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Re: "Best" power meter - money no object [RChung] [ In reply to ]
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If you work through the math (taking into consideration typical wheel and crank RPM), the zero offset resolution of a PowerTap hub is only about 1/10th that of the average SRM crank.

IOW, a fair bit of error can still be hidden in the offset of a "properly zeroed" PowerTap.
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Re: "Best" power meter - money no object [Newduguy] [ In reply to ]
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I’ve used rims from Open Pros (28 2x) to Flo 90s. (Full carbon 24h 2x Sapim CX-Rays). Both of those build up very nicely. I’d not be averse to racing on the Flo. I’m not a big fan of covers for myself. I’d pair that with a 60-70mm front.

If you go for a deep section carbon rim, make sure it’s not a faired type because the larger flange on the G3 will mean that the spoke holes won’t line up with the fairing for you.

As noted, some of the prebuilt Powertap wheels are pretty good in their own right.

Developing aero, fit and other fun stuff at Red is Faster
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Re: "Best" power meter - money no object [Andrew Coggan] [ In reply to ]
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Andrew Coggan wrote:
jens wrote:

If money is no object, the answer isn't one powermeter, but several. First, get a hub-based powertap for each rear wheel you will be using. Then, just so you can keep an eye on drivetrain friction, get an SRM or Power2max.

IMO, there is no substitute for a Powertap hub when it comes to field testing - particularly Chung testing. Crank and pedal based power are too loosely correlated with what actually gets to the wheel to be useful for many things.

If I had relied on my SRM alone, I would have blithely gone through life believing that Q-Rings and Osymmetric Rings were actually gaining me an extra 20 watts. The powertap set me straight on that. Looking back, the rolling resistance tests I did with the SRM are far more variable than the Powertap tests, which were dead-on repeatable.


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

I've often read that non round q rings would possibly decrease the accuracy of crank based pm readings. On the other hand P2M has stated various times that readings are not compromised by oval chain rings. My personal n+1 is: I'm riding a P2M with q-rings on a Tacx Neo. I'm not seeing differences of 20 watts between devices. Both power meters are rarely exactly identical in their reading, one is also somewhat slower than the other in picking up drastic changes, like at the start of a sprint. But using 30s rolling averages on a normal zwift training ride I rarely see differences exceeding 7 watts, (often they're closer) which is well within their respective 1% stated accuracy if you take into account a little bit of drive train loss.
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Re: "Best" power meter - money no object [surrey85] [ In reply to ]
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+1 for power2max. Great fit and forget PM. I have two now, one type s on my CX bike and NG on my tri bike. Both have worked brilliantly.
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Re: "Best" power meter - money no object [surrey85] [ In reply to ]
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P2M uses an accelerometer instead of a Reed switch to determine crank angular velocity, yes?

If they calculate power by multiplying the torque measured at points throughout the crank rotation by the near-instantaneous angular velocity measured at the same point, the data will be noisier, but use of non-round rings should not be an issue.

OTOH, if they simply use the accelerometer data to determine the overall average crank angular velocity (as with a reed switch) then non-round rings will inflate the power measurements, regardless of anything the company might claim.

Alex Simmons would likely know which of these two possibilities is correct. Hopefully he will see this and chime in.
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Re: "Best" power meter - money no object [el gato] [ In reply to ]
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el gato wrote:
If I were interested in an SRM, but wanted 165mm cranks, are the SRM's with Rotor cranks my only option?

I think so, unfortunately. I believe I purchased the last DA9000 SRM pm in 165mm that the CO folks had, and that was almost a year ago.
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Re: "Best" power meter - money no object [Bdaghisallo] [ In reply to ]
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With the switch to Look crank arms on the origin, Look only has their adjustable crank arms down to 170mm (ZED2 crankset).

https://www.lookcycle.com/en/components-bicycles/

While the ability to adjust crank length is awesome, SRM has now made themselves dependent on Look. Honestly, they should have just kept the DA9000 SRM along with the new Origin.

get comfortable being uncomfortable
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Re: "Best" power meter - money no object [stevej] [ In reply to ]
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stevej wrote:
With the switch to Look crank arms on the origin, Look only has their adjustable crank arms down to 170mm (ZED2 crankset).

https://www.lookcycle.com/en/components-bicycles/

While the ability to adjust crank length is awesome, SRM has now made themselves dependent on Look. Honestly, they should have just kept the DA9000 SRM along with the new Origin.

