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Home > Forum > Triathlon Forum > Power Difference between Powertap and Wahoo Kickr??

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Power Difference between Powertap and Wahoo Kickr??
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eloon
Oct 24, 14 13:49
Post #1 of 6 (4041 views)
Quick background: I started training with a coach about 6 months ago starting from scratch. I had lactate tests done at that time. The person that did the test used a computrainer (not sure if that's relevant or not) for power as I didn't have a power meter.

After 6 months of training my coach and I decided it was time to update the lactate tests since I've lost a lot of weight and improved my performance. I bought a PowerTap wheel off of eBay about 3 months ago and have been using that with my old power zones from the first test. The person that did my second lactate test yesterday used a Wahoo Kickr to control the power for the test. As such, I didn't have the benefit of recording my power output via my own PowerTap hub.

As I expected, I made significant gains in my power output. However, today I did my first ride in my new zone 2 on my trainer at home (Kurt Kinetic) and it felt way too hard. My HR was in zone 4 to maintain my new zone 2 power range.

So now I'm wondering if either the Kickr was wrong, or my hub is wrong. I have no idea when it was last calibrated since I bought it on eBay.

Does this seem reasonable? Are there any other explanations I'm missing?
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Re: Power Difference between Powertap and Wahoo Kickr?? [eloon] [ In reply to ]
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Mikemartin77
Oct 24, 14 15:44
Post #2 of 6 (3997 views)
Doing a threshold test using someone else's power meter / trainer is a complete waste of time. One of the main reasons for doing this test is to see what you can put out on a unit you can train on.i.e. you know how you stack up vs the "yard stick".

These units can easily be anywhere from 5 - 30 watts different, and from what I have seen with the Kickr, it tends to over-report power output.

The kickr is probably reporting high relative to the powertap. Big deal? I dunno. The test you did was a complete waste of time and you really don't know if you made any progress at all because you haven't tested these units against each other. Granted, it is tougher to test a Kickr vs a powertap. I tested my Kickr vs my SRM, and tested the same SRM vs my power tap. I find that the SRM reports about 5-7 watts higher than the powertap and the kickr reports about 15 watts high relative to my SRM (depending on power level).

You should do threshold tests on the power meter you train on.
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Re: Power Difference between Powertap and Wahoo Kickr?? [eloon] [ In reply to ]
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Dnowak
Oct 24, 14 21:21
Post #3 of 6 (3937 views)
I get about 20watt difference between kickr and my quarq. I add 20 watts to all intervals on kickr to account for this. I only use my quarq for FTP tests. Who knows which is right, but as I race with my quarq, that is what I use to set my zones.
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Re: Power Difference between Powertap and Wahoo Kickr?? [Mikemartin77] [ In reply to ]
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grumpier.mike
Oct 25, 14 8:40
Post #4 of 6 (3863 views)
Mikemartin77 wrote:
Doing a threshold test using someone else's power meter / trainer is a complete waste of time. One of the main reasons for doing this test is to see what you can put out on a unit you can train on.i.e. you know how you stack up vs the "yard stick".

These units can easily be anywhere from 5 - 30 watts different, and from what I have seen with the Kickr, it tends to over-report power output.

The kickr is probably reporting high relative to the powertap. Big deal? I dunno. The test you did was a complete waste of time and you really don't know if you made any progress at all because you haven't tested these units against each other. Granted, it is tougher to test a Kickr vs a powertap. I tested my Kickr vs my SRM, and tested the same SRM vs my power tap. I find that the SRM reports about 5-7 watts higher than the powertap and the kickr reports about 15 watts high relative to my SRM (depending on power level).

You should do threshold tests on the power meter you train on.
PowerTap measures power after the frictional losses of the drivetrain, so chain and jockey wheels. These are probably about 7-9 watts, so your PT and SRM measurements are consistent.
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Re: Power Difference between Powertap and Wahoo Kickr?? [grumpier.mike] [ In reply to ]
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Mikemartin77
Oct 25, 14 8:48
Post #5 of 6 (3859 views)
like Duhhh
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Re: Power Difference between Powertap and Wahoo Kickr?? [Mikemartin77] [ In reply to ]
Quote | Reply
Richard H
Oct 25, 14 9:17
Post #6 of 6 (3844 views)
Mikemartin77 wrote:
Doing a threshold test using someone else's power meter / trainer is a complete waste of time. One of the main reasons for doing this test is to see what you can put out on a unit you can train on.i.e. you know how you stack up vs the "yard stick".

These units can easily be anywhere from 5 - 30 watts different, and from what I have seen with the Kickr, it tends to over-report power output.

The kickr is probably reporting high relative to the powertap. Big deal? I dunno. The test you did was a complete waste of time and you really don't know if you made any progress at all because you haven't tested these units against each other. Granted, it is tougher to test a Kickr vs a powertap. I tested my Kickr vs my SRM, and tested the same SRM vs my power tap. I find that the SRM reports about 5-7 watts higher than the powertap and the kickr reports about 15 watts high relative to my SRM (depending on power level).

You should do threshold tests on the power meter you train on.

Two points I want to make here.

First, this illustrates exactly why accuracy is so important. They should be accurate, if they are not they shouldn't be called power meters. People may not want or be able to use the same power meter for all their training.

Second, if you can measure power, why do lactate tests?
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