This is the reason I switched to Quarq. That and the auto-zero issue with Garmin at the time.

For aero testing, it’s Powertap hubs for me.

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Developing aero, fit and other fun stuff at Red is Faster

I'm also in the money no object camp and I agree.... big fan of my Assioma Duos. They've been accurate and reliable. One added advantage is if you travel to races, you can pack them in your carry on. If your bike gets lost and you need to buy/borrow a loaner, at least you'll have your PM. The one con I see is maybe the pedals aren't as aero as something like a Keo Blade or Speedplay Zero Aero, and the pods are kind of ugly.

I just added a DL Dura Ace Pioneer to Speedmax SLX because I didn't want to have to swap pedals between bikes, and on first ride had some drop-out issues. So we'll see that goes.... but leaning toward buying another set or two of Duos and just keeping a set of each of my bikes.

I've heard nothing but bad things about Stages and haven't tried. I had two sets of Vectors and both had the battery door issue and dropout problems. One set pooped out on me in a race.

I had a PT hub in my old training wheel set. It was bombproof and reliable, but it's kind of a fugly hubset.

I'd consider Quark if I was running SRAM, but my bikes are Di2 and Campy Mech.

I don't quite get the SRM love, frankly. I mean, sure it's the "gold standard" or whatever, but it's feature set is actually kind of lacking. The non-user-serviceable battery is a deal-killer for me. Presumably if money is no object, the value of your time is high. I don't have time to be changing and shipping around cranksets whenever I need a new battery.

Can someone please explain the advantage of PT hub in aero testing? It would seem this is actually a limiter if you want to test different wheelsets (rather than just position changes, accessories, etc.).

You determine your aerodynamic drag (and your rolling resistance) by measuring your speed and power at the wheel (and then accounting for environmental factors -- grade, road surface, air density, wind, etc).

The problem with crank/chainring/pedal powermeters is they only give you an estimate of power at the wheel. Yeah, you can subtract 4-7 watts for drivetrain loss. But this number is not a constant. It's actually somewhat variable, being influenced by cadence, chainring/cog choice, etc. A Chung test, where you may change these factors systematically (because of the terrain), may therefore be systematically skewed.

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That's for the Vector 2 & 2S, not for the Vector 3 & 3S......

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-Brad Williams
Website | Twitter: @BW_Tri |Instagram: @BW_Tri | Strava | Co-Founder & Coach at: KIS Coaching
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Accuracy and precision are very good for starters with the G3. It’s also easy to install without needing calibration.

For aero testing where you’re interested in the energy delivered to the tyre rather than output by the rider, hub PM means you can, pretty much, ignore gearing and transmission losses.

Yes it limits rear wheel testing choices, but the impact of rear wheel on the rest of the system is extremely limited, and in the few cases* where we’ve been looking at rear wheel options, we could still use another PM, but then you have to factor in transmissison loss and gear changes in test. We do test that way, but hub PMs are preferred.

* front end changes are normally more significant. Most riders have a deep section rear and disc and use the disc unless it’s not allowed, or really hilly.

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Developing aero, fit and other fun stuff at Red is Faster

SRM for reliability, accuracy and customer service. Nothing fancy - just German quality and engineering. Over the long term they end up being cheaper than all the others.

As a test of quasi steady state power accuracy it was an interesting exercise in attempting to provide an absolute standard as opposed to comparing one or more meters with one another. It's actually not an easy task to provide an absolute standard that at least bears some resemblance to they way people actually ride.

While the accuracy of quasi steady state power scenario is of interest to most in the world of triathlon, it's by no means an indicator of measurement accuracy in other riding scenarios, e.g. during accelerations and for peak power measurement. And this is still a limitation to consider as I'll explain further down.

As has been said already, it helps to understand the manner in which you plan to use the data in order to choose a meter appropriate to your needs (or whether indeed a power meter is needed at all).

Sometimes you don't know what you might like to do with the data, or whether such things as accurate peak power measurement matters. Even for a triathlete I think it does matter, especially if you are considering ways of applying the more recent power duration modelling since the peak power measurement does affect all the model's parameters.

And a final comment - it's not just the meter but also the devices used to capture and upload the data, the firmware/software doing the post processing of data and how they all interact with one another. Sometimes errors are not due to the meter itself.

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Changing gear can affect the power accuracy of a Powertap as well (at a level that matters for aero testing). At least that's my experience when analysing such data from aero testing and is why when doing such testing we settle on staying in the same gear if we are using a Powertap.

