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Thread: PowerTap Disc

  1. #151
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    Yeah, Saris basically said it's not a huge deal but it is out of spec. They said currently it should read low, about 15W at 200W and about 60W at 400W. So it sounds like if your calibration is low it will read low, if it's high it will read high (which makes since because it's apparently the "raw torque value"). They told me I could spend some money to send it in and have the internals upgraded to SL+. They will basically replace everything inside the hub, axles, bearings, and torque tube for a pretty reasonable price. Apparently the new hub that just came out has SL+ internals but has a cheaper, heavier shell which allowed them to lower the price from $1600 to $1100.

    I changed the batteries when I did the ANT+ upgrade. Maybe I will fiddle with it some more but probably not because it's pretty delicate in there and I don't want to break anything. So apparently I have the 2.4 hub, and I've upgraded it to 2.4+. Considering this hub has thousands of miles on it I'd say it has held up pretty well. At least as well as any other bike parts do.

    Congrats on the PR! I love passing people out on the trails, especially when I'm doing a FTP/TT day! Some of those trail runners are pretty darn quick though

  2. #152
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    The Powertap torque tube replacement cost is surprisingly reasonable. It's a lot cheaper than if you were to buy a whole new Powertap hub anyway.

    The Powertap hub's torque offset figure is affected by temperature too. It might be worth checking what it is at the start of a ride, going out riding for a few hours and then checking it again to see whether it has changed.

    My Powertap hub started off at 523 this morning (11c air temperature), after 1h30 riding it had changed to 520 (17c air temperature). Auto Zero on the head unit should allow for this though. Whenever you stop pedalling on a Powertap hub with Auto Zero enabled it should automatically re-zero the torque offset figure to keep the figures consistent.

    (With a Quarq Quattro you need to have Auto Zero enabled and also remember to manually back pedal during the ride in order to zero the torque offset from time to time.)

    Looking at the first splits from today, where I was riding on the road, against similar split times from last year the power figures seem comparable. It's something that I'm going to keep an eye on though. eg:

    21 April 2012 (new Powertap Torque Tube): Distance 13.4 miles, Time 49m 52sec, Average Speed 16.1 mph, Average Power 183 watts, Max Power 488 watts, Normalized Power 205 watts

    25 August 2011 (old Powertap Torque Tube): Distance 13.4 miles, Time 50m 28 sec, Average Speed 15.9 mph, Average Power 181 watts, Max Power 477 watts, Normalized Power 207 watts

    One thing that seems to have genuinely boosted my power output was to change my cycling shoes. I've used Specialized BG Expert carbon soled shoes since 2008 but got some new Giro Code shoes at the beginning of March 2012. The Giro Code shoes have a very stiff Easton EC90 full carbon fibre sole and are basically a road shoe with some tread on the bottom. I've been setting new personal power bests across the board since then.

    The chart below shows my top 10 best power outputs for 2011- 2012. The highlighted section is after I switched to the new shoes. You can see how I've been managing new personal bests from the number of dots in that area at different time durations.

    Giro Code shoes
    Attached Thumbnails Attached Thumbnails PowerTap Disc-best_power_outputs_new_shoes.jpg  

    Last edited by WR304; 04-23-2012 at 02:37 PM.

  3. #153
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    I've mostly been doing offroad rides recently but yesterday I managed to wake up early enough to get out on the road club run. I haven't got any slick tyres for the Specialized Epic 29er yet so it was still on Specialized Ground Control 29x2.1" tyres, but pumped up to 50 psi for road use.

    The usual format for the club rides is to do a few hours and then stop at a cafe. I rode over, met up with the club, rode with them until the cafe stop and then headed home on my own to avoid too much sitting around.

    Total ride:
    4 hours 50 minutes ride time, 78 miles, average speed 16.1mph, average power 182 watts, Normalized Power 213 watts

    Riding to club meeting place:
    39 minutes ride time, 10 miles, average speed 15.9mph, average power 177 watts, Normalized Power 197 watts

    Riding with the Road Club:
    2 hours 2 minutes ride time, 38 miles, average speed 18.9mph, average power 200 watts, Normalized Power 237 watts

    Riding home through the hills:
    2 hours 9 minutes ride time, 30 miles, average speed 13.6 mph, average power 167 watts, Normalized Power 188 watts

    I've attached a few extracts from the ride below as they're quite a good example of what to look for. When riding with a group on the road you gain a large benefit from slipstreaming behind other riders. So long as you can stay in the slipstream it takes far less effort than it would to travel at the same speed if you were riding by yourself. Even on a mountain bike this can be enough that you find yourself riding at low intensities for much of the ride. Looking at just the club ride section of the ride I spent almost 30% of the time in the lowest "active recovery" power zone. On group rides it's very easy to end up riding gently and not as hard you'd expect. Fine as a social ride but not much good as a training ride. This is something that a power meter shows up very well.

