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Thread: PowerTap Disc

  1. #101
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    Hmm... You have a point there.

    If I go for the Elite+ I have enough cash for a Chorus 11 cassett so I don`t need mess about changing when I swap wheels.
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  2. #102
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    These are links to a few articles on Pez Cycling news about power meters. They're linked to from the active.com article in post #99 but you have to click through lots of webpages so I've put them together to make it easier if you want to read them.

    Power Profiling
    http://www.pezcyclingnews.com/?pg=fullstory&id=8983

    Power Profiling 2
    http://www.pezcyclingnews.com/?pg=fu...atname=Toolbox

    Fatigue Profiling as seen in links above (The Peakscoaching widget link doesn't work though...)
    http://tt-training.blogspot.com/2010...coggan-v2.html

    T-Mobile Pros
    http://www.pezcyclingnews.com/?pg=fullstory&id=3748

    Power Meter Reasons (Lots of links to other articles in the text)
    http://www.pezcyclingnews.com/?pg=fullstory&id=3660

    Cycling Efficiency
    http://www.pezcyclingnews.com/?pg=fullstory&id=850

  3. #103
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    love my 39-53 quarq

    When they come out with a mtb 2x10 quarq, I'll scrape the cash together. I've considered removing the 53t chainring from my sram red/quarq crankset and running the 39t as a single front chainring with an xx rear. Should work for most of my midwest races, but not low enough for races in breck, methinks.

  4. #104
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    Is the rotor a six inch rotor?
    Tom G.
    Long Island, NY

  5. #105
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    Quote Originally Posted by tg3895
    Is the rotor a six inch rotor?
    The MTB Powertap disc rotor is a standard diameter 160mm rotor. I don't think there are any compatibility problems using it with most brakes.

    Brake Rotor Width and Track
    I haven't got accurate calipers to measure the width but I think the Powertap rotor is probably 2mm wide which is the same as most popular brake rotors. It's surprisingly hard to find the standard widths of popular brake rotors. They don't seem to be listed anywhere but most are probably in the 1.8mm to 2.2mm range. There's some manufacturing variance between rotors of the same type too.

    About all I could find was this discussion from 2006:
    http://www.cyclingforums.com/forum/t...imano-xt-rotor

    Current Hope floating rotors are 2mm wide.
    http://www.hopetech.com/page.aspx?it...g62&langID=470

    The brake track on the Powertap rotor is 14mm deep. There are no clearance issues in that respect when used with a Hope Tech X2 caliper. The brake pads strike a litle bit low but it seems close enough. The picture below shows the clean brake track where the brake pads contact the Powertap rotor when used with a Hope Tech X2 caliper on my Specialized Epic.

    I'm using a Hope Tech X2 brake and it's ok with the Powertap rotor. The lever feel is slightly different (with less movement) but power and modulation is fine. It isn't noticeably better or worse than the 160mm Hope floating rotor I used before when riding.

    You'd think that such a bulky and heavy brake rotor would be completely straight but I found my Powertap rotor needed a little truing from new. After that the rotor has stayed round though.

    Pictured below: The 14mm brake track of the 160mm Powertap disc rotor lines up fairly well when used with a Hope Tech X2 brake.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-powertap_brake_track.jpg  

    Last edited by WR304; 02-02-2011 at 02:26 PM.

  6. #106
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    Here are some pictures showing the insides of a Powertap hub. It uses strain gauges to measure pedalling torque.

    Strain Gauge
    http://www.omega.com/literature/tran...e3/strain.html

    Inside the Powertap hub there are two hub shells, one inside the other. Your power twists the two shells in relation to each other. You're supposed to use equal 3x spoke lacing for the wheel construction so that the hub twists evenly.

    The picture shows the internal hub, known as the "torque tube". Strain gauges measure the deformation of this internal "torque tube" section of the hub. The strain gauges resistivity varies as you pedal. From these changes the torque in N.m can be calculated giving a power reading.

    Pictured below: The Powertap "torque tube" internal section of the hub shell.

