Eyedrop

Cyclops PowerTap 2 4 Wireless Zipp 404 Carbon 650 Tubular Rear Road Wheel | eBay

This one seems like a really good deal. Anything I should consider before possibly buying it? Would I be better off spending aittle more and buying new? Someone earlier said these things need maintenance.

Homebrew01

It's a tubular. Are you familiar with gluing on tires ? Or prepared to pay someone to do it ?

I hear Slowtwitch is good for used stuff, especially triathlon, so they may have some 650 wheels.

chaadster

As Homebrew said, the major issue there is that it's tubular, which is a whole other type of committment.

I disagree that Powertaps have servicing issues. In my experience, they're very reliable and durable, and will perform for many, many years without trouble. Batteries and bearings will have their normal life, but the PT specific components seem exceptionally well built.

Homebrew01

Same here. I bought 2 used older model powertaps and have been happy with them. Easy to replace batteries, unlike SRM (I think) that requires you to send it to them for battery replacement.
1 head unit eventually died, but the hubs have been fine.

For entry level power, I would do the same again, for less than an IBike which is a power "guesser", not a power "meter".

Another benefit of a real power meter is that it works on a trainer.

chaadster

In fairness, I believe the iBike is also a power meter, and not a power "guesser", the distinction being it measures indirect force rather than direct force.

It's probably an important distinction to make in order to separate meters from power guessers like Powercal and 'virtual power' systems which do not use force in their calculations at all.

That said, the point is taken that it's probably both easier and more accurate to measure direct force, but iBike has shown it's possible to have an accurate IF meter.

RChung

That's not a useful distinction. Every power meter on the market senses something that's converted into force. The "direct force power meter" is a neologism iBike created in order to differentiate themselves and people have bought into it. Strain gages measure changes in electrical resistance, which then have to be converted into force. A cheap bathroom scales measures the change in length of a spring, which then is converted to force. Thermometers measure the change in the length or resistance of something else, which then has to be converted into a temperature. The question isn't "does it measure force directly or indirectly" since every power meter on the market does it indirectly. The question is "how well do the measurements work?"

When I compare power meters I don't pay attention to *how* the data were generated. I only look at the quality of the data that *were* generated.

chaadster

Yes, I certainly hear you regarding quality of data as paramount; that's absolutely the bottom line.

I'm curious, though, if you do not see a relationship in quality of power data to the means by which it was gathered, namely between devices that measure force (e.g. iBike, Powertap) and "guessers" (e.g. Powercal) which do not, but which extrapolate power from HR or speed.

It seems that's a fundamental distinction to me, at least insofar as quality, accurate data is concerned.

RChung

It's slightly more complicated than that. No one needs more accuracy than they can use -- the problem is that most people don't know how much accuracy they need or will use in the future, so they don't think about it at all. They're the people who claim "consistency is all that matters."

I don't presume to know what people need, now or in the future. I evaluate power meters by the quality of their data and then point out the things they can do and the things they can't. Training threshold is a pretty undemanding use for a power meter, so the PowerCal or the iBike (or a HRM, or a wristwatch and a speedometer and a regular training route, or Strava and a smartphone) can do that pretty well. Lots of people will never demand more than that, so they may never see the need for more accuracy or data quality. Nothing wrong with that.

There are some people who need to train something specific, or to measure something specifically. If you're one of those people, you'll be unhappy with the PowerCal or the iBike (or Strava and a smartphone). The issue is that people don't always know what they'll need to do in the future. I began with fairly undemanding needs but quickly progressed to needing (wanting) to do more complicated things. But not everyone is like me, so I don't presume that everyone needs the same degree of accuracy that I do. I've pretty much maxed out my power (I'm at an age where my struggle is to not lose power -- I've just about given up ever seeing 4.0 watts/kg ever again) so in order to get faster (which I haven't given up hope on) I have to minimize drag. Measuring drag is one of those things that demands very high data quality.

So, different power meters produce different levels of data quality, no matter what sensors they have or algorithms they use to make those calculations. Different riders have different needs for data quality, no matter what sensors their devices have. I try not to focus on the exact sensors they have or don't have. I try to focus on identifying the level of data quality, and point out what you can (or don't need to) do with it.

yankeefan

+1

People do have different needs, which will determine the quality and type of data they need.

