Angle of Newton Power Meter

Angle of Newton Power Meter

Postby cheoherrera » Tue May 16, 2017 5:06 pm

Hi,

i use the old school Newton Power Meter for my TT Bike. i havent used a remote wind sensor as i have the PM set up in the middle of my aerobars and i dont use any hydration systems in the aerobars.

i raced Ironman 70.3 Gulf Coast on saturday, and my readings were off the chart, i had an avg watts of 365W, NP: 379W. this sounds crazy... could it have something to do with the angle of the PM and they way is set up?

i have added two pictures of my set up and the ride file of my last race (saturday at Panama City Beach 70.3)

Thanks
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Re: Angle of Newton Power Meter

Postby Velocomp » Tue May 16, 2017 5:17 pm

1) Your wind scaling was a bit high. I fixed this with the "Analyze Route" command

2) Your CdA is way too high for a TT bike. For a person your weight (and presumed size of around 5' 9"), your TT CdA should be around 0.25. I fixed this, too.

With these changes your watts drop to a much more believable 230W...still excellent!

Modified ride file and profile attached.
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Re: Angle of Newton Power Meter

Postby cheoherrera » Tue May 16, 2017 6:37 pm

thanks!

i have uploaded the new profile to my PM. is there anything i should do besides this to improve accuracy?
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Re: Angle of Newton Power Meter

Postby Velocomp » Tue May 16, 2017 7:41 pm

Post your next ride file on this thread
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Re: Angle of Newton Power Meter

Postby cheoherrera » Wed May 17, 2017 6:23 pm

here you go! easy 18mile recovery ride this morning (but bery windy)... i used the profile as modified by you

Thanks!
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Re: Angle of Newton Power Meter

Postby Velocomp » Wed May 17, 2017 6:47 pm

This looks much better!
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Re: Angle of Newton Power Meter

Postby triJay » Mon Jul 10, 2017 5:15 pm

I was all ticked off at my Newton yesterday with the opposite problem, as it kept showing super low watts while pushing pretty hard (by RPE and speed) on a 60mile ride with 4500ft of elevation gain. I set all kinds of segment PRs in Strava despite what appeared to be an easy Sunday spin in wattage terms. I have a similar setup, only my Netwon sits outboard of the aero bars (because I will be adding a BTA bottle soon). I checked the tilt at one point on a moderate uphill and it was showing -1 degree, which explained the low wattage calculation.

I couldn't figure out what went wrong and why the tilt was so out of whack. Then I noticed while putting my bike away that my whole cockpit was rotated downward... My base bar had been slipping and rotating slowly from the pressure on the aero bars, so the previously calibrated tilt was off by a few degrees. Woops. Rotated it back up, cranked down those stem bolts more, and will do a new tilt cal before my next ride.
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Re: Angle of Newton Power Meter

Postby Velocomp » Mon Jul 10, 2017 6:43 pm

Yup, if your handlebars are rotating randomly that is a problem... :-)

Note that, after 8 minutes of riding, Newton will recalibrate itself (assuming the handlebars aren't rotating still).
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