I don't know that SRM had that option. With Shimano introducing their own powermeter, and many of their Protour teams using the SRM DA PM, I don't Shimano were too excited about continuing to produce bespoke cranks for a competitor that might slow the adoption of their own powermeter.
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Re: "Best" power meter - money no object [RChung] [ In reply to ]
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RChung wrote:
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.

Yes, circa 2010 or so. If you put it in testing or calibration mode and display torque you get a decimal like 508.3? I only get whole numbers of in-lb.

The .csv export is in N-m, but it appears the data is converted from 1 in-lb steps. .11, .225, .335, etc. are the lowest values.
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Re: "Best" power meter - money no object [el gato] [ In reply to ]
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I didn't read all the comments but as of late or the updates the Garmin V3 pedals have been flat out amazing for me. They also read within 1-2 watts of my Kickr on any 1hr ride which is great to me. I think they are a fantastic choice "now" and should be considered if you want pedal based.


I think a year or so from now the SRM pedals are going to be killing it - but to me the V3 are the choice with a close following of the Assioma. Garmin really shot themselves in the foot on this deal but I think will make it after everyone forgets haha

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Re: "Best" power meter - money no object [Andrew Coggan] [ In reply to ]
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Andrew Coggan wrote:
P2M uses an accelerometer instead of a Reed switch to determine crank angular velocity, yes?

If they calculate power by multiplying the torque measured at points throughout the crank rotation by the near-instantaneous angular velocity measured at the same point, the data will be noisier, but use of non-round rings should not be an issue.

OTOH, if they simply use the accelerometer data to determine the overall average crank angular velocity (as with a reed switch) then non-round rings will inflate the power measurements, regardless of anything the company might claim.

Alex Simmons would likely know which of these two possibilities is correct. Hopefully he will see this and chime in.
I don't know the real answer.

Many moons ago P2M made a claim about measuring angular velocity data (I'm not going to search for the links to the reference conversation though) but when asked to supply data showing angular velocity measured with a frequency greater than once per crank revolution, they wouldn't.

What I don't know is if that also means they couldn't.

That did not leave me overly convinced about their claim.

I suppose the only way we'll know is for someone with sufficient experimental rigour to perform some tests.

http://www.cyclecoach.com
http://www.aerocoach.com.au
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Re: "Best" power meter - money no object [AlexS] [ In reply to ]
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I have a P2M NGEco power meter, sufficient experimental rigor (I'm a practicing engineer), and some time. Say I wanted to have fun on a Saturday morning and run some tests....

What would I do and what data should I collect? Or is this more of a complex exercise that needs a lot of experience?

I see that P2M does't have a high frequency mode in their app. Is this something that would be required?
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Re: "Best" power meter - money no object [Newduguy] [ In reply to ]
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Newduguy wrote:
I have a P2M NGEco power meter, sufficient experimental rigor (I'm a practicing engineer), and some time. Say I wanted to have fun on a Saturday morning and run some tests....

What would I do and what data should I collect? Or is this more of a complex exercise that needs a lot of experience?

I see that P2M does't have a high frequency mode in their app. Is this something that would be required?
Provided you can do a slope calibration test for each set of chainrings after fitting them and have a way to reliably compare with power delivered to the rear wheel (e.g. a reliable Powertap wheel), that would be enough for an initial set of tests.

http://www.cyclecoach.com
http://www.aerocoach.com.au
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Re: "Best" power meter - money no object [wintershade] [ In reply to ]
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wintershade wrote:
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.

Have you owned one? Serious question.

Battery life of road units is up to 3,000 hours. If you train 20 hours per week, every week of the year, that's 3 years. Most people (a) don't train that much per week (esp on a single bike) and (b) don't train that much year-round. 5 years of battery life is not unusual.

Sending a power meter (ANY power meter) in for a check-up every 5 years is not a bad thing to verify it is to-spec.

