The only thing I can refer you to is the zipp brochure

http://www.zipp.com/...ro_edge_flyer_11.pdf

for the 404 they claim
Aerodynamics – time and watt savings over 40k for 404 FIRECREST Wheelset: 80 seconds / 27 watts.

for the 808 they claim
Aerodynamics – time and watt savings over 40k for 808 FIRECREST Wheelset: 96 seconds / 32 watts.

I guess you need to assess how much you trust these claims


I was also wondering if there is a way to estimate watt savings using 'grams of drag' that HED gives on their charts.

aerodynamic drag increases exponentially with speed, so the faster you're going, the more time you save (sort of). so you do also have to factor that into the equation, but the received wisdom is that faster riders 'benefit more' from aero wheels (or gear generally) than slower ones.

-mike

p.s - i say sort of because if you're going faster, you're also spending less time on the course. i'll leave it to the mathematicians to figure that out. . .

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https://lshtm.academia.edu/MikeCallaghan

http://howtobeswiss.blogspot.ch/

Here are some pages that might help:
Wheels:
http://scottkmcmillan.wordpress.com/...-aero-wheels-or-not/
http://www.beginnertriathlete.com/...l.asp?articleid=1099
http://www.cyclingtipsblog.com/...ime-trial-equipment/
http://www.hedcycling.com/wheels/


Helmet:
http://www.examiner.com/...elmet-advantage-real

No.
The faster you go, the LESS time you save.
e.g.
New fancy aero gear = 10% time reduction
Slow rider takes 100 minutes to complete course
Fast rider takes 50minutes to complete course

The slow rider will save 10 minutes, but the fast rider will only save 5 minutes. This is an over simplified example, but the principle here is that the time savings is proportional to the amount of time spent on course. In this case, the slow rider actually benefits more from aero gear.

You can also think of it from the perspective of drag that you mentioned in the first line of your quote "As aerodynamic drag increases exponentially with speed".

This statement is correct, but your conclusion is wrong. The reduction of drag at high speeds will have a lower effect on speed than the same reduction in drag at a lower speed.

Not sure of exact difference between 404 and 808 but it is minimal. Keep in mind the manufacturers and studies are comparing a high quality wheel such as 404 compared to a stock 32 spoke non aero wheelset, such as might be on an entry level Trek bike. That is the 1.5 min difference they claim for a 40k. FWIW this is what I have seen on independent studies.

start here http://www.rocknroadcycleryracing.com/...me-trial-racing.html

After looking at the links Danielg put here, I'm starting to think:
1. In case I'l buy aero wheels, I should consider HED as well (until now I considered only Zipp)
2. I can skip aero wheels
3. I should reconsider TT helmet

Unfortunately, TT helmet is extremely not comfortable (for me) and I think it takes too much wearing time that it looses its advantage.

all of them?

what?

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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

If you have road wheels, a good set of aero wheels makes a notable difference.
An aero helmet does too. It only touches you in the same places a road helmet does. Why is that uncomfortable?

From what I've tried in the store (Giro's and Bell's) - they are too tight around the ears, it's hard to wear them (did I mention they're tight? :) ), they are a bit hot (I live in a bit hot and humid country) and the points where it touches the head (I'm bald), it's not cushioned enough.

Maybe I didn't meet "The One". :-)

Currently I have Mavic Ksyrium SL (which I love), on a Cannondale Six carbon (road bike) with aerobar.
The wheels really responsive, so speed changes are really fast and it's quite fast in general. So I don't know if investing in wheels will give me such a good advantage.
I know speed changes are redundant in TT, but I come from (and will return to) road biking...

Exactly. At lower speeds, the speed increase from a given amount of aero drag savings is bigger than at high speeds. Or in a more concrete way, suppose you are putting out 300 watts at 25mph, and it's all from aero drag. If you save 30 watts at 25mph, let's make the only-slightly-wrong assumption that that's equivalent to you putting out 30 watts more power -- that extra 30W gains you 0.8mph. For the same aero drag, at 20mph would only require 154W, and that 30W savings becomes 15.4 watts (scales the same way with speed) with aero wheels, and you gain 0.65 mph.

So in a 40K (25mi) TT, the numbers go:
300W, non-aero wheels: 60min
300W, aero wheels : 58.1min
difference: 1.9min

154W, non-aero wheels: 75min
154W, aero wheels: 72.6 min
difference: 2.4min



Pet peeve: Aero drag power is not exponential, it is a power law. An exponential dependence would be c^x, where c is a constant and x is the variable. A power law is x^c; in the case of aero drag power, x = speed, and c = 3.

Asad

Then don't get either, smile and be happy that you didn't.

The Limar Crono is your friend.

you could also look at the Rudy Project Syton Open helmet.

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"thoughts become things, choose the good ones"

I have HED Jet 9s front/rear. I was hit with a very strong headwind today- it was a DIRECT wind, maybe a degree or two off center and I could feel the wheels slicing through the wind. There was a moment or two when the road changed degrees and I could feel when the wheel fell out of that perfect spot and when it came back in. I was cruising pretty good despite the headwind and would say the wheels added at least 2-3mph in that situation.

Doesn't matter how much aero wheels will bring you. Fact is, they make you faster.
AND: You enjoy it to look at and use them. This is for me the real reason to drive aero wheels ;-)

PS: have a look at Xentis Mark1 TT

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RUBBERDUCK

When calculating savings for two wheels, 100g on each wheel for example. Can you use 200g savings for calculations or will making a change to the front wheel decrease the savings on the rear? Or is this negligible?

you kinda have to divide rear wheel savings by 4, or thereabouts. since they are shielded and in dirty air.

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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 think Zipp says multiply by 0.75 for the rear wheel.

Or Lazer Tardis. Very roomy and adjustable.

This does not sound right at all. Your fancy aero gear would reduce Cd by a fixed amount, let's say 10% as you did. This does not directly translate to 10% reduction in time at any speed.

Drag is proportional to Cd * V^2, so your slow rider going 1/2 as fast would only have 1/4 the drag. So the 10% savings is applied to the 1/4 drag number, not the double the time number.

When you carry this through, the rider going half as fast only saves 10% of 1/4 of the drag for 2x the time, so that's one eighth the average power savings or one quarter as much total energy savings as the rider going twice as fast.

No, not exactly. A reduction in Cd only saves a given amount of power at a given speed. At a lower speed, the power savings is lower. But drag power does not scale with speed, it scales with speed cubed!

you are on the right track here, but it turns out that within normal human cycling speeds (15 to 30mph) a slower rider saves more time than a fast rider over a fixed distance nonetheless, as the exponential drag curve is not yet that steep in this range.

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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