as you noted, your conditions changed throughout your ride with the wind increasing as the day went on. you are not going to get a good comparison. was same way at my tt yesterday, 100mi from you. the earlier you went the better off you were. my being 98th in line was not so good as it would have been to be 1

we also don't know if you rode in the exact same position at exactly the same time for both laps

Well from what I can gather from wonderful formatting numbers on the second lap:

Disc = 209AP/213NP and D9 = 221AP/229

Hmmmmmmmmm. Rode the same? I do not think so.

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Formerly TriBrad02

Single Bong?

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

"If ever the time should come, when vain and aspiring men shall possess the highest seats in government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams

I was going to say the same thing. Riding the D9 with ~10-15 more Watts will defiantly show the D9 to be faster.

yep, more like hack a lung. :) allergies last week became chest infestation Saturday afternoon. all I can do is cough now and try and recover over next 2 weeks, or 4. looks like more softball coaching and less riding for a bit

Ugh....struggling with allergies, too, but not that bad!

Was gonna do the Single Bong, but too much yard work was on the schedule so had to bail. At least it was warm this year!!

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

"If ever the time should come, when vain and aspiring men shall possess the highest seats in government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams

The "sailing effect" of a wind coming in from the side at just the right angle with a disc can be significant. You can actually feel the bike surging and you are not putting in more power!

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Steve Fleck @stevefleck | Blog

So, you went slightly faster, in higher wind, with lower watts when using the disc. Sounds like a win to me.

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Ready or not here I come!
Coaching NY's Southern Tier
Swift^3

Sorry for the formatting issue with the numbers. It looked good this morning on my desktop.

But to correctly state the AvgPower and Normalized Power values over the entire loop:
Disc: NP 224w and Avg P 218w
D9:NP 229w and Avg P 223w

A 5 watt spread over 4 hrs is pretty close. Assume I was in the aero position for most of the ride as well. Of course there are going to be some differences out there, but its not like I rode sitting up with D9 and aero with the disc.

 
In case some formatting helps...

Are you looking to see a bigger effect for your $2500 purchase? The thing is you probably wont. You are looking at roughly a minute or 2 and 5 watts saving in windier conditions. Versus the wheel you are comparing thats about the extend of it. Its VERY condition dependent as you can see with your splits of the Verona course. overall you *should* come out ahead with the disc, but its probably slight with all things else being equal.

Thanks for the feedback. At least I look fast. That's half the battle.

I played around with Best Bike Split after Ironman WI. Switching between disc and 90mm, if I recall, was less than 1 minute on that course. The biggest difference was switching between butyl and latex tubes. Latex tubes would have gained 7 minutes! Wish I would have played around with it before I actually did the race because I ran butyl. Maybe because of all the hills aero has a bit less of an effect??

I've been seeing the same thing on BBS with my model for IMTX. I'm actually faster by 3 minutes with front/rear wide 90s and latex than with a 90 front and disc (which I used last year). Very different course from IMWI, so this is kind of mind-boggling based on the 'disc-is-always-faster' adage. Depending on certain choices it may not be always faster and is very dependent on tire/tube, wheel width choices and conditions. As a rule of thumb with all things maximized then yes a disc is, but it might be close enough that in triathlon its not a big deal.

It depends, under the ideal head/tail wind condition, the difference between disk and deep wheel is not that much.
But IRL this condition will not really happen a lot. So yaw involves. And yes under side wind condition disk has a big advantage on normal deep wheel. When air goes through the spokes and hollow part of wheel turbulence occurs. Therefore drags you.
Your power data explained good, disk saved your watts. At most of time.
Also data shown that disk cover performs even better than normal disk wheels. But it's UCI illegal, not sure about Ironman. It's a better solution than $2500 purchase under certain circumstance

Remember hearing from a bike shop once that terrain matters when it comes to the disc ... i.e. a pancake flat course (aka more consistent speed) v. a lot of climbing & descending (aka speeding up and slowing down more). Any thoughts on that?

Try another bike shop.

I think that was one test, pitting one wheel cover against one disc wheel. I don't think it can be generalized to state that wheel covers are better than discs as a rule.

After using my $90 disc cover for the past 5 years, I can feel a noticeable difference.

Discs are not faster. Suggest two things. You send that D9 to me. I'll dispose of it. And next time we race together you should ride the $200 OEM wheelset the bike came with. They are all the same anyway. :)

Buys most expensive wheel on the market. Runs mediocre tires.

A disc is your fastest option....no one said it was massively faster than a 90mm rear. However, if you have access to both run the disc.

BTW, good on you for doing the test and sharing the data.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

18 mph on 225 watts on a TT bike with a deep front and a disc?

Were you wearing parachute pants?

Haha true, But I tried bunch of "disk" wheels, one is made by Hed, not the high end ones, I noticed it's basically a normal wheel has spokes covered by two piece of plastic/carbon?