Can anyone steer me in the direction of how to check the accuracy of a computrainer?
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Re: Computrainer [Mark57]
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External PM?
Re: Computrainer [Livio Livius]
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Thanks for the reply. I have a C1 (new) powertap which I assume is calibrated and there is a very large discrepancy ie powertap 200W, Computrainer (old) 175W. I guess it could be just loss due to chain, derailleur and wheel bearings but I don't want to embark on a wild goose chase trying to match them a bit closer if the computrainer is out of calibration. I don't think, or want to think, that there is that much loss from the chainring to the back wheel!
Re: Computrainer [Mark57]
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There would be difference in watts due to where the power meter is located. The chain ring meter is measuring at the chain ring and the Computrainer at the rear tire. I do not think that there should be a 25 watts difference but at least a few watts.
I used to have a Computrainer. Do use the roll down feature to measure pressure against the drum and wheel?
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Once, I was fast. But I got over it.
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Re: Computrainer [gabbiev]
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Thanks for the reply. Is an external dynometer how it was done in the factory do you know?
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Re: Computrainer [Mark57]
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As others have stated, the only way for a consumer to test the accuracy of a CompuTrainer is by comparing it to a carefully-calibrated power meter.
Having done so for multiple CTs, I wouldn't trust one any farther than I could throw it. In that regard, my experience matches the peer-reviewed literature, Chet Kyle's Project 96 dynamometer tests in particular.
The good news is that although the folks at RacerMate were apparently too lazy to ever fix the issue (even though it was pointed out to them repeatedly), CTs are at least linear. Thus, if you are patient and have good dexterity, you can tweak the single-turn potentiometer lurking behind the decal on the load generator until the CT matches a known standard (i.e., calibrated power meter). Of course, you need to make sure everything is warmed up and stays that way during this procedure (and it won't improve the CT's woefully inadequate inertial load).
Full credit to Rick Murphy for figuring out how to do the company's job for them.
Having done so for multiple CTs, I wouldn't trust one any farther than I could throw it. In that regard, my experience matches the peer-reviewed literature, Chet Kyle's Project 96 dynamometer tests in particular.
The good news is that although the folks at RacerMate were apparently too lazy to ever fix the issue (even though it was pointed out to them repeatedly), CTs are at least linear. Thus, if you are patient and have good dexterity, you can tweak the single-turn potentiometer lurking behind the decal on the load generator until the CT matches a known standard (i.e., calibrated power meter). Of course, you need to make sure everything is warmed up and stays that way during this procedure (and it won't improve the CT's woefully inadequate inertial load).
Full credit to Rick Murphy for figuring out how to do the company's job for them.
Re: Computrainer [Andrew Coggan]
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Great info. Thanks very much!
Re: Computrainer [gabbiev]
[ In reply to ]
Thanks.