This is really interesting stuff and will make sense to you straightaway if you've ridden a lighter modern bike and a heavier retrobike and thought the old bike was faster.
These guys did experiments with timed runs and power taps: I've precis-ed mercilessly, so I've removed a lot of the experimental detail, so if you want to check the likely validity of what I've quoted you need to see the full articles.
http://janheine.wordpress.com/2013/02/1 ... f-physics/
In the last issue of Bicycle Quarterly, we compared the performance of a 17-pound titanium racing bike and of a 26-pound steel randonneur bike. We were surprised when both bikes climbed at the same speed in a set of controlled experiments. Others shared our surprise, but added: “That cannot be true. Physics require that the heavier bike climbs slower.”
..If we always put out 600 Watts during these climbs, then any added weight will slow us down, all other things being equal. And an extra 9 pounds is significant enough that it should be measurable. There is little disagreement on this.
And yet the two bikes did climb at the same speed, despite their different weights. It’s clear then that our power output was not constant. On one bike, we were able to put out slightly more power than on the other – just enough extra power to equalize the weight handicap.
..Why did we put out more power on some frames than on others? In the above-mentioned double-blind test, we found that frame stiffness and how the frame works with our pedal strokes influences our power output. Here is how we think this works: There are different factors that limit our power output on a bike. Our hearts beat at their maximum, we are gasping for air, our legs start burning…
Our absolute maximum probably is determined by our maximum heart rate. As anybody who has trained with a heart rate monitor knows, it often is impossible to reach one’s maximum heart rate. (I used to reach ultra-high heart rates during runs that I could not achieve on my bike.)
Why can’t we always reach our maximum heart rate? The limiting factor is our muscles. If the muscles aren’t able to use the oxygen our heart pumps to them, then there is no use for our hearts to beat faster. And if one bike frame leads to more rapid muscle fatigue than the other, then our power output will be lower on that frame. (In running, I may use more muscle groups, so the cumulative oxygen use is higher, hence the higher heart rate.)
Most cyclists have experienced inexpensive bikes that simply were “dogs” and did not perform well. We often try to explain that lack of performance with extra weight or other factors, but these bikes don’t perform well even on the flats, so one has to look for other reasons. And most of these inexpensive bikes have heavy, stiff frames that may fatigue our muscles prematurely.
http://janheine.wordpress.com/2012/08/0 ... ance-bike/
Performance: Our research has shown that the frame determines the performance of a bike. The frame must work with the rider, allowing them to generate more power with less fatigue. Such a frame will encourage the rider to go faster and ride more.
It appears that the stiffness of the frame, and especially the balance of the frame tubes, is crucial for creating a frame that feels “lively” and eager to go. Based on the preferences of our testers, Jeff Lyon used thinwall tubes in standard diameters for our L’Avecaise test bike. The result one of the fastest bikes we have ridden.
Interestingly, the best carbon frames use a similar balance of the frame tubes – relatively flexible top tube, somewhat stiffer down tube, very stiff chainstays.
On the other hand, even small deviations from this formula, for example, an oversize top tube on an otherwise standard-diameter frame, do not seem to work well for many riders. Thinwall oversize tubing can offer great performance, as long as all tubes are increased in diameter, and the balance of the frame is preserved.