Over the past decade or more of doing field testing indoors, I've never been let down by those with SRMs on their bikes. However I typically find with many other meters, while they still enable us to do good work for most aero testing stuff, they tend to provide data with a higher variability and so being able to nail down very small changes (e.g. an assessment of shoe covers) is harder or not possible or requires collection of so much data it's not cost effective for the time required.

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http://www.cyclecoach.com
http://www.aerocoach.com.au

I did say ‘pretty much’. :) I stick with one gear where possible and do track gears when data is available. It’s certainly good enough for shoe and shoe cover tests for example.

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Developing aero, fit and other fun stuff at Red is Faster

I've been using a Quarq PM for years, and have no issues. I've sent it back for calibration once, when the numbers seemed to be off. That being said, I'll probably go with the new Look/SRM pedal for my next PM. This will give me the possibility to run Campy cranks with my Campy gruppo, and continue with my preferred pedal.

Skippykitten,
Do you have any quick recommendations for a value-minded wheel set to go with the G3 hub? I mean, like really on the cheap side. I'm still in my first year of cycling, so going super fancy would be overkill right now. The stock wheels that came with my bike are the Vuelta Zerolite Comp wheels and weight about 2050grams. I'm a "hobby" cyclist who wants to learn and do some at-home aero testing, so the hub is appealing.

I was considering ordering the DT Swiss R460 wheel set with G3 preinstalled since the set is rather inexpensive. Are there better options out there if I order everything separately and have the wheel built locally??


Thanks!

You shouldn't have needed to make any measurements to realize that non-round chainrings would alter the accuracy of the data.

If racing then a cheap and deep Chinese rim with a cover would be ideal. For training really any decent rim and build is fine, and you can cover that also for races. $550 for the DT460 wheelset from Powertap looks real good to me!

I never got data from Powertaps which enabled that level of precision with any reliability.

This is indoor track testing.

The torque zero would typically fluctuate such that you hit the limit with what was reliably testable. It was also my experience that some Powertaps were more susceptible to this than others. I've been through perhaps 30 PT hubs, and maybe one of them I could reliably test to this level, about half or so I could do aero work that was good enough for the session objectives, and the rest were fine as a power meter for general training but unsuitable for fine grade aero testing.

Prior to testing I always checked what meter we were using so I could set reasonable expectations on the typical precision limits. In some cases the rider themselves is the cause of most variability, especially if their bike fit is not so good and they are not rock solid stable on the bike.

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http://www.cyclecoach.com
http://www.aerocoach.com.au

I have a dt460 with a pt hub that i built myself. Very happy with the 460...strong rim that has taken some serious hits in the last 24 months. I ran over a 1/2" bolt last year. Jarred me something fierce. It snake bit the tire on both sides and the tube. The rim was completely undamaged. Didn't ever loose true.

Earlier this summer, I hit a wheel sized pothole. ... Long story... I swerved and missed it with the front, but the rear dug in hard. Again bomb-proof.

I run it covered for racing.

I noticed that on rollers. <100W @>30mph ends up being very little torque at the hub. And one in-lb resolution isn't very fine.

Besides the SRM was there another PM you thought was better than a PT hub?

Ouch. I'm a poet, not a scientist.

In my defense, I would point out that many others were misled by the bogus readings, including Bobby Julich and whoever was coaching him at the time. In fact the SRM guy I emailed about it insisted that the SRM was measuring the power accurately.

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My latest book: "Out of the Melting Pot, Into the Fire" is on sale on Amazon and at other online and local booksellers

So I started looking into these after seeing a few ppl strongly recommended them here. I was getting all excited... They looked great... until I learned the battery isn't replaceable?

What have you heard is the expected life of the battery? Kinda sucks to think that in 3+ years you could have a $1200 paper weight just bc the battery is no longer!

You'd need to ride a lot to wear out the battery in 3 yrs. It supposedly loses 20% of its capacity after 25,000 hrs. Still works just doesn't last quite as long between charges.

Fair enough... That sounds pretty solid. I only picked 3 years bc the warranty is good for 2 ;)

If I were interested in an SRM, but wanted 165mm cranks, are the SRM's with Rotor cranks my only option?

Hmmm. How old is your hub, and your head unit? I have 0.1 inch-lb resolution on mine.

It's an SL+, with a Joule GPS+.

Hmmm. Isn't SL+ prior to the G3's? I think they've been reporting at 0.1 inch-lb resolution for a pretty long time.