    This particular ride was quite mixed with several harder sections ridden at higher intensities. I was yo yoing on and off the back at these points. If you look at the ride data you can see why. The most efficient way to ride in a group is to always hold the wheel of the rider in front. So long as you can hold the wheel you get a big benefit from slipstreaming. As soon as a gap opens however there's no longer any slipstreaming benefit and it's much harder until it can be closed again.

    The graph below shows one point where I was temporarily dropped towards the end of the club ride section. It illustrates how much of a difference slipstreaming makes. I'd been following wheels, trying quite hard at 207 watts average power but staying in contact until a series of short but steep power climbs. Despite producing my best 1 minute power of the ride (360 watts) I was gapped slightly as the climb steepened. The consequence of that small gap opening was that it then took 5 minutes chasing flat out at 300 watts to eventually close the gap again. When I got back into the slipstream my average power output dropped to 152 watts due to being behind the other riders again. If I hadn't let that gap open then I wouldn't have needed to put in the big effort to catch up again.

    Once the club stopped for their cafe stop I headed home by myself through the hills. I was feeling a little tired by this stage. It was getting colder, beginning to rain and there was a headwind all the way back. This is where the power meter came in useful for pacing, helping to parcel out my remaining energy to hopefully avoiding blowing up completely.

    On the climbs I concentrated on trying to keep my power output in the Endurance/ lower end of the Threshold power zones without ever going too high. Seeing the power output going over 250 watts or so was a sign to change down a gear and back the pace down. If you're just riding on perceived exertion it's easy to feel comfortable and end up going harder than you want to, especially if the gradient changes and you put in short bursts. In this case I knew that there were several climbs coming up and it was nearing the end of a long ride so I concentrated on just turning the gear over. The third climb was probably a little too gentle but it was raining fairly hard by that point and I was concerned about cramping up.

    The graph also has a few clear signs that I was tiring. If you look at the flatter sections between climbs the power output trace is very intermittent. All those drops are where I was only pedalling for 1-2 minutes at a time before getting out of the saddle and freewheeling. When you see lots and lots of close pauses towards the end of a ride it indicates that I was a bit saddle sore and uncomfortable on the bike. If I was feeling fresh and still going well there would be far fewer pauses and fairly constant pedalling. On a typical long ride I'll really lift the pace for the last 30 minutes to an hour also but it doesn't happen here. Another sign that I was tired and just trying to get home.

    Pictured below: Power zones for just the 2 hour Road Club run section. Despite it being hard I still spent almost 30% of the time in the Active Recovery power zone

    The altitude scale on the two graphs below is different. The club ride was mostly flat so I've zoomed in the altitude scale on the club ride graph in order to show the small bumps where I was dropped. The hills on the second graph are longer more sustained climbs. The Power and Speed traces on both graphs have the same scale.

    An extract from during the road club run. I'm gapped on a short power climb. Without being in the slipstream it's a hard chase to get back on.

    The final two hours riding home by myself after leaving the road club at the cafe stop. I'm feeling tired and use the power meter to gauge my pacing up the climbs so that I don't push too hard and blow up.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-road_club_run_summary_22-04-2012.jpg  

    PowerTap Disc-road_club_run_22-04-2012_dropped.jpg  

    PowerTap Disc-road_club_run_22-04-2012_climbs_home.jpg  

    Last edited by WR304; 04-23-2012 at 04:23 PM.

  4. #154
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    This interview with Uli Schoberer (inventor of the SRM power meter) makes some interesting comments.

    A chat with Uli Schoberer - Slowtwitch.com

    If you're using a Cycleops Joule 2.0 head unit then this post about a new firmware for it might be useful. They still don't appear to have fixed the Windows 7 issue fully though.

    JOULE 2.0 AFTER 100km (Page 2): Triathlon Forum: Slowtwitch Forums

    "Hi everybody,

    Sorry for all the issues and lack of posting a response.

    To summarize we do acknowledge the issues discussed in this thread and others for some time now. To recap the issues they are:

    1. Distance resetting at random when an ANT+ speed sensor or combo spd/cad sensor is used
    2. Windows 7 recognizing Joule 2.0 or taking a long time to recognize
    3. 8.8 torque multiplyer (note this was a display issue only and did not effect power measurement or display)
    4. Battery drain

    Issues 1, 2 and 3 are being addressed with firmware currently in beta. Testing thus far has gone well and we plan a full release in the next couple weeks. If you would like access to the beta version please contact Eric via email at ealbers@saris.com The beta version of firmware is 14.082. Please note that despite our best efforts the only way to improve issue #2 is by disabling the SD card functionality.

