Question to the aero gurus - "non aero" frame vs Cervelo S5 frame / fork / seatpost

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youngs_modulus
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Location: Portland, OR USA

by youngs_modulus

I think I owe the forum an apology. I wrote my second reply late at night and, frankly, should have slept on it.

My second reply had way more snark than was helpful; I'm sorry.

To the OP, mbrider: Wingguy and I came down on you like a ton of bricks, it's true. I can't speak for him, but for myself, yes, I should have toned it down. I'm sorry that I didn't.

As long as I'm doing the mea culpa thing, I should point out that I somehow didn't see that the very first reply to your query came from Damon Rinard. Given the content of your question, I suspect you may be relatively new to this stuff and therefore may not know that Damon Rinard is one of the few people on the planet who is in a position to give you hard numbers.

He's spent significant time in the wind tunnel and running CFD (Star-CCM+, I believe) to understand/improve airflow for both of the bikes you asked about initially. His recollection of 25 watts is absolutely as high-quality an answer as you could hope to get without some serious metrology of your own. Go with his 25-watt number.

While my reaction was excessive, you might find it helpful to understand what I was reacting to. Again, I don't speak for Wingguy, but I suspect he was responding to something similar. Here goes:

You asked a vague question that was only somewhat answerable, which is just fine. If you knew the answer, you wouldn't have asked, right? Both Wingguy and I tried to explain why this was a hard question full of complicated (and nonlinear!) variables.

You essentially disregarded both of us, which is your prerogative, of course. But in doing so you announced that your question wasn't hard to answer and was in fact utterly straightforward.

You asked us to address your question, and when we did, your response read (to me) as "Nah, this isn't hard. It's easy. Give me an easy number." So, sure: it's irritating to try earnestly to give a helpful answer and then get that kind of response. There may have been a whiff of the Dunning-Kruger effect, too, which doesn't often help.

But none of this justifies the snark I unleashed on you. I'm sorry.

And again, Damon Rinard is about the only person on earth to (a) have hard data for drag on both bikes and (b) be able to compare those data, as they were likely generated in different wind tunnels. It's futile to try to compare absolute drag numbers gathered in different tunnels on different days and by different manufacturers. But since Mr. Rinard collected the data himself in all these cases, he could (and did!) give you a pretty good ballpark figure. Honestly, if I had not been so tired I missed his response, I wouldn't have posted at all. He had it covered.

Dez33
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by Dez33

mbrider wrote:My guess is that there is about a 10 - 15 watt advantage for the Cervelo S5.

What do you guys think?


I would say maximum 10-12. I remember posting the direct comparison between a TCR and Propel and the frame difference was well under 10 from memory. Cervelo obviously better than the propel but I would be surprised if the difference is more than 12. A bit of a guess without actual numbers though.

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1415chris
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by 1415chris

Guys don't waste your time. ...

mbrider wrote:*f##k* this forum - Im out

DamonRinard
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by DamonRinard

mbrider wrote:Specialized Tarmac SL4 with standard handbuilt clinchers 28/32 spokes / regular round bar / cables in the wind / standard brakes sticking out / regular pedals.

What would be the aero advantage of a Cervelo S5 with all the aero do dads (zipp 404s ~ 10 watt / Cervelo aero bar ~ 6 watt / SRAM Etap ~ 6 watt / TriRig front brake / EE rear brake ~ 2- 3 watt combined / aero pedals ~ 2 watt)

Would the aero advantage be 45 watts over the Specialized? 50 watts?

Lets keep this as a discussion about the bikes and not about position. Assume the same position can be achieved on either bike.


Yes, 45 to 50 Watts at 40 km/h is about right. Knock off about 1/3 if you're drafting.
Damon Rinard
Engineering Manager, Road Bikes
Cycling Sports Group, Cannondale
Ex-Kestrel, ex-Velomax, ex-Trek, ex-Cervelo

DamonRinard
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by DamonRinard

Thanks Youngs.

Actually I'm thinking of data from the same trip, same tunnel.
But I'm only recalling, I'm not really sure my memory is perfect...!
Damon Rinard
Engineering Manager, Road Bikes
Cycling Sports Group, Cannondale
Ex-Kestrel, ex-Velomax, ex-Trek, ex-Cervelo

Marin
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by Marin

DamonRinard wrote:Yes, 45 to 50 Watts at 40 km/h is about right. Knock off about 1/3 if you're drafting.



I ride an FM066, 50mm/23mm 20 spoke front wheel, 24mm wide front tire, 40cm aero bars with internal cables. 186cm 77kg rider, tight fitting normal jersey, aero helmet.

