coppercook62

I was thinking of getting one just to play around with. I know its not as accurate as a true power meter but the reviews seem taylored to the kind of rides I do. My question is do you get the one with speed sensor or does it not matter. Thanks for your replies.

jmX

Do you need a speed sensor? If so, go ahead and get one. If not, don't. The powercal itself has nothing to do with a speed sensor, and I'm not really sure why they even offer one in a package. If you've got a Garmin Edge, then you could just use GPS speed and live without cadence.

coppercook62

Thanks

gadabout007

A extremely cheap friend of mine bought the powercal and has been telling me for the last month how great it is and how I've wasted so much money on my two powertaps.

I borrowed the strap for the weekend so yesterday I did my Saturday workout with the powercal on my garmin 500 and the powertap on the my joule.

Powertap 58 minute workout

Average Power 217
Peak Power 941
5 Second 793
1 Minute 322
5 Minutes 278
20 Minutes 239

Powercal 58 minute workout

Average Power 231
Peak Power 1148
5 Second 974
1 Minute 397
5 Minutes 302
20 Minutes 263

My best recorded 20 minute threshold test was 244W in June of this year. My last test two weeks ago was 236W and it almost killed me hitting that number. If every possible variable was in my favor, there's still no way I could sustain 263W for 20 minutes. My best recorded PPO is 1326W which was oddly a one off and I haven't hit close to that number since. The 941W the the powertap recorded was when I sprinted through a yellow light and can guarantee that I didn't go over 1000W even for a second.

There were several times that I noticed that it was reporting power when I was coasting/recovering between intervals. It's a neat toy but the data collected is totally inaccurate and therefore useless for a serious training program or gauging your progress.

achoo

That's not "totally inaccurate". That's about a consistent 10% higher than the numbers you get from your PowerTap. Ummm, how do you know your PowerTap isn't reading 10% low?

Yeah, the PowerCal is not as accurate over short intervals as a PowerTap. But the PowerCal is also an order of magnitude less expensive.

DaveWC

Under those conditions the Powercal was 10% high. Next time, under different conditions it could be 10% low. If you relied solely on the Powercal you'd never know which it was doing. So your best 20 mins could be anywhere from 215-263 resulting in a FTP from 204-250. Given that all of your power zones run off of this number and the range of accuracy for the FTP and given that the watts displayed on a given day could be +/- 10% I don't see how you could train with this. It would be like having a calculator that gave a result that was +/- 10% of the actual number. Would you want such a calculator at any price? I guess if you just want to see a power # and you don't care that it isn't meaningful it would be ok, like the temperature reading on my Garmin 500... I know it's wrong but if it goes up while I'm riding I know the temp is rising.

jmX

When it first came out I logged a highly structured test ride on both a powertap and powercal at the same time, just to see how much it might be off.



And also 75minutes of 'riding around', no structure.

achoo

Where's the evidence supporting that assertion?

Just because it's off by 10% (or was it the PowerTap that was off? Gee, we don't know...), that does not make it inconsistent.

LowCel 

It's pretty safe to assume if one of the two is off it isn't going to be the one with strain gauges.

coppercook62

After messing around with it I came to conclusion its a neat toy but not really what I was looking for. Time to save up for a real one.

achoo

Interesting data. But there are a lot of relatively high-power/short-duration intervals in both those examples. Exactly the types of rides the PowerCal won't do well on.

I'd like to see 2x20 where your NP is not much higher as your AP - i.e., no 1 kW 5-sec power excursions that drive up NP and therefore IF and TSS but don't really do much otherwise.

Then compare the two outputs.

Heck, how about a 90-min z2 ride on a trainer? AP = NP = 180W, w/ max 1 sec power 190W.

Why do so many seem to have a need to throw rocks at a relatively inexpensive training aid that looks like it can provide 90% of what a power meter does for less than 10% of the cost? I own an SRM and a PT, and I don't feel bad about someone getting a tool that for $100 provides 90% of the data I get from devices I paid a helluva lot more for. Good for them. Knowing that my max 5-sec power is 1724W does what, anyway? Tell me I have a good sprint? Yay for me. No one needs a power meter to figure that out.