    Regarding battery life, the life expectancy depends on use and charging cycles (the number of times you plug it in to recharge regardless of how much juice the battery has when you plug it in). If you are not getting the expected 20+ hours replacement batteries are available from our customer service team, give them a call at 1-800-783-7257.


    Again, we apologize for the issues these bugs have caused and are working hard to eliminate them.

    Jesse Bartholomew
    CycleOps Product Manager
    Saris Cycling Group"
    Last edited by WR304; 05-01-2012 at 03:11 PM.

  5. #155
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    Garmin have finally released their firmware version 3.00 power update for the Garmin Edge 500 to add TSS/NP/IF etc.

    There are some details about the update here:

    DC Rainmaker: Garmin releases Edge 500 update, adds TSS/NP/IF & more

    From the comments the best way is to download the firmware update through the Garmin webupdater software.

    Garmin | WebUpdater

    If you delete any old activity ride files that were stored on the device then it will update faster also.

    I've updated my Garmin Edge 500 to firmware version 3.00 now. It seems to be working ok but I haven't ridden with it yet.

  6. #156
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    Thanks for letting us know.

    It's too bad the Garmin doesn't record torque, it would be nice to see. I mean, might as well right?

  7. #157
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    Quote Originally Posted by litany View Post
    Thanks for letting us know.

    It's too bad the Garmin doesn't record torque, it would be nice to see. I mean, might as well right?
    It is odd that the Garmin Edge 500 doesn't record the "Hub Torque" channel like the Cycleops Joule 2.0 head unit does with a Powertap hub. It still has a "Crank Torque" channel recorded though. That hasn't changed with the new firmware.

    The main benefit of the new Garmin Edge 500 firmware for me is that they've added a 10 second average power display option for whilst you're riding. If you use 10 second average power then the power figure display is much more stable and less jumpy, making it easier to pace yourself with.

    What you can do to see how this changes the displayed numbers is to make a new page: Settings - Bike Settings - Data Fields - Select a page. On the page add just the four different power options Power, Power-3s Avg, Power-10s Avg, Power-30s Avg. When you ride that allows you to see how the different smoothing options affect how jumpy the power numbers are. The 10 second average power is what I'll be using from now on.

    TSS, NP and IF aren't really things that I look at whilst riding. Garmin have missed an opportunity there as the Garmin Edge 500 post ride reports are still exactly the same as before (see Post #126 for what they look like). I was expecting them to be more detailed after the update. It means that if you want to view TSS, NP and IF on the Garmin Edge 500 you'll need to make an additional display page, in order to look at them before you save the ride file.

    My Powertap hub's calibration is quite confusing still. It started off at 512 late February with the new Torque Tube fitted. Over the next few months it drifted all the way up to 523. I checked it this morning with the new firmware before setting off and it had returned to 512 again. After 3 hours riding in 25-30c temperatures today I checked the calibration when I got home and it was down to 506.

  8. #158
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    Quote Originally Posted by WR304 View Post
    One of my big reasons for getting a power meter was for comparing ride intensity and trying to evaluate whether I was tired or not.

    The problem being that after a few weeks of solid riding my exercise heart rate response would be very low, even though I felt good. I'd end up ignoring the heart rate monitor most of the time as I simply didn't believe what it was telling me.

    What's the consensus for measuring power?

    My hope was that the power meter would give a more objective measure that I could rely on. So far this has been working quite well. When riding the drop in performance when you're tired, both in terms of Intensity Factor and average power is very noticeable. A quick glance at the report is all it takes to show which rides were good and which weren't so far this year.

    The WKO+ report below shows the rides that I've done so far in January 2011. The red line is average heart rate whilst the yellow line is average power for the same ride. You can see immediately that most of the rides have been fairly solid, apart from three which have much lower average power. The two days marked with a 1. are active recovery rides, whilst the ride marked with a 2. is the one mentioned in post #80 where I blew up badly. When you view the data in a report these stand out clearly as being different from the others. If you blow up it's reflected in the data.

    I mentioned that I found heart rate an unreliable tracking measure and you can see that pattern emerging here also. For the first week or so the red heart rate line is higher than the average power line, but then the trend reverses mid month and the red heart rate line falls below the average power line. It's most marked at the point marked 3. on the report where I was doing 2h30 each day. My average heart rate per ride drops badly to as low as 148 bpm, even though I'm still feeling ok and able to maintain the average power output of previous rides.

    The Intensity Factor for most rides was in the .85 to .93 range (assuming my FTP is right...) I've left IF off the report below because you can't adjust the axis scales in WKO+ reports. All the different lines and bars end up in a difficult to view mass. It's quite a serious omission from the WKO+ software.

