How Mountain Bike Gears Work

The gears in mountain bikes just keep getting more
and more intricate. The bikes of today have as many
as 27 gear ratios. A mountain bike will use a
combination of three different sized sprockets in
front and nine in the back to produce gear ratios.

The idea behind all these gears is to allow the
rider to crank the pedals at a constant pace no
matter what kind of slope the bike is on. You can
understand this better by picturing a bike with
just a single gear. Each time you rotate the pedals
one turn, the rear wheel would rotate one turn
as well (1:1 gear ratio).

If the rear wheel is 26 inches in diameter, then
with 1:1 gearing, one full twist on the pedals
would result in the wheel covering 81.6 inches of
ground. If you are pedaling at a speed of 50 RPM,
this means that the bike can cover over 340 feet of
ground per minute. This is only 3.8 MPH, which
is the equivalence of walking speed. This is ideal
for climbing a steep hill, although bad for ground
or going downhill.