New powermeter rumours

Discuss light weight issues concerning road bikes & parts.
sungod
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by sungod

interesting...

http://www.bikeradar.com/road/news/arti ... ent-37819/

...it gets gps, but only for logging, no navigation/mapping etc., surely it will still reduce run time before recharging, but seems a reasonable compromise

maquisard
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Location: France

by maquisard

SRM, coming to the market with design features five years after everyone else...

by Weenie


mentok
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by mentok

you will, almost certainly, be able to turn GPS off either via button combos, menus or SRMWin.

no mention of custom screen configuration and no mention of programming training sessions rules out any potential interest i may have had.

Geoff
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Location: Canada

by Geoff

@Tinea Pedis, we haven't had it before, though. Nice kit!

@maquisard, yeah, but Garmin is a company that is based upon GPS technology (no PowerMeter, though)...

senator52
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Joined: Tue May 24, 2011 1:38 am

by senator52

On the new Dura-Ace 9000 SRM cranks are you able to swap the chainrings (between a 53/39 to a compact setup) without having to send it back to get recalibrated? Or each time you swap, do you need to send it back to SRM.

sungod
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by sungod

you do not need to recalibrate an srm after changing chainrings, i've measured before/after and it's been the same, but maybe it depends on the chainrings to some extent

clean all mounting surfaces to ensue there's no grit/whatever in there and be sure to follow srm's instructions for chainring bolt torque

you may see a difference in zero offset, but slope should not be affected

you can always self-calibrate, just need an accurate heavy weight (hint: if you have accurate scales that will not take the full weight needed, you can weigh smaller ones, like 2-3kg dumbbell weights, and use several together, then you'll have a heavy weight accurate to a few grams)

viewtopic.php?f=8&t=77383" onclick="window.open(this.href);return false;

KWalker
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by KWalker

The PC8 will still be more reliable than a Garmin and have more accurate data collection since it collects and records more data packets per second.

As for calibration, the hanging a known weight method is kind of weird and should always be done with the same weight and same process. My advice to people is to redo it at home as soon as they get their PM if they are going to ever home calibrate in the future. I've seen fresh PMs have their calibration checked at home and have the numbers come back decently off. Apparently there is parasitic bias introduced when you calibrate the unit mounted on a bike vs. a jig in that some of the force is transferred outside of the unit into the bb and frame. Its small and depending on the weight of your weight can lead to inaccurately high reporting. Just a flaw with the method so as long as you use the same one over and over you should be close.
Don't take me too seriously. The only person that doesn't hate Froome.
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ms6073
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by ms6073

sungod wrote:you can always self-calibrate, just need an accurate heavy weight
I use a 45-lbs (~20 Kg) weight that was purchased at a local sporting and outdoor goods store. On the way home I stopped at both a UPS store and then the FedEx store down the street measuring the dumbbell 2 times at each store and always being careful not to drop the weight, I now use the average derived from those 4-trials each time I re-calibrate our powermeters.
Michael - The Anaerobic Threshold is neither...

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djconnel
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by djconnel

kevinkalis wrote:Am I missing something with all these new power meters coming to market at such high price points?


The Rotor has L-R power and torque "efficiency". I don't think it has instantaneous cadence, which would be needed to properly handle eccentric chainrings. SRM and Quarq both make errors with eccentric chainrings. Of course Powertap doesn't care what you're using, but people like more wheel flexibility.

airwise
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by airwise

Out of interest, what errors to crank based PM's make with eccentric chain rings?

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shoopdawoop
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by shoopdawoop

The formula that power meter use to calculate your output assumes uniform angular velocity. I believe non-round ring have error because this assumption is no longer true.

airwise
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by airwise

Thanks.

But what size of error are we talking about? Given that Powermeters are +/- 2%, drift with temperature, and produce figures that are seemingly read differently by competing devices and download software, how much should we be worried by this theoretical error?

IzzyODT
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by IzzyODT

at 400W it shows about 30W more.
This info is straight from the protour insiders - don't ask why that's just the info I got

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shoopdawoop
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by shoopdawoop

I've heard it is around 10% off on an srm.

KWalker
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by KWalker

airwise wrote:Out of interest, what errors to crank based PM's make with eccentric chain rings?


Power2Max is the only crank-based powermeter that can give accurate power readings with eccentric chainrings.
Don't take me too seriously. The only person that doesn't hate Froome.
Gramz
Failed Custom Bike

by Weenie


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