# power meter for trainer?



## DesnaePhoto (Jun 11, 2009)

I'm about to pull the trigger on a trainer. Either a Kinetic or a 1up USA (leaning HEAVY towards KK as comments on here indicate regular sanding of roller on the USA. Ick)

Anyway, I do not have a powermeter on my bike(s) but would like to have one that works with the trainer. Primarily for consistency of workouts. Especially since I've hired a coach for a winter training program. 

Coach suggested the iBike, but I can't pull the trigger on a $400 item right now. Not with buying the trainer. What have you used? What do you suggest? 

Thanks


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## kbiker3111 (Nov 7, 2006)

Suggest: http://cgi.ebay.com/PowerTap-SL-Wir...Accessories&hash=item1c16558916#ht_500wt_1156

You could always go the Kurt computer route, or write your own algorithm for speed->power, but they only work on the trainer, aren't super accurate and dont' give you the readout a powertap does.


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## patchito (Jun 30, 2005)

kbiker3111 said:


> Suggest: http://cgi.ebay.com/PowerTap-SL-Wir...Accessories&hash=item1c16558916#ht_500wt_1156
> 
> You could always go the Kurt computer route, or write your own algorithm for speed->power, but they only work on the trainer, aren't super accurate and dont' give you the readout a powertap does.


I'm not sure that the Ibike would work on a trainer. I think the algorithm it uses incorporates wind speed measurement, which you obviously are without when you're stationary. I have my older road bike with the older wired PowerTap wheel more or less attached to my 1UpUSA on a permanent basis. Since it's all wireless now, some older wired versions PowerTaps can be had pretty cheap I'll bet. 

My 1Up is all right, but it doesn't feel all that rock solid. I'd get a KK.


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## oroy38 (Apr 27, 2010)

I use a Kurt Kinetic computer when I'm on the trainer which calculates power.

Really, the accuracy of the measurement doesn't matter. What matters is precision, meaning it's off by the same margin consistently. As long as you have consistent measurement results, then you can structure your training around power.

Sure it's nice to know the actual numbers you're putting out, but what it boils down to is being able to rigidly structure your training around numbers, and as long as the results are consistent, the actual values don't really matter.


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## makeitso (Sep 20, 2008)

Isn't the Kurt Kinetic power meter just a glorified cycle computer? It bases your power via speed which you can find the chart on KK website, or at least that's how I understood it. So if you have a computer that gets a readout via the rear wheel then you shouldn't need the KK computer unless you really need a real time power number vs just correlating it against your speed. 

If you really want a power meter try ebay or craigslist for a wired powertap wheel. Because wireless has come out it has driven the wired version price down dramatically.


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## AdamM (Jul 9, 2008)

> Really, the accuracy of the measurement doesn't matter. What matters is precision, meaning it's off by the same margin consistently. As long as you have consistent measurement results, then you can structure your training around power.


+1 

Yep. If you're just interested in indoors, then speed at the rear wheel works just fine for creating a training program.


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## spade2you (May 12, 2009)

A friend of mine was hoping for good things for his KK PM, but was let down. 

I'd think a real PM might be what you need, but perhaps see what your coach thinks. A major benefit of a PM will be that you can hit the road and still use it.


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## DesnaePhoto (Jun 11, 2009)

oroy38 said:


> Really, the accuracy of the measurement doesn't matter. What matters is precision, meaning it's off by the same margin consistently. As long as you have consistent measurement results, then you can structure your training around power.


Financially, I cannot afford to get a PowerTap. Esp since I'll be going between my road and mountain bikes. Something I will consider when buying wheels. 

Precise measurements (not necessarily accurate measurement -- there IS a difference) will allow me to train with numbers. 

An 80% solution now is better than a 100% solution never implemented.


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## oroy38 (Apr 27, 2010)

DesnaePhoto said:


> Financially, I cannot afford to get a PowerTap. Esp since I'll be going between my road and mountain bikes. Something I will consider when buying wheels.
> 
> Precise measurements (not necessarily accurate measurement -- there IS a difference) will allow me to train with numbers.
> 
> An 80% solution now is better than a 100% solution never implemented.


Precision is really all you need when it comes down to it. Having _accurate_ measurements doesn't really make much of a difference.

Personally, I'd rather have a PM that's adding 100watts consistently, so I can at least feel good about myself rather than think I'm a poor weak bastard.

Even if you can't shell out the extra cash to get one of their computers but you already have a rear wheel based computer on your bike, you can still use those speed numbers and apply the formula that KK has on their site (Avg. Speed for Avg. Power and so on). The KK computer uses speed as the basis for their power conversion because the computer calculates power as a function of speed, with the restriction that the equation only works on their specific power curve accurately and precisely.

You can use the same formula on other trainers, and it will be precise, but not accurate, assuming you don't perform and resistance adjustments as is possible with some trainers.

I'm actually thinking that you can probably use their power calculations on the road too assuming you perform another FTP test on the road using their computer's numbers. It'll still be precise, just off by a different margin.


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## simonaway427 (Jul 12, 2010)

If you have a Kurt Kinetic, just use the website formula - or go all out and get a proper power meter.

I made an excel spreadsheet based on the KK formula, taped it to my wall next to the trainer. A quick glance at the chart based on my cyclocomputer speed tells me the power I'm making.