    The bearings and axle inside the Powertap hub.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-powertap_torque_tube2.jpg  

    PowerTap Disc-powertap_hub_internals2.jpg  

    Last edited by WR304; 02-02-2011 at 02:56 PM.

  7. #107
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    WR304: Thank you for all the great info!
    Tom G.
    Long Island, NY

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    When you see those pictures of the Powertap axle a lot of the components are all a push fit. You can pull most of the hub apart without needing any tools. There aren't any preload adjustments on the hub bearings either.

    I've been trying to get rid of some lateral play which I think may be down to the non drive side axle end cap. There was enough play that the brake rotor could be pushed onto the brake pads easily.

    The non drive side axle end cap is just an aluminium plug with two rubber o-rings on. From new this wasn't seated quite right so I pulled it out, put some waterproof grease on the o-rings and put it back in. This seemed to seat it a bit better. After tightening the DT RWS wheel skewer as tight as it would go there seems to be less play now.

    Pictured below: The Powertap hub with its push fit non drive side axle end cap removed. The blue on the hub is marine grease that I hadn't wiped off.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-powertap_nds_axle.jpg  

    Last edited by WR304; 03-02-2011 at 03:16 PM.

  9. #109
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    I've been seeing a few videos on youtube where real time power output and speed gauges have been overlaid onto the recorded footage of cycling. You can watch the performance of the rider at the same time as the footage to see what they were doing.

    Go Pro cameras
    http://gopro.com/

    The overlaid gauges showing the rider's power meter and speed data in real time were added to the video footage using Dashware software. I'd been wondering for a while how it was done.

    http://www.chasecam.com/catalog/25

    Here's a youtube video from a recent California criterium to give you an idea of what the real time gauges look like. 5:45 of the video is the best bit.

    "2011 E4 Cherry Pie Criterium in beautiful Napa, CA"


  10. #110
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    Quote Originally Posted by WR304
    Today's ride was all above sea level but if you do a ride where the altitude is below sea level then WKO+ interprets any altitude readings from Joule 2.0 below sea level as a fixed -3ft. Any altitude data below sea level is ignored.
    This problem has been fixed with the newest version of WKO+ 3.0 Build 48. Altitude readings below sea level from the Cycle Ops Joule 2.0 head unit are now displayed on the graph. That's useful as it lets you see the altitude profile and elevation changes of the ride, even if the actual values are completely wrong still. I wasn't actually riding at -470ft on the graph below. The lowest altitude point should have been around sea level.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-wko_build48_fixed_altitude.jpg  


  11. #111
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    New question here. Question

    For training purposes, does it help one’s coach more to display power and cadence with or without zero averaging?

  12. #112
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    Quote Originally Posted by lassiar
    For training purposes, does it help one’s coach more to display power and cadence with or without zero averaging?
    Including or excluding zeros and the level of smoothing only affects the displayed figures on your power meter head unit. You'll normally include zeros in the power on the power meter head unit so that your figures aren't artificially inflated.

    When you download the recorded data onto your computer and look at it in a program such as WKO+ 3.0 or Cycle Ops Poweragent the zero watts are automatically included in the power average. The data recording isn't affected by the settings in the head unit.

    My display settings for the Cycle Ops Joule 2.0 head unit are:

    Power Smoothing - 5 seconds
    Power with zeros - Yes

    Cadence Smoothing - 3 seconds
    Cadence with zeros - No

    Speed Smoothing - 1 second
    Speed with zeros - Yes

    Zero Watts
    Knowing the times where you produced zero watts is something which can be one of the most useful aspects of having a power meter on the bike. Zero watts is a sign that you aren't pedalling. You typically want to be pedalling as much as possible throughout a training ride to get the most benefit from the time spent on the bike. It's worth trying to reduce the amount of time spent at zero watts if you can. It can be very eye opening just how much time you spend freewheeling during a ride, especially offroad.

