Effects of design on speed? I'd like to understand more about how the design of a bike affects its speed (assume a normal, two-wheeled bike with gears).


Can I assume that weight has little effect, on level ground, except when starting and stopping? If not, why not: what is the effect and how big is it?
Are the two biggest factors wind resistance, and tire rolling resistance?


Can you point me towards data for the above:


Rolling resistances for various types/sizes of tire at different speeds
Wind resistances for different rider positions at different speeds


Specifically how much difference is there between e.g. a 700x23 mm tire, and a 700x32 mm tire at 90 psi?
I like to use an excellent power calculator to answer questions like these. Play with the numbers, and you can see the exact effects on wind resistance of different rider positions or changing the type of tire.

In short, at race speeds, wind resistance requires by far the most power to overcome. It ends up being anywhere from 85%–90% of your overall power expenditure. For example, with that calculator, it takes a fully-crouched 150lb rider somewhere around 650W to maintain a 35mph pace. Remove air resistance entirely and it only requires an astonishing 50W. At the same power output (650W), with no air resistance, the same rider could reach a ridiculous speed of 475mph.

Sheldon also covers the topic, providing an excellent cost–benefit breakdown for various aerodynamic improvements. And Wikipedia makes the claim that "lowering a bike's weight by 1 lb&hellip; will have the same effect over a 40 km time trial on flat ground as removing a protrusion into the air the size of a pencil".