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I am getting some data together about various things aero wise for my use in the future. The first test was Wheel cover (ie disc) V no cover and staying aero v not staying aero. Some of you may have read it before but some not. I am doing some other things tomorrow so will put them all together in this thread.
Having been playing with a Power Tap for a while now I decided that it is just about a requirement for a race like Bussso so I went and got a wheel cover from Wheel Builder. It cost me $160 something OZ dollars when it finallly showed up on my credit card inclusive oof express postage from Fed Ex.
As many tests are done at 40km/hr I am not so sure they give a legitimate idea of savings or not that can be had for the everyday Ironman athlete. As a 5 hour flat bike at Busso will put you in a very good place for a mid to latter 9 hour finish, I decided that 36km/hr was to be my test speed. It ended up being a little over that.
Anyway, the test was three parts. Once with a wheel cover installed and position was sitting up and in no way aero to demonstate any power isssues you have by not staying aero. Second was Aero with Disc Cover and third Aero with NO Disc Cover. All three were done in stanndard raod riding kit and a normal road helmet. I paid close attention to the positioniing of my person on the bike with a few points of referennce for my hands, elbows and banus. The rest was just a matter of trying to hold a consistent speed and power output. All three tests were done in the same gear at 53/16 so that cadence variations would not have an influence on power. All data sampled was cut and pasted in WKO+ removing the period of acceleration and deceleration as I did an out and back course that was sheltered at each end and a cross wind section in the middle.
Sit up with Cover
Ave Speed 36.3
Ave Power 283
Norm Power 297
Disc Cover Aero
Ave Speed 37.0
Ave Power 253
Norm Power 260
No Cover Aero
Ave Speed 37.0
Ave Power 260
Norm Power 270
These figures were then analysed a llittle further by a bloke called Alex Simmonds who is a bit of a power guru in OZ and he came up with.....
I have made a few assumptions on conditions etc:
Air density: 1.2 km/m^3
Crr: 0.005
Getting the exact assumptions may change the absolute values in the VE but not the shape of the plots.
What this suggests is the following CdA values:
Road Position and wheel cover: _ 0.370 m^2
Aero with wheel cover : _______ 0.300 m^2 (81% of road CdA)
Aero without wheel cover: _____ 0.315 m^2 (85% of road CdA, 105% of wheel cover CdA)
On the basis of this limited data set, it suggest an approximate 5% improvement in aero from using the wheel covers.
That is equivalent to ~ 1.5 seconds/km saving by using the covers.
Compared to road position/no covers it's a saving of ~ 6.5 sec/km.
Test tomorrow will be aero helmet v road helmet, spare tyre behind the seat v spare tube in rear pocket, tri suit v cycle jersey.
Having been playing with a Power Tap for a while now I decided that it is just about a requirement for a race like Bussso so I went and got a wheel cover from Wheel Builder. It cost me $160 something OZ dollars when it finallly showed up on my credit card inclusive oof express postage from Fed Ex.
As many tests are done at 40km/hr I am not so sure they give a legitimate idea of savings or not that can be had for the everyday Ironman athlete. As a 5 hour flat bike at Busso will put you in a very good place for a mid to latter 9 hour finish, I decided that 36km/hr was to be my test speed. It ended up being a little over that.
Anyway, the test was three parts. Once with a wheel cover installed and position was sitting up and in no way aero to demonstate any power isssues you have by not staying aero. Second was Aero with Disc Cover and third Aero with NO Disc Cover. All three were done in stanndard raod riding kit and a normal road helmet. I paid close attention to the positioniing of my person on the bike with a few points of referennce for my hands, elbows and banus. The rest was just a matter of trying to hold a consistent speed and power output. All three tests were done in the same gear at 53/16 so that cadence variations would not have an influence on power. All data sampled was cut and pasted in WKO+ removing the period of acceleration and deceleration as I did an out and back course that was sheltered at each end and a cross wind section in the middle.
Sit up with Cover
Ave Speed 36.3
Ave Power 283
Norm Power 297
Disc Cover Aero
Ave Speed 37.0
Ave Power 253
Norm Power 260
No Cover Aero
Ave Speed 37.0
Ave Power 260
Norm Power 270
These figures were then analysed a llittle further by a bloke called Alex Simmonds who is a bit of a power guru in OZ and he came up with.....
I have made a few assumptions on conditions etc:
Air density: 1.2 km/m^3
Crr: 0.005
Getting the exact assumptions may change the absolute values in the VE but not the shape of the plots.
What this suggests is the following CdA values:
Road Position and wheel cover: _ 0.370 m^2
Aero with wheel cover : _______ 0.300 m^2 (81% of road CdA)
Aero without wheel cover: _____ 0.315 m^2 (85% of road CdA, 105% of wheel cover CdA)
On the basis of this limited data set, it suggest an approximate 5% improvement in aero from using the wheel covers.
That is equivalent to ~ 1.5 seconds/km saving by using the covers.
Compared to road position/no covers it's a saving of ~ 6.5 sec/km.
Test tomorrow will be aero helmet v road helmet, spare tyre behind the seat v spare tube in rear pocket, tri suit v cycle jersey.