    Power data gives an idea of how much aerobic training benefit you may be getting from your mountain bike rides. The TSS, IF and average power from my mountain bike rides look terrible in comparison to similar duration rides on the road. You have to be very wary of this - riding offroad is fun and challenging but it can often end up counting as "junk miles" with little aerobic training benefit. That's where doing at least some road work comes in useful for building fitness. Having the power data to compare from both my on and offroad rides is very revealing in this respect. The difference is much greater than I thought it would be.

    Whilst riding on the road by yourself your power data will usually show pedalling nearly all the time. Apart from traffic lights and junctions you normally don't stop either. The only time there is much freewheeling is on descents, or if you momentarily stop pedalling to stretch your legs. You can concentrate on pedalling hard and maintaining a constant effort nearly all the time.

    Riding offroad your power output can vary a great deal. There are often much larger amounts of time spent freewheeling or soft pedalling. On easy sections your power output is often very similar to riding on the road but on harder sections your power output can become much more variable as you have to react to the terrain. The limiting factor becomes bike handling rather than how hard you can pedal.

    I've attached a short extract from today's ride showing 20 minutes riding along a rocky, deeply rutted farm track (It ended up on the dual carriageway so I had to do a u-turn and come back the same way.) It's a good example because I was having to concentrate on picking my way through the rocks and trying to avoid catching pedals on the edges of the ruts at the same time. You can see there was quite a lot of freewheeling and stop - start riding. Although I didn't do much hard pedalling on this farm track the sections where I did need to pedal often involved short sharp bursts to get over rocks or through mud.

    This is the sort of situation where having recorded power data can be useful as it lets you evaluate how well you're riding different sections. If you spend a lot of time freewheeling and going slowly then that will cost you time. You can compare power data between rides to see just how much better you may be riding sections or whether different lines are faster also.

    Pictured below: Riding along a rutted farm track (U-turn midway). On tarmac this would have been pedalling constantly with no freewheeling.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-power_farm_track.jpg  

    Last edited by WR304; 03-22-2011 at 05:29 PM.

  13. #113
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    Quote Originally Posted by WR304
    (21 January 2011) - I replaced the batteries in the Powertap hub.
    ...
    The original batteries only lasted for approximately 60 hours of riding. I'm hoping that starting with fresh batteries means the hub will last a bit longer before they need replacing again.
    This time the batteries lasted 83 hours of riding.

    I've been getting low battery warnings from the Powertap hub all week so replaced the batteries again today. Hub Battery warnings flash up on the screen of the Cycle Ops Joule 2.0 head unit when they're getting low. My bike was broken for most of February so the Powertap didn't get used much in that month.

    Something which I noticed today is that there appears to be corrosion and brown marks inside the Powertap hub. The marks definitely weren't there when it was new. So far as I can tell all the seals are in place and have lots of marine grease round them. It isn't obvious how the moisture got in there. Condensation perhaps? The hub electronics are working ok but it is a bit worrying.

    Whilst I had the wheel off the bike I gave the freehub a service at the same time. It's been getting very loud and clicky so probably needed doing. Removing the Powertap freehub is completely tool free - take the skewer out, pull the cassette and the entire freehub just comes off in your hands. There are three pawls and they are held in place by a springy band (the recessed groove in the picture below). There aren't any springs and only one rubber seal. The seal isn't great so the pawls clearly look like they're going to need servicing frequently.

    There was some light grease still but everything inside was quite dirty and one of the pawls was quite sticky. I cleaned it up and re-assembled the hub with Slick Honey grease as that's quite thin and what I had lying around. You don't want to use a thick waterproof grease because the pawls will stick. I was thinking about trying some Pedros Road Rage lube as that's what is recommended for Mavic Crossmax SL freehub pawls.

    Apparently the recommended grease for the freehub is Kluber NB52 or Dupont GLP226 grease though so I'll probably get some of that for in future.

    http://www.bikeforums.net/showthread...tap-conversion

    http://www.saris.com/pdfManuals/308.pdf

    Kluber NB52 Grease
    http://www.klubersolutions.com/pdfs/...%20NB%2052.pdf

    Dupont GLP226 Grease
    http://www2.dupont.com/Lubricants/en...226_K20067.pdf

    With the freehub cleaned and regreased it's very quiet again. I think it's a lot like the Mavic Crossmax SL freehubs in that a quiet freehub means its working ok and noisy means the freehub needs servicing.

