Assuming the cover fits well and is well secured, not much... as in less than 5secs/40km. Lower hanging fruit elsewhere. If the cover doesn't fit well or isn't well secured, that's a different ballgame.

There is a new company making carbon fiber disc covers that weigh about half what most wheelcovers weigh. Company is called Catalyst. My guess is you train and want to race with power and don't want to invest in another powermeter and a real disc.

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Sometimes it is MORE aero than a standard disc, depending on the standard disc in question, and what frame it is on.

For the most part is makes no difference at all though, on a bike, the difference between different disc wheels in very very small.

Tape it on and it might even be a little faster still:

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

PT Disc wheels are few and far between and pricey. The Powertap provides much more benefit, and the wheelcover provides much more flexibility. If you are running the HED Belgium upfront replacing that with a deeper wheel would be higher on my list than a disc.

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Rodney
TrainingPeaks | Altra Running | RAD Roller
http://www.goinglong.ca

Jack did you trim your wheelcover to fit "inside" the rim? Thoughts on that vs. the traditional taped on the rim?

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Rodney
TrainingPeaks | Altra Running | RAD Roller
http://www.goinglong.ca

No I just asked for the normal Hed Jet 9 trim, without holes for the plastic bolts.

There is no warpage at all, it is a nice fit.

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

I had a Stinger disc that was damaged. Went back to my Belgium PT training wheel and put a cover on it. Don't have any empirical data. Maybe a tad slower than the Stinger, but still pretty damn fast. I run it tubeless, but now I've found out the tire I had on it had terrible rolling resistance and I was still seeing good bike leg results.

With your existing set up one thing you can do to buy some speed cheap is if it is not optimum make sure your tire setup is fast. Schwalbe Ironman tubeless is a pretty good choice, or the Conti 4000S w/latex tube if your running clincher. Depending on what tire you're using now, an improvement there could be worth more than the choice of disc.

Great data: http://bikeblather.blogspot.com/...-tires-clincher.html

FWIW, I'll be replacing the Stinger w/ a Flo disc shortly, running IM tubeless setup.

I'll have to call them and ask. I like the way that fits.

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Rodney
TrainingPeaks | Altra Running | RAD Roller
http://www.goinglong.ca

Wow, that looks a hell of a lot like a Jet or Flo disc! Nice.

Jack I know you answered this somewhere else but are you also taping on the inside (cover to spokes) to avoid warpage? Or is it literally just taping the cover onto the rim as can be seen in your (awesome) photo.

Just taping as seen, no tape on the inside.

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

Tom A did some nice testing on the new IRC Roadlite tubeless tires. Basically the same Crr as the Continental 4000s with latex tubes. So you still have a road tubeless option.

Years ago, when the the first 808 came out, Johnny Carron (JohnnyO on ST) tested a covered 808 against a Zipp 900 disc. The covered 808 was faster.

80-90mm deep rear wheel with a cover just gives you more options.

Any special tape used? Duct tape?

Super 33+ electrical tape.

Yeah 3M brand electrical tape.
Do not use generic, they often do not stick very well.

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

Thank you guys! Appreciate it.