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Vehicle Speed basis of engine rpm, tire size and gear ratios

Power Transmission Design and Engineering
Engineering and Design Applications

Vehicle Speed on basis of engine rpm, tire size and gear ratios.

The following generally applies for the calculation of the driving speed on the basis of engine speed, tire size and overall ratio:

v = ( 0.06 · nMot · U ) / ( iG · iv · iA )

v = Driving speed, in km/h

nMot = Engine speed, in 1/min

r = Tire radius, in m

U = Tire rolling circumference, in m = 2 π r

iG = Transmission ratio

iv = Transfer case ratio

iA = Final drive ratio of the driven axle(s)

Theorectical Maximum Vehicle Speed

Warning: This calculation is used exclusively to calculate the theoretical final speed on the basis of engine speed and transmission ratios. The formula does not take into consideration the fact that the actual maximum speed will be below this speed when driving resistances offset the driving forces. An estimate of the actual achievable speeds using a driving performance calculation in which air, rolling and climbing resistance on the one side and tractive force on the other offset each other, can be found in Section 8, "Driving resistances".

On vehicles with a speed limiter in accordance with 92/24/EEC, the design top speed is generally 85 km/h.

v = ( 0.0624 · nMot · U ) / ( iG · iv · iA )