HUGE Discrepancy in Avg. Watts

[Sarg]

I did an individual TT in Philly today and I am not sure about the data that I got. The "raw" data said that my avg. watts were 247, the Auto analyze 307 and the Analyze Tilt/Power 338! Which one is the most accurate? Any coments, suggestions or help would be greatly appreciated.

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[racerfern]

Assuming that the course was relatively flat, your tilt was way off. Look at the average slope of -1.14 degrees. That's a pretty substantial downhill over an 8.4 mile distance.

Also, if you're going to analyze tilt and power you should also confirm the wind settings. That could account for some of the difference between auto and manual. I usually end up with a slight difference between auto and manual analysis. However, your basic tilt setting and wind calibration has got to be good to start with.

In the Tilt and power screen, click advanced and take a look at the green line. If it sloping down from the start you had a bad tilt. If it starts to slope down somewhere along the ride, then something threw the tilt off.

[Sarg]

Thanks for the reply Fernando! Before the correction the green line in the advanced sreen is sloping downward at around a 30 degree angle. To correct this problem should I do a tilt calibration or do I need to re-do the coast downs and 4 mile ride also?

[racerfern]

IF your tilt calibration for your coastdown rides was correct, then you should only have to do a tilt calibration before each ride. If you are not sure, then you should do your coastdowns over. Probably the most important tilt calibration is the one you do before the coastdowns. That's the one that "teaches" the iBike how to adapt to you.

Another way to try and determine if your tilt calibration is somewhere in line is to run the software, click on Profiles, Edit Profiles, click on your current profile, then click the "Advanced Profile Settings..." button. Toward the right side of the new screen that popped up you will see "Riding Tilt (%). Depending on your weight and position on the bike, this could be anywhere from -0.100% to -0.500%. It should never be positive and in your case would probably be very close to zero since you are light and you were in a TT positon. I am assuming you have your iBike mounted below your TT bars. If this number is positive or if this number is not there, then something is wrong.

Let me know.

[Sarg]

My riding tilt % from the profile is -0.173 and from what you said it sounds like this could be good data. I have the Ibike unit mounted beneath the TT bars so it can get a good shot at "clean" air.

Concerning coast-downs, if I did future wind offsets and tilt calibrations in a controlled environment, like my basement, and then rode to where I do my coast-downs would this be ok or would that mess everything up? Since the tilt calibration for coast-downs is so critical I would like to do it in exactly the same spot on a very smooth surface so as to hopefully get very accurate data. All of my current profiles were done outside immediately before doing the coast-downs.

Thanks for the help!

John

[racerfern]

It sounds like you just had a bad tilt cal for the ride. There's nothing wrong with doing your setup in your basement as long as the temp in the basement is about the same as outside (for the wind zero offset calibration). You just don't want drastically different conditions from your basement to the outside temp and barometric pressure. Wind offset will be affected by that.