    Pictured below: Powertap disc freehub pawls (cassette still attached) and the hub with the freehub removed.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-powertap_freehub_pawls.jpg  

    PowerTap Disc-powertap_freehub_pawls2.jpg  


  14. #114
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    Quote Originally Posted by WR304
    one of the pawls was quite sticky. I cleaned it up and re-assembled the hub with Slick Honey grease as that's quite thin and what I had lying around.
    My Powertap hub has done 3,100 miles (218 hours approx) in total and the pawls in the freehub are starting to stick, even after servicing it again. The freehub pawls use a metal band for spring tension and that metal band appears to be getting a bit baggy. There's still plenty of grease in the freehub but it doesn't sound right when you spin the wheel.

    I'm hoping that I can get a replacement metal band for it instead of needing to buy an entire freehub body.

    Joule 2.0 History Errors
    I've been wondering why the history summary reports on the CycleOps Joule 2.0 head unit always seem to be completely wrong. Individual days are ok but the 2 week, 4 week summaries are way out. Looking at the History folder on the head unit it's clear that the head unit is writing multiple history files, even though I haven't pressed Stop and Save from the menu. If you look at the screenshot below this shows the contents of the Joule 2.0 head unit history folder.

    On 03 May 2011 for example it wrote three history files. According to WKO+ the ride began at 10.26am and lasted for 2h11 total time. You can see when the files were created from the modified dates: One at 10.24am (presumably when I pressed Stop and Delete to reset the file at the start of my ride, although this may have been user error by me as Stop and Save and Stop and Delete are next to one another in the menu.) One at 12.39pm (this would be the main file when I got home) and then another at 13.59pm (possibly when I connected the Joule 2.0 to the computer).

    It isn't consistent though. On some days there's only one file created whilst on other days there are more than one file. My routine for using the Joule is the same each day (wake up hub, reset Joule 2.0 using Stop and Delete option, ride, save file, connect to PC later) so I'm not sure why it only happens on some days. It's clearly a bug of some kind. The times the duplicated files are created are very odd. 18.26pm on 28 April 2011 for example. It could be related to connecting it to a PC but I would most likely have downloaded the data from the unit well before that time.

    Although these history errors are annoying they don't really affect the function of the unit. The summary information for each individual ride is ok. If I'm going to look at historic report summaries then I'll usually do it in WKO+ anyway.

    Pictured below: CycleOps Joule 2.0 head unit history folder contents viewed from a PC. Note the multiple files with the same date. There should only be a single file created for each day.

    CycleOps Joule 2.0 History file list showing multiple files with the same date (format is yyyy/mm/dd) and four week summary report showing how it affect the summaries as the unit shows an average speed of 4.7mph for the last four weeks. The power information is also affected making the summaries inaccurate.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-joule_multiple_history_file.jpg  

    PowerTap Disc-joule_multiple_history_unit.jpg  

    Last edited by WR304; 05-07-2011 at 08:23 AM.

  15. #115
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    Has anyone had to send their Powertaps back to Saris for rework?

    I have an SL+ that I've had for a little over a year, only about 3500 miles, and recently it's started getting really flakey -- both the head unit and the hub. The head unit randomly fades in and out, and turns off occasionally.

    The hub is under-reporting toque. I was afraid I was really out of shape the last few rides! It's under-reporting by about 50-60 watts. I checked the offset value in the setup menu which is suposed to be in the range of 512, and it's reading 360ish.

    I called Saris today and they said because it is a few months over a year old I will need to pay $350 and send it back to them to have it rebuilt. This seems ridiculous to me, for such an expensive piece of equipment, to only get one season out of it before needing an expensive rebuild. I will not purchase another Saris product.
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  16. #116
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    The batteries in the hub need replacing again. They lasted a little longer this time. 101 hours before the head unit began showing low battery warnings.

