Hey Rappstar, how much will the way the rider's body affecting the airflow change the raw bike's aerodynamics. I'd imagine that is completely possible that riding knees in vs knees apart could affect the relative benefits of a P3C type cutout vs some other bike. Also, if I recall correctly, John Cobb once showed that when riding a softride it was better to go downhill in a tuck with your knees actually clamped to the top tube/beam but instead apart. The idea was that the air could reattack better behind the legs when apart than when together touching the top tube. Of course, this would not apply to a conventional bike, however it goes to show that rider position and style might also affect the aero benefits from one bike vs another, adding to or negating a particular bike's positive qualities?

Number one...will you all please stop letting science get in the way of our purchases!


Second...I am willing to bet that the person to win Kona will be the one who is most fit...no matter what bike they ride....


Three...golly jeepers I hope it is Pink!

Second...I am willing to bet that the person to win Kona will be the one who is most fit...no matter what bike they ride....

With the P3C, TTX, BMC, or DA how much are they just splitting hairs as to which is the fastest bike? Intentionally omitted Specialized, Ordu, new Slice, Willier since they are very new designs and haven't seen any data or anecdotal evidence on them. Walser could probably be added but was not because to the best of my knowledge is not a mass production design ( Is mass production of a niche market a real term?)

Also, you seem to know a few people, is the Bontrager bottle on the front of Lieto's bike a one off, pre-production, test, Dremel-mod?

The stats are not for the TTX, but rather the new TTX SSL.

I'm constantly amazed at the resiliency of these threads on ST. Bottom line: the difference in aero performance of the top bikes is negligible, and more than canceled out by body position and/or the strength of the rider. So why must we continue to post wind tunnel tests, charts graphs, etc. when it really doesn't matter? Is it because it's the off-season?

Personally, I'm constantly amazed at how many people think that none of this stuff "matters" ;-)

IMO, it's because doing well in timed cycling events ( i.e. TTs or Tri bike legs) is ALL about attention to a BUNCH of little details. This is one of those details. It's up to the person looking at the numbers to decide if they are significant enough to worry about. They, and they alone, get to decide if it "matters".

Personally, I'm constantly amazed at how many people think that none of this stuff "matters" ;-)

the difference in aero performance of the top bikes is negligible, and more than canceled out by body position and/or the strength of the rider. So why must we continue to post wind tunnel tests, charts graphs, etc.

It happens with all equipment based hobbies, part of the fun. . . . .

Thousands of years ago, when our species was still evolving, obsessive and persistent acquisition of the very best weaponry (spears, clubs, arrows, etc.) was a trait that had tremendous survival value. For example, with a slightly improved spear, you could overwhelm an otherwise vastly superior foe, armed with the old, non-dimpled spear. So this trait was honed and bred into us through natural selection. Thus, in modern-day sport (i.e. sublimated warfare), it's only natural for us to hew to this strongly imprinted trait.

Spoken like a real 'watt trader', Tom.....

Is it just me, or do those drag numbers not add up for a 130lb TT specialist??

those numbers are off if they are for Levi. Allied confirmed he tested at like 0.19, lowest they'd ever seen.

Trek's press release stated they were for Levi ...

Hmm. As Colonel Klink used to say, "interesting.....veeerrrrryyyy interesting."

what do Cervelo have to say? ;-)

Wrong fictional German soldier:

okay .. the name Colby Pearce comes to mind ... just fishing .. .

What do you find most interesting about the.019? Do you think that's low for Levi (I don't), or that they haven't tested any male athletes lower? He's pretty damn small.

Ummm...aerodynamically speaking (i.e. the "stats" shown in that plot), the TTX and TTX SSL will be identical.

Thanks, I guess I'm just a dumbass, but I'm guessing that he found having the bottle on the front was better than nothing at all. I don't really understand that, but I'll take the word of people smarter then me. Nice touch with the straw coming out, that makes it not a fairing?

