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PostPosted: Fri Jul 11, 2014 11:37 pm 
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Location: Bremerton, WA
I am in the market for a new power meter, and in true WW fashion, I am very concerned about the weight penalty incurred by using a power meter vs. normal equipment. This site: http://www.cyclingpowerlab.com/powermeterreviews.aspx has a lot of information laid out for different power meters, *including weight penalty.

*The weight penalty numbers used are only from individual examples, so we can treat these as nominal values :smartass:

Per standard procedure, I created a table for cost/weight saved for various PM's, using a 300g weight penalty as the benchmark. The prices are approximate.

Results (PM, ~cost, ~WP, ~$/g, comments):

Stages, 800, 20, 2.86, vs. standard crankarm
Powertap 800, 71, 3.49, vs. Dura Ace 7900 hub (heavy)
Garmin Vector, 1400, 28, 5.15, vs. Keo2Max Carbon
Polar/look, 1500, 77, 6.73, vs. Keo2Max Carbon
Power2Max, 1000, 206, 10.64, Rotor 3D+ cranks
SRM, 2500, 80, 11.36, Dura ace 7900 crank
Quarq, 1500, 228, 20.83, FSA SL-K Light crank

The results have me leaning towards a powertap (on ebay for $600 usd right now). The left only thing kinda turns me off of stages, and I'm not interested in pedal based systems at this point. Powertap would also allow me to switch wheels between TT and road rigs easily.

Thoughts?

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PostPosted: Sat Jul 12, 2014 1:12 am 
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Location: Seattle, WA | Gjøvik, Norway
Nice comparison chart. It sounds like you already made up your mind based on good criteria. I am completely new to power meters myself, so cost and simplicity were my two deciding points. So I was tempted by a good deal on an almost new Stages SRAM GXP crank arm on eBay. I consider it an experiment. It means I will have an aluminum left crank arm, and carbon right, but in addition to the price and the simplicity, the reviews seem good. It fits well with my Garmin Edge 510. If it doesn't work out, the re-sale loss won't be too great.

I don't really need a power meter, being forever weaker from a heart valve replacement surgery, and a high tech carbon leaflet valve (lightweight!) ticking audibly in my chest. But as many hours as I spend on the bike, and the progress I have still made, I figure it can't hurt to improve my poor training methods, even if at a much lower level than strong riders.

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Posted: Sat Jul 12, 2014 1:12 am 


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PostPosted: Sat Jul 12, 2014 1:35 am 
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looks good. keep in mind, powertap restricts your wheel options. if you really get into it then you will ALWAYS want power so swapping wheels to race becomes an issue. this also means that every new wheelset comes at an $800 premium. this starts to make other options look more appealing from a cost perspective. this also assumes that you go through wheels at a faster rate than you go through hubs and it assumes that you don't have heaps of different bikes that makes swapping power cranks harder than swapping power wheels.

also, i personally see stages' L/R estimation as too much of a functional limitation to make it a valid option. for normalized power, TSS and stuff like that it's probably good enough, but if you're doing really specific interval sessions i fear it's not good enough due to existing or induced L/R imbalances. YMMV though...


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PostPosted: Sat Jul 12, 2014 1:40 am 
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My PT adds about 400 grm to the equation. I only use it for training purposes, so it doesn't count if I ever go climbing or elsewhere for a ride outside of when I'm looking at the numbers.


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PostPosted: Sat Jul 12, 2014 4:14 am 
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The Powertap G3 hubs are only 325 grams, so only about 150 grams heavier than even the lightest of hubs. So far it seems to be on par with most crank based systems (besides Stages, which I am not into)

I think I'd be okay with only having power on one wheelset, since I mostly want it for training and maybe time trials. I know my body well enough to gauge my efforts in road races, crits, etc.. The power meter will be first and foremost a training tool. Although it does sound pretty sweet to always have power on your bike even through wheelset upgrades, etc. That being said, my other favorite option is the power2max, which is somewhat affordable, but nowhere near as cheap as powertap.

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PostPosted: Sat Jul 12, 2014 5:15 am 
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dgasmd wrote:
My PT adds about 400 grm to the equation. I only use it for training purposes, so it doesn't count if I ever go climbing or elsewhere for a ride outside of when I'm looking at the numbers.


you must have an old one... G3 weight 325g


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PostPosted: Sat Jul 12, 2014 5:43 am 
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As another point of reference, my specialized SRM spider weighs approximately 80g more than the stock spider. The crankset is also light (arms, spindle...plus your choice of rings). That is for a 110 bcd version. The 130 is 20 or 30g heavier. Don't have my numbers in front of me but those weights are about right.