    I'm hopefully going to be getting some spare Powertap freehub pawl bands and a spare set of pawls. I haven't got them yet though.

    The picture below is an example of the power output for a 4 minute interval that I did the other day. It was the 5th of a 6x4 minute set. This was outdoors riding the mountain bike but on the main road. If you do intervals on a turbo trainer then there will be less variation. Turbo trainer intervals tend to look much smoother with little variation in speed or power output. The orange gradient line shows that the road wasn't flat. I started off up a drag, went down a slope and then back up another drag for the final few minutes. The average cadence for the 4 minute interval was about 89rpm (the same average as for the entire 2h 39 ride).

    If you look at the red heart rate trace there are two things to note. The first is that heart rate lags behind power output. I've been going flat out for 30 seconds+ before my heart rate begins to respond. The other is that power output during the interval changes even though my heart rate stays at a constant level. Towards the end of the 4 minute interval my heart rate rises, even though the power putput is dropping.

    The power output and speed traces show the difficulty of maintaining your interval pacing outdoors. The initial 30 seconds is a hard sprint to accelerate up to speed and then trying to maintain the pace for the remainder of the four minutes. I speed up to 25.9 mph on the downhill slope part way through but the power output falls away dramatically. This is probably the main thing that a power meter shows up. If you want to maintain your power output on downhill sections you have to shift up as many gears as you can as soon as the road drops in order to try and keep the power output constant.

    If you hold the gear and pedal faster downhill your speed will increase but the power output will drop badly. Looking at the speedo or heart rate monitor and congratulating yourself on going faster is misleading (remember that heart rate lags behind). Heart rate may not drop even though you're no longer making a hard effort.

    The final minute of the interval is a bit scruffy. You can see how speed and heart rate stays constant but the power output falls away. I was fading a little but if you look at the orange gradient trace the slope was flattening off slightly - another place where you have to be careful as in order to maintain the same power I should have tried harder and possibly changed up a gear.

    Pictured below: Outdoor 4 minute interval power output compared to heart rate and speed.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-power_4min_interval.jpg  


  17. #117
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    Apparently CycleOps will be releasing a new Powertap G3 hub and also new cheaper CycleOps Joule and Joule GPS computers. There's no mention of whether there will be a MTB version of the Powertap G3 hub though.

    http://velonews.competitor.com/2011/...heelset_178521

    http://www.dcrainmaker.com/2011/06/f...joule-and.html

    Powertap G3
    "Coming in August, the PowerTap G3 is a 325-gram power-meter hub that has wider flanges but a smaller overall profile than previous PowerTap models. Selling for $1,299, the G3 houses the majority of its electronics, plus the battery and the antenna, in the replaceable end cap. The strain measurement components are still in the hub. When PowerTaps fail, typically it’s the electronics that go. This new design allows a quick fix, as the company can mail out a new cap to customers."

    Joule GPS
    "Finally, in November, the company intends to have two new cycle computers, including a version with GPS. The $169 Joule features upgrades from the company’s 2.0 — it’s cheaper, smaller and easier to navigate — but with much of the same data (TSS, historic reporting, customizable dashboard and more). Its battery life is 300-400 hours.

    The $269 Joule GPS is similar to a Garmin 500. There are no on-screen maps, just a record of your GPS data. ”We are looking at this first and foremost as a computer for cyclists who train with power,” Bartholomew said. “But we realize GPS data is a valuable feature, especially after the ride.”

    The Joule GPS has 18 metrics that are customizable on screen. The battery is rechargeable."
    Velonews.com

    Pictured below: New CycleOps Joule GPS computer on left, CycleOps Joule on right
    Attached Thumbnails Attached Thumbnails PowerTap Disc-joulegps_velonews.jpg  

    Last edited by WR304; 06-15-2011 at 01:02 PM.

  18. #118
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    Quote Originally Posted by XCFred View Post
    Has anyone had to send their Powertaps back to Saris for rework?

