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July 4th 18, 08:15 AM posted to rec.bicycles.tech
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On Tuesday, July 3, 2018 at 11:15:12 PM UTC+2, sms wrote:
On 7/3/2018 11:58 AM,
On Tuesday, July 3, 2018 at 7:14:03 PM UTC+2, jbeattie wrote:
On Monday, July 2, 2018 at 10:41:15 AM UTC-7, Frank Krygowski wrote:
This has been the talk of the house.
100 watt savings descending? Really? I suppose if you have an incredible spin and are drag racing straight descents, although 100 watts still seems like a stretch. 2 kilo weight penalty going up.
My son's peak power output descending on the way to work this morning was 1,100 watts. That was on a 16% descent with no pedaling. Got to love strain gauges. The road is so broken up that when you have the crank arms horizontal and you hit a bump while posting, the power spikes.
-- Jay Beattie.
Power is force times speed. If his crank arms are stationary while hitting a bum he doesn't suppose to measure a power spike. Besides that the force on the left en right crank are in opposite directions. I don't know what power meter he uses but if it is the garmin Vector 3 pedals the power spikes are caused by a ****ty designed battery holder.
Some crank-arm power meters just have one strain gauge, and it's
accurate enough to just double the amount. Peaks are meaningless anyway.
The firmware should be filtering out obviously bogus data.
I know that's why I asked. Power meters have an accuracy in the 1-2% range. A left right balance of 52-48% is not unusual. At a typical total power value of 250 Watt doubling one side measurement gives you a total of 2*(250/100)*52 = 260 Watt; 10 Watts error. That is 4%. If you want accurate values I don't understand the one sided option.
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