To determine the gear ratio pairs of gears in the main transmission as it is easier and faster, look in the manual to the vehicle on which the transmission is used. From a mathematical point of view, to determine the gear ratio of two gears, count the teeth on both and divide the driven gear teeth on the teeth leading. For example, if the driven gear has 128 teeth and the leading 26, the gear ratio is calculated as 128/26=3,54.
To calculate compound gear ratios of the transmission first calculate the aforementioned manner, the gear ratios of the main transmission and the speed included in the transmission. Then these two values multiply one by the other. For example, if the gear ratio of a transmission is equal to 3 and 54, and the gear ratio is high transmission of 0.88, then the compound gear ratio of the transmission for the transmission (in this case, the first) will 3,54*0,88=3,115
If you want to calculate the theoretical speed of the car at certain engine speeds, the amount of rotations and multiply by the outside diameter of the tire in inches. The received result divide into its component transmission ratio multiplied by 530,616. For example, tires 245/40R18 outer diameter is equal 65,32 see If the engine speed is 5000 rpm, the calculated speed will be 5000*65,32/(3,115*530,616)=197,6 km/h. Real car speed at these revs will be lower because the formula does not account for the resistance force acting on the car.
According to the formula calculate the speed calculate the theoretical maximum speed of the car, knowing what maximum rpm can develop the engine under load. Also, using this formula, calculate compound gear ratio of the transmission required to achieve the calculated maximum speed. To do this, the maximum engine speed under load and multiply by the outside diameter of the tire in centimeters and divide first to the target speed, and then 530,616.
To calculate the outer dimensions of the tyres for the calculation of car, the target maximum speed of this vehicle compound, multiply by the gear ratio of the transmission and на530,616, and then divide by the maximum engine speed under load.