A simple gear train consists of two gears with a gearwheel A and a pinion B that has 25 teeth. If the velocity ratio of the system is 3:1 and the system has a module of 6 mm, calculate: The PCD of gearwheel A.

• Pinion B has $T_B = 25$ teeth.
• The velocity ratio of the system is $VR = 3:1$. For a simple gear train, the velocity ratio is also the ratio of the number of teeth of the gearwheel to the pinion, so $\frac{T_A}{T_B} = 3$.
• The module of the system is $m = 6$ mm.
• The formula for Pitch Circle Diameter (PCD) is $D = m \times T$.

Using the velocity ratio:

Substitute the value of $T_B$:

Using the module formula:

Substitute the values for $m$ and $T_A$:

The PCD of gearwheel A is $450 \text{ mm}$.