No, a disc will be aerodynamically faster. But, some discs are really flexy and that can be a big issue. So I'd still be somewhat picky on the type of disc you get. But in general, 90mm (88mm for zipp) are pretty close to discs in low yaw angles. It is when you get the side winds that the differences really appear.

I would typically agree but check out the plot of the D3 9 with R4 tire in the link I provided above. Of course you cant really compare numbers across different tunnels and even different visits to the same tunnels, but it definitely looks better than the data for the FLO disc and the HED Jet.

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"One Line Robert"

One big difference there could very well be the tire. Its pretty widely agreed that tires and the way the fit to the wheel can affect there aero performance greatly. Another thing with rear wheels and disks is that stand alone wheel test are not the best as the way a wheel reacts to the frame has an effect of there aero performance as well.

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hoppersportsperformance.com

The graph looks phenomenal, but I'm not sure I could buy wheels from a company that espouses this:

Shallower is better.When you run shallower wheels, you reduce weight, decrease the watts required to climb, increase acceleration out of corners, and improve handling on windy days

slightly in pink.

I'm certain Carl didn't have a say in that bit. Sounds like marketing speak to me!

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"One Line Robert"

Other than shallower is better, which is frequently not true due to the increased aero benefits, what else in the paragraph isn't true?

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Styrrell

"shallower wheels increase acceleration out of the corners"

that being said; if i'm wrong so be it, but the original post has nothing to do with arguing over semantics. so that's enough for me.

That's true, all else being equal (including weight and aerodynamics), as shallower wheels will have a lower moment of inertia and require less energy to spin up, hence higher acceleration. But the effect is very small.

I was in the tunnel yesterday with this wheel in the tubular version along with some others and I was shocked how they performed against my Lightweight Disc. Very different results when I was on the bike vs me not on the bike with the different set ups. The conventional ST wisdom certainly did not apply to me.

Details?! Please clarify that next to last sentence.

I was in the tunnel yesterday with this wheel in the tubular version along with some others and I was shocked how they performed against my Lightweight Disc. Very different results when I was on the bike vs me not on the bike with the different set ups. The conventional ST wisdom certainly did not apply to me.[/quote]

[/quote]
I will post details soon. I am still trying not to believe the numbers. The Reynolds RZR 92.2 on the front and rear tested out the best for me.

The disc and Razor were similar at 0 degrees but then the Razor pulled away quite a bit after that.

Again, the numbers were better with me actually on the bike. With me off the bike, the disc was better. The engineer folks I spoke with said this is the case for every person they have tested.

Say whaaaa? Yes definitely more details. Are you going to open a new thread or post within here? Just want to keep an eye out for it.

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"One Line Robert"

I've had the exact same results in the tunnel - various discs were only superior to the 808's and Reynolds 92's at 0 degree yaw. Unfortunately, you're almost never at a 0 yaw.
You'll have better luck convincing the ST crowd that the earth is flat, than convincing them that a disc isn't always faster. I wouldn't even bother trying, just prove it on race day.

Interesting. Things you might want to include when posting details:

Which tires (brand, model, width) on each wheel (and what is the width at the brake track of each wheel), which frame (how well did it fair the rear wheel), and how many repeats of each setup, especially with you on the bike, and what did the variation look like between repeats? Also, rotational drag is likely a bit lower on the disc so this should be taken into account when judging the whole system's drag.

Hello nightfend and All,

It appears the Bonty 90 has a bit deeper rim than the Zipp 808 Firecrest at 81mm (Zipp website: http://zipp.com/...t---carbon-clincher/# ) with at stated rim depth of 90mm.

That may contribute to the excellent stall characteristics of the Bonty 90.

ST's Greg Kopecy wrote some interesting articles on the subject:

http://www.slowtwitch.com/..._Challenge_2991.html

As previously stated the Bonty looked very good on the plot:



http://www.slowtwitch.com/...013_Review_3043.html

http://www.slowtwitch.com/..._Rim_Width_2803.html

Who makes the rims for Bontrager? - The website state OCLV process and that would be Trek .... or is it another company?

Cheers,

Neal

+1mph Faster

I would love to see the windtunnel results that show a disc is slower than a 90mm rear. Especially an RZR, which does not use a blunt nosed rim design, but instead a sharp knife edge style rim.

I will say that it is not just the Slowtwitch crowd that believes discs are faster. If you look at even track racing events, especially with countries like Great Britain and Australia who have spent sizable money on aerodynamics, it has always been conventional wisdom that a double-disc is fastest. The idea is obviously that spinning spokes will always create more turbulence from anything but exactly zero degree yaw that a solid disc would.

Now, someone smarter that me could probably model this on a computer and try and show that at a certain spoke length (ie very short, with a deep rim), that a small amount of extra turbulence near the center of a wheel would actually clean up the airflow on a bike with a rider, thereby making it faster than a disc.

Well it's not just the turbulence of the spokes, but also the idea that, at higher yaw angles, the disc acts like a sail. All this talk about discs being faster only at zero yaw is odd because I always thought they were best at relatively high yaw.

On another note, I've owned a set of Bonty 7 D3 clinchers for several weeks now. Probably have about a thousand miles on 'em (training for B2B relay -- 112 mile TT). When I got 'em, I took a set of Hed Jet 6 C2s off my Shiv TT and put the Bontys on. Haven't taken 'em back off. This will be my third time doing the B2B relay. I'm training hard, but I've trained hard every year. The Shiv has been a nice bike, but I own a P4 that has been my go-to race bike. But the Shiv TT with these Bontys has been a whole new ballgame. I'm setting PRs on route after route and ride after ride (and I'm about to turn 57, don't see many PRs anymore). I asked Carl about a hilly half-iron relay I have coming up and if he thought I'd be better off going with a disc or just sticking with my 7 on the back. He said go with the disk. I'm not so sure anymore. I put wheel covers on the 7 today and rode that hilly half course. I rode it two weeks ago without the covers. Seemed slower on the hills and faster on the flats with the covers. Duh. Net net, it seemed like a toss-up. In the end, speed about the same.

If I could get an Aeolus D3 9 to put on the rear for race day, I'd be all over it. Not available yet. Bummer!

Qualitatively, my 7s are my favorite wheels I've ever owned (and I've owned a LOT of nice wheels).

.

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Stay aero my friends.

Super interesting that you both saw similar results with those Reynolds. I had written them off since the trend has been towards the more blunted shape.

Definitely looking forward to 7summits detailing his findings.

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"One Line Robert"

Are you ready to post details yet on your trip and the different wheel tests? I'm very interested and I'm sure others are as well.

Thanks

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"I swim because that's how I get to ride my bike."

1. you are probably seeing the 9 front wheel compared to a rear wheel which may have a cassette or at least a freehub on it, and different dish or width of hub.

2. most tunnel tests only show the translational drag, not the rotational, which is always less with a disc

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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

Where have you been all my life!?

Could have used your no nonsense commentary earlier! Though I did stick with a disc. Always use disc. Always use disc...

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"One Line Robert"

How many yaw did you test out to?

Did you compare rear wheel vs rear wheel with identical cassettes and tires on them? Or front wheels vs rear wheels?

and so on.

did you measure the rotation drag of each wheel?

and so on

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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

Bobby11- Now that Bontrager is finally selling the D3 9 clinchers are you planning on getting a set? I would be really interested to know how they feel in general and compared to the the D3 7 clinchers. I have the D3 5 and absolutely love them. I've been waiting, a long time, for the D3 9 clinchers for my TT bike.