Wheel questions

sparknote_s said:

1) What is bad about a wheel not being true? If it doesn't hit the brake or anything, is it still dangerous to ride on because it's weaker or something?

2) When you go over bumps, are the wheels the only main part affected? I ask because there are so many goddamn road cracks where I live its like bump bump bump.

1. It may not be "dangerous", but it increases the risks of early failure... due to being weaker. Once a spoke becomes slack the nipple can un-wind and make that spoke tend to slacken easier. Once a spoke is slack it doesn't contribute to handling the dynamic load... and the more spokes that are loose the more risk of permanently bending the rim.

2. All weight bearing parts are affected. Fatter tires can help absorb more shock. Shock absorbing forks, stems, seatposts, and frames all help. The riders knees and other joints can help too, especially when you flex in correct timing.

sparknote_s said:

1) What is bad about a wheel not being true? If it doesn't hit the brake or anything, is it still dangerous to ride on because it's weaker or something?

Puts more stress on the other spokes. Spokes break because of accumulated fatigue over time.

Wheels are pretensioned structures. The Spokes work because they have static tension and because of this tension, each spoke can take a compressive load. Try plucking the bottom spoke on an unloaded wheel and then pluck the same spoke in the bottom once the bike is loaded (and still). Now try the same with the top spoke.

The rim must take the spoke tension load by compression, just like an arch of bricks can support a large load placed on top of it, even without any mortar between the bricks. When the rim is prefectly true, the rim is very resistant to compression. A slightly untrue rim is slightly less stiff in compression and thusly, slightly weaker and more prone to collapse.