    The power meter is useful for ensuring active recovery rides are in the right zone too. It's all too easy to end up going harder than you'd think. Keeping the power output low enough on an active recovery ride seems to involve bottom gear whenever there's any sort of slope at the moment.

    Pictured below: My Average Power and Average Heart Rate trends for January 2011 so far. It shows that my heart rate and power output aren't always closely related.
    Hey WR304, thanks for this as well as all your other posts in this thread about Powertaps, I just recently started doing a structured training program myself and have been wondering about getting a power meter.

    Your detailed analysis and pictures are very helpful

  9. #159
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    Also, can anyone tell me what's a fair price for a used Powertap disc laced to a so-so wheel? I'm looking at the wheel alone with no head unit.

  10. #160
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    I've ridden with a Powertap since the end of October 2010 now. As the amount of historic recorded information that you have increases it becomes possible to see some "big picture" trends emerging. Looked at year on year the Powertap data shows whether you're improving, where you're improving and also when you're improving. From that you can then look at the aspects in more detail if needed.

    Overview
    Compared to the same period of time in 2011 my overall power output for all miles ridden at 22 June 2012 is up by around 1.8% so far this year. (01 Jan 2011 - 22 June 2011, 252 hours, average power 165 watts, NP 187 watts / 01 Jan 2012 - 22 June 2012, 336 hours, average power 168 watts, NP 191 watts).

    A useful chart to make for this type of summary in WKO+ 3.0 is a custom Periodic Chart on the Chalkboard. Add Hours, Miles, Average Power and Normalized Power as data series and then set the Days Per Point to 999 before clicking Apply. What you can then do whenever you want to see your totals is change the dates in the Calendar screen to the period you're interested in and click "Update Chalkboard". You can then go to this chart on the Chalkboard page and quickly read off the period totals from the individual points.

    Mean Maximal Power Year On Year
    Looking at my Mean Maximal power outputs for 2011 compared to 2012 there hasn't been an even across the board increase. At short durations (up to about 2 minute efforts) I'm only equalling, or even slightly below my power bests from last year. From 2 minutes up to around 2 hours I'm consistently around 3-5% higher for my best efforts this year when compared to 2011.

    Where the power meter really shows an improvement is over longer rides though. This is what I've generally been concentrating on in 2012. 3-4 hour rides done on consecutive days. At 3 hours duration my 2012 best power output is 7.04% higher (average power 185 watts 2011, average power 199 watts 2012) and at just under 5 hours it's 9.5% higher (average power 164 watts 2011, average power 182 watts 2012). Knowing this is useful as it shows what sort of fitness improvements I'm gaining from the particular workouts that I've done. Doing longer rides has helped with endurance and sustained work rates but hasn't made me a better sprinter. Being able to see the results helps to target the workouts towards what you're aiming for.

    Predicting Best Fitness During The Year
    Along with this it's possible to look at where the best power outputs were during the year. If you take my best power outputs chart and change the date range to include both 2011 and 2012 then a clear pattern emerges, showing where my best form is likely to be. This pattern is one that I've always suspected from previous years but the power data confirms it. There are two clear groupings of power bests for me in these particular years. From the start of March 2011 through to the end of July 2011 and then from the start March 2012 through to today (22 June 2012). The rest of the year is very sparse with few power bests being achieved. This is an indication that with my normal riding schedule I can expect to be going well during March to July but then not quite as strong for the rest of the year.

    Pictured below: My Mean Maximal Power Outputs 2011 (dashed line), 2012 (yellow line) showing how I haven't improved equally across all time durations. Where the yellow line is higher than the dashed line it shows that I have managed a higher average power for that duration this year than last year. The main improvement has been over longer endurance rides. At very short durations I'm about the same as last year.

    My personal power bests 2011 - 2012. The highlighted sections with the greatest concentration of dots during the year are where I'd expect to have the best fitness.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-2011-2012_power_bests_mean_maximal.jpg  

    PowerTap Disc-2011-2012_power_bests.jpg  

    Last edited by WR304; 06-22-2012 at 07:28 AM.

  11. #161
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    I did a 1 hour time trial as an FTP test today. This was on an out and back flat route on the road but quite windy and raining. It was mostly crosswinds apart from lap 5 which was straight into the wind. Towards the end of the ride I had to get through some traffic lights and over a few roundabouts which is why the power and speed traces jump around.

    What I like to do when reviewing a ride such as this one is to break it down into smaller segments. I'll add in a lap marker every 10 minutes as a way of seeing how well my pacing worked. I was aiming to keep my power output between 231 and 269 watts, my "Threshold" power zone for the entire ride. As you can see from the graph and split times I didn't quite manage it. I started out strongly for the first 20 minutes but my power output sagged a little mid ride, falling below the target power zone for laps 3 and 4.