    I have an SL+ that I've had for a little over a year, only about 3500 miles, and recently it's started getting really flakey -- both the head unit and the hub. The head unit randomly fades in and out, and turns off occasionally.

    The hub is under-reporting toque. I was afraid I was really out of shape the last few rides! It's under-reporting by about 50-60 watts. I checked the offset value in the setup menu which is suposed to be in the range of 512, and it's reading 360ish.

    I called Saris today and they said because it is a few months over a year old I will need to pay $350 and send it back to them to have it rebuilt. This seems ridiculous to me, for such an expensive piece of equipment, to only get one season out of it before needing an expensive rebuild. I will not purchase another Saris product.
    I had the same problem with mine powertap after 1.5 years of usage.(it was the first version with steel 12mm axle)
    Mine offset values were similar to your's, and I was getting readings about half the power then before.
    Saris offered a full service for 350$, but I had i done here in Europe.

    Now it's new version with alu axle 15mm, all new inside. Will see how long does it last.

    I was hopping that somehow mine got damaged, but now I see you had the same problem
    "If everything seems under control, you're just not going fast enough."

  19. #119
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    Quote Originally Posted by WR304 View Post
    This Youtube video is where DC Rainmaker tests the weatherproofing of several power meter head units: The Garmin Edge 800, Garmin Edge 500, Garmin Edge 705 and Cycleops Joule 2.0. They seem to fare quite well.

    http://www.dcrainmaker.com/2010/12/f...ion-tests.html
    I've attached a picture of my CycleOps Joule 2.0 head unit after today's ride in the rain. I've been getting caught in heavy showers all week with lots of spray. This is the first week I've got properly drenched since March as it has mostly been warm and sunny this year. The last few months were warm and dry with very little rain.

    The head unit has been filling up with water whilst riding (you can see it sloshing inside around the edges of the screen) and a lot of condensation has been forming inside the screen. The condensation is drying out now but after several hours it still hasn't cleared properly. The actual computer is still working but I'm very concerned about how easily water is getting in as it shouldn't be happening. It was fine all last winter in the rain but this week it doesn't seem to be weather proof at all.

    I'm going to see if it's covered under warranty but it might be time for a different head unit.

    Pictured below: CycleOps Joule 2.0 head unit showing the water and condensation in the screen after a wet ride today.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-cycleops_joule20_water_inside2.jpg  


  20. #120
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    I got a Garmin Edge 500 to replace the old head unit. I've attached a picture showing it alongside the Cycleops Joule 2.0. The Joule 2.0 steamed up straight away today as it still has water in. I rode with both computers fitted today in order to compare the information. You can connect multiple head units to the same Powertap hub. The Cycleops ANT+ heart rate strap works with both head units also.

    There are a few significant differences in terms of how the data appears when you download the ride files into WKO+ 3.0 from the Garmin Edge 500 and Cycleops Joule 2.0. I was hoping that the data would be identical but it isn't, even though the information came from the same Powertap hub. The main difference seems to be to do with how WKO+ 3.0 interprets starting and stopping from the different head units but there are some other things too.

    I'm not sure how useful the GPS track is. The GPS route on a map was fairly close to the actual route. In places on today's ride it was extremely accurate in open country with little cloud and no trees. Overlaid on Google earth you could even see where I had changed lanes in the run up to a roundabout and exactly where I had taken a shortcut along the pavement at one point! Under tree cover and in built up areas the track was jumping around a bit though.

    Pictured below: Garmin Edge 500 and Cycleops Joule 2.0 alongside each other. You can customise the displays of both units. The screen of the Joule 2.0 is larger and has a bigger text size that is easier to read with multiple items displayed. Something had gone wrong with the heart rate strap. I'm fairly sure that I wasn't actually doing 152bpm whilst taking the photo!
    Attached Thumbnails Attached Thumbnails PowerTap Disc-garmin_edge_500_joule_2.jpg  


  21. #121
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    I would regard the Garmin's data as better than the Joule. On my road bike, I've used my PCVI and 705 together and the ride stats a basically identical, AP within 1-2watts (this only varies because I use autopause at 2mph on the Garmin), TSS is exactly the same, etc.

