Power Tap C1 Drifting

Apr 26, 17 6:49

Post #1 of 17 (2337 views)

Hey everyone,

Having an issue with my Powertap C1. It shows a low power reading for the first ~30-45 min of every workout. During that time, if i hold my speed/ cadence steady on the trainer at a fixed gear the power will slowly rise until it reaches the correct power reading where it will be accurate for the rest of the workout. It's almost like its "warming up". I use a fluid trainer and I've heard of those warming up, but that should result in the opposite effect of what I'm seeing. In the attached example from my last 20 min test (ignore the solidly MOP numbers), you can see during the 20 min that even as my speed/ cadence slowly decline my power number still trends upwards until the end where it finally levels out.

For a long ride I suppose this wouldn't be a huge issue, but for all of my 1-1.5 hour sweet spot work on TrainerRoad this problem it presents a huge annoyance. For refrence I calibrate the powermeter before each ride.

Is there some quick fix for this, or will I have to send it back to PowerTap? I don't have a replacement chainring, so If I had to send it back I would be without a bike for a week or two.

Re: Power Tap C1 Drifting [Eyes0fTexas] [ In reply to ]

Apr 26, 17 7:03

Post #2 of 17 (2322 views)

If you have a friend or cycling class you can go to you could compare your power meter numbers to the smart trainer during a 60-90 min. workout. Seems very odd that the numbers would be off for half the workout.

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Re: Power Tap C1 Drifting [Eyes0fTexas] [ In reply to ]

Apr 26, 17 7:04

Post #3 of 17 (2321 views)

Focus on your Power and adjust your cadence accordingly, power is the key metric not speed or cadence, I am sure your C1 is fine. Once your are at the correct power intensity make minor adjustments to your cadence to stay within the correct power zone. The harder your push with a fluid trainer the more resistance your should feel.

Re: Power Tap C1 Drifting [Eyes0fTexas] [ In reply to ]

Apr 26, 17 7:07

Post #4 of 17 (2314 views)

It's your fluid trainer.

Until you get a second power meter, like a Powertap, you'll never know 100%.

I also ride a C1 on a Fluid2 trainer, and if I rode the same cadence at the same gear, I'd probably have the same result. In my unit, the fluid actually gets harder to pedal in the first 10-15 minutes. There is a really easy fix for this: Just change the gear. Variability in resistance is one of the strengths and weaknesses of using a Fluid trainer.

Re: Power Tap C1 Drifting [nickwhite] [ In reply to ]

Apr 26, 17 7:10

Post #5 of 17 (2308 views)

But since it's a chainring based power meter, if the fluid was harder to pedal in the beginning it should result in higher power output with a decreasing trend as the fluid warms and becomes easier to pedal. My situation seems backwards if that was the case

Re: Power Tap C1 Drifting [Eyes0fTexas] [ In reply to ]

Apr 26, 17 7:14

Post #6 of 17 (2305 views)

This is really strange looking. The phenomenon looks like it occurs 30 minutes into the workout. So, by then, any trainer warm-up and device (C1) fluctuations should have long stabilized. Assuming that your gear and trainer resistance are unchanged, the power should not change like it did. The power during the preceding 5 minute interval looks like it matched the starting power of the 20 minute interval, while the cadences and speeds for both are similar.

I vote that something is wrong in your system somewhere. If the C1 is correct, that means that your trainer has some pretty strange behavior. Alternatively, if the C1 is in error, that means it is kind of recalibrating itself while at very low power levels, and then it changes its calibration while under sustained load. It looks like that recalibration period takes at least 10 minutes.

What kind of trainer do you have, and how old is it?

Re: Power Tap C1 Drifting [exxxviii] [ In reply to ]

Apr 26, 17 7:18

Post #7 of 17 (2302 views)

exxxviii wrote:

This is really strange looking. The phenomenon looks like it occurs 30 minutes into the workout. So, by then, any trainer warm-up and device (C1) fluctuations should have long stabilized. Assuming that your gear and trainer resistance are unchanged, the power should not change like it did. The power during the preceding 5 minute interval looks like it matched the starting power of the 20 minute interval, while the cadences and speeds for both are similar.

I vote that something is wrong in your system somewhere. If the C1 is correct, that means that your trainer has some pretty strange behavior. Alternatively, if the C1 is in error, that means it is kind of recalibrating itself while at very low power levels, and then it changes its calibration while under sustained load. It looks like that recalibration period takes at least 10 minutes.

What kind of trainer do you have, and how old is it?

