I also have a PowerCal. Scoff all you like, but the NP readings have been curiously similar to the Stages, so I use that rather than swap cranks.
Probably not a bad bet if you just want an NP and to work out a TSS for a ride, especially given the price. I may check it out. Need a new HR strap anyway. Would it be any different to the values something like training peaks works out based on your HR data though?
I also have a PowerCal. Scoff all you like, but the NP readings have been curiously similar to the Stages, so I use that rather than swap cranks.
Depends on the rides. I'd have thought that the more gradual the changes in intensity, the more HR will reflect the effort. There will still be some errors and things you can't escape from with HR but as you say, in a lot of circumstances HR derived measures of effort aren't too bad at all. NP is itself is a measure not suited to very variable efforts (MTB particularly inappropriate due to a large number of very short, very high efforts) yet people like to blindly apply NP/ IF/ TSS/ etc to everything without any account for the signals measured or how the analysis works...
I've used hrTSS on non powermeter equipped rides and as the guys have said, its accurate enough for a TSS figure to keep your data up to date.
It won't cope well with a couple of sets of anaerobic intervals but for a long steady tempo ride or 2x20 it won't be far off.
Durian rider does a very good comparison video on these and the guy rides ALOT
Stages Cycling Power Meter Review #2:
I've used hrTSS on non powermeter equipped rides and as the guys have said, its accurate enough for a TSS figure to keep your data up to date.It won't cope well with a couple of sets of anaerobic intervals but for a long steady tempo ride or 2x20 it won't be far off.
To be honest though, if you've got access to a PM most of the time, previous experience will tell you to within a few points what the TSS will be. After using a PM for 8+ years I can put the head unit in my back pocket and tell you the NP/IF/TSS for any given ride to 1 or 2% accuracy.
[b]LS - Member
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To be honest though, if you've got access to a PM most of the time, previous experience will tell you to within a few points what the TSS will be. After using a PM for 8+ years I can put the head unit in my back pocket and tell you the NP/IF/TSS for any given ride to 1 or 2% accuracy.
True
Except when it comes to the TSS out of a race for me. It always feels about 50% harder than the true figure 😯
Where hrTSS is pretty much useless too
I've had a P2M for a while now, maybe even a year. It's been absolutely flawless, even after being ridden through an insane reliability ride that consisted of a shit load of nigh hub deep water with the final "puddle" being deep enough to cover my foot at the top of the pedal stroke! The only thing that is irritating is the battery, no one seems to stock 'em.
Dc Rainmaker reckons either P2M or Stages will do the job. However I've been using the P2M with Rotor 3D cranks for 2 and a half years now through all sorts of weather and in the Alps with no problems so if I were getting another power meter I'd probably go for another P2M.
What's the crack with the battery on P2M? The DCRainmaker review mentions it has to be a certain brand, but surely not?
Ya, it's got to be a Renata CR2450N. I've seen other CR2350's (can't remember if they had the "N" prefix) and they were different, the Renata one is a real chunky sucker with a broad shoulder.
OK ta for the heads up. Less than a fiver from Amazon, just as well coz I've never even heard of the brand.
shame these wont fit
http://www.chainreactioncycles.com/sram-srm-power-meter-double-bb30-chainset/rp-prod51611
It's almost worth trying to adapt to long cranks for that price 🙂
TiRed, did you do anything to calibrate your PowerCal? Ordered one on a bit of a whim as I needed a new HRM anyway and it wasn't much more cash. May come in handy when when riding without a proper power meter.
Planet x have the same cranks for £99 on sale - so really - you don't have to adapt. Insane price. Breaking my heart and mind thinking about it!!!
Didn't realise it was a fairly easy job to swap cranks on an SRM... now that is worth thinking about 😕
Can you hurry up and buy it and get a mate to buy the other one too please
I found pedaling efficiency to be interesting - I was appalling and by concentrating on this saw rapid improvements. This was on an old polar, which was a real rough approximator, but still useful. I increased average speed on my sunday ride by 10% in a few months by concentrating on style...
Cheaper still (than SRAM above) is barrykellet's £99 crank + p2m type s meter w/o crank = £850.
No good for my BSA BB, like.
Cheaper still (than SRAM above) is barrykellet's £99 crank + p2m type s meter w/o crank = £850.
Or the normal P2M for even less. No good for me either, irritatingly.
Rotor do a BB that fits BSA threads and takes a BB30 crank.
The winner for me is still the old P2M in rotor 3ds. The SRAM setup would be a fair bit heavier I think.
I'm in the states in sept...do you think there will be any warranty support issues if I buy over there and bring back to the uk?
Rotor do a BB that fits BSA threads and takes a BB30 crank.
this
plus e13 do one as well, but its a bit shit but cheaper
Yeah, same here. If only Stages were about 400 quid, I'd have brought two or three by now 😕
stages not compatible with a Krampus as i found out the other day 🙁
My powercal is compared with my Stages. Now i have two head units, i'll run some direct comparisons for commuting, training and racing. I have a couple of datasets for srm and powercal, and i have deconstructed their algorithm for one dataset.
I'm in the states in sept...do you think there will be any warranty support issues if I buy over there and bring back to the uk?