    I'm not sure if the Joule autozeros, but the Garmins do, which is a quite nice.

    For the Garmin HR straps, using some conductive get like this works well
    performancebike.com/bikes/Product_10052_10551_1028575_-1_20000__400132

  22. #122
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    SRAM 2x10 SRM

    I've been very happy with my PowerTap hub for a while now but with a new bike and a new rear axel standard i had to look for something new.
    PowerTap Disc-imag0084.jpg
    PowerTap Disc-imag0086.jpg
    Pretty good at everything, but not really good at anything!

  23. #123
    aka: SpeedyChix
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    Quote Originally Posted by gnriden View Post
    I've been very happy with my PowerTap hub for a while now but with a new bike and a new rear axel standard i had to look for something new.
    Click image for larger version. 

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    Click image for larger version. 

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    Nice!! I'm holding out for the Quarq 2x10.
    What bottle cage / mount are you using on the seat post? Does it retain the bottle well in rough terrain? So many of them launch the bottle.
    Thanks.
    Race joe Drakes Coffee
    Race rigs by Kent Eriksen

  24. #124
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    Here's the power data from Saturday's ride after it has been downloaded into WKO+ 3.0. This was a steady ride on the road. I had both power meter head units fitted running from the same Powertap hub on the same ride. There wasn't much stopping but I had to wait at traffic lights a few times.

    I've manually cropped the ride files so that they cover exactly the same period with the start and end of the ride where I was stopped removed.

    The Garmin Edge 500 had the "Autopause when stopped" option enabled and an identical wheel circumference to the Joule 2.0 entered. The Garmin Edge 500 uses the Powertap hub for calculating speed, distance and power which overrides any GPS data. They both record at 1 second intervals.

    "Elapsed Time" and "Time"
    When you press "start" to begin a ride on the Garmin Edge 500 there are actually two timers. You have "Elapsed Time" which will increase continuously until the file is closed and saved (press Stop once and then hold down Reset for 3-2-1-0 until the prompt disappears to save the file). "Elapsed time" continues counting up even if you press the "Stop" button and equals the total time that you were out.

    There is also "Time" which is your moving ride time. "Time" is stopped and started by the start/ stop button. When using auto pause the "Time" timer stops and starts automatically whenever you stop (or the speed drops below a certain level). The total of "Time" is the amount of time you spent riding. If you were out for two hours but spent 30 minutes stopped then "Elapsed Time" would equal two hours whilst "Time" would equal 1h30. Your average speed would be calculated using "Time".

    The CycleOps Joule 2.0 also operates in the same way when it is set to use speed for starting and stopping, although the "Elapsed Time" timer is hidden.

    WKO+ 3.0 Import
    When the data is imported into WKO+ 3.0 it treats the data from the two head units differently. This issue is a WKO+ 3.0 one as to how the information is interpreted. Stationary time is clearly identified with the CycleOps Joule 2.0. After 3 seconds of no speed the time is then shown in WKO+ 3.0 as being stationary until you set off again.

    With the Garmin Edge 500 it's much more patchy. You need to be stationary for at least 20 seconds before WKO+ 3.0 identifies that you have stopped, even though the Garmin Edge 500's "Auto Pause" has stopped the timer shortly after you stopped. If you're stopped for less than 20 seconds then WKO+ 3.0 doesn't show any stationary time, which is what happened on Saturday as the lights changed quickly. The duration time in brackets shown for the CycleOps Joule 2.0 is total time whilst the time alongside is ride time. The Garmin Edge 500 data in WKO+ 3.0 shows all the 1h54m11s as ride time because all the stops were short.

