Bicycle Mechanics - Solid Wheel
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10-21-08, 09:50 PM
Excuse my noob status. Anyone care to give me an articulate explanation, from a physics standpoint, as to why racers have solid wheels in the back, and wheels with spokes on the front?
A bridge between optimal aerodynamics and fear of losing control in a cross wind.
Front wheels are for control and handling and a strong cross wind will make handling impossible so unless you are racing in the doldrums, using a full disc up front is not advised.
The back wheels carries a lot more weight so it is less affected by the same wind therefore a full disc is more common there.
Having air flow in random directions around you spokes causes more resistance than giving the air one smooth (though sometimes dimpled like a golf ball) surface to flow over.
Note the skin suits that have barely exposed seams, the shoe covers that hide all the lumpy buckles, the helmets that have very few if any vents, the full disc chain rings, and the visors instead of sunglasses that all add, sometimes minutely, to the same effect.
Or did you want numbers and formulas and stuff? The only science I do is social science so I can't really do any better.
10-21-08, 10:46 PM
Laminar flow. The energy available to maintain this flow decreases in relation to the angle. A falling water-drop shows the most optimal shape requiring the least amount of energy to re-join the air behind it.
Geez, Danno you know everything.
Or you are just very good at research and reference and should be a lawyer.
10-22-08, 12:24 AM
If he was a lawyer he wouldn't know nearly as much.
10-22-08, 09:34 AM
Due to the angle of the head tube, the centre of the front wheel is in front of the steering axis. Tis makes the front wheel aerodynamically unstable so you need to reduce the side area of the wheel. A mudguard on the front wheel will improve the aerodynamic stability since most of it is behind the steering axis, however it wont reduce the aerodynamic drag.
Joshua A.C. New
10-22-08, 10:10 AM
A niggly thing: laminar flow at bicycle-like scales is difficult to achieve (you can scale a wing, but you can't scale the air), and in real-world applications like actual bicycles covered in actual humans with the wind going wherever, just about impossible. The dimpled surface is, like a golf ball, to make a turbulent (but thin) layer of air, called the "boundary layer", stick to the surface, rather than separating and making a thick, chaotic parachute of air. It's much easier to create and maintain that laminar flow.
Also, it's not that the rear wheel has more weight on it. It's that the leverage is totally against moving your entire body sideways, skidding the tire. On the front wheel, it only has to make the wheel pivot a little bit at the wrong moment to require dental work.
Unfortunately, most of the drag on a bike is from the front spokes, as they're going twice as fast through the air as the rest of the bike at the top of the wheel and nothing else has moved the air out of the way yet. That's why front wheels often have three or four wing-shaped spokes.
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