Car Speed Calculator

To calculate the speed of any car, we need these variables;

1. all the gear ratios of the car’s gearbox

2. the final ratio of the same gearbox

3. the original tyre size

Then we need the formula to put all the figures together and calculate.

Below is the example to calculate the speed for the Civic ES;

The gearbox mated with the D17A2 engine has the following gear ratio;

1st – 2.722, 2nd- 1.468, 3rd- 0.975, 4th- 0.674

Final ratio- 4.067

The formula is, Vh = Ct x Ve x 60/Gr x Fr/1000, where

Vh- vehicle speed in kmh

Ct- tyre circumference in metres

Ve- engine speed in rpm- revolution per minute

60- since we are calculating the speed per hour, we have to multiply by 60 (60min= 1hour)

Gr- gear ratio

Fr- final ratio

For the Civic ES 1.7L, the standard tyre is 195/60/15. With this size, Ct works out to be = 1.93 metres.
(if you don’t know how to calculate this, please tell me)

So in 4th gear, the vehicle speed at 3000rpm is,

Vh = 1.93 x 3000 x 60 / 0.674 x 4.067 / 1000 = 126.78 kmh