aero wheel differences??
Mark Scardiglia
Can anyone point me to a site or provide info that can help me determine
the performance differences (i.e. time saved in a 40K tt) between
various kinds of aero wheels?
I'm debating whether to save up for a front TriSpoke or get a slotted
hub, some bladed spokes, a v-section rim, andlace it up radially. Also,
at 165 lbs., how many spokes should I use? These would be event day
wheels only.
Thanks.
Mark
David Rees
An excellent chart exists at http://www.cervelo.com ;although lacking a few
current models, it gives a good indication of what sort of advantages can
be expected. Personally, I'd always opt for a wheel that can be fixed/trued
unless a one-piece design offered a real difference that I needed to win.
Campy has moved from 12 back to 16 spokes in their high-end aero wheels,
and 20 spokes in their other aero wheels, and I think that 12 is the lowest
spoke count that is available in any wire-spoked wheel. Building up wheels,
you'll probably have trouble finding hubs with the drilling you want, and
I'm unaware of any rims sold that are as deep as Shamals, eg, except for
the very expensive Zipps. Buying a complete front wheel may prove to be
your only recourse.
Mark A.
In article <356417E8...@erols.com>
Mark Scardiglia <am...@erols.com> writes:
Mark,
Here's an article detailing the differences between wheels. To
determine how much time you'll save, approximate how fast you think
you'll be going, look up the appropriate table, then take the cube root
of the percentage difference plus one, then subtract 1.
Example:
Estimated speed: 35 kph (~22 MPH)
Difference in power between 36 spoke wheel and aero wheels: ~6% (207
vs. 190 Watts)
Difference in time: ~2% (1.06^1/3-1) or about 1 1/2 minutes.
Remember these numbers are for aero front *and* rear wheels. Contrary
to conventional wisdom, the rear wheel is actually more important than
the front according to this data.
Regarding the number of spokes, I'd say you could go as little as 12
with a V section rims (they're very strong).
Mark Atanovich
ssc...@aol.com
The german bike magazine "Tour" (www.traxxx.de/tour) has tested 10
Aero-Wheels in the issue Nr.9 from September 96. I' ll try to
translate the article and summarize the main aspects:
THE TEST:The wheels were tested on a Faggin - frame, which was
equipped with the SRM - measure technic. the special crank is a
special edition of the well known SRM - crank: with 24 "flexible
measurement stripes"("Dehnme吱treifen") between crank and chain-
wheels it seizes precisely, how strong the cycler pushes and
calculates the impulse power. The computer at the handlebar records
the driving power of the cycler and the speed.
The test - cycler (Lars Teutenberg, a german professional) had to
drive several times several rounds at the exact speed of 45 kmh; after
every test the data of the SRM - measure technic were transferred on
a computer. This way all wheel - units were measured.
To create equal conditions, all wheels had the same tires with the
same pressure. a special construction on the saddle forced the test -
cycler to maintain just one certain position. The tester was alone on
the course to avoid turbulences in the air. Other given Parameters
were a chain wheel with 53 x 15 teeth ( ca. 102, 5 rounds per minute )
and a constant temperature of 22。.
DISCS: Very big advantage of the concurrence. 12,7 % less power
needed ( with 45 kmh ) than conventional wheels with 36 round shaped
spokes ( 2 mm ) and angular rims/ conventional rims.
In Numbers: instead of of 403 Watt the driver just needs 352 Watt and
saves 51 Watt.
CHEAP AND FAST HIGH PROFILE AERO SPOKE - WHEELS: on the second rank
are the Campagnolo 12 - spoke wheels, type "Shamal". The high profile
rim with less spokes saves 9,7 % power compared to conventional wheels
during a test. The following ranks show Mavic Cosmic, Citec and
Spinergy. The relationship between Cosmic and Shamal does explain the
similar results. The rims are equally high, but Mavic uses 16 instead
of 12 spokes. On the same niveau are the 12 spoke wheels of Citec with
very much lower rim. Ergo: the height of the rim is not the only
criterion for good aerodynamics. Fitting to this result the Spinergy
wheels ( extreme profiled rim with 8 plain carbon - spokes between rim
and hub) and the HED - wheels ( high volume rims with carbon encased,
2 x 28 spokes ) test a bit worser, because they do not manage to tame
the wind.
SURPRISINGLY GOOD: Messerspeichen/ AERODYNAMIC SPOKES:
A good result was achieved by a Wheel - set of Rigidas DP - 18 - rims
( average profile ) with 18 respectively 24 aerodynamic spokes.
Reaching the same results like distinctively more expensive
constructions the wheels take a very good rank by using a higher rim
profile and less, aerodynamic shaped spokes. Allthough the wheel can
easily be managed in repairs and is just a little bit more expensive
than usual wheels.
