# Why tri-spoke Hed3?



## tom_h (May 6, 2008)

It's a mystery to me why even well-resourced teams, like Sky Procycling, would continue to use the "old school" tri-spoke wheels.

Test reports I've read, including this 18 month old test from German TOUR magazine,
TOUR QTR 4-2011
show several conventional spoked wheels having less aero drag, lighter weight, and lower costs.

So why do tri-spoke wheels still keep showing up?


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## Zen Cyclery (Mar 10, 2009)

Marketing.


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## cxwrench (Nov 9, 2004)

I don't think it's marketing as much as some guys just like them and want to use them. An outfit like Sky is pretty much a free-for-all when it comes to wheels, much like HighRoad used to be. If Froome wants a tri-spoke, Froome gets a tri-spoke,


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## AM999 (Jan 22, 2007)

tom_h said:


> It's a mystery to me why even well-resourced teams, like Sky Procycling, would continue to use the "old school" tri-spoke wheels.
> 
> Test reports I've read, including this 18 month old test from German TOUR magazine,
> TOUR QTR 4-2011
> ...


There is nothing more aero than a front trispoke with a parabolic profile tire at low yaw (and these guys go so fast that just about everything is low yaw) on a flat course. They also don't stall, seem reliable and strong, but they are relatively heavy. They were fairly inexpensive a few years ago but the prices have gone up with increased popularity.


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## tom_h (May 6, 2008)

But the TOUR test result (p.102) shows Zipp 808 and Hed Jet9 are superior at all yaw angles, although near 0 yaw the graph is hard to read. 
Even the Zipp 404 is superior up to yaw 12º.


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## AM999 (Jan 22, 2007)

tom_h said:


> But the TOUR test result (p.102) shows Zipp 808 and Hed Jet9 are superior at all yaw angles, although near 0 yaw the graph is hard to read.
> Even the Zipp 404 is superior up to yaw 12º.


The aero performance is very dependent on tire size and model. The H3 is a narrow rim. The max size tire would be 20 mm actual width. Unfortunately it appears that the interactive HED aero wheel chart is not available ?? When it was you could clearly see the advantage of the HED 3 with a narrow tire at low yaw. I've also seem other data sources that support this data. I haven't seen the Tour magazine data - does it state what tire was used ??


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## tom_h (May 6, 2008)

AM999 said:


> ... I haven't seen the Tour magazine data - does it state what tire was used ??


Conti GP 4000S clinchers. Apparently 23mm tire width, but I had to dig thru article to infer it. Inner tube was not stated. Note the Hed model tested is the H3D.

This is the 2011 TOUR wheel test, it opens up in one of those annoying readers that mimic a magazine page:
TOUR QTR 4-2011

Another article in the same issue tested "everyday" alloy wheels.


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## AM999 (Jan 22, 2007)

tom_h said:


> Conti GP 4000S clinchers. It appears 23mm width, but I had to dig thru article to infer it. Inner tube was not stated.
> 
> This is the 2011 TOUR wheel test, it opens up in one of those annoying readers that mimic a magazine page:
> TOUR QTR 4-2011
> ...


Yeah, that's much too wide a tire for the HED3 for good aerodynamics. I have 2 front HED 3 wheels - one a clincher with one of the old Bonty AeroWing 19 tires with latex tube and one a tubular with one of the old Vittoria Crono 20 tires. If it's calm they are the wheel to use but they can be a handful in a strong crosswind. Each time a spoke goes behind a fork leg the XS area changes slightly.


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## tom_h (May 6, 2008)

So the improved aero of the narrow 19-20mm tire, more than makes up for the probably worse Crr ?


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## AM999 (Jan 22, 2007)

tom_h said:


> So the improved aero of the narrow 19-20mm tire, more than makes up for the probably worse Crr ?


The lighter version of the AeroWing 19 (which is out of print) and the Crono 20 tubular have excellent Crr's. But you are right, both aero and rolling resistance combine to determine speed.


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## Lelandjt (Sep 11, 2008)

So at 0° Yaw is a dimpled disc the most aero, followed by a tri-spoke (both with 20mm tires), followed by a deep wide rim with low spoke count (with 23mm tire?) 20mm tires are always better at 0° yaw cuz less frontal area? 23mm tires with wide, deep, low spoke wheels are only better when there's side winds and rough roads?


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## looigi (Nov 24, 2010)

Many well funded teams do their own aero testing, so may know things others don't, or come to their own conclusions as to what's best under specific conditions. And of course, as already mentioned, rider preference comes into play too, and that can be based on superstition as often as science.


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## tom_h (May 6, 2008)

AM999 said:


> The lighter version of the AeroWing 19 (which is out of print) and the Crono 20 tubular have excellent Crr's. But you are right, both aero and rolling resistance combine to determine speed.


Apropos, came across this blog with an entry on tire rolling resistance testing,
_Blather 'bout Bikes: More Continental GP4000S testing...including a 20C
More Continental GP4000S testing...including a 20C

_and the 4000S is the tire used in the TOUR magazine wheel tests.

Summarizing, Average Crr 
Conti 23mm = 0.0034
Conti 20mm = 0.0041

That's a huge Crr difference, it would take some serious aero advantage for the narrow tire to be net better.

Throw in the quantifiable variables of wheel design, rim width, yaw angles ... and there's a lot to optimize!

As _looigi _mentions above, seems reasonable to assume Sky has their own internal data to justify their choices.


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## asgelle (Apr 21, 2003)

tom_h said:


> Summarizing, Average Crr
> Conti 23mm = 0.0034
> Conti 20mm = 0.0041
> 
> That's a huge Crr difference, it would take some serious aero advantage for the narrow tire to be net better.


Using rough numbers and analyticcycling.com, at 27 mph (12.069 m/s), rolling resistance (Crr=0.0034) accounts for 9% of the total force compared to 81% for drag (level ground). Increasing Crr by 21% to 0.0041, requires a decrease in CdA of only 2.4% (0.25 to 0.244) to give the same resistance. Going from a 23 to 20 mm tire reduces A by 13%.


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## AM999 (Jan 22, 2007)

tom_h said:


> Apropos, came across this blog with an entry on tire rolling resistance testing,
> _Blather 'bout Bikes: More Continental GP4000S testing...including a 20C
> More Continental GP4000S testing...including a 20C
> 
> ...


That's Tom Anhalt's site and data. He has taken up the testing from me.

But sure, you have to select a narrow tire with a low Crr. In general a narrow tire of the same construction as a wider tire will not roll as well. The balance penalty against the aero gain.


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## tom_h (May 6, 2008)

asgelle said:


> Using rough numbers and analyticcycling.com, at 27 mph (12.069 m/s), rolling resistance (Crr=0.0034) accounts for 9% of the total force compared to 81% for drag (level ground). Increasing Crr by 21% to 0.0041, requires a decrease in CdA of only 2.4% (0.25 to 0.244) to give the same resistance. Going from a 23 to 20 mm tire reduces A by 13%.


13% reduction in A for the _tire alone _... but the "A" in "Cd A" needs to be the TOTAL frontal area of the cyclist on the bike.

How much the narrower tire affects total frontal A -- not obvious to me. Even if the tire width was "0", the width of the wheel rim, the outlines of the head/down/seat tubes, etc, would still be "visible" if viewed head-on.


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