Master gear, belt, chain, and worm drive calculations for the Red Seal Industrial Maintenance Mechanic (433A) exam — Blocks C & D.
mwredsealprep.ca · Industrial Maintenance Mechanic 433A · Blocks C & D
Gear ratio and speed calculations appear across Block C and Block D. They're some of the most calculation-friendly questions on the exam — straightforward formulas with clean numbers — and a reliable source of marks for prepared candidates.
The same core formula applies to gears, belt drives, and chain drives. Master it once and you can handle all three.
Output Speed
Input Speed × (Driver ÷ Driven)
Output Torque
Input Torque × (Driven ÷ Driver)
Inverse of speed — speed↑ means torque↓
When speed goes up, torque goes down — and vice versa. Power is conserved (minus losses).
Gear Drive
Number of teethOutput RPM = Input × (Driver teeth ÷ Driven teeth)
Belt Drive
Sheave diameterOutput RPM = Input × (Driver dia. ÷ Driven dia.)
Chain Drive
Sprocket teethOutput RPM = Input × (Driver teeth ÷ Driven teeth)
Worm Drive
Gear teeth ÷ Worm startsRatio = Worm Gear Teeth ÷ Worm Starts
Can you solve gear ratio problems under exam pressure?
Test yourself with timed Red Seal–style drive calculations.
Try to solve each problem before revealing the solution.
Worked Example
Gear DriveProblem
A driving gear has 20 teeth and turns at 1,800 RPM. The driven gear has 60 teeth. What is the output speed?
Small driver → Large driven = Speed reduction, Torque increase
Worked Example
TorqueProblem
The driving gear in Example 1 produces 50 ft-lbs of torque. What is the output torque (ignoring losses)?
Worked Example
Compound TrainProblem
A gear train has three stages: Stage 1: 15-tooth driver → 45-tooth driven. Stage 2: 20-tooth driver → 80-tooth driven. Stage 3: 25-tooth driver → 50-tooth driven. Input is 1,200 RPM. What is the final output speed?
Worked Example
Belt DriveProblem
A motor turns at 1,750 RPM and drives a 4" diameter sheave. The driven sheave is 12" diameter. What is the output speed?
Belt drive uses sheave diameter in the formula
Worked Example
Belt DriveProblem
A motor runs at 1,750 RPM. You need an output speed of 875 RPM. The driver sheave is 6". What diameter driven sheave is required?
Worked Example
Chain DriveProblem
A drive sprocket has 17 teeth and turns at 900 RPM. The driven sprocket has 51 teeth. What is the output speed?
Worked Example
Worm DriveProblem
A single-start worm meshes with a 40-tooth worm gear. Input speed is 1,750 RPM. What is the output speed?
Driver vs driven confusion
High RiskAlways identify which gear/sheave is the driver (power source side) and which is the driven (load side). Swapping them reverses your answer.
Compound trains — multiply, don't add
High RiskFor multi-stage gear trains, multiply all stage ratios together. Never add them.
Belt drives use diameter, not radius
Watch OutUse the full diameter measurement in the formula, not the radius. A very common arithmetic error.
Idler gears don't affect the ratio
Watch OutAn idler gear changes rotation direction only. Do not include it in your ratio calculation — ratio is always first driver to last driven.
Speed up vs speed down
Watch OutDriver smaller than driven → speed decreases, torque increases (reducer). Driver larger than driven → speed increases, torque decreases (increaser).
Randomized drive ratio problems — try to solve before revealing the answer.
Practice Problem
Randomized every time
Solve This
A motor sheave is 4" diameter and turns at 1300 RPM. The driven sheave is 8" diameter. What is the output speed?
Last updated: June 2026 · Based on the Red Seal Occupational Standard (RSOS) for Industrial Maintenance Mechanic (Millwright) 433A
Gear ratios are one part of the 433A exam. Build your knowledge across all six Major Work Activities.
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