Gear ratios in bicycle drive trains

The “speed” is determined by the maximum gear ratio (the largest gear in the front plate corresponds to the smallest gear in the rear flywheel). When pedalling the same number of revolutions, the greater the gear ratio, the faster the speed.


For example, the maximum gear ratio of a typical 27-speed mountain bike is “44T front, 11T rear, gear ratio = 4”. When the rider is pedalling the rim, the wheel will turn 4 times. The speed is the fastest, but the torque of the rim is the smallest. The rider’s relative pedalling force should be the maximum , in order to maintain the torque needed to keep the bike moving forward.


“Gear ratio = number of teeth on the front big plate / number of teeth on the rear flywheel”. Basically, the function of a bicycle gear and chain drive system is to “convert the energy (horsepower) of the rider’s pedalling into torque on the tyres“.


The smallest bike gear ratio calculator is used when “climbing” (the smallest gear on the front plate corresponds to the largest gear on the rear flywheel). Lowering the gear ratio increases tyre torque subject to the number of pedal revolutions.


For example, the minimum gear ratio for a typical 27-speed mountain bike is “22T front, 34T rear, gear ratio = 0.65”. The driver is pedalling the wheel for 0.65 revolutions, so all the driver’s physical effort is converted into torque to lift the bike up the hill.


It is important to note that when the road is slippery, high torque will cause the tyres to slip, which means that when the torque is greater than the friction on the ground, it will not be possible to move forward. In addition, the idler wheels may tilt when climbing with high torque.


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