Thinking about getting PowerTapped up...
Comments
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Captain Fagor wrote:Jesus, this thread is enough to put anyone off buying a powermeter.
Personally, I don't want to be shell out a large amount of money, only to have to be fannying around calibrating equipment, installing software, doubting the data produced, etc etc.
TBH if the thought of installing a bit of software and calibrating occasionally puts you off a power meter then you probably wouldn't get much out of owning one anyway.More problems but still living....0 -
To be fair, an operating system emulator (as is seemingly required for a meaningful calibration) doesn't sound like your average software installation though.
I like the thought of having power data (albeit only if collected from a transferable unit such as metric gear's concept), but for the financial outlay I really could do without all the apparent associated hassles.0 -
Perhaps you didn't read the thread closely enough.Captain Fagor wrote:To be fair, an operating system emulator (as is seemingly required for a meaningful calibration) doesn't sound like your average software installation though.
I like the thought of having power data (albeit only if collected from a transferable unit such as metric gear's concept), but for the financial outlay I really could do without all the apparent associated hassles.
If you use the bar mounted computer that comes with that power meter (e.g a Powertap CPU with a Powertap power meter), then the calibration check is fairly trivial process.
It's no different to checking a set of bathroom scales is reading correctly. i.e. zero mass reads as zero and a given known mass reads correctly.0 -
Alex_Simmons/RST wrote:
Perhaps you didn't read the thread closely enough.Captain Fagor wrote:To be fair, an operating system emulator (as is seemingly required for a meaningful calibration) doesn't sound like your average software installation though.
I like the thought of having power data (albeit only if collected from a transferable unit such as metric gear's concept), but for the financial outlay I really could do without all the apparent associated hassles.
If you use the bar mounted computer that comes with that power meter (e.g a Powertap CPU with a Powertap power meter), then the calibration check is fairly trivial process.
It's no different to checking a set of bathroom scales is reading correctly. i.e. zero mass reads as zero and a given known mass reads correctly.
Hardly trivial. There is much that can go wrong.0 -
Alex_Simmons/RST wrote:Perhaps you didn't read the thread closely enough.
If you use the bar mounted computer that comes with that power meter (e.g a Powertap CPU with a Powertap power meter), then the calibration check is fairly trivial process.
It's no different to checking a set of bathroom scales is reading correctly. i.e. zero mass reads as zero and a given known mass reads correctly.
That doesn't sound like calibration of power measurement to me. Yes it's zero'd, but as you say yourself (below), that doesn't guarantee the accuracy of the readings once loaded.Alex_Simmons/RST wrote:No, because all that is telling you is the zero loaded value. It does not tell you a loaded value and therefore whether the meter is reporting accurately.
For a non-user of powermeters like myself, how long would a powermeter be relied upon to perform accurately? Or to put it another way, would owners have to perform regular calibration (i.e. zeroed) and validation of loaded readings once the unit had been in service for (say) a couple of years?
If the answer is "yes" to the latter question, then data would potentially be inconsistent with time, which is obviously not good. IMHO, this would undermine the credibility of what is an expensive product unless the need for periodic calibration/validation was made clear in the advertising blurb. It's not good enough to find out about these things in the small print of the owner's manual after you've shelled out the cash.
I'm hoping you can tell me that none of these points are a genuine concern. That way I can keep aspiring to own a power meter at some point in the future.0 -
@Captain Fagor that first quote Alex's finshes with this:zero mass reads as zero and a given known mass reads correctly
The given known mass reading correctly is a stomp test so you have both parts of the equation. You know if the power meter reads zero when no torque is applied by checking this on the computer and you then do a stomp test to to check that a known weight over several gears are correctly displayed (with a bit of maths). It's this bit I wouldn't class as trivial myself however I guess it's a matter of opinion.
Zeroing should be done as a matter of rountine. On the powertap you simply spin the back wheel then press and hold the right button on the watts row until it flashes (all off the bike). When it goes to zero hit that button again. Get on the bike and ride. Takes seconds and becomes routine.
As for how accurate they are. Well they are pretty robust generally however I've had 3 powertaps in a year so not that impressed myself though I wouldn't be without it
It was obvious to me that they were not working right so no stomp test required to confirm what I knew. 0 -
Thanks doyler78.
For some reason, I wasn't absorbing the full meaning of that (very eloquently worded) sentence until you pointed it out. To me, it's a bit of a leap of faith that because it reads as zero when unloaded that it will also give accurate measurements once loaded. However, if that's what the manufacturers say, then fair enough.
The whole calibration / validation issue is something I'll keep in the memory banks for whenever I begin to seriously consider purchasing one.0 -
Captain Fagor wrote:Thanks doyler78.
For some reason, I wasn't absorbing the full meaning of that (very eloquently worded) sentence until you pointed it out. To me, it's a bit of a leap of faith that because it reads as zero when unloaded that it will also give accurate measurements once loaded. However, if that's what the manufacturers say, then fair enough.
The whole calibration / validation issue is something I'll keep in the memory banks for whenever I begin to seriously consider purchasing one.
Yeah leap of faith however, whilst not mass market products, they still have a lot of people using and in the main they have tended to be highly technical people so if there were real issues with consistency and/or accuracy I expect they would have been screaming from the roof tops. Just look at any discussion of Garmins headunits when used for power recording to see just how hot a debate can become over accuracy and/or consistency
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I own or have owned 5 SRMs and 10 Powertaps. I also coach or have coached many dozens of riders with all the major power meter types and so get a pretty broad spread in terms of what's reliable.Captain Fagor wrote:Or to put it another way, would owners have to perform regular calibration (i.e. zeroed) and validation of loaded readings once the unit had been in service for (say) a couple of years?
By and large, the PT and SRM are pretty good. There are some specific issues that have crept up at times over the years (mainly PT) but usually addressed by the manufacturer. Quarq is still pretty new - they are working very hard to be very good at supporting and backing up their product. There have been teething problems as experienced by my clients with them.
My 5 year old Powertaps are as accurate as the day I got them. My even older track SRM is just as accurate as when it started out - although its slope has drifted ever so slightly over the years.
I had two Powertaps fail in 2006, which were both replaced under warranty. I have another that's gone back for warranty repair this year. The SRMs have only ever needed battery replacement roughly every 2 years.
In general, out of the box the PTs are pretty good. SRM's factory calibration used to be a bit off once installed but that seems to be better now days with all the new models.
No matter - it always pays to check - it's not overly difficult (OK maybe not trivial), but hanging a known mass from the pedal spindle, reading the torque number and entering into a spreadsheet along with the zero reading ain't that hard to do.
Disclosure:
I sell SRM and I hire out Powertaps0 -
Thanks for the information - very helpful. My confidence in the units (and desire to eventually buy one) has been reinstated! 0