    If you look at the orange altitude trace you can see that this 20 minute segment is slightly downhill. Keeping your power output high downhill is hard to do. If the speed seems fast enough it's easy to fall into the trap of not going as hard as you could. I should probably have pushed a bigger gear there.

    By looking at the ride in sections it shows where the weak points were. If I'd done better and managed to sustain the early tempo mid ride then my average power output could potentially have been nearer to 240 watts than the 232 watts that it actually was. Because I can see what went wrong this time I know what to work towards the next time that I do the same ride again.

    If you were to try and look at it purely on average speed without seeing the power output change then it would harder to identify the problem. Speed is heavily influenced by factors such as wind and slopes. Looked at using average speed lap 5 (slightly uphill into a headwind) would appear to be a weak spot, even though I know from the power output that I was trying hard there.

    On the way back I lifted the pace for the final 15 minutes, trying to make it count and setting my best power outputs of the ride.

    Pictured below: 20 mile time trial FTP test on a flat route. The yellow dotted lines indicate the upper and lower edges of the target power zone that I was aiming for. With one minute smoothing applied the graph gives an idea of how well I stayed within it.

    Individual lap split detail
    Attached Thumbnails Attached Thumbnails PowerTap Disc-20_mile_tt_22-06-2012.jpg  

    PowerTap Disc-20_mile_tt_22-06-2012_splits.jpg  


  12. #162
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    It's been very wet here since April. It seems like almost every ride has been in a torrential downpour but my Powertap hub is still going strong.

    What works well is to put sta-lube marine grease around the rubber seals of the Powertap battery compartment, along with on the non drive side bearing. It makes sure that the water will stay out.

    Search results for "SL3120" | CRC Industries

    That's more than can be said for the rest of the bike. The rear suspension pivot bearings had to be replaced after just three months as they were creaking and in a bad state.

    If you're out riding in the rain then this will affect the Garmin Edge 500's barometric altimeter. The small holes underneath the unit used for the altimeter must fill with water. This often means that your altitude trace and climbing totals will be completely wrong on wet days.

    What you can do in WKO+ 3.0 is to correct the altitude using GPS. Right click on the range bar for "Entire Workout" and select "Fix Elevation Profile Using GPS". This will bring up a screen showing the before altitude profile. Choose "Ground Control" from the drop down and click Begin. Once the progress bar reaches 100% a yellow line showing the updated GPS altitude will appear which can then be applied, changing the altitude trace. For longer rides the GPS correction is much quicker if you create some smaller ranges and then correct each range individually. The GPS correction can sometimes get stuck if you try and do the entire ride in one go.

    The GPS trace isn't as accurate as the barometric altimeter would normally be so you'll see more spikes. For dry rides I'll leave the original Garmin Edge 500 altitude trace untouched. I'll only use GPS correction if it's been wet and the altitude needs to be fixed. If there are any big spikes on the graph after you have used GPS correction then these are GPS errors. Note the time of each one and change the graph view to Raw Data. You'll see the incorrect altitude number there. Type in a new number close to the adjacent ones to remove the altitude spike before saving the file again.

    Pictured below: sta-lube marine grease

    Using GPS in WKO+ 3.0 to correct the altitude trace of a wet ride where it has gone wrong.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-sta-lube_marine_grease.jpg  

    PowerTap Disc-wko_gps_altitude.jpg  


  13. #163
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    Making yourself ride slowly enough on recovery rides is something that I'm quite bad at. I'm more likely to end up riding at close to my normal pace, even when it's supposed to be an easy day.

    Recovery rides are one place that pacing yourself with a power meter is often at its most useful. If you usually ride hard or fairly hard on most rides then you get used to that level of exertion. Your body grows to expect to be riding at or above a particular preferred exertion every ride. By strictly riding to the power meter's display on recovery rides it helps you to avoid getting carried away and riding harder than you intended.

    The graph below shows my power outputs during today's recovery ride. After a few solid weeks riding I'd had two days completely off the bike beforehand and had considered having today off too, until a gap in the rain appeared. After quickly getting ready I set off but it was immediately obvious my legs were feeling very tight and there was no point pushing it.

    I ended up doing a 1 hour active recovery ride targeting the 0-141 watt range. If you're trying to do an active recovery ride be prepared for how slow it feels. On this flat ride I averaged 116 watts and had an average speed of only 13.4mph.