That was kind of my thinking as well. It's a CyleOps Fluid 2, probably about 4-5 years old

Re: Power Tap C1 Drifting [Eyes0fTexas] [ In reply to ]

Apr 26, 17 7:25

Post #8 of 17 (2294 views)

I would figure out some way to put the bike on another trainer to see if the behavior persists. My guess is that it is the C1. The one thing missing from the chart is HR. If your HR is climbing with the power, then that points to a change in resistance (probably a trainer problem). However, if HR is generally flat while power climbs, then the issue is the C1.

Re: Power Tap C1 Drifting [Eyes0fTexas] [ In reply to ]

Apr 26, 17 7:26

Post #9 of 17 (2291 views)

Eyes0fTexas wrote:

But since it's a chainring based power meter, if the fluid was harder to pedal in the beginning it should result in higher power output with a decreasing trend as the fluid warms and becomes easier to pedal. My situation seems backwards if that was the case

My trainer actually adds resistance when it warms up. The older units like mine have a sharp, very noticeable, sudden increase in resistance. Newer units are better in that respect, but will add more resistance as you go, until it is fully warmed up.

Also, how was the temperature during your ride? Did the room you were in heat up dramatically?

One more question, have you checked the firmware version on your C1 with the mobile app?

Last edited by: nickwhite: Apr 26, 17 7:27

Re: Power Tap C1 Drifting [nickwhite] [ In reply to ]

Apr 26, 17 7:33

Post #10 of 17 (2282 views)

nickwhite wrote:

One more question, have you checked the firmware version on your C1 with the mobile app?

On that note, is Power Tap ever going to release an android app? Two years and 2 power taps on 2 bikes and no love for the android. It makes me wish I had brought another Quarq.

"...the street finds its own uses for things"

Re: Power Tap C1 Drifting [nickwhite] [ In reply to ]

Apr 26, 17 7:37

Post #11 of 17 (2277 views)

nickwhite wrote:

My trainer actually adds resistance when it warms up. The older units like mine have a sharp, very noticeable, sudden increase in resistance. Newer units are better in that respect, but will add more resistance as you go, until it is fully warmed up.

Also, how was the temperature during your ride? Did the room you were in heat up dramatically?

One more question, have you checked the firmware version on your C1 with the mobile app?

Interesting! I was under the impression that the reverse was true. The room usually heats up some unless I set up my box fan. I'll have to check the firmware when I get home today!

Re: Power Tap C1 Drifting [Eyes0fTexas] [ In reply to ]

Apr 26, 17 10:20

Post #12 of 17 (2232 views)

Eyes0fTexas wrote:

if the fluid was harder to pedal in the beginning it should result in higher power output with a decreasing trend as the fluid warms and becomes easier to pedal

This was not the case with my old CycleOps fluid trainer that I had a few years back. It was more difficult to pedal, not easier, as the fluid got warmer.

Re: Power Tap C1 Drifting [AutomaticJack] [ In reply to ]

Apr 26, 17 11:12

Post #13 of 17 (2216 views)

AutomaticJack wrote:

nickwhite wrote:

One more question, have you checked the firmware version on your C1 with the mobile app?

On that note, is Power Tap ever going to release an android app? Two years and 2 power taps on 2 bikes and no love for the android. It makes me wish I had brought another Quarq.

Yup, I agree. I had to borrow my tween's iPhone to check/update mine.

Re: Power Tap C1 Drifting [Eyes0fTexas] [ In reply to ]

Apr 26, 17 11:26

Post #14 of 17 (2203 views)

I can 100% assure you it's your trainer. I'm using the exact same set-up and mine does the same. It only warms-up after 15 min of hard pedaling and it even fluctuates after short brakes (6 min). The reason why I'm convinced it's your trainer is because mine does the same and it definitely feels like it too.

Re: Power Tap C1 Drifting [Eyes0fTexas] [ In reply to ]

Apr 26, 17 12:07

Post #15 of 17 (2192 views)

Another vote for it being the trainer. I don't have it any more but the Cyclops Fluid trainer I owned went through a couple of phases of warming up before settling down after 12-15 mins.

As someone else noted there was a noticeable change after 6-8mins and it finally settled at 12-15, dependent on how hard I was working. The higher the power the quicker it settled.

Re: Power Tap C1 Drifting [ In reply to ]

Apr 26, 17 12:39

Post #16 of 17 (2180 views)

Thanks everyone,

I'm guess for now I will just assume it's the trainer. I just found an older thread and similar to what everyone here is saying, this seems to be a very common CycleOps Fluid issue. I'll have to watch it the next time I'm outside to make sure, but in the meantime I guess I'll just HTFU!

Re: Power Tap C1 Drifting [Eyes0fTexas] [ In reply to ]

Apr 26, 17 18:48

Post #17 of 17 (2128 views)

Might want to watch this video to find out why Kurt Kinetic fluid trainer doesn't have this issue: https://www.youtube.com/watch?v=NZkEezODNbo

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