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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [ In reply to ]
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I did some testing early this morning ,as the wind was low (UK).
Was testing 40cm bars vs 44 and surprised to find the 44s ' faster'
Looking at the weather data,the temperature went up by 2--3degC,and the solar radiation doubled (from ~50w/m2 to ~100) during the time I was on the road.
I set off from the house, so tyres were 'warm' then presumably cooled outside, then I switched the bars (inside the house),and went back out.
I didn't do ABA ,so am unsure if this is a real difference,and wonder if anyone has experience of w/m2 affecting crr?
( I compensated for ambient temp change)
Interestingly the garmin recorded a swing of ~9 deg C over the time I was out,compared to 2 deg from the weather station.
Thoughts welcome!
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [kevinkeegan] [ In reply to ]
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That's a big swing in temperature. Depending on what the starting conditions were, a 9 deg C. increase in temp can mean 2-3% decrease in air density, and also a decrease in Crr. The smaller the change in position or equipment, the more careful you have to be in tracking changes in conditions. Was the difference between the 40 and the 44 on that order of size, or was it larger than that?

[edited to add:] This method is sensitive enough to detect changes in the weight of air. Fortunately, if you keep track of the temperature and barometric pressure (humidity makes a small amount of difference, too) you can calculate the weight of the air and account for it. That's pretty cool.
Last edited by: RChung: May 12, 19 20:21
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
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The swing between setups I get as 3.8% (road bike,drops,from 40cm to 44 cm bars,44 being faster
Using the weather station data (about a mile away)- the air density reduced by a max of 0.85%

Looking back at the data:
The weather station recorded a +3 degree (celsius) temp change outside.
(It also showed zero wind at the beginning,going up to between 1 & 2 kmh by the end of testing)
The Garmin showed a 6 degree drop during '40' testing,but no drop on '44' testing ( the sun had come out a bit more)

I am wondering that if the Garmin showed this,were the tyres experiencing something similar ?

I do have an infrared thermometer (at work),that I will try out if I get a chance
Last edited by: kevinkeegan: May 12, 19 22:16
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [kevinkeegan] [ In reply to ]
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kevinkeegan wrote:
I do have an infrared thermometer (at work),that I will try out if I get a chance
Better to use something that measures air temp (and isn't in direct sunlight), not surface temp (highly influenced by emissivity and sun exposure).
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [MattyK] [ In reply to ]
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MattyK wrote:
kevinkeegan wrote:
I do have an infrared thermometer (at work),that I will try out if I get a chance

Better to use something that measures air temp (and isn't in direct sunlight), not surface temp (highly influenced by emissivity and sun exposure).
Right, air temp is really what to measure.

Did you [kevinkeegan] zero your torque between the runs? I do that when there are wide swings in temperature -- even though some PMs say they compensate for (or are immune to) temperature variation, it's good practice to do so. And, of course, some PMs are better for this sort of thing than others.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
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Did you [kevinkeegan] zero your torque between the runs? I do that when there are wide swings in temperature -- even though some PMs say they compensate for (or are immune to) temperature variation, it's good practice to do so. And, of course, some PMs are better for this sort of thing than others.[/quote]
I didn't zero torque.Am using powertap wheel,and did plenty of coasting.
The air temperature didn't actually vary much(from 6 to 9 degC)
Will zero torque the next time
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [kevinkeegan] [ In reply to ]
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kevinkeegan wrote:
...
I didn't do ABA ,so am unsure if this is a real difference
...

I hope this doesn't come off as too negative. But if you didn't do ABBA and convince yourself you can reproduce your results it is pretty hopeless for any of us to try to draw conclusions. I wasted quite a bit of time/runs back when I was doing this kind of testing working with poor protocols and thus having junk results (it has been a few years since I did any aero testing). I wish I had been urged more strongly to do ABBA testing as the very first thing and not move on to anything else until I was sure I had that nailed.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [jbank] [ In reply to ]
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jbank wrote:
I wish I had been urged more strongly to do ABBA testing as the very first thing and not move on to anything else until I was sure I had that nailed.

If possible do ABABAB etc...

Seems to me that a good first step is to see what SD or CV you can acheive when you are not changing anything.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [rruff] [ In reply to ]
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I don't think it's always necessary to do ABABAB... testing. Sometimes it's clear after an AB comparison that something is wrong and you should either postpone to another day|venue|PM|speed sensor| or else measure your rho more carefully or else convert the test session to practice runs to refine your protocols.

Even a bad run can provide you with good information -- just sometimes what you learn is what not to do the next time.
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