Yeah...a CdA of ~0.25 - 0.26 does seem a bit high for Levi. But, like I've said, not knowing the details of the comparison, it's tough to put any value on the differences shown in that chart. I'm thinking the comparison may actually have been from Basso (who would've had a P3C to compare to, right?).
--------------------------------------------------------------

Do you remember this photo:




Note the yellow drag history that the rocket scientists at Pezcyclingnews neglected to blur out. Way back when I pixel counted that to determine that Basso's drag was, in fact, .254. I think I posted the calcs here and on weightweenies somewhere at the time.


-- jens

err .. thinking of a 'low aero drag' male candidate .. that's all ..

As to why it matters...because when people go and buy a new bike, lots of people would rather spend the money on what is proven to be the fastest. They may not be right, but it definitely exists!

Nope, the frames are in fact different (at least 07 TTX vs. 08 TTX SSL; not sure if they made the changes to all TTX models for 08). New fork, new downtube placement, and some other changes. They cover them in the article.

I'm thinking the comparison may actually have been from Basso (who would've had a P3C to compare to, right?).

part of the confusion (here and in numerous other threads) is the generic use of "TTX". There are three basic model families, across a couple years of production:

TTX - the original, roadie geometry, 1-size only

Equinox TTX - inspired by the above, steeper geometry, several other diffferences (1.125 steertube fork, some tube shape deltas both subtle and obvious, etc)

Equinox TTX SSL - lightweight version of the above


I claim no knowledge of head-to-head aero differences between the first one and the following two. But absence of evidence is not evidence of absence :-)


Carl

in the article, it says "Now we've opened the flood gates of debate there are a couple of key features that make the TTX an interesting Time machine. At the all important front a wider bladed fork blade allows air pulled along by the tyre, rim and spoke to pass more freely through the fork.

Which raises an interesting question: what are the odds that the bike was tested using a HED3? (I now need to go look again at that pic that Jens posted.)

It appears to be a Bontrager Aeolus front.

Here's the whole article:

http://www.procyclingnews.com/...ullstory&id=4807

This is pretty clear about the comparison between the frames. They even matched up his outline on the screen to make sure he was in the same position on each frame

It appears to be a Bontrager Aeolus front. Here's the whole article:

http://www.procyclingnews.com/...ullstory&id=4807

This is pretty clear about the comparison between the frames. They even matched up his outline on the screen to make sure he was in the same position on each frame

Note the yellow drag history that the rocket scientists at Pezcyclingnews neglected to blur out. Way back when I pixel counted that to determine that Basso's drag was, in fact, .254. I think I posted the calcs here and on weightweenies somewhere at the time.

Well, just putting my micrometer on the screen and measuring the ratio of the low point of the yellow drag history vs. the height of the graph, I get 15mm/20mm for the P3C and 5mm/7mm for the Trek.

That would give the Trek 5% less drag.


-- jens

Wait, no what a dumb***. The scale doesn't start from zero. It goes from 2000 to 3000, so it would be a third of that: 1.6%


-- jens

1.6%? But I thought someone said "the top frames only have 0.2% difference between them?" ;)

You're kidding right? One guy puts a micrometer up to his computer screen and you're willing to make frame choices based on this?[code]

You're kidding right? One guy puts a micrometer up to his computer screen and you're willing to make frame choices based on this?[code]

Of course. That's where I get all of my numbers.

As we've discussed, that graph probably doesn't represent Lieto. It's more likely Basso.

And yes, it's quite possible that a different rider -- particularly one who pedals with his legs at a different width -- would interact differently with the two frames. But , Ceteris Paribas (that's Economist-speak for "let's assume away everything"), I would put my money on the Trek.


- jens

the drag/speed numbers imply a Cda around 0.245-0.255. For a small guy like Levi that's surprisingly large. Perhaps he ought to hire Jens/Tom/AC as consultants :-)

If the numbers have been 'adjusted' to protect his true data that should have been stated ...

Something does not quite compute ... else my spreadsheet is just way off.

