Most of the bikes in our store whether is MTB, ROAD BIKE, HYBRID BIKE, FOLDING BIKE, CITY BIKE are equipped with SHIMANO / SRAM bike gear components. Your bike may equipped with Shimano/Sram 18 speed (spd), 21spd, 24spd, 27spd, 30spd, etc. The greater the number the speed, the more gear combinations you can have. Use the bike gear effectively allows you ride the bike further and faster.
What is your bike shifter?
There are few types of gear shifter in market namely, THUMB shifter, GRIP shifter, TRIGGER shifter, Flight Deck shifter (road bike). You must know how to use the gear shifters in order to shift the chain to different gears.
(NOTE: Do not to shift gear when bicycle is not moving)
How to calculate those 21speed / 24 speed bike?
For example, your bike has 24 speed gears which has 3 gears [1 2 3 ] in Front Cogs (Chainwheel) and 8 gears [1 2 3 4 5 6 7 8] in REAR Cogs (cassette sprocket / freewheel).
FRONT gear  can pair with REAR gears [1 2 3 4 5 6 7 8] FRONT gear  can pair with REAR gears [1 2 3 4 5 6 7 8] FRONT gear  can pair with REAR gears [1 2 3 4 5 6 7 8]
Speed = Gear combinations.
What are the functions of FRONT and REAR gears?
Left hand side gear shifter control the FRONT gears [1 2 3] Right hand side gear shifter control the REAR gears [1 2 3 4 5 6 7 * ] .
* Smaller number means LOW gear, larger number means HIGH Gear.
What gear combinations should I be in?
Low gear combinations: FRONT gear , REAR gears [1 2 3 4 ] Medium gear combinations: FRONT gear , REAR gears [4 5 6 7] High gear combinations: FRONT gear , REAR gears [4 5 6 7 8]
Why can not use FRONT gear  pair with REAR gears [4 5 6 7 8]?
You can use that combinations, but it can weaken the drive chain as it is running curve line (see last image below).
* Above sample for 24 speed (3 x 8) MTB Bike.
What are the effect of using HIGH, MEDIUM, LOW gear combinations?
High gear – Heavy in pedaling (low cadence) but bike move fast (normally flat road).
Medium gear – Slight lighter than high gear, but bike move slower (normally leisure ride).
Low gear – Light in pedaling (high cadence) but bike move slow (normally slope or uphill).
Cadence = Pedaling Speed. * Pedaling speed is depending your legs strength
What gear combinations for beginner rider?
Medium gear. Put middle gear constant to  and just shifter the rear gear [4 5 6]. You will feel the slight heavier when you shift the gear from 4 to 5 or 5 to 6.
TIPS: If you feel heavy in pedaling, just shift the right gear to smaller number. If you feel light in pedaling, just shift the gear to larger number.
Practice makes perfect![/quote]