Triguy

Cannondale is slightly right, that their Evo is probably more aero than their Supersix. However, as was pointed out, CdA is a two part equation; frontal area and coefficient of drag. Cannondale is blowing smoke. Cervelo, Felt, Specialized all created aero bikes with a lower frontal area and aero shaped tubes.

Anyway, about 8 years ago time trial frames were this way. I was talking with Steve Hed and he said that the round tubed steel bikes of the 90s were as good as many of the first carbon time trial frames (like Scott's original Plasma) because the downtubes were soo friggen massive and the shapes not that refined.

c3hamby

If you use steel it makes the wind disappear.

Not good on hot days, makes ya sweat more. And ya can't get a tailwind either.

Debusama

OK, so this is the article I was referencing: https://velonews.competitor.com/2011/...six-evo_171341

As much as Id like to think reviewers on Velo News are accurate and objective, I'm sure ad revenue from Cannondale had some influence on what went into the article. Nonetheless, all the arguments presented in favor the aerodynamics of the skinny round tubing of the Supersix sounded equally applicable to skinny steel bikes.

"It’s skinny Though the Evo frame has little or no aerodynamic shaping of the tubes, Denk, who tested the bike extensively in the wind tunnel, chose to concentrate on frontal area rather than the shaping most designers of aero frames focus on.
To understand this, consider a number of frames being compared in a wind tunnel at a given wind speed. The formula for drag force is:
A = frontal area (surface area facing the wind)
cd = drag coefficient for the object. This is altered by changing the shape or surface texture of the object.
(X is a multiplication sign only)
However, we can ignore the quantity ρv2, because it will be the same for all of the bikes, since ρ is the mass density of the fluid (air, in this case), and v2 is the speed of any of the bikes relative to the wind.
That leaves us with:
(times a constant, for the sticklers).
It is very common for bike designers to focus on the shaping of the frame, in other words, to try to reduce cd, the bike’s drag coefficient. But if the tubes are large, they can still end up with a high drag force slowing the bike, because the drag force equals the bike’s drag coefficient cd multiplied by the bike’s frontal area A.
Denk has done very little shaping of the tubes on the Evo, but he has made the tubes narrower (he’s reduced A but not cd). By going from a 1.5-inch lower headset bearing to a 1.25-inch one, he reduced the head tube diameter by 11 percent. He made the fork blades 15 percent thinner. He made the down tube 20 percent less wide. Also, the narrow midsection of the top tube allows the rider’s knees to come in closer, thus reducing drag.
By sticking with a round down tube, which is the stiffest shape there is when opposing torsion (twisting), the most important force the down tube deals with, Denk eliminated the problems of forces going around corners in non-round tubes, which create forces pushing the walls in or out. And a round shape, especially when it’s cutting through the air at an angle the way the down tube does, is not bad aerodynamically; it’s far better than a rectangular tube, which creates a large low-pressure area behind it pulling it back, as well as whose walls pop inward and outward under torsion. Denk further stiffened the down tube by using the carbon lug it slips over (the lug is part of the bottom bracket shell, molded in a single piece with the seat tube) to stabilize the shape of the very thin down tube so it won’t beer-can under torsion or lateral forces."

asgelle

Note while Zinn says it's common fo focus on Cd, he provides no source or data for this assertion. In fact, the better designers focus on the force and work with Cd and A to acheive the lowest force consistent with the other desired performance parameters. In other words, Zinn should always be read with a high degree of skepticism

tanguy frame

When I studied fluid mechanics we looked at drag vs. surface roughness at a variety of Reynolds Numbers and found that there is a dip in Cd at an optimal roughness, then drag increases with roughness. I made the comment that birds will ruffle their feathers in flight to optimize drag, instinctively taking advantage of this phenomenon. Of course , they all looked at me like I fell off the moon, but you can't argue with truth.

When will frame maufacturere impart surface roughness to their finishes to optimize drag? Actually - I want adjustable surface roughness. And sensors to automatically control the degree of roughness to minimize drag.

JohnDThompson 

What portion of the total drag is due to the frame? I suspect the rider contributes significantly more to the total drag.

KendallF

I used to have (and wish I hadn't sold) a Rex TT bike with steel aero tubing. It had a microscopically short head tube, an elliptical down tube that was probably 1/2" wide, bladed seat stays, an aero extended seat mast..it was pretty trick. I would bet on it beating the majority of "aero" frames out until the last 3-4 years (i.e., the P4/Shiv/Speed Concept bikes).

caloso

Being from Sacto and all, I see quite a few of Steve's bikes, but this may be the prettiest one of all. That's awesome.

mvanderk

Give me a brak..........Some people need to get a life........

Seattle Forrest

Rider is the most significant, then frame and wheels are about neck and neck.

bisiklet

FIFY

As far as I can remember, a blunt (even hollow) rear profile causes an inwards (positive) turbulence which helps lessen the drag. It boils down to the direction of turbulence at the rear gap. Outwards or irregular turbulence increases drag, while inwards turbulence decreases it. It's sensible, as inwards turbulence would fill the vacuum gap at the rear which is the main source of drag. So, while it's a heavier drag than an ideal "tear drop" rear profile, blunt or hollow rear profile has lighter drag than a cylindrical one. This is surely a more detailed subject but again, AFAIR.

Jsiegs

Round is not aero, even if it is super skinny...it's physics.

bidaci

A round tube is round at 90 degrees into the wind. But you downtube is not at 90 degrees. It you tilt into the wind a round tube it becomes more elliptical to some extent. Add that the downtube is behind a tire and the seatube is behind the tire as well as the rider around both, it probably only matters at an elite level.

Debusama

Well, I guess that settles it!

asgelle

The time savings from an aero frame for a 40 km TT are on the order of 10's of seconds (more for slower riders). If you think places aren't decided by less than that in non-elite competition, you aren't paying attention/

bidaci

You are right and I agree 100% on an aero frame over round tube or lighter. What I meant was the difference in drag between a round tube at 90 degrees vs a tilted round tube.

canam73

I think my family is really happy that I don't sweat the places that an extra 10 seconds costs me in a non-elite competition. They're not wrong.

justkeepedaling

Your family might be, but I'm sure Heinrich's parents are happy that he does.

https://www.youtube.com/watch?v=DvpWMjMF9GE

canam73

Invalid, he's a pro. We were talking non-elite.

Soloist Assassin

Most races are decided, by a second or less. I think that is what he is alluding to.

pallen

Frame aerodynamics are less of an issue in mass start races like that though. Its more about you teammates and a hundred other factors. TTs are another story.

asgelle

Have you ever gotten tired in a flat road race? Why do you think that is?

canam73

I got that part. My commentary was directed towards the idea that most amateurs aren't independantly wealthy and that if they have a family that depends on them then their time and resources would be better spent on something other than f***ing around over a 10 second aero advantage.

pallen

Not saying it isn't an issue at all, just less of a factor.

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