    Any short uphills will see spikes in your power output so you have to gear right down. You can see on the graph how the blue speed trace is as low as 7mph on the short uphills as I shifted down through the gears to the 33x32 in an attempt to keep the power output low. Even then I was riding in the Endurance power zone (142-192 watts) for most of the short uphills. There are also a few spikes where I went way above the top of Endurance power zone but as soon as I realised I sat up and backed off again.

    Pictured below: Using a power meter for a 1 hour active recovery ride to try and keep the power output low.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-active_recovery_ride.jpg  

    Last edited by WR304; 07-04-2012 at 03:25 PM.

  14. #164
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    Here's what a crash looks like. If you're ever looking at a power file an extremely sharp deceleration is often a sign that it was a fall. A bike is fairly limited in how quickly it can slow so an abnormally fast stop to stationary is something to look out for.

    On Saturday afternoon I was coming up to a roundabout on the main road. I was doing around around 16mph. I paused, went for a gap in the traffic but as I accelerated hard my right SPD pedal came unclipped. My right foot flew forwards into the front wheel, breaking several spokes and jamming between the fork leg and wheel. The bike flipped straight over and I landed hard on my left shoulder and left thigh, still attached to the bike by my right foot.

    Fortunately there was no car directly behind as I ended up lying on the ground in the middle of a main road with my right foot trapped between the wheel and fork. Some people stopped and forced the front wheel backwards to get my foot out and I slowly crawled out of the road to lie down on the grass verge.

    I've attached the power data just before I fell off. I hardly slid at all as the bike went straight over and came to a rapid halt. You can see from the sharp drop in the speed trace how sudden it was.

    I've attached a picture of the front wheel too. The hard carbon sole of the Giro Code cycling shoe mostly protected my foot from being crushed so it's bruised but the wheel came off worse. You can see where the shoe went through the wheel and broke the spokes.
    Attached Thumbnails Attached Thumbnails PowerTap Disc-falling_off_roundabout_18-08-2012.jpg  

    PowerTap Disc-2012_epic_broken_wheel.jpg  


  15. #165
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    Quote Originally Posted by WR304 View Post
    Coffee King (CK) pointed out that wheelbuilder.com now have a Powertap 142x12mm axle conversion kit available. The conversion kit allows you to use your existing Powertap hub with newer bikes such as the Specialized Epic and Trek Superfly 100 which have 142x12mm thru axle rear dropouts.

    Once converted the Powertap hub can also still be used with standard 135mm QR rear dropouts by simply swapping the end caps.

    Wheelbuilder PowerTap MTB 142mm x 12mm Axle Conversion

    There isn't any mention of warranty on the product page so it would be worth checking what implications this has before ordering. I'd guess that swapping the axle will probably void any existing warranty on your Powertap hub.

    Pictured below: Wheelbuilder.com 142x12mm axle Powertap hub conversion kit
    Saris told me that having wheelbuilder do the conversion did not void the warranty on the hub. So that's good to hear. I asked Saris if they offered 142x12 or if they could convert it for me and they said no, go to wheelbuilder so they are clearly 100% aware of what wheelbuilder is offering. According to wheelbuilder they actually worked with Saris on some of the hubs, providing input on flange dimensions and things like that.

    So I basically did the same thing as you with my powertap for my new bike. After sending it to Saris for new internals I took the SL+ 2.4 Disc, powertap hub straight to wheelbuilder.com to get it converted to 142x12. However after getting the wheel built up I realized I hit a big snag. The rivets on the rotor (between the carrier and the rotor itself) rub the frame on my Pivot Mach 5.7 Carbon's integrated post mount. Apparently this is a problem on some carbon Specialized frames (the epic I think wheelbuilder said?) So I'm kind of surprised you didn't run into this as well but it looks like your frame doesn't have the integrated post mount so that's probably why. I'll call wheelbuilder and saris tomorrow to see if they have a solution.







    Honestly this rotor carrier seems like huge overkill. It's a rear rotor so it doesn't get that much force, it has 8 bolts holding it on the hub at a pretty large radius with a 4mm thick piece of what looks like aluminum. By comparison the front rotor I'm using is also a two piece 160mm but by formula and the bolt circle diameter for the six bolts is much, much smaller and the aluminum is only 2mm thick. Realistically this all shouldn't matter much as the friction between the rotor and the hub will be holding it in place rather than a shearing load on the bolts themselves. My biggest challenge here is going to be trying to mill this thing perfectly flat so the rotor remains true when mounted to the hub. I plan to remove 1-1.5mm of material.

    To clarify I won't have to mill down the whole face of the rotor carrier, just the circled area. The hub is actually machined out between the bolt holes so there is no need to cut between them.
    Last edited by litany; 09-07-2012 at 12:57 AM.

