Aerodynamics vs. Weight

Quoted post said:

Originally posted by isdsms
I just thought it would be somewhat interesting... Does anyone know of a ratio of how a quanity of drag compares to weight? I've been looking at two different bikes; the Cdale R2000 and the Kestrel Talon. The Cdale Caad7 frame is about 2.4 pounds. However the Kestrel is about a pound more, but is aerodynamicly(if thats a word) designed. I've ridden them both- they're both very lively frames and seem to be a perfect fit for me. I've got to admit however that I'm somewhat leaning towards the Kestrel just because of the sex appeal. Any advice towards this alternatives? Thanks in advance for any feedback.

About the ratio thing- Could anyone also apply this towards wheels? Such as a 1800g tri spoke vs a 1400g 34 mm deep rim?

isdsms

Take a look at the article, formulae, and charts at URL:
http://www.sheldonbrown.com/rinard/aero/formulas.htm
Especially look at the chart "Power requirments for different bicycles"
Then URL:
http://www.bicyclesports.com/aerodynamics.asp

What kind of riding are you doing?
How fast will you be going?

Quoted post said:

Originally posted by isdsms
I just thought it would be somewhat interesting... Does anyone know of a ratio of how a quanity of drag compares to weight? I've been looking at two different bikes; the Cdale R2000 and the Kestrel Talon. The Cdale Caad7 frame is about 2.4 pounds. However the Kestrel is about a pound more, but is aerodynamicly(if thats a word) designed...About the ratio thing- Could anyone also apply this towards wheels? Such as a 1800g tri spoke vs a 1400g 34 mm deep rim?

Weight on a frame is static, and will only make as much difference as you can feel while riding it (especially while accelerating and going uphill). If you *feel* no perceivable penalty, then it's not much of an issue. In any case, a more aerodynamic frame will give less drag at speed.

Wheels are a bit different because they are turning with respect to your speed. Two wheels can have virtually identical weights, and yet can behave very differently. It is the distribution of weight which is important. If one wheel has a lot of its mass near the edge, it will require more effort to accelerate it. Typically, there is some trade off between aerodynamics and acceleration. Which you get depends on what you need.

Oh yeah, and then there is the motor that is pedaling the bike...

Quoted post said:

Originally posted by isdsms
I just thought it would be somewhat interesting... Does anyone know of a ratio of how a quanity of drag compares to weight? I've been looking at two different bikes; the Cdale R2000 and the Kestrel Talon. The Cdale Caad7 frame is about 2.4 pounds. However the Kestrel is about a pound more, but is aerodynamicly(if thats a word) designed. I've ridden them both- they're both very lively frames and seem to be a perfect fit for me. I've got to admit however that I'm somewhat leaning towards the Kestrel just because of the sex appeal. Any advice towards this alternatives? Thanks in advance for any feedback.

About the ratio thing- Could anyone also apply this towards wheels? Such as a 1800g tri spoke vs a 1400g 34 mm deep rim?

isdsms

Wind resistance doesn't come into play heavily until you reach higher speeds say 20 mph or so and its not linear with speed. Mass plays a minor role in acceleration and decceleration, but mostly plays a role with gravity when you are climbing.

On a level surface mass only affects the amount of work required to change your velocity. At a constant speed mass has no effect at all. Wind resistance affects both the work required to increase velocity and sustain it, but again comes into play at higher velocities. So aerodynamics are much more important at higher speeds where wind resistance dominates over mass in affecting the amount of work to both accelerate and maintain speed.

When climbing you are typically at speeds where wind resistance is much less dominant than mass. When climbing more mass requires more work to gain elevation. The steeper the hill the slower you will be going and the more dominant mass will be over wind resistance.

For the case of your frame you need to decide whether all out speed (aerodynamics) or climbing ability (mass) is more important. Having said that the difference in drag between the frames will probably have less impact on speed than the mass difference will have on climbing ability.

The same concepts apply to the wheelsets as well, but for the wheelsets there is one other factor to consider and that is where the mass is concentrated on the wheel. If the difference is in the rims and spokes then the mass difference will be concentrated further away from the rotation center. This is called rotational mass, and less rotational mass means less work for equal acceleration.

These two variables are so insignificant in relation to one another, they are not worth thinking about Get the Kestrel because of how it makes you feel.