Debusama

So, in reading the pitch on the new Supresix evo, Cannondale claims that the reason why the aero-shaped tubing on other bikes is necessary is because they need to compensate for the larger frontal area of the thicker tubing that is required to provide the necessary stiffness. They claim the Supersix is more aerodynamic because Cannondale had developed some kind of extra spiffy super-stiff carbon that doesn’t require such thick tubing and that the smaller frontal area of skinny tubes trumps Aero shaping for drag reduction.
Assuming there is at least some truth to this claim, why not make more TT bikes from steel. Since the main focus of TT bikes is aerodynamics rather than weight, one would think that Strength to surface area ratios would be more important than strength to weight. Even for an all-around race bike, wouldn’t the Aerodynamic advantages of the skinny steel tubing compensate, at least to some extent, for the weight penalty? One other thing that wasn’t mentioned, but that came to my mind because I live in an area where cross winds are a fact of life, is that the flat aero-shaped tubing is more susceptible to cross-winds than a frame that gains its aero-advantage with skinnier tubing.

For those of us who can't afford, or aren't willing to pay for a new Supersix Evo, Wouldn't it seem that a Steel frame is Actually a better alternative to comparably priced fat-tubed CF and Aluminum bikes than we give it credit for?

RacerOne

Stop talking this non-sense. Everybody knows more expensive bikes are faster.

Spookeay Bird

Yep whats the rule? 1 grand removes 1 gram? or something like that!

Nerull

From Sheldon Brown:

In (17) Kyle presents investigations of commercial frames. Compared with a Gios steel road frame, an aluminum Cannondale frame with rider brought a reduction in aero drag of around 1.6%; a Trek aluminum frame was appropriately even with the Gios, a Kestrel 4000 composite frame brought a reduction of 4.7% and a very complex aero bike by Gleb - this time with 32 aero spokes instead of the 36 round spokes with the other bicycles - obtained an advantage of 7%. The track machines for the 4000 m individual pursuit riders of the US team in the 84 olympics showed an aero drag reduction of about 16% compared to the Gios road bike.

This is with 1984 tech.

Frontal area is not always more important than shape, or velomobiles wouldn't exist (And be much faster than road bikes).

patentcad

coasting 

I must be going nuts because this kind of makes sense in my addled little mind.

MrTuner1970

No comment on your mental state, but it sort of makes sense to me also.

AdelaaR

Aerodynamicity is not especially related to "frontal area" and more to "not creating turbulence and drag".
Carbon aero frames will always be better over all, be it only slightly.

Inertianinja

I was under the impression that round tube bikes are very non-aero compared to other designs...the round tube makes for very dirty air streams.

FlashBazbo

In simple terms, it's a math problem. (For our closet physicists, let's keep this in layman's terms.) Roughly, the relevant equation is "frontal area" times "coefficient of drag" equals what I'll call "drag." (Not technically accurate, but close enough for cyclists' discussions.)

IF you keep the coefficient of drag the same, you can save a ton of drag by reducing the frontal area. If you want/need a bigger frontal area, you've got to reduce the coefficient of drag in order to keep total drag the same.

If big aero bike tubes were round, the little steel tubes would be vastly more aerodynamic. But they aren't. Tube shaping tries to make up the difference by reducing the coefficient of drag. No doubt there are aero frames built today that beat the old round steel tube on total drag. On the other hand, I strongly suspect there are "aero" frames being sold today that are not as nearly as aero (frontal area x coefficient of drag) as an old, steel bike frame. They look cool -- and they probably have a much better coefficient of drag -- but you factor in their relatively huge frontal area and the total drag goes way up. It is hard to make up for a doubling in frontal area. A lot of stylish aero bikes offer twice the frontal area and more.

adclark

Just something else to think about is how much power is wasted when flexing a steel bike. I don't know exact figures but it may very well make up for the better aerodynamics. I have a steel Bianchi which has slightly oval tubing and a carbon bike with a huge, completely unaero downtube. I notice that for the same perceived effort, the steel bike flexes a lot more than the carbon bike which hardly flexes at all. I don't know if this actually wastes much if any power, but just something to think about. Of course you could always make thicker tubing for any of the bikes and probably add strength at the cost of weight.

StephenH

Looking in the Fluids textbook, drag coefficient based on frontal area is 1.2 for a cylinder, 0.6 for a 2:1 ellipse aligned with the wind. (Or, 0.3 and 0.2 for turbulent flow, and all at a Reynolds number of 100,000). The moral is, changing the shape has a major effect on drag, and a tube can be considerably larger and have the same or reduced drag if it has a superior shape.

Also, when looking at overall drag, a lot of the frame is either behind other frame members or behind the front wheel, as opposed to just being a tube out in clear air.

FlashBazbo

Okay, I posted the basic equation.

Now, let's talk reality. The wind doesn't always come from straight ahead. The rider's helmet aero properties have a greater impact than the bike frame's aero impact. And, once you add that saddle pouch for your spare and your bike computer on the bar, you've eliminated any benefit that multi-thousand dollar aero frame treatment might have given you without them. It's vastly cheaper and vastly more effective, aerodynamically speaking, to wear a skinsuit all the time. (The rider represents the biggest frontal area / aerodynamic load by a multiple over the rest of the bike combined.)

Or . . . lose five pounds, wear the next size smaller jersey, ride the un-aero steel bike, and you're probably ahead of the game.

Soloist Assassin

....and then there are aero bikes designed to reduce frontal area, and beat the wind.

david58

I figger I've saved over $20K just by losing weight. In another $20K worth, I might consider something aero. Like maybe a tight jersey.

I don't have the reference at hand, but I think the biggest bang for the buck for aero is to install and use Aerobars. After losing weight.

However, my round belly is more aero than your flat one, isn't it?

pallen

This is true. A small round tube is much worse than a slightly bigger aero shaped tube. I still love my steel bike though because all of this is just a tiny slice of the pie.

canam73

Some of them old schwinns had some skinny tubes PLUS solid bladed forks. That would be too fast.

merlinextraligh

And how do you think this flexing is wasting power? The energy has to go somewhere, such as being returned when the flex rebounds ( which is one reason people often refer to steel frames as being "lively")

Unless your frame is smoking (from the heat being given off) I doubt your losing any meaningful amount of power to flex.

pallen

yes, steel is very elastic, which means that very little energy is "lost" in deflection and return. It may go into a non-useful direction, but it is not lost.

Fedor

pallen

That frame has damping devices that are designed to remove energy from the system. Steel is elastic and has very little dampening effect.

AdelaaR

A general misconception indeed.
If you are moving at a speed of 25mph, which is a normal speed for TT's and thus the reason aero frames exist at all, there will be a constant "headwind" of 25mph even when there isn't any actual wind.
This means that you need at least a 25mph tailwind to not have any effect at all when travelling at this speed.
This means that if there is, for instance, a slight sidewind of, let's say, 10mph ... that you still have a much bigger headwind of 25mph added to that slight tailwind.

I don't know about you ... but personally I seldom go out riding on extremely windy days where wind is over 25mph.

asgelle

You need to work on your vector skills.

Seattle Forrest

Balderdash! Red is the fastest color.

pallen