The exact estimate will depend, as I said, on wind direction (pure head/tail wind, or quartering headwind out, quartering tailwind back) and the tires/tubes/road surface but let's ignore those things and say .26 m^2 is right. Are you extremely tall? If not, I'd say .26 m^2 is good but not great, and you have some room to improve. That H3 is quite good when used with with a narrow tire and in pure head/tail wind conditions but less so at non-zero yaw, or when used with a medium width (like, 23mm) tire.


The eyeball isn't a very precise estimator of CdA, but it can often be useful in making suggestions about what to do next.

I'm 6' even. The tt ran straight south to a turn around then north. Also many car, motorcycle, running and bike injuries over the years. Bulging discs at S1 and L5 and degenerative disc disease at C6 and C7 so getting my neck back is a challenge, I use a Rudy Project aero helmet. Even though I do have good flexibility.

I will get some pictures up.

_________________
-For my next trick I will set myself on fire!
-This board and the world in general would be a much nicer place if everyone could just take themselves a little less seriously.
-Sticky Fingers John Rockefeller
-First one over the cliff wins!

Ah. Sorry. I missed the post about the cross wind and speed. It appears from the Garmin Connect graphs that it was very slightly downhill from the start to the turnaround, but your outbound speed was slightly lower and your outbound power slightly higher than inbound. So either the wind wasn't exactly due west or you adjusted your position to be considerably more aero on the way back. I presumed it was the wind, and that you had a net headwind out and net tailwind back. If not, just do what you did on the way back.

So, it sounds like you think you've got some limit in going low. How narrow/wide are you? What's the shape of your back, how'd you decide on that helmet, where are you carrying your water, skin suit or separates, gloves/bare hands, buckles on shoes, tires/tubes, UCI rules or not, type of front brake, how was your number attached, what's your crank length? The Brezzas are sexy as hell but on a flat out-and-back course like this do you need a basebar or could you (should you would you) go AOD (I once laughingly explained AOD to my wife and she unlaughingly forbade me from it)? Just as a reference point, one 6' tall guy has, via anal-retentive OCD and frequent measurement, dropped his CdA down into the .21 m^2 range. But he's nuts.

I believe the wind may have been slightly from the south that day. As far as narrow I go as narrow as the pads will adjust. I,m sure my back is rounded but when I post the pictures that will tell. Yes I do wear a skinsuit and had a short sleeve on that day. No gloves and Aero booties over Bont A-one shoes. I chose the Wingspan because my neck injuries only allow me a tilted view down the road more head down. my Giro Advantage 2 would stick up since cranking my neck all the way back is something I can only do for short periods of time. At the shorter distances like this run we don't use numbers and I don't have any water bottles on the bike, no cage either. If I were in a 40K I would have a single water bottle on the bike.

Lastly, I think I'm low. My stem is -17 degrees but I do have 8mm of spacers under the stem. Here is a side picture of the bike to give an idea of drop. Then bike is a size medium.

_________________
-For my next trick I will set myself on fire!
-This board and the world in general would be a much nicer place if everyone could just take themselves a little less seriously.
-Sticky Fingers John Rockefeller
-First one over the cliff wins!

Nice looking bike. I wish the Egg brake fit better to the fork, and I've never been a huge fan of the side cable on that thing. Sometimes a bottle between the extensions (especially if they're *very* slightly inclined) will be better than no bottle at all. Sounds like a good reason to use the helmet you do -- at least, compared to the Giro. As you probably know, helmets should be chosen for the back (and possibly shoulder width) so the helmet that's best on one rider probably won't be best on a different rider. You've (obviously) got the major things taken care of -- the issues that are left are going to be small, incremental, and tedious. A guy I know, just a bit shorter than you (maybe 5'10"), started off at .25 m^2 and through the accretion of lots of .005 improvements is now ~.21 m^2. That took him a lot of field testing over about 18 months.

I use a Garmin 910XT with clip-on aero bars. Man - I would have killed to have your bike during the Wildflower race this past weekend.

Anyways - The way I get over not having to stare at my Garmin throughout my bike leg is to use the watchstrap on my aero drink attachments.

_________________
Cervélo S2 2012 Red
Great minds think alike... sadly, so do the mediocre ones.

Last question until I post pictures or a video. I ran my H3 with a Bontrager aerowing 19 tt tire and Michelin latex tube, would it have been better to run my Zipp 808, not Firecrest, with a 20mm Continental Supersonic tire and a Michelin latex tube?