I can duck pretty well and I'll need about 330W to hold 40km/h.

A 50W saving would be more than 10% of the power I'm using, or give me an extra 2km/h - and I wonder if my whole bike even eats that much power?

topflightpro
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by topflightpro

Youngs, I don't think you need to apologize so much. Yeah, you were snarky. But that is pretty standard on any forum. I think the OP was overly sensitive to your comments.

Also, there are several other threads that discuss this or that could have provided a reasonable answer. The OP was new and lazy. This is one forum where there is littler tolerance for people who do not do a search first or who ask very basic questions. It's one of the things I appreciate about this forum.

DamonRinard
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by DamonRinard

Marin wrote:I ride an FM066, 50mm/23mm 20 spoke front wheel, 24mm wide front tire, 40cm aero bars with internal cables. 186cm 77kg rider, tight fitting normal jersey, aero helmet.

I can duck pretty well and I'll need about 330W to hold 40km/h.

A 50W saving would be more than 10% of the power I'm using, or give me an extra 2km/h - and I wonder if my whole bike even eats that much power?


In rough terms, sounds about right.

http://sheldonbrown.com/rinard/aero/formulas.htm

See Figures 2 & 3.

Image
Image

Lots of differences in the details, but in general not far off.
Damon Rinard
Engineering Manager, Road Bikes
Cycling Sports Group, Cannondale
Ex-Kestrel, ex-Velomax, ex-Trek, ex-Cervelo

jorisee01
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by jorisee01

Why is it called Dutch style upright? Like with our normal bicycles?


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DamonRinard
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by DamonRinard

jorisee01 wrote:Why is it called Dutch style upright? Like with our normal bicycles?


Looks like this:

Image
(2nd and 3rd images on this page: http://sheldonbrown.com/rinard/aero/measuring.htm)
I translated it from Dr. Pivit's German language, so I guess that's how the Germans identified that bike style in 1990. :-)

Original language here:
http://lustaufzukunft.de/pivit/aero/messung.html
Damon Rinard
Engineering Manager, Road Bikes
Cycling Sports Group, Cannondale
Ex-Kestrel, ex-Velomax, ex-Trek, ex-Cervelo

jorisee01
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by jorisee01

Made me laugh!


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DamonRinard
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by DamonRinard

"A blast from the past!"

LOL :-)
Damon Rinard
Engineering Manager, Road Bikes
Cycling Sports Group, Cannondale
Ex-Kestrel, ex-Velomax, ex-Trek, ex-Cervelo

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Calnago
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by Calnago

Hey Damon.... this is kind of a bit of an aside question, but since you're present in this thread and it is aero related I seem to remember an article in Velonews quite some time ago on the subject of disc brakes in aero applications, and you were asked about that. While you didn't give many specifics you implied you were present for some testing of disc braked setups in the windtunnel, and that you said something to the effect of (paraphrasing to the best of my recollection)... "preliminary results weren't promising". Care to elaborate on that at all, given that quite a bit of time has passed since then? Has anything changed since then? I don't think it's at all surprising but I just find all the marketing around it quite humorous. And I understand if you're not at liberty to discuss since you're still in the industry and all, and disc brakes will be all the rage this year, and probably next, since the manufacturers have had it in their development schedules for all this time. The wrench in the whole marketing plan continues to be the UCI's continued ban on their use. And it's too late for the manufacturers to just flip that OFF switch till the UCI decides it's ok at the Pro Tour level.
Last edited by Calnago on Fri Sep 23, 2016 12:25 am, edited 1 time in total.
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BRM
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by BRM

DamonRinard wrote:
jorisee01 wrote:Why is it called Dutch style upright? Like with our normal bicycles?


Looks like this:

Image
(2nd and 3rd images on this page: http://sheldonbrown.com/rinard/aero/measuring.htm)
I translated it from Dr. Pivit's German language, so I guess that's how the Germans identified that bike style in 1990. :-)

Original language here:
http://lustaufzukunft.de/pivit/aero/messung.html


No it doesn't look like that.
Sorry to say but you were inconsequent in your translation.

The Original Figure 3 speaks about different bikes. Bikes, not style and not a mix of both.
You translated Hollandrad into a style. However right translation would be Holland bike or Dutch bike.
The pic here above you refer too is from another section where they talk about a comparison between a Hybrid Bike versus Aero Racing Bicycle. Its not a Holland bike but a Hybrid.

A Dutch bike is a conventional bike like this >
Image

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cobrakai
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by cobrakai

BRM wrote:
Sorry to say but you were inconsequent in your translation.


Image

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