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Technical Topics

Before commencing on looking for the right bike, one should ask what is the terrain that he/she will

pedal mostly on

• Straight and level

• Slightly inclined long distance hills

• Short distance inclined hills

• Mostly Moutainous terrains.

 

This answer to the above question will influence the kind of transmission system you will need on your

bicycle. This is explained by using the concept of gear ratio. Gear ratio is the ratio between the front and

rear gear sizes. To illustrate this concept, we shall use the below parameters as an example:

Choosing the right bike

With two gears linked together by a chain, so if the front gear turns at a speed of 60 RPM (which is a

common cyclist cadence), then the rear gear rotational speed can be computed as:

(20 cm / 10 cm) * 60 RPM = 120 RPM

So the rear gear will turn twice as fast as the front one. This is the basis of how a cyclist can change the

speed of his bicycle while keeping the same pedaling cadence.

It is important to note that THE HIGHER the gear ratio is, the HARDER it is on your leg muscles peddling

the mechanical system.

If you are still following so far, you can now understand that the gear ratio of any given bicycle will have

a great impact on its effective speed limits, as well as the effort you will have to provide to make it move

forward in various road conditions.

In reality, as all gear teeth geometry is constant over all gears (since the same chain must run around

any of them), we can in fact use the teeth count on any given gear to compute the gear ratio. In our last

example, let's say the front gear had 50 teeth, the rear gear must have had ... 25 teeth. So we could have

simply counted each gear teeth count and compute the ratio as follows:

(50 teeth / 25 teeth) * 60 RPM = 120 RPM for the rear gear

The following table lists the typical ranges of gear teeth count for the rear and front gear of a bicycle,

and what are the road conditions they are typically used.

From the above table, the gears are adjusted to the lowest gear ratio as road conditions get harder for

the cyclist. We also note that the range (from lowest to highest gear ratio) gets narrower for mountain

conditions while its wider for straight and level conditions. These values basically describes typical race

bicycles (at the top of the table) to the other end which are MTB bicycle (at the bottom of the table).

Keep this in mind as you shop your bicycle. You can either ask for the technical data sheet of the bicycle

you are interested in, or you can simply count the number of teeth present on the biggest and smallest

front and rear sprockets and quickly compute the ratios like we just explained above. (extracted from

bikes.jump-gate.com)