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PostPosted: Fri Apr 08, 2011 3:41 pm 
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Joined: Wed Dec 27, 2006 6:36 pm
Posts: 107
subzro wrote:
So, until I see test results with two bidons onboard to compare to no bidons on board then aero tests aren't worth the paper they are written on. There is too much dirty air going on around a road bike to make aero tests meaningful.


That info has been available for a long time:

http://www.slowtwitch.com/mainheadings/techctr/waterbottles.html


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Posted: Fri Apr 08, 2011 3:41 pm 


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PostPosted: Fri Apr 08, 2011 4:11 pm 
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Posts: 7918
Location: San Francisco, CA
The issue is the interaction between frame design and bottles. Not all frames will be affected the same. Case in point: Litespeed which was optimized for a bottle on the downtube. There's another slowtwitch report, recently reported here, where that effect is examined on tri bikes. Good stuff:

http://www.slowtwitch.com/Tech/Cervelo_ ... _1929.html


The result? The ordering of bikes at high yaw where the difference was greatest was the same with and without the round bottle. So these "results are junk if there's no bottle" critics are throwing away perfectly good data.

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PostPosted: Fri Apr 08, 2011 5:42 pm 
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Posts: 43
Location: Michigan
If I'm reading the chart correctly, the CDA's of the aero frames is between .01 and .02 different than the test frame at various yaw. That works out to a 1 to percent difference in speed. I think Cervelo themselves has said they thought it would be about 1.5 percent.

That sure doesn't seem like alot to me, but every little bit helps assuming you don't have sacrifice in other areas such as ride quality or stiffness.

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PostPosted: Fri Apr 08, 2011 5:57 pm 
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swalburn wrote:
If I'm reading the chart correctly, the CDA's of the aero frames is between .01 and .02 different than the test frame at various yaw. That works out to a 1 to percent difference in speed. I think Cervelo themselves has said they thought it would be about 1.5 percent.

That sure doesn't seem like alot to me, but every little bit helps assuming you don't have sacrifice in other areas such as ride quality or stiffness.


1-2% difference in speed.

0.01 = 3% of 0.33, a typical CdA for an optimized race position, and it takes around a 3% difference in power to yield a 1% difference in speed.

Whether that's a lot or not is up to you. 1% = 6 seconds per 10 minutes.

And I agree: Cervelo integrity is looking very good with this test.

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PostPosted: Fri Apr 08, 2011 6:08 pm 
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Location: Michigan
I've never been on any of the aero road frames for an extended period of time so I have to speculate how they ride. Obviously, if you had an aero road frame that road as well as the best riding "traditional" road bike you would be all set. Either way I really love the science behind these frames. I've always lusted after an S2 or S3 but could never justify the cost as my team sponsor doesn't sell any brands that have aero road frames. They do sell Scott but have had a horrible time getting frames from them. I would love to see the F01 up close but don't expect to see one in the flesh before this time in 2012. I think that frame is going to be something special. I almost held out for the F01 but ended up with something else.

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PostPosted: Sat Apr 09, 2011 5:25 pm 
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Comparison of Felt versus Cervelo, Tour test and VeloNews test:

Image

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PostPosted: Sat Apr 09, 2011 6:33 pm 
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Wouldn't it have been easier to graph out the results on a simple one-quadrant graph with the two lines overlapping?
Y axis = CdA
X axis = Yaw
No negative values.

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PostPosted: Sat Apr 09, 2011 6:43 pm 
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prendrefeu wrote:
Wouldn't it have been easier to graph out the results on a simple one-quadrant graph with the two lines overlapping?
Y axis = CdA
X axis = Yaw
No negative values.



The issue there is that the Tour CdA's are 3 times bigger due to the human dummy.

Also they used different wheels, so you'd be comparing Mavic to Zipp as well as Felt to Cervelo.

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