  16. #166
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    Quote Originally Posted by WR304 View Post
    The Powertap torque tube replacement cost is surprisingly reasonable. It's a lot cheaper than if you were to buy a whole new Powertap hub anyway.
    Yeah, the cost for this is probably one of the biggest advantages the powertap has. Honestly the powertap is the most cost effective power meter you can get. Compared to the quarq and the pedal based meters it's cheaper to buy, and new internals are also cheaper so it's cheaper to maintain. I really hope SRAM doesn't ruin Quarq's customer service.

  17. #167
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    Quote Originally Posted by litany View Post
    So I basically did the same thing as you with my powertap for my new bike. After sending it to Saris for new internals I took the SL+ 2.4 Disc, powertap hub straight to wheelbuilder.com to get it converted to 142x12. However after getting the wheel built up I realized I hit a big snag. The rivets on the rotor (between the carrier and the rotor itself) rub the frame on my Pivot Mach 5.7 Carbon's integrated post mount. Apparently this is a problem on some carbon Specialized frames (the epic I think wheelbuilder said?) So I'm kind of surprised you didn't run into this as well but it looks like your frame doesn't have the integrated post mount so that's probably why. I'll call wheelbuilder and saris tomorrow to see if they have a solution.
    ...
    My biggest challenge here is going to be trying to mill this thing perfectly flat so the rotor remains true when mounted to the hub. I plan to remove 1-1.5mm of material.
    My current bike is a 2012 Specialized Epic Expert 29er. It has a post mount 140 rear disc brake fitting but the rear triangle is M5 alloy, rather than the carbon fibre rear triangle of the S-Works Epic. There's plenty of clearance between the brake rotor and frame and it didn't need any modifications to fit. You can just about see it if you zoom in the picture in post #144.

    If you only need 1-1.5mm of clearance then I'd file down the inside of the frame post mount until it doesn't catch on the brake rotor. Removing that small amount of material isn't going to affect the frame structurally. It's also in a place where any filing isn't visible.

    If you grind down the brake rotor that could cause two issues.

    - If you don't take exactly the right amount off then the brake rotor will be out of true to begin with, making it virtually impossible to align the rotor to stop it rubbing.

    - By moving the brake rotor 1-1.5mm inwards, away from the frame mounting points, you could find that there isn't enough left-right adjustment of the brake caliper to centre the brake caliper on the rotor. There isn't much you can do if that happens.


    I would do a photo showing the clearance on my frame but after crashing three weeks ago I still can't move around enough to even get to my bike. My left leg isn't working at all and my shoulder is a mess. It's looking like at least another three weeks of almost total bed rest.

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    So saris does actually have a solution to this! Apparently when they converted my hub to a 15mm axle that shifts everything over and they mill down the carrier .5mm to compensate. They forgot to do this for mine and sent me a new rotor that was milled down. Looks like 1mm was taken off, seems to fit fine now!

    Sorry to hear about your injuries, what a bummer. Get better soon!

  19. #169
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    Quote Originally Posted by litany View Post
    So saris does actually have a solution to this! Apparently when they converted my hub to a 15mm axle that shifts everything over and they mill down the carrier .5mm to compensate. They forgot to do this for mine and sent me a new rotor that was milled down. Looks like 1mm was taken off, seems to fit fine now!

    Sorry to hear about your injuries, what a bummer. Get better soon!
    That's interesting to hear.

    Was it Saris or Wheelbuilder who modify the rotor? There doesn't seem to be anything about a different rotor on the wheelbuilder site?

    It's the sort of thing you really need to know before buying.

    It's taking a long time for my left leg to settle down. After four weeks lying in bed or propped in front of the TV on a recliner chair I'm getting a bit tired of being stuck indoors. On the plus side it's better to be at home recovering than as a hospital inpatient for once.

    Still, it will make for a good graph showing how much detraining and loss of power output there can be from inactivity when I do finally get back on a bike again. At the moment I've no idea when that will be though.

  20. #170
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    Quote Originally Posted by WR304 View Post
    That's interesting to hear.

    Was it Saris or Wheelbuilder who modify the rotor? There doesn't seem to be anything about a different rotor on the wheelbuilder site?

    It's the sort of thing you really need to know before buying.

    It's taking a long time for my left leg to settle down. After four weeks lying in bed or propped in front of the TV on a recliner chair I'm getting a bit tired of being stuck indoors. On the plus side it's better to be at home recovering than as a hospital inpatient for once.

    Still, it will make for a good graph showing how much detraining and loss of power output there can be from inactivity when I do finally get back on a bike again. At the moment I've no idea when that will be though.
    Saris is the one who does it. When I sent my hub in they put all new internals on it. Even a new free hub. Apparently this change brought the axle to 15mm, this is different from the conversion wheel builder does. Saris are supposed to mill down the rotor carrier when they do this upgrade. The wheelbuilder conversion doesn't seem to change the offset at all. In fact they said it only works with the 15mm axle and not the old 12mm axle the hub had before it was upgraded to the new (current for the new hubs they came out with a few months ago) internals.