Then again, you rarely see meters of many brands that will actually work after 5 years -- a 5-year old SRM still has value on the used market; that's not the case for most other products. That is sad to me as none of these products are inexpensive.

(I own, service and sell a variety of meters, including SRMs. Personally I have several of both road and MTB units in active rotation, going back 7 years. They just work*, which has extreme value to a busy person.)

* - Any electronic device on a bike exposed to the elements can have a problem; SRMs tend to have fewer than most other brands, but they are not completely immune.
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Re: "Best" power meter - money no object [CPT Chaos] [ In reply to ]
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CPT Chaos wrote:
SRM easily. The latest has a replaceable battery to avoid sending it in, which I actually believe is not a good thing. Sending in SRMs every 3-5 years for a battery replacement allows SRM to do a full PMCS on it and I believe that extends the life, as I have 3 SRMs, aging from 10 years old, 7 years old and 1 year old.

I think you mean "rechargeable", not "replaceable", correct?

The latest (Origin) SRM power meter has a rechargeable battery *as an option*.

Some customers insist they want this, but I personally do not use it. Why? The discharge properties of rechargeable batteries are different than regular cells, and the latter tend to retain more consistent voltage over their usable life, which affects power readings.

Unless someone *really* has a special use for it, I advise them to get the non-rechargeable versions.

As you said, sending the meter in once every 3-5 years is actually valuable, though we would all prefer to never send any device in for servicing.
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Re: "Best" power meter - money no object [commendatore] [ In reply to ]
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commendatore wrote:
Does SRM have active temperature compensation yet?


"Yet" would imply that it is necessary.

Their hardware design makes their meter immune to temperature swings. The delta between a morning temperature in my garage vs peak ride temperature can be 50F, yet the zero offset on my SRMs changes <1% (=~3w @ 90rpm) at any point in a ride. I've tested and observed other meters to vary up to 10% for the same conditions -- and even in temperature-controlled environments!

(Yes, I was SHOCKED when I did the detailed testing.)

Software temperature compensation was sold as a feature, but it is using software to solve a problem that did not have to exist in hardware.
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Re: "Best" power meter - money no object [tetonrider] [ In reply to ]
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tetonrider wrote:

The latest (Origin) SRM power meter has a rechargeable battery *as an option*.

Some customers insist they want this, but I personally do not use it. Why? The discharge properties of rechargeable batteries are different than regular cells, and the latter tend to retain more consistent voltage over their usable life, which affects power readings.

Unless someone *really* has a special use for it, I advise them to get the non-rechargeable versions.

I'm no engineer but to me as a layman it would seem like a pretty bad design by SRM if the smallish powerdrop you see on a typical discharge curve of rechargable batteries at very low currents would actually significantly affect power readings. But then most discharge curves you find online seem to indicate that many rechargeable batteries actually have less vdrop than button cells or typical alkaline batteries.

Getting your unit looked at and checked by the manufacturer at certain intervals seems great but having to send it in for exchange of battery seems ridiculous.
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Re: "Best" power meter - money no object [surrey85] [ In reply to ]
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surrey85 wrote:
tetonrider wrote:


The latest (Origin) SRM power meter has a rechargeable battery *as an option*.

Some customers insist they want this, but I personally do not use it. Why? The discharge properties of rechargeable batteries are different than regular cells, and the latter tend to retain more consistent voltage over their usable life, which affects power readings.

Unless someone *really* has a special use for it, I advise them to get the non-rechargeable versions.


I'm no engineer but to me as a layman it would seem like a pretty bad design by SRM if the smallish powerdrop you see on a typical discharge curve of rechargable batteries at very low currents would actually significantly affect power readings. But then most discharge curves you find online seem to indicate that many rechargeable batteries actually have less vdrop than button cells or typical alkaline batteries.

Getting your unit looked at and checked by the manufacturer at certain intervals seems great but having to send it in for exchange of battery seems ridiculous.