_________________
-For my next trick I will set myself on fire!
-This board and the world in general would be a much nicer place if everyone could just take themselves a little less seriously.
-Sticky Fingers John Rockefeller
-First one over the cliff wins!

It's hard to beat the H3/Aerowing 19 at zero yaw. The place where the new FC Zipp 808 (and possibly 404) do better is at moderate non-zero yaw -- IIRC, they take a small zero yaw hit in return for better drag at non-zero yaw. I don't remember how the non-FC Zipps compare. You know what would be handy? Having an on-bike instrument to measure and record wind speed and direction. I'll bet people could do some cool things with that.

Cheers for that wheel information rchung! What tub do recommend for a h3 then? Currently on a vittoria cx-tt 21.

Here's my latest TT, yesterday evening: http://connect.garmin.com/activity/176958413

For context- I'm 38 years old, 72kg and a max HR of about 165-170.

I was pretty happy with my average power considering that I've just finished a big block of endurance training with very little speed work (preparing for an ultra). The average speed was okay too. I thought it might be a little slower because I used my ultra bike which has the bars set quite high compared to my TT bike.


Now I'm wondering whether it's any slower at all (or if I can have my aero cake and eat it in comfort ). Does anyone know an easy way to estimate CdA? I have data from TTs on my TT bike. My power is about the same, but they're not over the same course.

What I'm not happy with was a slight fading of my power and drop in cadence early on the second lap.

... and here's a gratuitous pic of the scenery where the race was (Bavois, Switzerland) :

Depends on what you mean by "easy," and the degree of precision you need. The easiest way is in a wind tunnel; precise, but expensive.

There are various ways you can estimate your CdA with a power meter. Some are more precise than others. If you have a flat calm road, the easiest but not terribly precise way is this:



If you don't have access to a flat venue but can find something traffic-free and protected from the wind, you can use the virtual elevation method with an appropriate test protocol, which is what is used by Golden Cheetah's Aerolab module. Another implementation can be found here: http://www.cyclingpowermodels.com/CdAEstimation.aspx Click on "About" to read an explanation.

As promised a few details of some of my races/intervals. First images is of a 50 mile TT from 2010 with slightly dodgy pacing and a puncture. And the other image added today is a 20min hill climb interval.



A CdA of 0.21 is pretty impressive rchung! Am doing some testing at the moment to reduce mine, being 6'1" with broad shoulders doesn't help. I think I've got down to 0.23 with the latest changes (to a Levi style mantis position), I just have to find out if i can pedal at the same output in that position!

Club TT on Wednesday night for more data collection so will post that too.

Scratching my head a little here. Don't have a power meter on my TT bike, but have one on my road bike, and the possible conclusions are interesting or maybe plain wrong

The TT in question was done on a "squared circuit", 2 laps of 6km each, sea level, sunny evening but around 10 C of temperature only, pretty slow wind and many trees around, so I'd guess the wind impact was quite minimal, certainly I didn't feel much.

For the 12km, I produced an average speed of 39km/h which was 2.3km/h improvement from my road bike testing of the same circuit last year. In TT, my HR was pretty close to max sustainable for that length of the interval, and therefore I'd guess the power as well. Now the kicker - on my road bike I could produce approx 300W for the duration, so I'd guess, even if my TT position was pretty uncomfortable (which personally doesn't seem to be the case), I should have put out at least 270W.

From the power models, producing 270W at sea level for 39km/h would solve approx for 0.35 CdA which seems to be quite a high value for a TT bike. For instance, Privateers TT above for his speed and power solves for CdA of 0.28. Too rough of a calculation , do I have the most "unaero" TT position ever , or something else not taken into account? Will post a pic of me from the finish line of the TT in question later.

Using this modeller http://www.cyclingpowermodels.com/Power ... arios.aspx
(Only disadvantages to this site are the inability to change the pressure and temp figures, which are too favourable for the uk! not many low pressure 20 degree days over here!)

I get privateers to be roughly 0.25-0.24 ignoring elevation changes on the overall power average.

and for yourself assuming 270w we get 0.28-0.29, Room for improvement certainly but that's what this game is about. It takes me weeks of turbo+road training on the TT bike to acclimatise to the position or to positional changes to even come close to replicating my road power on the TT bike.

Maybe try swapping the PM over to the TT bike for some testing?? I have to use my Powertap on box section rim for testing which is a significant compromise over a disc, but the accurate information is essential.

One question, I'm assuming the squared course means it has roughly 4 corners, or is a loop, as slowing to corner and lack of pedalling can have large impacts on the figures too. 8 corners would have a large effect on final results.