If you follow a detailed training regimen, ride competitively and therefore need to know your FTP and W/kg then you need a powermeter that is accurate (and consistent, though accuracy implies consistency).

If you ride for general fitness and recreation, a "power guesser" that is inaccurate but consistent can be quite valuable for tracking changes in your fitness and in-ride pacing, to some extent. Its all about relative changes rather than absolute measures. Of course as (if) you progress as a cyclist and need greater feedback on your training (e.g. compare your stats to predetermined benchmarks) then these power guessers become useless. I'm not at that point as yet, but I suspect (if I continue on my current trajectory) next year I will probably outgrow Powercal and will need an actual powermeter. Hopefully one year from now my pocketbook will grow as well

There is a lot of HR bashing by people with a vested interest in power meter sales (not just companies, but even coaches, authors, etc) and as such a lot of people are suckered into buying a power meter who really don't need that level of accuracy, but think they do because "HR is too unreliable". Don't get me wrong, HR does indeed have its limitations and can be quickly outgrown as a training tool, but I certainly do think there is a viable market for "power guessers" (assuming they can be sold at substantially less than a power meter) that relies on other metrics than force being generated through the drive train. The problem with "power guessers" is that they don't have their own unique data field on Garmin/Timex/etc so they have no choice but to use the power data field, which will invariably lead people to try and use them in a similar manner as real power meters then complain about their inaccuracy. They were never meant to be accurate from the moment the engineer conceived the idea, though some of them have tried to market themselves as such.

In any case iBike is useless given that 4iiii is cheaper and finally started shipping.

Dunbar

I own a G3, I'm not saying they're unreliable but all power meters require service. The older Powertaps had moisture issues and torque tubes can go bad in time. There is a very real risk your used Powertap will require a $350-400 repair in the first year or two. But my main point was that you can buy a new one for $700-800 so I wouldn't spend too much on a used one. Back when new Powertaps went for $1k+ I think used Powertaps made a lot more sense. With Powertap about to release a $700 crank based power meter that changes things a bit too.

bikepro

That seems a little high for that PowerTap model. It's fairly old, as well. I would look for a used G3. They are newer, the batteries last longer and are easier to replace and they can be serviced locally, rather than always being sent back to CycleOps.

chaadster

That's one of the wordier question dodges I've read in awhile.

chaadster

Your conclusion contradicts everything you just wrote and everything to which you were +1ing.

Also, as someone who owns a 4iiii product, I'm cautious in my optimism about what they're shipping in their PM product. Specifically, is it going to be as fully developed, refined, and "ready for prime time" as the segment leading PMs?

RChung

No one's perfect.

chaadster

True! However...

You've got a lot of PM knowledge and experience, and I appreciate it when you share your insights.

achoo

The riders on my team who I know have iBikes have all expressed a wish they had spent their money on something else.

And most of them eventually have done just that - buying a PowerTap, Stages, or Quarq.

Eyedrop

I'm about to pull the trigger on that ebay auction: https://pages.ebay.com/link/?nav=item...d=141404607542

I already have a tubular zipp 400 front wheel with a DA hub, and a new set of conti sprinters that we're given to me. I put the sprinted on the rim without glue yesterday and it seemed even easier tgan a clincher! The only thing is carrying a bulky tire around and having to pump up constantly.

For $500 plus a $100 joule, I think it will be my best bet. Especially considering my budget and the kit I already have. I think it will help to "complete" the bike. It deserves tubulars.

Anything I should consider before I buy? How much money does it cost for powertap to replace the battery in the 2.4 wireless?

merlinextraligh

It's do it yourself, with batteries available at the drug store, under $10. There's a tool for it, but a rubber grip designed to open jar lids works as well.

Drew Eckhardt 

Under $2 from amazon. $9 with free shipping gets you 10 Energizer batteries which is 5 changes:
https://www.amazon.com/Energizer-Batt.../dp/B000RB05LG

1/3 of that for get generic batteries.

They're consistently good for somewhat over 200 hours; I swapped mine twice over the last 12 months and 6000 miles.

Keep track if you don't want to deal with the annoyance of loosing a ride. While the Cervo little yellow computer can give you a low battery indicator, Garmins do not. I have no clue about the Joule - AFAIK the battery status message is only in the proprietary CycleOps protocol which that generation of hubs always sends, but not the ANT+ packets.

