# Gears and speed

• Automotive

## Main Question or Discussion Point

When you are in a particular gear (say 2nd) , you can vary the speed of vehicle. So what actually is varied in the system as you are not changing the gear, iis it the amount of charge or rpm of the engine is varied to increase speed in a particular gear???

Also while changing gears, does the rpm of engine changes or amount of charge coming in increases or something else increases....???

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You will have heard this every time you travel in a geared vehicle. Every time the gear increases the engine note drops, indicating that the rpm drops, but each 'cog' moves the axles by a greater amount. Does that help?

Sorry if can elaborate more it will be of great help for me

actually the gearbox is the combination of the different gear wheels with different diameter thus having the different no. of teeths.
the gear wheel of the first gear is large amoung all gear wheels and thus having the larger no. of teeths and moving from ist gear to top gear the diameter of the respective gear wheels decreases and thus the no. of teeths decreases.
speed of the gear wheel in rpm is inversely proportional to the no. of teeths higher the no. of teeths lesser will be the speed in rpm and vice versa.
the maximum and minimum value of the torque produced by the engine is independent upon the gears , gears are only used to vary the velocity ratio and nothing else, the power and torque delivered by the engine depends upon the amount of charge injected inside the cylinder portion both in case of the petrol or diesel engine i.e, more we press the accelerator pedal more fuel will be injected inside the cylinder and more combustion occurs thus producing the thrust and hence toque on the crankshaft.
if we press the accelerator full either in 1st gear or 5th gear same power is delivered by the engine.
there is a speed limit for each gear just like :
1st gear - 0 to 10 kmph
2nd gear - 10 to 35 kmph and so on... ( depending upon the gearbox)
thus vehicle can only run in certain gear ( say 2nd) when it attains the speed ( greater than 10) else it will try to stop the engine automatically.

i hope u understand what u want ..

When you are in a particular gear (say 2nd) , you can vary the speed of vehicle. So what actually is varied in the system as you are not changing the gear, iis it the amount of charge or rpm of the engine is varied to increase speed in a particular gear???

Also while changing gears, does the rpm of engine changes or amount of charge coming in increases or something else increases....???
You increase the pressure in the engine, which increases the drive thrust and speeds up the car, the result being the engine speed rises.