Marginal differences, I'd guess on the order of a few seconds at most over 40K.

The biggest difference, however, is that the older discs are narrower, so to get full aero benefits you need to run the narrower, higher rolling resistance tires.

  
Until recently I used to have one of those older model hed disc wheels. Raced the crap out of it for years over some horrible roads. I stood up well to all the abuse I threw at it. The only reason I sold it was because I bought new tri-bike and I wanted a newer set of race wheels to go with it. Providing it is true and round there is little reason to discount it. As posted above, any aero difference between this wheel and the newer ones is probably minimum.


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Once, I was fast. But I got over it.

Even if I get an old narrow disc I plan on using 25 mm tires. Bad idea?

Personally I'd use 23mm! But it's not a bad idea in the sense that it's anything worse than giving up a few more seconds/40K.

I'm thinking in the back with part of the rim and tire being hidden behind the frame, and with the turbulence, gainings in rolling resistance and comfort would outweigh the extra drag from 25 mm tire on 19 mm rim. Probably splitting hairs anyway :-)

This.

OP: Based on the limited data I've seen on such subjects, the answer is very minimal. Also the HED DEEP in that first picture is legit, albeit heavy. Those may have been the first toiroidally shaped wheels (circa early 90s I believe). From before Zipp was a factor in the wheel game. Steve Hed was way way way ahead of the curve with this stuff, RIP.

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Jordan Oroshiba --- Roadie invading Triathlete space for knowledge access

The old HEDs were heavy too. 1200g or so

Yeah, I was about to say that the difference in drag is so tiny, you might want to consider weight more than drag.

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^^^^^This.

Tire width has much less of an impact on a disc since it is both shielded behind the seat tube and the airflow doesn't have to repeatedly vary (like with a deep-V). I know Jordan races with a 25mm tire on the rear due to the minimal drag difference, but the gains in comfort, handling, and reduced rolling resistance. Personally, I run a 23mm Conti on a 19mm Renn 575 disc.

Used discs are a great deal. Since they are race-only wheels they typically have very low mileage. The "true" discs (structural carbon, not a cover over spokes) are typically bombproof (they have to be since truing is not an option).

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ECMGN Therapy Silicon Valley:
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So, i had this delima a while ago, though it was with an HED3 not a disc, but i talked to HED and they said that on a tri/tt bike, a 23mm tire on a 19mm rim is fine because the frame hides the wheel anyway. So, if you run a disc, go for it with a wider tire on the back. HED says that it doesnt affect aerodynamics

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Just. Be aware that old wheels may only take thread on freewheels, not cassettes. Just check the compatibility, if it's a thread on freewheel then it won't work with 9/10/11 speed freehubs/cassettes.

[URL=http://s1285.photobucket.com/...zps1f0c73f4.jpg.html][/url]

not sure that the freehub versions of that disc can be converted to 11speed either.

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Get the old disc

It's a freewheel. I've got 34/50 in the front so if I can find a 7 speed 12-18 freewheel it should be ok.