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Home > Forum > Triathlon Forum > Power Tap readings leap all over after cassette replacement. Help..

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Power Tap readings leap all over after cassette replacement. Help..
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lutzman
May 9, 18 19:12
Post #1 of 9 (1470 views)
I've got a PowerTap power meter that I purchased from Wheel Builder on a Zipp 808. It's always been a great, reliable device. I recently replaced my cassette (identical replacement) due to wear. Two outcomes. Even on 3 second averaging the watts now leap all over. I can be on my trainer with no change in effort or cadence and I'm seeing 30-40 watt fluctuations constantly. It's a bit better at 10 second averaging, but still bounces all over. Out on the road it's even worse.

The other thing I noticed is I used to get at least a couple months on the PowerTap battery. Now the batteries are going out in two weeks or less.

I took it into my LBS to have them check it out. They said the cassette and PowerMeter all check out fine. I've begun to wonder if the PowerCap is going out?

Anyone had a problem like this and solved it?

Thanks for any ideas.
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Re: Power Tap readings leap all over after cassette replacement. Help.. [lutzman] [ In reply to ]
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iruntrails
May 10, 18 5:28
Post #2 of 9 (1398 views)
Try replacing the batteries, they may have been replaced recently but it's a cheap and easy thing to do. At least take the batteries out and put them back in if you don't have extras.
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Re: Power Tap readings leap all over after cassette replacement. Help.. [lutzman] [ In reply to ]
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Grantbot21
May 10, 18 5:31
Post #3 of 9 (1396 views)
Contact powertap and let them know what is going on. I had to send a wheel back to them, the hub ended up having issues and they sent a brand new one even though I wasn’t the original owner. They’re really easy to work with.
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Re: Power Tap readings leap all over after cassette replacement. Help.. [lutzman] [ In reply to ]
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klehner
May 10, 18 7:03
Post #4 of 9 (1355 views)
lutzman wrote:
I've got a PowerTap power meter that I purchased from Wheel Builder on a Zipp 808. It's always been a great, reliable device. I recently replaced my cassette (identical replacement) due to wear. Two outcomes. Even on 3 second averaging the watts now leap all over. I can be on my trainer with no change in effort or cadence and I'm seeing 30-40 watt fluctuations constantly. It's a bit better at 10 second averaging, but still bounces all over. Out on the road it's even worse.

The other thing I noticed is I used to get at least a couple months on the PowerTap battery. Now the batteries are going out in two weeks or less.

I took it into my LBS to have them check it out. They said the cassette and PowerMeter all check out fine. I've begun to wonder if the PowerCap is going out?

Anyone had a problem like this and solved it?

Thanks for any ideas.

What kind of readings did you get when you put the old cassette back on?
----------------------------------
"Go yell at an M&M"
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Re: Power Tap readings leap all over after cassette replacement. Help.. [klehner] [ In reply to ]
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lutzman
May 10, 18 7:36
Post #5 of 9 (1332 views)
klehner wrote:
lutzman wrote:
I've got a PowerTap power meter that I purchased from Wheel Builder on a Zipp 808. It's always been a great, reliable device. I recently replaced my cassette (identical replacement) due to wear. Two outcomes. Even on 3 second averaging the watts now leap all over. I can be on my trainer with no change in effort or cadence and I'm seeing 30-40 watt fluctuations constantly. It's a bit better at 10 second averaging, but still bounces all over. Out on the road it's even worse.

The other thing I noticed is I used to get at least a couple months on the PowerTap battery. Now the batteries are going out in two weeks or less.

I took it into my LBS to have them check it out. They said the cassette and PowerMeter all check out fine. I've begun to wonder if the PowerCap is going out?

Anyone had a problem like this and solved it?

Thanks for any ideas.


What kind of readings did you get when you put the old cassette back on?
Good question. I haven't tried putting the old cassette back on. Nor can I. I tosssed it.
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Re: Power Tap readings leap all over after cassette replacement. Help.. [lutzman] [ In reply to ]
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Physiojoe925
May 10, 18 11:52
Post #6 of 9 (1280 views)
lutzman wrote:
I've got a PowerTap power meter that I purchased from Wheel Builder on a Zipp 808. It's always been a great, reliable device. I recently replaced my cassette (identical replacement) due to wear. Two outcomes. Even on 3 second averaging the watts now leap all over. I can be on my trainer with no change in effort or cadence and I'm seeing 30-40 watt fluctuations constantly. It's a bit better at 10 second averaging, but still bounces all over. Out on the road it's even worse.

The other thing I noticed is I used to get at least a couple months on the PowerTap battery. Now the batteries are going out in two weeks or less.

I took it into my LBS to have them check it out. They said the cassette and PowerMeter all check out fine. I've begun to wonder if the PowerCap is going out?

Anyone had a problem like this and solved it?

Thanks for any ideas.


Any chance your last rides with that cassette were extremely wet, a crash, or some other variable that could have caused the Powertap issue?

I have 2 Powertaps (1 of which is an 808 as well) and have used them for almost 10 years. I have had a couple issues, but none related to swapping cassettes.

The Powertap really is "ignorant" of the gears you have on your back wheel. All it knows is the forces being exerted on the wheel. I cannot think of any way that changing the cassette would alter Power readings if everything else stays the same.
-Physiojoe
Instagram: @thephysiojoe
Cycling coach, Elite racer on Wooster Bikewerks p/b Wootown Bagels
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Re: Power Tap readings leap all over after cassette replacement. Help.. [lutzman] [ In reply to ]
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mike s
May 10, 18 13:06
Post #7 of 9 (1254 views)
What head unit are you using? Is it transmitting a power number when you’re coasting? What’s the calibration value?
Last edited by: mike s: May 10, 18 13:28
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Re: Power Tap readings leap all over after cassette replacement. Help.. [mike s] [ In reply to ]
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lutzman
May 10, 18 14:57
Post #8 of 9 (1198 views)
Hi Mike:

I'm using a Garmin 510. When I coast I'll get either zero or 1 watt just from my feet on the pedals. Generally the calibration is 519-521. Torque is .19.
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Re: Power Tap readings leap all over after cassette replacement. Help.. [lutzman] [ In reply to ]
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mike s
May 10, 18 16:00
Post #9 of 9 (1180 views)
The calibration is well within tolerance of 512 +/- 12 if I remember, no issues coasting check, the last three bits of advice I would give is:
1. Ensure you have the latest firmware for the Powertap
2. Repair the Powertap to the Garmin, why I don’t know sometimes it just works
3. Don’t use cheap batteries in the Powertap, I had the same issue in my SL+, come to find it was when I used no name batteries, they worked good for 10 minutes or so then went bonkers
I’m going to assume you do a zero offset prior to each ride
Last edited by: mike s: May 11, 18 14:09
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