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.

To go faster you'll need a different ratio. To

ride downhill at 25 MPH with a 50 RPM cadence at the

pedals, you'll need a 5.6:1 gear ratio. A bike

with a lot of gears will give you a large number

of increments between a 1:1 gear ratio and a 6.5:1

gear ratio so that you can always pedal at 50 RPM,

no matter how fast you are actually going.

On a normal 27 speed mountain bike, six of the gear

ratios are so close to each other that you can't

notice any difference between them.

With actual use, bike riders tend to choose a front

sprocket suitable for the slope they are riding on

and stick with it, although the front sprocket can

be difficult to shift under heavy load. It's much

easier to shit between the gears on the rear.

If you are cranking up a hill, it's best to choose

the smallest sprocket on the front then shift

between the nine gears available on the rear. The

more speeds you have on the back sprocket, the

bigger advantage you'll have.

All in all, gears are very important to mountain

bikes as they dictate your overall speed. Without

gears you wouldn't be able to build speed nor would

you be able to pound pedals. The gears will move

the pedals and help you build up speed.

There are all types of gears available in mountain

bikes, all of which will help you build up a lot

of momentum if you use them the right way.