drew Eckhardt 
Senior Member
 
Drew Eckhardt's Avatar
 
Join Date: Apr 2010
Location: Mountain View, CA USA and Golden, CO USA
Posts: 6,341

Bikes: 97 Litespeed, 50-39-30x13-26 10 cogs, Campagnolo Ultrashift, retroreflective rims on SON28/PowerTap hubs

Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 548 Post(s)
Liked 315 Times in 221 Posts
Originally Posted by Falchoon View Post
Neither does an SRM/Quarq/Powertap/Stages etc...
Power is the product of force and velocity which are both measured directly by power meters like the SRM/Quarq/Powertap/Stages/etc. Those power meter measure force via strain gauges. They multiply measured RPM by 2 pi times the strain gauges' distance to their center of rotation to get velocity. One multiplication returns instantaneous power.

This smart phone application can measure position (via GPS) and acceleration (via accelerometer) from which it can derive velocity.

The big forces on cyclists are the component of gravitational force parallel to the road (zero where it's flat), aerodynamic, and rolling resistance. While the smart phone knows what direction you're headed and where gravity is due to the accelerometer so it can arrive at that force based on your weight, it can't measure anything to do with aerodynamic forces or rolling resistance so it can't come up with an accurate total force and therefore power.

Given actual knowledge of CdA at a variety of angles, Crr, wind speed, and wind direction it could calculate those but it's limited to approximations which aren't enough.

Last edited by Drew Eckhardt; 02-13-14 at 10:57 PM.
Drew Eckhardt is offline  
Old 02-13-14, 10:49 PM
  #45  
halfspeed
Senior Member
 
halfspeed's Avatar
 
Join Date: Nov 2003
Location: SE Minnesota
Posts: 12,275

Bikes: are better than yours.

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Originally Posted by Falchoon View Post
Neither does an SRM/Quarq/Powertap/Stages etc...
They are making a direct measurement, not trying to guess.
__________________
Telemachus has, indeed, sneezed.
halfspeed is offline  
Old 02-13-14, 11:53 PM
  #46  
j814wong
Senior Member
Thread Starter
 
Join Date: Feb 2013
Posts: 221
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
So the general consensus is that +-15% is junk compared to normal powermeter accuracy. Is the innards of a powermeter really such that a $1000 price tag is warranted? One poster brought up that older PowerTaps can be found for $200 or so. Asides from obvious technical improvements that result in greater accuracy, is there really much significant difference between those older models at that price and the newer fancier models?
j814wong is offline  
Old 02-14-14, 06:43 AM
  #47  
Homebrew01
Super Moderator
 
Homebrew01's Avatar
 
Join Date: Jul 2004
Location: Ffld Cnty Connecticut
Posts: 21,652

Bikes: Old Steelies I made, Old Cannondales

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 1066 Post(s)
Liked 496 Times in 359 Posts
The older wired powertap hubs are very good. They do not have more recent "bells & whistles". Brand new Powertaps are well under $1000.
If you really want a power meter, then first decision is wheel based.or crank based.

Best to start a new thread if you decide to go for it.
__________________
Bikes: Old steel race bikes, old Cannondale race bikes, less old Cannondale race bike, crappy old mtn bike.

FYI: https://www.bikeforums.net/forum-sugg...ad-please.html
Homebrew01 is offline  
Old 02-14-14, 06:45 AM
  #48  
WhyFi
Senior Member
 
WhyFi's Avatar
 
Join Date: Jan 2010
Location: TC, MN
Posts: 35,525

Bikes: R3 Disc, Haanjo

Mentioned: 346 Post(s)
Tagged: 1 Thread(s)
Quoted: 17405 Post(s)
Liked 6,130 Times in 3,159 Posts
Originally Posted by j814wong View Post
So the general consensus is that +-15% is junk [strike]compared to normal powermeter accuracy[/strike].
Fixed - it doesn't even need to be compared to a real power meter.

Originally Posted by j814wong View Post
Is the innards of a powermeter really such that a $1000 price tag is warranted? One poster brought up that older PowerTaps can be found for $200 or so. Asides from obvious technical improvements that result in greater accuracy, is there really much significant difference between those older models at that price and the newer fancier models?
a) ~$200 is the used price
b) those are the wired units - you need a sensor on the seat stay that is wired to the computer/head unit. This locks you in to that head unit and means that the wheel is not compatible with a Garmin or the like
c) significantly heavier than the new units
WhyFi is offline  
Old 02-14-14, 07:42 AM
  #49  
Myosmith
Lover of Old Chrome Moly
 
Myosmith's Avatar
 
Join Date: May 2011
Location: NW Minnesota
Posts: 2,949
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 142 Post(s)
Likes: 0
Liked 20 Times in 15 Posts
Originally Posted by halfspeed View Post
Sounds like it's worth exactly what it costs.
IMHO, sounds like it costs $8 more than it's worth. I'd guess most cyclists could estimate their power +/- 15% just based on perceived exertion. Calling a 30% range, inaccurate, is being generous.
Myosmith is offline  
Old 02-14-14, 07:57 AM
  #50  
mr645
Senior Member
 
Join Date: Jun 2013
Location: Boca Raton, Florida
Posts: 129

Bikes: Fuji Altamira

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
I don't see how this could be remotely accurate. I recently did a ride with a small group and one of us had a power meter in the pedals. We went North at 23 to 23.5 mph and even leading this pace was not too hard thanks to a nice tail wind. While toward the back of the line, this was pretty easy.

BUT we then turned around into the wind and we all worked a lot hard to maintain about 18 mph. Even though Strava said I was using less power going South into the wind, I assure you I was working a lot harder. The actual power meter on the other bike said he was generating more then twice the wattage then Strava said I was using. But on the Northbound tailwind part of the ride, Strava said I was at twice the power output then the actual power meter was.
Ok, sure, were talking about two different riders on two different road bikes, but we were in the same pace line so it should have been pretty close, a lot closer then +/- 100%
mr645 is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.