real answer: you will never know. (far too many variables to lock it down)

answer you WANT to hear: 3:01 faster


take which one you like.


Tim

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Tim

Well, I know the real answer is I wont ever know.. but what is the likely answer? 10 seconds or 60 seconds?... I know going from regular aluminium wheels to disc is a huge difference but from a 404 to a disc, probably not a big difference right?

Is it just a few seconds on a 40k?

Somewhere between zero and ~8W depending on wind. 8W would be around 70 sec. Discs provide the most benefit when there is a high crosswind.

Actually if it is hilly and calm, the disc would lose you time.

Yeah not huge

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Tim

Get a wheel cover from Wheelbuilder.com for $89 and get back to us on how much time you save.

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''Sweeney - you can both crush your AG *and* cruise in dead last!! 😂 '' Murphy's Law

32s.

That is not correct. Roughly speaking, 50g of drag savings @ 30 mph = 5W = 20 seconds time savings over 40K.

So, if the savings were really 8 watts, he'd be saving 32 seconds over 40K.

I can't find a yaw sweep for the super 9, but there's a pic showing it at -32 grams of drag on zipp's website. The 404 drag on zipp's chart bottoms out at around 80 grams at 15 degrees yaw. So the minimum delta between these wheels is likely in the ballpark of 100 grams. So realistically, he'd be looking at around 40 seconds of time savings. Probably more if there is a strong crosswind, probably less on a perfectly calm day.

There is also less watts required to spin the disc, a factor not generally shown on yaw sweeps.

Don't remember how big of a deal that is, I think "not much"

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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

Very true. I don't think I've ever seen that quantified anywhere (Tom A would be the one to ask), but in theory that makes sense.

If you dig through the search, you might find the Zipp rep mentioning it.

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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

You will look faster. Thats reason enough to get the disc.

So, if the savings were really 8 watts, he'd be saving 32 seconds over 40K.

Not sure how I screwed up there, but this is the calculation I was trying to do. Assuming nominal power of 230W currently.

(238/230)^.38= 1.013... .013*63*60= 49 sec ... not the 70 sec I posted earlier.

I verified this with a detailed physics model and got precisely the same result. How do you arrive at 32 sec?

At TT speeds an average yaw of < 10deg is normal. The gain with a disc doesn't become significant unless the crosswinds are pretty high.

The aero drag of a 404 Firecrest can be compared to 3 different disc wheels here: http://www.tour-magazin.de/...r/epaper_4_2011/page96.html


EDIT: I see the likely source of your error. 8W at 38km/hr is very different than 8W at 30mph.

8W is 8W no matter how fast you're going ;)

Now, I *think* the assumption that 100g of drag @ 30mph = 10W = ~1 sec/k takes into account the scaling down of speed to typical race speeds. But I don't know that for sure. I've found this rule of thumb to be pretty close in my experience. In other words, comparing wattage data from the same TT course on days with similar conditions, it comes out to be that 10W = ~1 sec/k. My average speed is around 25-26 mph.

And the sound. Also worth the price of admission.

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Amateur recreational hobbyist cyclist
https://www.strava.com/athletes/337152
https://vimeo.com/user11846099

I tried measuring the spin difference between a 404 and a covered 404 at 25 mph on a stand with a quarq and couldn't see any difference. I saw about 4 Watts difference between a round spoke training wheel and the covered 404' so my guess is not much.

8W is 8W no matter how fast you're going ;)

When we are talking about aero drag, 8W at 38 km/hr is 16W at 30mph.

Zipp used to have a very nice chart that showed the time savings in a 40k for it's various wheel sets. I looked, but didn't find it. I think it was pre-Firecrest.

I think the savings with an 808f/900r vs. and 808f/808r was 8 seconds. I'm not sure, though and I'm also not sure if it was the 900 or the sub9.

What you wanted I think :
[URL=http://imageshack.us/...ppaeroedgeflyer.jpg/][/url]