This is pretty clear about the comparison between the frames. They even matched up his outline on the screen to make sure he was in the same position on each frame



-- jens

Back in March, Trek got Pezcyclingnews to write an article on the February tunnel testing with Basso on a Equinox TTX and a P3C and the difference was "within the margin of error". According to several people who were at the tunnel, it took 2 days of changing Basso's position before they could get his drag as low as on the P3C in his original position, so the TTX was only as fast as the P3C because they improved his position, not because the bikes were equally fast. According to my sources, there was a significant difference in favor of the P3C when the rider positions and the parts used were the same.

Coming from a gov't economist, nice use of "ceteris paribis!" A better translation would be, "all else being equal" but you got the idea of it.

"Now, with the endless options in carbon material, lay-up, shapes combined with the intense lack of know-how in most of the industry means that the variation is much bigger in the overall spectrum"


Could it be that the options for variation are much more than the options for significant gains? Hence, why we have marketing departments.

You're right. This is all highly questionable. Collectively we put this together and didn't realize the implications.... I retract putting my money on the Trek bike. FWIW, my $ seem to be on Cervelo bikes, given that I've spent more on them than on my car.

-jens

The outline on the screen method is next to useless. We did that in the past, but the line is so thick relative to the rider size that you can easily have a 1-2cm change in rider position without noticing, and that can make quite a big difference in drag. The one thing you can see with the outline is that a rider never keeps his position during a test, and therefore that it is impossible to make the sort of equipment comparisons that Trek is trying to make. It's not that the movement of the rider is a problem per se for the aerodynamics, it is that you cannot guarantee that the rider will make the same movements from one test to the next, and so that comparison is invalid. That is again why we use the test dummy, so that we can make the comparisons between equipment without having to wonder if we are really measuring equipment changes or rider changes.

. . .

Interesting. This implies that wind-tunnel testing of individuals is not that worthwhile.

We're creatures of habit: maybe a static pose will come out different. But I suspect when you get on a bike and pedal for five minutes, on average, your movements are going to be very close to identical. In my own field testing experience, I get very consistent numbers in the same position. Also, I can click my camera timer, then run and hop on the bike and get identical photos nearly every time -- and that only gives me about 15seconds. In the tunnel, the adjustments needed to match the outline were quite minimal.

Boy, that wind tunnel seems about as leaky as a certain drug testing lab in France...

It seems that no testing is done at 15 or 20 mph, always at 30mph. You could model the results and calcualte for slower speeds, but how do you know your perfect 30mph shape doesn't stall out at 18 or 20mph and is actually worse for your average Joe? Is it a limitation of the wind tunnel?

...even the Kestrel KM40 (not the Airfoil, due to tube shapes)...

The Zipp 2001/3001, Lotus, Cat Cheetah, Corima Fox, Softride, and even the Kestrel KM40 (not the Airfoil, due to tube shapes) all bring something special to the table that just can't be replicated under UCI rules. I am not saying that every one of these bikes is faster than a P3C, but I know some of them are

ETTX (and SSL variant, for that matter) to original TTX...relative to the bold stuff anyway.

There used to be a nice "side by side" (top and bottom, really) picture of the two right here...tried calling it up last night and the pix weren't there anymore. Odd, since one of them was mine. Maybe you can resurrect?

Carl

Thanks for the response. What I am gettting at is: Let's say at 30mph you have your rider and and your smoke gun and you see perfect airflow from their shoulders down to their butt. If you then slow down to 18mph and the airflow is the same, I agree with your linear relationship. But if at 18mph the airflow breaks off mid way down the riders back, wouldn't that negate the linear relationship?

Because I've tested every one of the bikes I mentioned except the Cat Cheetah and Lotus on the same track under the same conditions with the same (and different) position/wheels/aerobars/etc. The numbers are obviously only good for me and are dependent upon my body, flexibility, riding style, etc. I have held and measured a Cheetah though, and it's every bit as well designed as the Fox in most parts, and better in several.

