You'll save about a minute over 40 kms with an aero frame. But do consider that even some of the "aero" frames aren't really that aero. Some of the high end carbo bikes have downtube aspect ratios around 1.6 to 1. That's not that aero. At least Cervelo has got the tubing thing correct.

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"You'll save about a minute over 40 kms with an aero frame. But do consider that even some of the "aero" frames aren't really that aero. Some of the high end carbo bikes have downtube aspect ratios around 1.6 to 1. That's not that aero. At least Cervelo has got the tubing thing correct."

I've been unable to find wind tunnel data that supports this claim of one minute per 40 km. for aero tubes. What is your source for this number?

We'll be making an aero frame soon, just want to know if it's worth bothering with aero tubes or we should get more radical with aero frame design.

Craig Calfee

Get radical. Although I think there is room for both. Something like a bike with an aerodowntube as an entry level bike, easy to make with lugged construction (like the new Elite). Then something crazy as your creme de la creme...

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"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp

Can you grow bamboo with a 5:1 aspect ratio and NACA approved form - that would be pretty radical

"I've been unable to find wind tunnel data that supports this claim of one minute per 40 km. for aero tubes. What is your source for this number? "


http://home.hia.no/~stephens/aero.htm

Thanks for the info.

Looks like around 5 minute improvement over 180 km.

The reason I want to just change out the frame set is because all my racing stuff is 650. Plus I like 650s.

Conrad

Unless you do sub 5hr bike split, i shouldnt bother, you are only really going to get noticable advantages at ave speeds of at least 20mph +.

On the other hand, if you want a new toy - buy it! You will feel faster, which will also make you ride faster! Triathlete psycology - look good, feel good, race good!

Here's an interesting article: http://www.blackwellresearch.com/...Bicycle%20Tubing.pdf

I have completed 9 IM some were on big round tubes, some on aero tubes, some with STI some with bar end shifting, I can't find any stat difference in the times which range between 4:55 and 5:15.

My advice find the bike that your comfortable on, as the bike won't make much difference, but the run now were talking about making up time, oh but I forgot people don't care about the run on ST.

Damn it Craig, when you going to get it out? I was just talking to Skeen yesterday about a new Calfee ride but now I hear this! I am saving my pennies already.

I am on it when you build it!

Those "estimates" are all based on someone averaging 30mph. Anyone have any data on more typical IM speeds (17-21 mph)?

The flow regime at 17-20mph is really no different than at 30mph. At slower speeds, you'll actually save more time. The percentage savings in terms of aerodynamic drag will be lower, but your net time savings will be higher because you will be on course longer. People seem to think that airflow at 30mph is *totally* different than at 20mph. Air at 300mph is very different in terms of the fluid dynamics involved vs. air at 20mph. 30mph is the common test ground for a couple reasons -- 1) it is the speed that most pro cyclists go during TT's, and those guys are generally where the big money goes, and 2) windtunnel scales are only so sensitive, so it's easier to pick up the larger differences in drag at 30mph. Since flow at 20mph and 30mph are basically indentical, it makes sense to test at a higher speed where you can actually pick up the changes in CdA more easily, since interpolating down to 20mph is quite accurate. Cervelo gives good estimates for the changes in speed at 30/25/20mph in the tech section of their website.

The real issue with riders at 17-18mph is that they are probably less committed to remaining in the aerobars "at all costs" the way a sub 5-hour rider would. If you are on the bike for 6-7 hours, you probably don't care quite as much about being as aero as possible all the time. So if you are out of the aerobars for a long stretch of time, that makes such a huge difference in your CdA that an aero frame is probably less important than a frame that is comfortable and allows you to be comfortably in the aerobars, whether that frame is aero or not.

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"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp

once again, 30 mph is typically referred as "apparent" speed. This is a combination of rider speed and the wind they are riding in to. John Cobb, 10 years ago, stated that it is quite easy for the average age grouper to see 30 mph of apparent speed (riding 20 mph into a 10 mph wind, etc.).

For more data, I'm not sure if Cervelo still has their info on their site, but at one point it actually demonstrated why slower riders gain more of an advantage (because they are out on the course longer).

The one thing NOT mentioned thus far is, while the frame may end up saving 1 minute over 40k, this can easily be negated by less than optimal positioning. If that QR round tubed bike is the old 78 degree seat angle model, the person originating this thread may suffer position issues if he is comfortable on that steeper bike. Also, the QR forks worked great at reducing drag with aero wheels. At the time, Steve Hed actually told me that the Hed 3 was the fastest wheel on the market using the Carbonaero fork, but with a standard fork, was actually one of the slowest (thus demonstrating the relationship between wheel and fork is more important than either independently).

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Craig Preston - President / Preston Presentations
Saving the world with more professional, powerful, and persuasive presentations - one audience at a time.

No wind tunnel data here but estimates of drag based on an aero frame having .3 pounds less drag at 30 mph.

Cobb measures an aero down tube at less than .01 pounds drag but doesn't give the drag data at the same windspeed for a round tube.

Anything more out there with just the minimal amout of data to prove a result?

