RATIO
Ratio may be determined when any of the following factors is known:
• Numbers of Teeth (T)
• Pitch Diameters (PD)
• Revolutions per Minute (RPM)
GEAR RATIO–QUANTITY OF TEETH
The gear ratio is the number of teeth on the gear divided by the number of teeth on the pinion. It is always the larger number of teeth (as found on the gear) divided by the smaller number of teeth (as found on the pinion). Thus, the ratio of a pair of gears with 72 teeth on the gear and 18 teeth on the pinion is 4 to 1.
Now let’s apply those factors to some sample problems.
Problem: Find the ratio of a pair of bevel gears with a 15-tooth pinion and a 60-tooth gear.
• Ratio = Number of Teeth in Large Gear (60) ÷ Number of Teeth in Small Gear (15)
• 60 ÷ 15, or
• 4 to 1