Until more precise tests take place it seems that 18 respectively 24
spokes can bear a weight of the cycler up to 75 kg. More spokes on the
back wheel are efficient if the cycler has more weight or takes
extreme stresses. If one takes a 40 mm rim with 18/24 spokes like FIR,
Basso and others from the beginning, the more stiff rim profile gives
enough security and good aerodynamics.
LESS ADVANTAGE: TRI - and FOURSPOKES: not many specimen tested.
Delivery Problems ( Spezialized, Habo ), production stops ( Spin
wheel, Mavic, Zipp ) and other impediments left only three wheels to
be tested. With 6,7 % less need of power Spengle takes the last rank
within the complete sets. The single Corima - front wheel, tested with
a 36 spokes back wheel is compared to the combination Shamal - front
wheel/ 36 spokes back wheel worse, too.. the results show the problems
of this type of wheel: carbon wheels are expensive and relatvely
heavy; the aerodynamics are worse than amongst the spoke wheels.
SET OR SINGLE ?:The measure results show that the back wheel is very
important for the aerodynamics of the combination bike/ cycler. The
actual test shows that the Shamal set saves 39 Watt, the front wheel
alone with a 36 spokes back wheel only 18 Watt. This suggests that
back wheel could save even more energy. BUT: due to possible failures
in the measurements and the actual small data - basis a final
conclusion could not be made. Only the tendency that both wheels are
equally important for the aerodynamics seems to be proovable.
The measurements were made at a constant speed of 45 km/h. For the
other tables the values were calculated, the roll-resistance and other
resistances taken with 4,5 N; chain efficiency: 0.98
Test table 1:
Power: Watt
30 km/h
Disks: 125,50
Shamal HPW 12: 129,10
Cosmic: 129,69
Citec 12 Spokes: 129,99
Spinergy: 130,58
HED Jet: 132,36
Rigida DP 18: 132,36
Spengle Tri-Spoke: 132,66
Shamal FW/36S BW: 135,32
Corima VR/ 36S BW: 136,21
Standard 36S: 140,66
Test table 2:
Power: Watt
35 km/h
Disks: 183,25
Shamal HPW 12: 188,89
Cosmic: 189,84
Citec 12 Spokes: 190,31
Spinergy: 191,25
HED Jet: 194,07
Rigida DP 18: 194,07
Spengle Tri-Spoke: 194,54
Shamal FW/36S BW: 198,77
Corima VR/ 36S BW: 200,19
Standard 36S: 207,24
Test table 3:
Power: Watt
40 km/h
Disks: 257,92
Shamal HPW 12: 266,35
Cosmic: 267,76
Citec 12 Spokes: 268,46
Spinergy: 269,86
HED Jet: 274,08
Rigida DP 18: 274,08
Spengle Tri-Spoke: 274,78
Shamal FW/36S BW: 281,10
Corima VR/ 36S BW: 283,21
Standard 36S: 293,74
Test table 4:
Power: Watt
45 km/h
Disks: 352,00
Shamal HPW 12: 364,00
Cosmic: 366,00
Citec 12 Spokes: 367,00
Spinergy: 369,00
HED Jet: 375,00
Rigida DP 18: 375,00
Spengle Tri-Spoke: 376,00
Shamal FW/36S BW: 385,00
Corima VR/ 36S BW: 388,00
Standard 36S: 403,00
Test table 5:
Power: Watt
50 km/h
Disks: 467,90
Shamal HPW 12: 484,36
Cosmic: 487,10
Citec 12 Spokes: 488,47
Spinergy: 491,22
HED Jet: 499,45
Rigida DP 18: 499,45
Spengle Tri-Spoke: 500,82
Shamal FW/36S BW: 513,17
Corima VR/ 36S BW: 517,17
Standard 36S: 537,86
Test table 6:
Power: Watt
55 km/h
Disks: 608,50
Shamal HPW 12: 629,96
Cosmic: 633,61
Citec 12 Spokes: 635,43
Spinergy: 639,09
HED Jet: 650,04
Rigida DP 18: 650,04
Spengle Tri-Spoke: 651,87
Shamal FW/36S BW: 668,30
Corima VR/ 36S BW: 673,77
Standard 36S: 701,16
Green Eggs and Ham
You wrote :
I asked:
I went to the Cervelo web site and was not able to find the table that
you
were talking about. Could you tell me were I might find it on the site.
Thanks,
Scott
David Rees
http://www.cervelo.com/welcome.html , click on 'Articles', then
'Aerodynamics of cycling'. I was wrong about this chart having specific
models: here's the correct url for that:
http://www.cs.umd.edu/users/humphrie/wheels.html