    Hopefully you can ride again sooner rather than later!

  21. #171
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    Quote Originally Posted by litany View Post
    Saris is the one who does it. When I sent my hub in they put all new internals on it. Even a new free hub. Apparently this change brought the axle to 15mm, this is different from the conversion wheel builder does. Saris are supposed to mill down the rotor carrier when they do this upgrade. The wheelbuilder conversion doesn't seem to change the offset at all. In fact they said it only works with the 15mm axle and not the old 12mm axle the hub had before it was upgraded to the new (current for the new hubs they came out with a few months ago) internals.

    Hopefully you can ride again sooner rather than later!
    Thanks for clearing that up. So the rotor spacing issue is down to starting off with the older 12mm axle version of the Powertap hub shell and rotor. Fitting the newer 15mm axle Saris internals changes the rotor spacing slightly.

    That would explain why I didn't have that problem. My 2010 Powertap hub came with 15mm axle internals so the rotor spacing wouldn't already be correct and not need adjusting.

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    > Replacing the bearings in the Powertap hub is quite straightforward. Tap out the old cartridge bearings and press new ones in. For the 17mm inside diameter drive side bearing we used a headset press to make sure it went in square. Everything went well initially - speed readings, torque offset etc were all fine on the hub after replacing the bearings. The wheel bearings and freehub span freely when not fitted in a frame.

    Thanks for your post, very informative! I'm having trouble removing the freewheel/cassete body. I've removed the end caps but the cassete body seems to be locked in place. Is there anything else that should be done besides pulling/forcing the cassete body out ? It does look straightfoward on the youtube videos covering the road model but i wonder if there is an additional step fot the MTB model ?

    Thank you,
    Fernando

  23. #173
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    Quote Originally Posted by laudares View Post
    > Replacing the bearings in the Powertap hub is quite straightforward. Tap out the old cartridge bearings and press new ones in. For the 17mm inside diameter drive side bearing we used a headset press to make sure it went in square. Everything went well initially - speed readings, torque offset etc were all fine on the hub after replacing the bearings. The wheel bearings and freehub span freely when not fitted in a frame.

    Thanks for your post, very informative! I'm having trouble removing the freewheel/cassete body. I've removed the end caps but the cassete body seems to be locked in place. Is there anything else that should be done besides pulling/forcing the cassete body out ? It does look straightfoward on the youtube videos covering the road model but i wonder if there is an additional step fot the MTB model ?

    Thank you,
    Fernando
    Which one do you have? For mine you just pull the free hub off but it can be quite hard. One thing I do (dt Swiss told me to do it when I was having trouble with my 240 free hub) was to leave the cassette on and hammer it off from the back. I made sure not to just hit one spot but to do more of a star pattern. I set a big Allen key against an old cassette and hit it with a rubber mallet.

  24. #174
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    Hello Litany, my model is the original powertap MTB disc model, which looks like the SL+ but with the proprietary rotor connections on the non-drive side. I've got it second-hand and altough it looks great the bearings look really finished.
    I did tried your technique - i only hit a few times in different points, but it looks stuck. Being in Brazil, I'm not considering sending it to Saris. Should i try to hit it harder or might be something else holding the freebody in place ?
    Thanks, Fernando

  25. #175
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    Quote Originally Posted by laudares View Post
    > Replacing the bearings in the Powertap hub is quite straightforward. Tap out the old cartridge bearings and press new ones in. For the 17mm inside diameter drive side bearing we used a headset press to make sure it went in square. Everything went well initially - speed readings, torque offset etc were all fine on the hub after replacing the bearings. The wheel bearings and freehub span freely when not fitted in a frame.

    Thanks for your post, very informative! I'm having trouble removing the freewheel/cassete body. I've removed the end caps but the cassete body seems to be locked in place. Is there anything else that should be done besides pulling/forcing the cassete body out ? It does look straightfoward on the youtube videos covering the road model but i wonder if there is an additional step fot the MTB model ?

    Thank you,
    Fernando
    Old Powertap road hubs had locknuts and also needed an allen key. I don't think that the older versions came as a MTB Powertap disc hub though.

    http://www.cycleops.com/pdfManuals/Archive/Comp/308.pdf

    Do your hub's endcaps and axle look like the ones in post #106 and #113? If so, the hub should be the toolless model. With the endcaps removed the freehub should pull off by hand. If you leave the cassette attached it gives more leverage to pull the freehub body off.

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