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735xt Math Fail Rant
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My 735XT recorded my average power for a 1:45 - 30 miles ride last night 202 watts. That seems about right.

It recorded my best 20 minutes power average for the same ride as 191 watts.

Not that either is a worthwhile metric, but seriously?

"...the street finds its own uses for things"
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Re: 735xt Math Fail Rant [AutomaticJack] [ In reply to ]
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Without seeing your power chart for the ride, I don't see why this can't be a reality. The average of the whole could be more than the average of a 'best of' portion. For example for each 5 minutes chunk of time breaks down like say 100w/10w/10w/10w/100w/10w/10w/10w/100w. Best 20 minute would be 100/10/10/10 or average of 32.5w. Overall average would be 40w. This is an extreme example, but depending on what intervals you were riding, the math is probably sound. Why I took the time to calculate this I have no idea.
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Re: 735xt Math Fail Rant [AutomaticJack] [ In reply to ]
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Are you stopping at stoplights? Could be a moving average vs. elapsed average. Also are you sure it's not NP?
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Re: 735xt Math Fail Rant [AutomaticJack] [ In reply to ]
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Makes total sense if you were not riding at a steady power. I bet your NP was very high relative to your AP.
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Re: 735xt Math Fail Rant [exxxviii] [ In reply to ]
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I had this explained to me once because I saw it in Trainingpeaks for my peak power durations and didn't get it.

Imagine in Strava clicking on the analysis and dragging the zoom to a duration of time. Then slide this selection along the route, looking at the power. What is shown as the largest here is what your best for that amount of time is.

So, it becomes possible for shorter efforts to have less power than longer efforts. Imagine doing intervals with rest sets. You can pair sets of ON and OFF such that your best 8min might be higher than 5 min because your sets are 3min with 2min rest. The 8min will cover two 3min sets and one rest set, but the 5min will only ever cover one work set and one rest set.

So:
3min at 300w plus 2min at 100w will average lower than 3min at 300w plus 2min at 100w plus 300w at 3min

Make sense?
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Re: 735xt Math Fail Rant [exxxviii] [ In reply to ]
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NP was 222.

I see everyone's explanation of how this "could" happen but all those special sets of circumstances required to get a screwy result should be nearly impossible to replicate outside. The most likely reason is the sampling frequency is set too course on the 735. My 520 over the same course and a similar effort give more believable results. Last time out my average power was 200 and the 20 minute average was 211 using the 520.

Even in Cat 3 races where there are bust of near 4 digit power followed by periods of 2 digit power the 520 still never produces this type of mismatch. In some of those races I've had NP read almost 1.5 times average power.

"...the street finds its own uses for things"
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Re: 735xt Math Fail Rant [AutomaticJack] [ In reply to ]
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AutomaticJack wrote:
NP was 222.

I see everyone's explanation of how this "could" happen but all those special sets of circumstances required to get a screwy result should be nearly impossible to replicate outside. The most likely reason is the sampling frequency is set too course on the 735. My 520 over the same course and a similar effort give more believable results. Last time out my average power was 200 and the 20 minute average was 211 using the 520.

Even in Cat 3 races where there are bust of near 4 digit power followed by periods of 2 digit power the 520 still never produces this type of mismatch. In some of those races I've had NP read almost 1.5 times average power.

You'd have to look at the power file to confirm. All it really takes for that type of mismatch to take place is for the hard efforts to be just over 20 mins apart.

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Re: 735xt Math Fail Rant [AutomaticJack] [ In reply to ]
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Garmin Connect is what does the 20 minute calculation, not the watch. So, as others suggested, you would have to study the power file or charts to see if you had some funky patterns in the power data that could have caused that.
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Re: 735xt Math Fail Rant [AutomaticJack] [ In reply to ]
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Quote:
I see everyone's explanation of how this "could" happen but all those special sets of circumstances required to get a screwy result should be nearly impossible to replicate outside

It's really quite common. I honestly can't tell you how many times I have seen this occur in training client data files, and more than once in personal ones.

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