If a PowerCal provides consistent enough data to allow accurate training with power over intervals, say, 5 minutes long or longer, it provides data good enough for it to be at least 90% as useful as a PowerTap, Quarq, or SRM.

Because for road cycling, it's aerobic power that matters. FTP too low? You're dropped. FTP high enough? You're doing the dropping.

jmX

The 2nd ride was NP almost equals AP. 60min was 233, while 10min was 251. Basically steady state with maybe 2 short efforts over the entire 75 minutes.

You touch on a critical point, and one my charts are clearly highlighted in pink to show. Short efforts just don't get measured right when it comes to powercal. So, what does? Steady state? Think about this....for steady state the only information it has to go off of is a steady HR. At that point it is worth nothing over a HR monitor. It's only when effort is changing that it can take into consideration the derivative of HR and apply modifiers to the power levels. When i was going steady state at 300w, it says 230w. When I'm doing steady state at 200w it says I'm doing 180w. When I'm going steady 165bpm, how much power does it think im doing? Am I a fat 60 year old newb putting out 140w? Am I Cadel doing a 30mph TT? In 2 years will it still say Im doing 230w at this HR? Of course it will, because all it has is 165bpm coming in for minutes or hours at a time. What else *can* it say? Given this, it will never show me improving, and that sounds pretty depressing (and useless) to me.

The only thing worthwhile of the powercal "algorithm" comes in when the HR is changing, and even then it falls short.

DaveWC

Here's the proof that at one time, under one condition it could be 10% high and other other conditions 10% low (or in this case 20+% low)

I don't knock the device because it's cheaper than what I own. I knock it because it's inaccurate. Would you buy a heart rate monitor that was 10% high one day and 20% low the next? If the number is meaningless the device is useless.

Cowboy905

reviving this thread. I was looking at getting a powercal and yes, the numbers are slightly inaccurate but at the same time, for the price, it's pretty good.

Someone mentioned it's no good if you're fitness training. Wouldn't this be a good tool if you've never trained with power before so you ONLY see these numbers? if it's consistent with itself, i would imagine you could still get some good training out of it and see results.

I think i'm going to get one once i upgrade my Garmin (forerunner 305 can't do power)

Bah Humbug

Just train with heart rate. No need to use fake power...

AdelaaR

Thanks for that review.
Guestimating power from heartrate nonsensical ... so purely by design every sane person knows that the whole "powercal" is just a silly idea ... but your data clearly shows that it is indeed completely useless for any serious use

Cowboy905

but i mean, if you set your bar with 'fake-power' and it's consistent 'fake-power' then theoretically, shouldbn't you be able to see your progress and gains? i'm a very goal driven person and unfortunately with that, i have to constantly see my progress.

i have a trainer at home for the winter and a forerunner 305 watch. I have the HRM which is great but don't have a cadence sensor so all i can see right now is my heart rate.

DaveWC

You assume that the unit is always wrong in the same direction by the same %. What if there is little consistency? It might record 10% high one day and 20% low the next day, maybe because one day you're doing intervals and the next you're just going all out at one speed. Wouldn't that render it useless?

Cowboy905

right.

i did assume that. I thought i read a review somewhere that it is off but it was consistently off...which i'm ok with. But if it's inconsistent and all over the place, it'd be completely useless to me....might as well wear a bra strap.

jmX

I seriously doubt you can use a powercal to track your progress.

When I started, 160bpm would maybe be 220w, now 160bpm might be 280w. How would the powercal ever know the difference?

I wear my powercal during mountain biking and CX races, just so my TSS score is calculated roughly for me, but beyond that I stick to my power meters on everything road related. Even then, I sometimes delete the powerdata from my powercal rides as it screws up my mean maximal power curves, as it might show me peaking at 1900w sometimes.

popeye

My HR is so over the map that PC would be a hundred dollar joke. I have 4yrs PT data but
I have not worn the HR strap 6 times in the last year. The one thing HR does tell me is that if my HR is lagging I need more recovery.

waterrockets 

Just to reach back in time and address this statement: I test my PT with 38 lbs of postal-scale-measured weights hanging off a pedal. I know how far off it is, and it's consistent.

There is no way to zero out a PowerCal. It will be all over the place, and is worth no more than a novelty as far as power is concerned. Even just normal HR drift will show a power increase that isn't there once you start getting dehydrated and hot.