So before my time at Zipp, they made a 3 spoke..actually the whole wheel progression went disc, 3 spoke, spoked deep section rim..which is surprising to people. The 3 spoke was initially looked at as more of a disc with cutouts to allow for better handling. In the mid 90's testing was done that showed the performance of these wheels was diminished in frames and forks.
I went to the tunnel in 2002 in preparation for a USPS team test and and looked at this quite extensively. We found that of the out of production Zipp, the Hed/Dupont 3 spoke, Mavic iO and Mavic 3G, the 3G was the best performing in the bike in terms of aero. The Hed 3 was best in wattage to spin, and all 3 of them suffered 2-5 watts of translational or rotational drag when placed in a fork or frame compared to their wheel only performance. The guys at the tunnel suggested we use sound pressure equipment to look at the contribution, and we found a good 1-2 (maybe more, hard to remember..) watts of sound pressure lost to those pulses of air when the blade suddenly cuts through the fork legs. Doing the math, many of those forks had the air-space between blades diminished by a third when the blade of the wheel cut through. We ended up building a quick and dirty fork concept out of Indy Car A-Arm strut that had 100mm fork crown and parallel fork legs. It looked goofy and was terrible to ride because it wasn't stiff, but as of 2 years ago when I left Zipp, it was the fastest fork we'd ever seen in the tunnel. It also notably diminished the noise from these types of wheels AND improved aero in testing. However, by then we were on to the 808 which was way faster than anything we'd tested previously and really from then on, just never looked back at the composite spoked wheels.
I will say that composite spoked wheels really look great, and I think are loved by pros as they not only look awesome, but sound cool and feel fast as they tend to be pretty harsh vertically. We went through a whole 3 days of testing trying to convince Alberto Contador to ride the 808 as he insisted on riding the 3 spoke and it was like a scene from a Monty Python movie..he'd go out and do test loops on both wheels and every time come in saying 'see I am faster on the 3 spoke' and every time he had put out more watts on that wheel..this happened multiple times and finally he says, 'yes, but I do not trust this 'data' I know what I feel...' and that was that. Like all of us, those guys like to feel fast and feel like they look fast!
I haven't tested anything since 2013, so I have no idea where this stands today. I see many companies going to much wider fork spacings and also the composite spoked wheels are evolving..so I'm sure it's very interesting!
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