The order of performance has been:

1. Zipp 2001 (this was/is not mine unfortunately)
2. Softride Rocket TT w/ custom internal cable routing and fairing to fill the poorly executed area in front of the rear-brake and some work around the beam joint. A Bonty speedbottle works really well there.
3. Corima Fox - I had to do a lot of work to get this to fit me reasonably well. It was really too small for my leg length although the TT length was fine. Had to build a custom seatpost to acheive proper seat height and angle.
4. Kestrel KM40 (despite it's lower level of aero performance, this is a fast and comfortable bike that I prefer to ride most of the time)
5. Aegis Trident

Some of the ordering on the lower end (3, 4, 5 changes with different wheelsets. The KM-40 specifically does better than the other two with Nimble Crosswinds).

Now obviously I am not working with Trek or Cervelo's funding and I have constrained myself to bicycles that use 650c wheels, but I suspect there aren't more than two or three non-professional fitters/aerodynamics folks out there who spend more time testing than I do. I am working with minimal wattage that doesn't seem to improve that much with training, so the application of my brain is all I've got.

Chris

Felt testing put the Lotus, Zipp, and Felt DA all ahead of the P3C. I don't recall all of the details, but at the very least those 3 were mentioned.

In grad school, I had the good fortune of getting the noted economist Jagdish Bhagwati as the professor for one of my econ courses. With his Indian accent, it sounded like he was saying "get her asparagus." It took us days to figure out what he was talking about. Great course, though, and this is coming from someone who is abysmal in economics.

Big Mig's hour record Pinarello, Ulle/Riis Pinarello from 1997 TDF, , Carbonsports Total Eclipse,

No, I can't score a P3C or Felt 650c in my size, since I have a 36.5" inseam. P2 classic and P3 alu are both options, but given that Cervelo asserts that the P2C is faster than the P3 alu, I didn't think it was worth bothering with that one. I am still intending to put a P2 classic through it's paces vs. the Softride.

I am in no way asserting that Cervelo isn't doing their homework or working tirelessly to create some beautifully aero bikes. I also don't believe the TTX design is faster (though maybe in the same range) they are clearly both using a lot of FEA and CFD as well as tunnel time to develop the bikes. What I don't like is discounting entire designs based on poor implementations of a core idea (like removing tubes). With the advances in carbon over the past 10 years, certainly a narrower, better shaped softride/zipp could be constructed using the expertise of Cervelo's engineers.

Chris

When did I say that my theoretical improved design wouldn't include a rear wheel fairing?

In point of fact, it does (currently made out of shaped foam glued to a piece of aluminum that is screwed into my lower bottle cage mount.

It's the space above the wheel but below the rider that I tend to dislike, mostly because I have a 37" saddle height and there is a LOT of space there for me.

When my fairing is actually finished and usable, I will post a picture.

Chris

No, I test on a 3/8 mile auto race track. Very windy most of the day, but calm in the morning.

I test with wind direction/speed, temp, humidity, etc all being recorded at 5 second intervals on my laptop. It's good to have an in with the physics department where I went to high school.

The orientation of the track I test on is approximately perpendicular to the wind coming off of the bay in Eureka, Ca. Variation seems to be only about 10 degrees during the summer afternoons at this location. It's an oval track, so the bike/rider/wheels will see pretty much every yaw angle possible.

I originally started with an SRM Amateur system and then moved up to an SRM Pro.

Spot the engineer!

the major flaw that I've always seen in these designs (since I was a little kid in fact) was that the air separates after the down tube and then must be broken again by the wheel with all of downfalls that you mentioned. Filling the gap so that air is only broken by the down tube and then remains attached all the way along the rear wheel gives you the advantages of both worlds.

Really? I assumed that you were based on the advice you've been giving people and the questions you were asking!

Sorry 'bout that.

No need to apologize - I've been called worse. ;-)

That's right...he could have called you a physician.

Cees,

Are you referring to the new Giant TT bike? It seems to be a step back from the new age TT-bike thought.




Never had I considered non-uci bike as obsolete as after this thread. Very eye opening.

That almost looks like a geometry prototype. It's neither the Trinity Alliance nor the Trinity Carbon. Wonder if it's a one off built to test a specific geometry (or for the specific needs of a given rider)?

Rapp, any chance you'll expand on your initial thought in the BTR insiders?