    The big difference between the two head units is in how they respond after you have stopped. When you begin riding again the CycleOps Joule 2.0 responds straight away so that there isn't a gap between setting off and it recording again. The Garmin Edge 500 however is much slower to begin recording again as there is a pause before it resumes. The Garmin Edge 500 also stops recording at one second intervals and you get a few data points covering longer 4 second + time periods immediately after starting. What happens is that you end up with a few data points of bad data for these sections with the Garmin Edge 500 every time you set off, adding in several seconds of high wattages that shouldn't be there every time you stop then start again. On Saturday for example my best 5 second power was actually shown as 7 seconds at 596 watts.

    If you look at the best power outputs below you can see that the shorter duration power outputs are much higher for the Edge 500 than the Joule 2.0. This is where the bad data has been included in the totals giving inflated power outputs. Coming back into town I accelerated hard away from some traffic lights trying to stay with the traffic. The bad data from the Edge 500 when setting off from these sets of traffic lights has distorted the picture. What you can't see from the numbers is that several of the longer best power outputs are in different places in the ride because the additional high wattages riding back through town have moved the best sections also. You can clearly see this from the different maximum power outputs for the longer best power outputs.

    If you disable Auto Pause then you don't get this bad power data on the Garmin Edge 500. The problem then is that the "Time" counter doesn't stop and WKO+ 3.0 doesn't flag any of the stationary time. Your short power outputs are ok but you end up with a lower average power and lower average speed than you would have otherwise because of all the stationary time added in.

    Other Differences
    The other differences that are worth pointing out are the differences in distance between the two head units (possibly related to starting and stopping), the missing Hub Torque channel from the Garmin Edge 500 and a difference in total ascent from the barometric altimeters of each unit. The altitude trace from the CycleOps Joule 2.0 is more detailed and sensitive to small changes in terrain than the Garmin Edge 500. Those are minor things though.

    Pictured below: CycleOps Joule 2.0 and Garmin Edge 500 power data recorded from the same Powertap hub on the same ride. It shows the differences and errors that were introduced as a result of stopping and starting.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-cycleops_joule20_garmin_edge_500_power09-07-2011.jpg  

    Last edited by WR304; 07-11-2011 at 11:03 AM.

  25. #125
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    I had a look on the Wattage group as I was sure that other people must have had the same problem.

    (You have to be signed in to view it)

    http://groups.google.com/group/watta...b1bf2a77fe37bb


    Correcting Garmin Edge 500 Power Data in WKO+ 3.0
    Apparently WKO+ 3.0 can't handle the Garmin Edge 500's auto pause function. This is the problem which creates the bad data in the files. A workaround is to disable auto pause on the Garmin Edge 500 and leave the unit recording all the time, including stationary time such as stopping at traffic lights.

    Your average speed and power displayed on the Garmin head unit post ride will be wrong but you can edit the recorded data in WKO+ 3.0 so that your recorded power and speed data will be correct with moving and stationary time identified. In order to do this you have to go through and manually cut out the stationary time.

    Step 1: Import the Garmin Edge 500 .fit data file into WKO+ 3.0 using Device Agent.

    Step 2: Open the ride graph with no smoothing and identify the first point in the file where you stopped (zero speed).

    Step 3. Select the point two seconds after you stopped and holding down the left mouse button drag it to highlight in blue the period where you were stationary. Stop highlighting two seconds before the power and speed traces resume. You need to leave a gap of at least two seconds each side.

    Step 4: Select Edit - Cut from the top menu. This will remove the highlighted stationary time, leaving a blank section in the graph.

    Step 5: If you're happy that you have done it correctly save the file and then continue on to the next place where you stopped and repeat the process. If it's gone wrong then close the file without saving and re-open it to try again.

    When you've finished the tidied file should clearly distinguish between the time that you were stationary and the total time that you were out. This lets you see how much time you were stopped at traffic lights / opening and closing farm gates etc during a ride.

    Pictured below: The steps for correcting a Garmin Edge 500 data file in order to make it display correctly in WKO+ 3.0.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-garmin_edge_500_wko_repair1.jpg  

    PowerTap Disc-garmin_edge_500_wko_repair2.jpg  

    PowerTap Disc-garmin_edge_500_wko_repair3.jpg  


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