Powertap questions

[inc]

You get NP from your analysis software.  I can see no reason at all to have NP displayed on the head unit like the Joule does (unless of course you don't have a computer with which to analyse your ride).  Personally I find having a head unit that does power and GPS quite nice for post-ride analysis.

That was just one thing, there are loads,  I have a GPS, mostly for OSM mapping but Garmin do not support Linux, quite the opposite, so I choose not to give them my money. Here are a list of recent Garmin firmware changes, If you want a GPS that also does power great. I don't.

Change History
Changes made from version 2.90 to 3.10:

    * Added ability to use waypoint elevation as the starting elevation for an activity when the user starts within approximately 30m of this waypoint.
    * Fixed issue where workouts using power zones based on percent of FTP or heart rate zones based on percent of maximum HR were saved incorrectly.
    * Fixed issue where Garmin Training Center could give a data transfer failed error if the unit had a bike profile name longer than fifteen characters.
    * Fixed issue with inaccurate display of history dates in some languages.
    * Added support for updated Australia Daylight Saving Time start and end dates.
    * Updated translations.

Changes made from version 2.80 to 2.90:

    * Added support for high capacity SD cards. (4GB, 8GB, etc.)
    * Improved power and speed data recording to minimize spikes.
    * Added 3 and 30 second moving average power data fields.
    * Fixed issue storing empty/unnamed speed zones in user profile.
    * Fixed issue where viewing a Scheduled Advanced Workout causes it to be deleted.

Changes made from version 2.70 to 2.80:

    * Restructured activity logging to reduce the number of invalid TCX files.
    * Corrected issues from 2.70 that could possibly corrupt the 'History' directory.
    * Removed potential spikes in the power data after periods of coasting.
    * Increased the allowable digits in the 'vertical to point' field to 4.
    * Increased the allowable digits in the 'calories' field to 5.
    * Updated translations.

C

[Greenbank]

You get NP from your analysis software.  I can see no reason at all to have NP displayed on the head unit like the Joule does (unless of course you don't have a computer with which to analyse your ride).  Personally I find having a head unit that does power and GPS quite nice for post-ride analysis.

Indeed. NP is based on (or just is) the 4th root of the 30 second average of the fourth powers of the power readings over that period. It's not a realtime reading.

I've just taken all power related values off my usual display fields on the Edge 705 as I'm not really interested in them whilst riding (I'm not racing or TT-ing). I'd much rather go with 'feel' and to push myself and use the power data post-ride.

Obviously a 10 or 25 mile TT you would benefit from seeing the avg power values during the ride, but I'm not doing that so I don't...

[Greenbank]

P.S. I find myself lusting after a fixed version of the PowerTap hub.

I know they're available, but the acquisition of such an item would be noticed in the GB household, as would the absence of one of firstborn's kidneys (required to fund such item).

Gah!

[inc]

NP is based on (or just is) the 4th root of the 30 second average of the fourth powers of the power readings over that period. It's not a realtime reading.

There is a quite interesting thread about NP on the GC mailing list which Andy Coggan has posted on. My simplified interpretation is that it is more relevant than average power where there is a lot of variation of pace or load So for example where I live and ride in the Welsh hills one hour spent equally between 360W climbing and 0W freewheeling  gives 180W average as would  one hour steady in the fens at 180W quite clearly the training load is different and NP attempts to address that, Looking at the Joule manual it looks like  normalised power is one of the 36 values that can be selected for dashboard display so I would assume it is a realtime value.

[inc]

If you have a GPS cpu for your powermeter there is a nice feature in the latest version of Golden Cheetah where your ride is shown on GE. You will have to build the latest version from their git repository or wait for the upcoming 1.4 release. Aerolab is also there which looks like it may be interesting. Aerolab: Work in Progress | NY Velocity - New York bike racing culture, news and events

[inc]

Well a little update, it has taken a month but finally got there. I just bought the hub as I didn't want a Mavic rim. I built the wheel in a couple of hours and configured the Joule . I had already bought Andy Cogan's book, the recent 2nd edition  so went as suggested for the one hour FTP ride, it is a long time since I have made that sort of effort so I was disappointed to find that the Joule had not recorded the ride. I thought I had done something wrong so did it again two days later to find that ride hadn't recorded either. A trawl of the relevant forums seem to indicate others with the same problem. I emailed  and rang Saris and they sent me a link to a beta PowerAgent 7.5.2.2 but it did not made any difference. There was a new version of firmware for the Joule, which may have helped but it would not load ( via Poweragent) others with Windows, Mac and Linux were having the same problem. Powermeters lent me a standard head which worked fine so I sent the Joule back for replacement. The new one arrived and the first ride it recorded OK, yippee, second ride no downloadable ride although there is a file on the memory ( it won't import either ). The final straw was the altimeter, it has no zero so with the recent high pressure it was showing an altitude of 97m when it should be 265m the first Km of any ride I drop 100m so for all the ride I had no functioning altimeter. Bob sent me a Garmin 705 Saturday and it works great, files work fine in PowerAgent but especially with Golden Cheetah and the new map function where the whole ride is shown on Google maps with the power display colour coded on the road in my zones. The Joule is a nice bit of kit but still has teething problems and now compared with the Garmin seem overpriced as well. I also found I can extract a gpx from the tcx files with Gpsbabel so it is OK for OSM as well.

[simonp]

I got a new wireless powertap.  The old one would record for 30h.  The new only records for at most 24h.  So at the speed I ride, no longer enough to record the power data for a 600k.

The wireless head unit does have a couple of features the old one didn't but reducing the memory size seems crazy to me.