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## hrumpole (Jun 17, 2008)

I did the exact same thing. But boy do I covet a PT.


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## PissedOffCil (Jan 3, 2008)

I calibrated a speed->power curve for the 1UP using a Powertap. Results can be found here :

http://www.zonefivesoftware.com/sporttracks/forums/viewtopic.php?p=50833#50833

I''ve started building a power->speed zones Excel spreadsheet to automate the job of getting speed zones that I can then set in my Edge 705. It works very well, I'll add it to the same thread when complete.


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## burkeqc (Sep 25, 2006)

I did exactly what AdamM explained in his reply with a rear wheel speedometer. For consistant results, the same rear tire must be equal pressure each session & if the bike is remounted, the screw setting the resistance to the roller must be the same as previous.


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## iliveonnitro (Feb 19, 2006)

My KK was off by 5% (too low) compared to my powertap. I never checked its precision...or if I did, I don't remember the results.


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## PissedOffCil (Jan 3, 2008)

PissedOffCil said:


> I calibrated a speed->power curve for the 1UP using a Powertap. Results can be found here :
> 
> http://www.zonefivesoftware.com/sporttracks/forums/viewtopic.php?p=50833#50833
> 
> I''ve started building a power->speed zones Excel spreadsheet to automate the job of getting speed zones that I can then set in my Edge 705. It works very well, I'll add it to the same thread when complete.



Here is the spreadsheet : http://www.zonefivesoftware.com/sporttracks/forums/viewtopic.php?p=52016#52016


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## Bruce2 (Jul 6, 2006)

I did some testing with my powertap and Kurt Kinetic. In addition to the powertap (for measuring wheel speed) I used a good old-fashioned bike computer. Wheel Speed reports were identical.

Based on the power curve (published by Kurt), the powertap readings I am getting are consistently 11% lower than as estimated by the wheel speed! While I agree that precision is important, and accuracy is not, it would be nice to know which measurements are accurate (I'm hoping it is that my PM reads low)!


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## PissedOffCil (Jan 3, 2008)

A lot depends on the setup. Last night I got my first ride with my new Powertap. So I get on the trainer on which I trained using speed but because of the slightly larger tire/rim? I needed to move my flyweight. I also swapped tires to a trainer tire.

So I go and do my 2x20. It feels a lot easier to get up to speed than normal. Once up to FTP, it felt a bit easier than what was provided by the power curve I had calibrated. After the ride I send the workout ot the PC. I was very surprised to notice a 40 watts difference between recorded & speed based power, that is over 15% difference.

So, the slight changes in setup lead to a big difference in power required to get a certain speed, 40 watts less @ FTP. Keep this in mind. Personally I'm glad to have my PM now and to have results I trust.

P.S. I'm also glad I was training harder than I thought and it explains the difficulty I had training @ FTP in the past weeks. I would have been pissed had the results been inversed.


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## pwork (Feb 25, 2009)

PissedOffCil said:


> I was very surprised to notice a 40 watts difference between recorded & speed based power, that is over 15% difference.


The wifey just did the same thing...had been using the KK computer and just put on a PT. Her FTP was off 50w in a test (but she had been sick). We still ride in the cold so she was taking the bike on and off. Nice to have the PT now for some consistency.


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## PissedOffCil (Jan 3, 2008)

Yeah, I must say though that I doubt my speed calibration was off by much but since I changed the whole setup it certainly had an impact. My guess is that it was off by at most 10 watts but it's good to have a consistent reading and not having to pay too much attention to the setup anymore. Yesterday for inst6nace my tire started slipping, I could jsut tightren the roller back a bit and I knew my readings we're still valid. Had I used the pwoer it would have had an impact.


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## robdamanii (Feb 13, 2006)

I have to say, my Kinetic Road fluid trainer is probably the nicest trainer I've been on. No comment on the computer module (I went Powertap route) but to echo everything else:

The absolute value is not important. Consistently repeatable data is the biggest factor.


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## spade2you (May 12, 2009)

iliveonnitro said:


> My KK was off by 5% (too low) compared to my powertap. I never checked its precision...or if I did, I don't remember the results.


Think there could be that much difference with tire and wheel variables?


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## rbart4506 (Aug 4, 2004)

Just had a look at my PT numbers from last night's trainer session, I also have a KK, and my wattage numbers off my PT are about 15% lower the the KK power curve...

That explains why I'm hurting this year compared to last even though I'm using the same FTP as a basis for training...


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## framesti (Jan 26, 2009)

my trainer eats up tires


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## robdamanii (Feb 13, 2006)

framesti said:


> my trainer eats up tires


Use a trainer tire.


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## iliveonnitro (Feb 19, 2006)

I'll report back on Tuesday what the calibration is like. I'll just do the test again.


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## Blue CheeseHead (Jul 14, 2008)

simonaway427 said:


> If you have a Kurt Kinetic, just use the website formula - or go all out and get a proper power meter.
> 
> I made an excel spreadsheet based on the KK formula, taped it to my wall next to the trainer. A quick glance at the chart based on my cyclocomputer speed tells me the power I'm making.


+1. I printed out a spreadsheet that shows power at .2mph intervals.


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## Blue CheeseHead (Jul 14, 2008)

framesti said:


> my trainer eats up tires


Use tires that are too warn for the road.


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