IIRC one of my headset wrenches fits the wrench flats on the SL/SL+/SLC/2.4/2.4+/Pro/Pro+ carbon window generation hubs although the official plastic wrench is more convenient.

Eyedrop

How likely is it that the used powertap will need a torque tube? Judging by the pictures and braking surface, it dosent look very used. Should I just pull the trigger guys?

DunderXIII

I have a powercal too that I use to get TSS & IF that I kinda of calibrated (I mean, getting a virtual FTP ..). For this its actually not that bad. For commuting too, I don't risk getting it stolen and get reasonable TSS value.

But I'm curious, is there a trick to use it as an in-ride pacing tool? Any power reading you get is foobar. What I do in-ride is look at IF & TSS.. it's sometimes interesting. Is there a better way to use it?

yankeefan

The devised a neat system that allows me to use the numbers for in-ride pacing; its not foolproof, but more informative than HR zones (especially when caffeine/fatigue/weather/etc starts messing with HR).

First of all you have to use 30s AVG power. Instantaneous, 3s, 5s, & 10s power will fluctuate too much for you to hold a certain number of "watts". Also, 30s avgs smooths over sharp spikes/falls in HR due to a stimulant or rapidly changing core temp.

Do the FTP test (30 min time trial). It won't translate neatly into the standard power zones, but it'll give you an idea of what numbers will pop up when you're going full gas for an extended period. This is how PowerCal was meant to be used -- to pace yourself on extended steady state intervals.

Assuming you've done the 30 min time trial, it means you've found a location where you can ride 30 minutes at full gas relatively uninterrupted. This is good. Typically loops around a local park works best. Now you want to do repeated laps on the same terrain at varying intensity levels (use a combination of HR & RPE is gauge your intensity). My local park loop is 3.33 miles long so I did 9 laps broken up into 3 lap segments -- Low, Moderate, High. Roughly corresponds to Zone 1-2, 3-4, 4+. Doing it in this order is important due to the "drifting effect". During extended periods of exercise your heart raise will steadily rise even if your power output is constant (aka drifting -- the fitter you are the less pronounced this effect will be). PowerCal does a very good job of decoupling this drift effect since its calculates power based on HR variability (essentially the rate of change in HR -- if you've done calculus this makes total sense) and not raw HR. Its not perfect but good enough for its intended use. Also, make sure you use the lap feature on your head unit so that when you upload to strava you'll get power averages for each lap. Finally, avoid stimulants when you're doing this test. Stimulants don't mess with PowerCal too much over the course of a longer ride, but since you're doing averages of short laps the spike in power will skew the calculations.

Now for the post ride analysis. The average power (+/- 20%) for your low intensity rides because your power zone 1, aka active recovery. The next cutoff is your moderate intensity average power. Think of this as your all day cruising zone. The next cutoff is your "FTP" from the 30 minute TT. This is your tempo zone, and pretty much your sweet spot. Finally the last cutoff should be your average from your high intensity laps. Think of this as your full gas zone; you probably won't be able to hold it for more than a couple of minutes. These zone are baselines and the cutoffs aren't rigid so feel free to fine tune them as you ride and learn more about your body's physiological response to exercise. Also, as your fitness increases you'll need to redo the tests. But as I said earlier, PowerCal fails when you have a steadily rising core temp -- it interprets a gradual increase in HR as you doing more work but really its just you needing to ditch the arm warmers and full finger gloves. Its been especially problematic for me lately due to the varying temperatures throughout my ride and my laziness to add/remove layers when appropriate. Great tool once you work out the quirks.

I'm in no way qualified to give exercise advice. Just a geek who likes stats, politics and gadgets.

Drew Eckhardt 

I'd go for it.

There's a small chance you'll need a $350 service before you would with a brand new powertap. If that happens you'll have brand new G3 internals and still spent less than pairing a new hub with an otherwise used wheel.

Dunbar

Are you going to be training on (650c) tubular tires? The main benefit of power is training and most of us train on clinchers. I would personally get a new alloy rear G3 clincher wheel for $800-900 and run a disc cover for races.

Eyedrop

Thanks, that's a good point. I just bought it! Does anyone know if my Nike Triax C8 HRM strap will work with an entry level joule?