You would most likely have to send it back to the US if there were any issues but I think I wouldn't worry about the smallish postage costs vs massive initial saving. Don't think it should cause any problems besides this don't think they should refuse to warranty it just because you are in the UK for example).
i have deconstructed their algorithm for one dataset
So how does the Powercal go about it's business? Do tell 😀
It uses a regression of power as a function of heart rate and its first derivative. I also looked at second derivative, but this didnt improve prediction. It could be incorporated into any HR monitoring head unit
Dunno about having to use a particular brand of battery in the P2M. I use Duracell's in mine and they work fine
Thanks TiRed, I was more just wondering how you actually set the thing up. Is there some sort of field test to calibrate it so it gets an idea of how your HR and power correlates?
Probably a dumb question but has anyone compared the figures strava comes up with as estimated power vs a real power meter? Is it widely different? If it is a consistent variance, like always 10% more or less it is still useful for training and tracking improvements...
Reckon I will pick up a stages when in the us. Random question, anyone know of a shop in San Francisco that would likely have stock of the rival crank?!
If it is a consistent variance, like always 10% more or less it is still useful for training and tracking improvements...
I am no physiologist but I would have thought 10% variance is way above anything useful. No idea how Strava goes about its business but if it has similar outcomes to Powercal described above then it sounds like it would be pretty reasonable for long duration, constant efforts without a lot of short and high power sections. Well... ignoring cardiac drift and so on... which begs the question... why use it over HR on a practical level? I understand the difference in the calculation but does the Powercal tell you anything about your effort that you couldn't have gained directly from HR? I can't really get my head around this
Powercal doesn't use calibration for subject. They tried but found it added no additional accuracy. It sends to ANT+ signals; HR and power, and you can deconvolve power to reconstruct the algorithm (or a rough version of it). I don't know which algorithm Strava uses for HR.
I bought my Stages in the US just as they were launched. Stages have been absolutely faultless in supporting their product, despite two failures, and have sent me replacements immediately. Give a few bike shops a call and ask hem to order you one for collection.
EDIT
does the Powercal tell you anything about your effort that you couldn't have gained directly from HR
It tells me I've stopped at traffic lights 😉
More seriously, it gives me a reasonable 30 sec average power that I have used when on other bikes to fill in data and monitor Normalized Power. It's not going to help with 3sec sprinting efforts.
More seriously, it gives me a reasonable 30 sec average power that I have used when on other bikes to fill in data and monitor Normalized Power. It's not going to help with 3sec sprinting efforts.
I'm not sure on the exact response of HR to effort but HR seems to too slow to respond to even 30s or 1 minute efforts when you look at power and HR side by side. Going from recovery/ endurance pace in to a 10 minute interval at Threshold for example takes around a minute for HR to raise to a stable level which then rises of the duration of the interval (despite constant power). So, the fact you get a 30s moving average of HR is nice but you wouldn't think should relate to power particularly well given that the time it could take for HR to respond to a change in power (the response time and window length together must miss a lot of information). Suggesting too that everyone produces the same power at the same HR is odd too (or at least that an individual will not change their HR/ Power relationship- energy efficiency?- with training). I just don't get it 😕
It looks like it gives some nice different numbers but actually HR isn't such a bad thing for most people to use to gauge effort (is the Stages and Powercal measurements tie up as they seem to above).
Sherwood without power meter - estimated 20m weighted power 270W
Sherwood with a Stages - 20m weighted power 300W
so not that far out, thats the quickest comparison i can make
Dalby - 2:11 lap on the Krampus in the pouring rain - 20m estimated 129W - no HRM data, so i assume some of the estimate comes from that
Dalby - 1:47 lap on Tallboy with Stages 20m 279W
DanW. powercal uses an algorithm based on HR and rate of change of HR. It is rather neat and i read the patent a few times. I use it on 30 sec, but i use my stages on 10 sec averaging
Thanks for all the info TiRed- always interesting to learn more about this type of thing
Powercal doesn't use calibration for subject. They tried but found it added no additional accuracy.
Was just reading that over at dcrainmaker. Wonder how it would work out power then as my HR at a specific power would be very different to someone else's HR at the same power. Am puzzled. Shall give it a go though and see how it does.
I thought that too. So i tested it on a 1st cat racer in a club chaingang with his srm. It was still accurate for summary measures. It is not a power meter, but is better than it has any right to be. I have one on circulation in the club - out with a tt'ist this week, and just ordered another after my HR strap died.
Running two head units to compare was a bigger expense!
Thanks TiRed, sounds like witchcraft to me! I'll run it alongside the powertap and see how it does.
Still no closer to deciding on a proper PM though. The Stages was edging it by being easily swappable between bikes (though complicated by running different crank lengths on different bikes - and you can swap the P2M between cranks) but I've now heard some mixed reviews from club members on theirs.
Sherwood without power meter - estimated 20m weighted power 270W
Sherwood with a Stages - 20m weighted power 300Wso not that far out, thats the quickest comparison i can make
That's quite a way out! IME Strava power is utter bobbins.
This is easy.
One is pretty much futureproof to all bottom bracket standards, measures power from both legs and hasn't had a myriad of issues when it comes to water(though this has been fixed for most, not all).
The other one is a bit cheaper.
Look at the iBike Newton. Accurate, easily moves from bike to bike, fits any bike. And inexpensive. www.ibikesports.com
