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Until recently, mountain
bicycles had road bicycle style frames and geometry. Mountain biking has
since become more mainstream with riding styles becoming more aggressive.
Newer frames are better-designed, lighter, and stronger, with a geometry
that allows for much more spirited riding over obstacles like logs, rocks,
wooden bridges, and man-made ramps.
Newer mountain bikes have either 21, 24, or 27 speeds, with 3 gears in the
front and 7, 8, or 9 gears at the rear wheel. 30 speed mountain bikes are
currently unworkable, as a slimmer 10-speed chain is not strong enough. The
critical angles in bicycle geometry are the head angle (the angle of the
head tube), and the seat tube angle (the angle of the seat tube). These
angles are measured from the horizontal, and drastically affect the rider
position and performance characteristics of the bicycle. In general, steeper
angles (closer to 90 degrees from the horizontal) are more efficient for
pedaling up hills and make for sharper handling. Slacker angles (leaning
farther from the vertical) are preferred for high speeds and downhill
stability.
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