I could be mistaken about the voltage drop -- it may be another property of the battery -- but suffice to say that power meters are quite sensitive to battery. anyone that has owned a Quarq and seen even the slight difference in a CR2032 cell (maybe it's an old CR2032 or a different brand) can attest to this.

that said, a "user replaceable battery" was touted as a feature way back when SRMs had battery life of ~1 year. yes, sending in a unit annually was a hassle. doesn't a battery you can replace at home sound amazing?

HOWEVER... how many owners of Quarq units or Stages or any other meter with a "user replaceable battery" have discovered that the battery cover is a common failure point for the ingress of water? almost every user i've known of those meters (myself included) has had one or more fail that way. SRMs *tend* to perform materially better in inclement weather for the very reason that the batteries are NOT easily replaceable by the end user*.

with up to 3,000h of battery life, i'd wager that having to send it in is not really an issue any longer and is only held up by people who want to find a reason not to get an SRM.

and that's fine -- all power meters involve trade-offs.

i'd argue that a non-user-replaceable battery is a FEATURE, not a bug. each to his own, of course.
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Re: "Best" power meter - money no object [el gato] [ In reply to ]
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el gato wrote:
If I were interested in an SRM, but wanted 165mm cranks, are the SRM's with Rotor cranks my only option?


Was just reading through this thread and saw your question again. SRM has recently announced that they will be offering an aluminum Origin crankset for their powermeter and this will be available with both 160mm and 165mm arms.


http://store.srm.de/origin-powermeter.html
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Re: "Best" power meter - money no object [el gato] [ In reply to ]
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IQ2

_________________________
27 years and counting
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Re: "Best" power meter - money no object [el gato] [ In reply to ]
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el gato wrote:
Back when there were only a handful of players in the market, SRM used to be the 'gold standard'. Nowadays, I'm not so sure that's the case any more. It seems to me that the top offerings from many manufacturers rival the accuracy of the SRM, and most don't involve the hassle of having to send in your PM for service periodically. So, if you were to buy a power meter today and had an unlimited budget, what would you buy, and why? For argument's sake, let's assume that it will live on one bike permanently, so things like being able to easily swap from one bike to another aren't a factor.

I’m going to say the Verve InfoCrank and then do some carbon work to make it aero. SRM used to be the gold standard but I find it to be much hassle than its worth at least once a year when I have to send it back for battery issues.

I’ve also heard that Rotor has something new in the works so I’ll hold further judgement until then.
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Re: "Best" power meter - money no object [Ohio_Roadie] [ In reply to ]
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Ohio_Roadie wrote:
I’m going to say the Verve InfoCrank and then do some carbon work to make it aero.

You sure that won't affect the readings? Seems like anything that would effect the stiffness would be bad.
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Re: "Best" power meter - money no object [Ohio_Roadie] [ In reply to ]
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Ohio_Roadie wrote:
SRM used to be the gold standard but I find it to be much hassle than its worth at least once a year when I have to send it back for battery issues.

That hasn't been the case in quite a while. SRM has been producing powermeters with 2K hours plus battery life for a number of years now.
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Re: "Best" power meter - money no object [Bdaghisallo] [ In reply to ]
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SRM also offers rechargeable powermeters.
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Re: "Best" power meter - money no object [Ohio_Roadie] [ In reply to ]
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Ohio_Roadie wrote:
el gato wrote:
Back when there were only a handful of players in the market, SRM used to be the 'gold standard'. Nowadays, I'm not so sure that's the case any more. It seems to me that the top offerings from many manufacturers rival the accuracy of the SRM, and most don't involve the hassle of having to send in your PM for service periodically. So, if you were to buy a power meter today and had an unlimited budget, what would you buy, and why? For argument's sake, let's assume that it will live on one bike permanently, so things like being able to easily swap from one bike to another aren't a factor.


I’m going to say the Verve InfoCrank and then do some carbon work to make it aero. SRM used to be the gold standard but I find it to be much hassle than its worth at least once a year when I have to send it back for battery issues.

I’ve also heard that Rotor has something new in the works so I’ll hold further judgement until then.

Have been quite impressed with the InfoCrank recently installed on my wife's Premier Tactical so far. Just wish it looked sexier.

I'm racing 2019 IM Arizona as part of Team Smile Train. Will I implode? Will I finish strong? Donate to find out more!
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