Do I have to go rent a wind tunnel?

Yes you do and also hire people that know what they're doing.

I remember back in the day when Cervelo started to show up with the P2 and true aero-tubing. They started to sell well and I remember Dan Empfield with a position very similar to yours now. He eventually made some changes, first with the carbon gusset on the Kilo PR and then the Redstone came out. This was almost 10 years ago...

The Redstone is such a badass frame. I want one for my collection someday for sure. Not many going across ebay these days though :-(

Chris

Craig, some of Ed burkes books and the newer one edited by Asker Jeukendrup have apparent times obtained by Cobb and Jim Martin. This may be enough for you. My advice would be that unless you really are going to go very VERY aero you can take anecdotal design cues from your other competitors.

Personally I'd like to be part of some velodrome tests to give me a better idea of differences that i could view in real time to get my head round this tricky question.

or he could probably just call John Cobb. John likes to talk to people....alot :-)

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Craig Preston - President / Preston Presentations
Saving the world with more professional, powerful, and persuasive presentations - one audience at a time.

No...30mph of headwind is 30mph of headwind. It very nearly* takes the same watts to ride 20mph into a 10mph headwind as it does to ride 30mph on a calm day. The only reason the watts aren't exactly the same is because rolling resistance will be a little lower at the slower speed.

*EDIT: See post below for calculations. There is a difference in watts, and it's not as small as I first guessed.

John Cobb knows this, and almost certainly never said what you're attributing to him.

I just want to reinforce this point. At slow, AG speeds, you actually save MORE time from aero improvements than the elites do!

Any time you hear somebody going along the lines of, "you have to go 30mph for it to make a difference, or ride <5 hours for it to matter...," you can immediately conclude that they have no frigging idea what they're talking about. Don't take any aero advice from such people. Politely excuse yourself and walk away.

Did you use a powermeter, and ride the courses on days with no wind? No? Then you can't make that conclusion.

If you're going to throw out references to statistical differences, you are bound by the rules of using statistics. It would be more appropriate to just guess, and say that you're just guessing. It's not cool to just make stuff up and present it in a scientific wrapper.

Actually, you are incorrect. John and Steve Hed also discuss the theory of "apparent" wind in a video they made back in the 90's (Wind Tunnel Magic). I have a copy somewhere in the garage (it is the same video where they discuss the aspects of bone length in the legs determining location of foot over the pedal spindle). There have been NUMEROUS occasions where John has discussed usage of 30 mph and how it applies to "apparent" speed. Years ago, it was even posted on his Bicyclesports website.

30 mph does NOT mean you MUST produce 30 mph of speed on the bike alone. You actually just pointed this out by stating "It very nearly takes the same watts to ride 20mph into a 10mph headwind as it does to ride 30mph on a calm day". It is for this reason that the average, every day middle of the pack triathlete can still make use of the numbers even when they reference a "speed" of 30 mph.

I'm VERY familiar with much of what John has said over...well...I'll narrow it down to the past 10 years (as are many others who have been around the sport that long).

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Craig Preston - President / Preston Presentations
Saving the world with more professional, powerful, and persuasive presentations - one audience at a time.

You missed something -- you correctly agree that it takes nearly the same watts to ride 20mph into a 10mph headwind as it does to ride 30mph on a calm day (it's not exactly the same power, due to (1) rolling resistance, and (2) the lower ground velocity in the wind resistance portion of the equation).

However, you then go on to say that an every day MOP triathlete would have that experience of pedaling at 20mph into a 10mph headwind. Au contraire! An MOP triathlete CANNOT pedal at 20mph in a 10mph headwind for more than a few seconds! That's a 349 watt effort (CdA=0.27; Crr=.005). In a 10mph headwind, an MOP triathlete will be going <15mph (in a 40k; less in long course). Therefore, it is NOT TRUE that an MOP triathlete will experience a 30mph headwind for more than a few seconds, under any conditions whatsoever (expect going down a hill).

Example: 200 watts with a 10mph headwind yields a 14.96mph road speed (CdA=0.27). Net effective headwind = 24.96mph. 200 watts with no wind yields a 19.93mph road speed, and effective wind.

What Hed and Cobb are apparently doing is talking hypothetically. Real, live MOP triathletes will never, ever have 30mph of wind coming over the bow in any situation other than a descent. I'm not an MOP triathlete on the bike, and I sure can't ride at 20mph in a 10mph headwind.

Look, Cobb is cited as a co-author of the seminal paper on the mathematical model of cycling. Using the equations and conclusions of that very paper, all of the above is true. If he appeared to say something different in another context, I can only assume he was talking hypothetically. Feel free to send J. Cobb this post and tell me what he says.

Chicanery

If you want a Redstone QR - you dont need to do ebay. RAcycles has a "brand-new" 51 in their triathlon "sale products" section - 800USD in size 51cm.

Would buy it myself if it would fit, but i normally ride 58cm and the stem and seatpost would just be toooo long.

So if you are shorter than me : here is a link to the best x-mas gift to yourself: http://www.racycles.com/...tone__00_3791135.htm