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PostPosted: Sat Jul 12, 2014 6:12 am 
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Get a stages it only adds 14 grams. And if your pedaling is half decent it should be accurate. It is also super user friendly. And let's face it if it's good enough for team sky it's good enough for you.


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PostPosted: Sat Jul 12, 2014 2:36 pm 
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You should add up the reliability factor. My Powertap has been if for service 5 times since I purchased it. The best thing that happened to that wheel, is that it was stolen with my bike.

Now the insurance company is buying me another set of Vectors. Maybe a weight/cost penalty but a much higher in reliability.


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PostPosted: Sat Jul 12, 2014 2:38 pm 
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Image

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Weight delta depends, of course, on reference. For Powertap, if you have multiple wheels, for example carbon fiber aero and light carbon fiber race wheels and a few sets of Al-rimmed training wheels, the weight penalty would apply if you get Powertaps for all of them, but if you're going to restrict yourself to a single PT hub, then you need to compromise on wheel choice, and that means a big penalty relative to the race wheels (or else trash your expensive, delicate race wheels training on them). And, obviously, if the race wheels have Extralite hubs, then the penalty will be much larger than for Dura-Ace.

BTW, I've got a PT wheel and my GF has one, and although mine tested out of calibration on a torque test (hers is spot on, and also tested well against Vector), I've never had any reliability problems on the hub itself.

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PostPosted: Sun Jul 13, 2014 3:22 am 
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Things to consider:

-You're going to want to have power ALL the time and this includes at races. A wheel-independent system will always be on your bike and provide you more data points as you'll never be limited by wheel.

-Lest you're planning on doing some very specific left/right leg training you won't need left/right data.

-Customer service and product reliability WRT power meters is huge- if your PM is out of service for a week while you're training what good is it.

Of course you'll have to make the final decision but my experience having owned PowerTaps, a Quarq and now a Stages is that the PowerTap was only useful as an entry -level device. Limiting my wheel selection was a big factor in races and as such I didn't have an data from races for a full season. The PowerTap was also into service several times a year when the torque tube failed or the electronics shorted. They were always great about getting me a new one gratis but I lost the PM for a week every time and that was terribly frustrating.

The Quarq was amazing. I had data all the time, the weight penalty was almost nothing and it was totally reliable. It did have trouble with temperature compensation but I understand that the new models handle that better than the early ones. The customer service (before SRAM bought them) was great. when my teammate's quarq failed they overnighted him a loaner one and repaired his gratis and got it back to him in two days.

The Stages is great too. There's really no weight penalty, I have data all the time and their customer service is fantastic. When my battery housing cap cracked they overnighted me a new one along with a prepaid return label for the old one. I don't notice any issue with the left x2 model that they employ- my power readings are totally useable and I haven't seen anything that would convince me that their algorithms are off. The only thing I have found is that the Stages is a bit slower on the uptick- that is, it takes a second or two to register your power as it relies on the left leg. This really isn't an issue for most of one's training, and the only time I can see it being one is for very short repetitive intervals. That said, the device seems to read longer than others so perhaps it's compensating for the first missed second or two.. I dunno.

Anyhow, the on e thing to remember about all power meters is that they're just tools and you need to learn how to use them- do some reading hook up with a seasoned power meter user or a coach and really try and understand the $1k purchase you just made.

G'luck!!


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PostPosted: Sun Jul 13, 2014 4:02 am 
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I run a powertap g3 with 45mm enve classic tubular wheels I love them. And they are super light 1250 grams


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PostPosted: Sun Jul 13, 2014 4:19 am 
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Hmm, my calculation for Garmin Vector gives me a different penalty:

Claimed weights:

Pedal: 152g
Pod: 23g
total: 175g

Keo Ti: 95g

penalty: 2x80g = 160g


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PostPosted: Mon Jul 14, 2014 5:28 am 
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Location: Bremerton, WA
Yeah, I didn't spend too much time with the whole weight penalty thing, I was just going off what the site listed.

It would be nice to have power all the time, but that would mean I'd have to eventually get one for the TT bike as well. Right now cost is a lot more prohibitive than preference. I will reconsider Stages.

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Posted: Mon Jul 14, 2014 5:28 am 


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PostPosted: Mon Jul 14, 2014 5:57 am 
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I think the delta weight unfairly penalises quarq, which is one of the lighter options. When I changed from specialized carbon spider 130bcd (55g) -> s works quarq spider 130bcd (137g) I gained 82g. BUT I not longer needed the garmin speed/cadence sensor to give me my cadence (29g) So total gain was 53g from a non-power meter setup.

My stages added 27g, because I went from a SISL non-drive (143) to an SI(170g) non-drive side crank as they had stopped producing stages SISL/SISL2 arms.

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