### Transmission Gear Ratio Equation and Calculator

The following equations and calculators will estimate the resultant vehicle speed at a known engine rpm for a manual transmission with up to six forward gears.

To determine the distance the vehicle will travel for one revolution of the engine by dividing the circumference of the tire by the combined gear ratio of the transmission and differential.

d = ct / (grt x grd)

To determine a vehicles speed from the engine speed by multiplying the circumference of the tire by the engine speed and dividing by the combined gear ratio.

vc = (ct x ve) / (grt x grd)

Where:

d = distance
ct = Circumference of tire
grt = Gear ratio transmission
grd = Gear ratio differential
ve = Engine speed
vc = Vehicle speed

Tire size calculated

Diameter = [ Width · Profile / 100 · 2 ] / 25.4 + Wheel size ] · 25.4
Note: The height of the tire represents 1/2 of the tire. The tire is a donut shape, thus there are two Rim to outer thicknesses calculated from the % of width profile.

Where:

Diameter = Outside diameter of tire mounted on wheel, mm;

Width = Tire thread width, mm;

Wheel size = Also called "Rim" - this is what the tire mounts to, in;

25.4 mm = approximate conversion to 1.0 inches

Profile Height = width x ( % / 100 ) - which is one half the of the tire from where it mounts on the Rim to the outer diameter

 Transmission Gear Ratio Calculator Data for 2004, Chevrolet Corvette C5 Z06 with six speed manual transmission Width (mm) = Enter the tire width size used Profile (%) = Enter the tire profile size used Wheel (Rim) (inch) = Enter the wheel size used Diameter (mm) = The tire diameter calculated (mm). Axle Ratio (Final Gear) = Enter the Final Gear Ratio used Gear 1ST 2ND 3RD 4TH 5TH 6TH Gear Ratio Enter the gear ratios above Calculated Road Speed in Each Gear for Engine RPM vs Speed kilometers/hour km/h 1ST 2ND 3RD 4TH 5TH 6TH Engine Speed Calculated Road Speed in Each Gear for Engine RPM vs Speed miles/hour mph Engine Speed 1ST 2ND 3RD 4TH 5TH 6TH 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

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