So I'm thinking 705 with external power now, combine navigation and power etc.  If I got a Joule, it's limited to 20h battery life so I'd have to have external power for that too.

[inc]

I suppose you could get two standard heads for the price of a Joule and just change them at 20 hours and merge the rides with your software.

[simonp]

Genius!  I never thought of that!  Probably the simplest solution.

[Greenbank]

Shiny 705 goodness. You know it makes sense.

My recent 200km Audax took up ~45MB recording position, elevation, cadence, HR and power every second (in a horribly wasteful XML format containing a big URL in each data point).

That means the ~1GB internal memory (not the SD card used for holding the maps) would be good for a 4500km Audax recording a data point every second.

Actually that's quite scary that if I'd used this to record every bit of my cycling last year I'd be chomping through 2GB a year.

[Greenbank]

My present to myself next year will be one of these:-

Powertap SL track hub only

[simonp]

My present to myself next year will be one of these:-

Powertap SL track hub only

Git.

[inc]

My present to myself next year will be one of these:-

Powertap SL track hub only

24 spoke only ?

[simonp]

My present to myself next year will be one of these:-

Powertap SL track hub only

24 spoke only ?

24-32 on the drop downmenu, I think.

[inc]

Yes, reading it again it looks like black only in 24 spoke

[Greenbank]

My present to myself next year will be one of these:-

Powertap SL track hub only

24 spoke only ?

24-32 on the drop downmenu, I think.

20 silver
24 silver
24 black
28 silver
32 silver

Since mine would be for Audaxing I'd be going for 32 and building it into an Open Pro.

Just have to sell a kidney to fund it first...

[dasmoth]

Powertap SL track hub only

Oooh.

I wish I hadn't seen that...

[Greenbank]

I'm hoping to have one in time for a little trip over to France in August, ideally way before this for the qualifying rides (albeit not the K&SW).

I'm not overjoyed by being limited to the White Industries splined sprockets though. I would have hoped for a traditional threaded hub although I can see why the splined mounting would make it less likely to thread the hub...

[dasmoth]

I'm not overjoyed by being limited to the White Industries splined sprockets though.

<checks>.  Hmmm, they are kind-of pricey, but if I were to splash out on the hub I don't think I'd stress too much over the £35 sprocket to go with it.  The mention of 14-16T on the Cyclepowermeters site must be a typo, White Industries offer them up to 19T (UK site) or 20T (US), so there's a reasonable choice of gears without going for tiny chainrings.

[dasmoth]

By the way, do you know what happens to the strain gauges under leg braking?  I assume this has all been thought through at least to the extent that it won't break them or throw them out of calibration.  But will they actually give "negative" readings?

Could actually be quite fun to monitor leg-braking performance...  Hmm...

[simonp]

By the way, do you know what happens to the strain gauges under leg braking?  I assume this has all been thought through at least to the extent that it won't break them or throw them out of calibration.  But will they actually give "negative" readings?

Could actually be quite fun to monitor leg-braking performance...  Hmm...

The hubs seem to be able to register negative torques.  I'm not sure how autocalibration works when you're riding fixed.

[scherrit]

I have one of these beasties (fixed wireless), very promising after breaking (bad design, not superior legs.... alas) the previous version.

You have to disable the auto zero and manually zero the head unit before each run on the track (or possibly after a few miles on the road)- it's mostly temp which causes the zero to drift I think.

The white cogs are a necessary evil, you need to avoid reverse torqueing the hub (that's what killed the previous iteration, usually) - there are fasteners holding the torque tube in place and they are right hand threads. In the new version, they have removed the requirement for un threading cogs (probably the highest reverse torque the hub ever "sees") and glued the hub together as well. I personally would hold off skiddy braking, these are only approved by the manufacturer for track use, no idea how hard they are to break, but kinda pricy! The old stylee ones used to set me back about 300 each and then I'd carry the conversion stuff across each time (Surley fixxer and wheelbuilder.com axle)- typically they would last 2 years but a mate got unlucky and bust one after  2 weeks. This old style is no longer supported so each bust hub is for throw-away only.

If you are considering getting one of these (new stylee wireless), by all means call me at the bike whisperer number, I can do you a good deal or talk you through getting it second hand- basically you need to find a new type wireless or even wired hub and send it for conversion to Wheelbuilder.com in the US- it's what I did for my hub, not being minted.

[Greenbank]

Interesting, thanks for those comments.

I'd actually considered the track on for everyday use on my fixed (including Audaxing and even PBP). If there are any reliability issues then I'd rather not risk an important ride on one. Nor do I want to spend large sums of money on something that's going to break.

I'd expect it to be tough enough to survive year round commuting at least, or at least be cheap to repair should normal wear and tear get to it.

Purchase on hold anyway (as I'm skint...)

[Greenbank]

I've emailed Cyclepowermeters to see if they'll do a PowerTap SL Track as a rental to give it a play.

I've also asked them what they think of the reliability and suitability of them being used on the road in all weather (I've no plans to use them on the track). I'll post a summary of any response I get.

[Greenbank]

I've emailed Cyclepowermeters to see if they'll do a PowerTap SL Track as a rental to give it a play.

I've also asked them what they think of the reliability and suitability of them being used on the road in all weather (I've no plans to use them on the track). I'll post a summary of any response I get.

No response, will try emailing them again.

(I don't know whether they're crap or their replies aren't getting to me. I don't want to have a go at them only to find out they dutifully replied to my emails but I never saw any response. Does anyone have any experience of Cyclepowermeters.com?)