Modern Mountain Bike Design & Geometry

Until the late 1990s, mountain bicycles often had road bicycle style frames and geometry. In the 2000s, mountain bikes often use frames designed for off-road use, which strengthened to withstand jumps and impacts and which use a geometry that allows for much more spirited riding over obstacles like logs, rocks, and ramps. In the 2000s, mountain bikes often have either 21, 24, or 27 speeds, with 3 gears in the front and 7, 8, or 9 gears at the rear wheel. Thirty-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.