“In this Tire Speed Calculator, we will show you how to find your vehicle’s speed in just a few seconds.
We will also help you understand the speed formula, what each term in the formula means, and how it all works together.
What is tire circumference?
What is the final drive ratio?
How do engine RPM and gear ratios affect vehicle speed? Find all the answers here, along with examples and reference tables to make it super easy to understand!”
Tire Speed Calculator
Vehicle Speed Formula
Formula:
Vehicle Speed (MPH) = (RPM × Tire Circumference) / (Final Drive Ratio × 336)
Where:
- RPM = Engine revolutions per minute
- Tire Circumference = Distance around the tire in inches (Diameter × π)
- Final Drive Ratio = Transmission Gear × Differential Gear
- 336 = Conversion constant to turn inches-per-minute into miles-per-hour
Real-world Applications
| Vehicle Type | Typical Tire Diameter (inches) | Transmission Gear | Differential Gear | Expected Speed (MPH) at 3000 RPM |
|---|---|---|---|---|
| Sedan | 25 | 4 | 3.73 | 57 |
| SUV | 30 | 5 | 3.91 | 68 |
| Truck | 34 | 6 | 4.10 | 70 |
Problem Statement
A sedan has a tire diameter of 25 inches. It is in 4th gear, with a differential gear of 3.73. If the engine is running at 3000 RPM, calculate the vehicle speed.
Solution:
Step 1: Given Data
RPM = 3000
Tire Diameter = 25 inches
Transmission Gear = 4
Differential Gear = 3.73
Step 2: Calculate Tire Circumference
Tire Circumference = Diameter × π = 25 × 3.1416 ≈ 78.54 inches
Step 3: Calculate Final Drive Ratio
Final Drive Ratio = Transmission Gear × Differential Gear = 4 × 3.73 ≈ 14.92
Step 4: Apply Vehicle Speed Formula
Vehicle Speed = (RPM × Tire Circumference) / (Final Drive Ratio × 336)
Vehicle Speed = (3000 × 78.54) / (14.92 × 336) ≈ 46.9 MPH
Answer: Vehicle Speed ≈ 47 MPH
Tire Speed Reference Cards
Reference cards for different vehicle types showing tire diameter, gear ratios, and approximate speed at 3000 RPM.
Sports Car
Tire Diameter: 26 in
Transmission Gear: 5
Differential Gear: 3.91
Speed at 3000 RPM: 59 MPH
Motorcycle
Tire Diameter: 22 in
Transmission Gear: 6
Differential Gear: 2.90
Speed at 3000 RPM: 72 MPH
Minivan
Tire Diameter: 28 in
Transmission Gear: 5
Differential Gear: 3.55
Speed at 3000 RPM: 55 MPH
Pickup Van
Tire Diameter: 32 in
Transmission Gear: 5
Differential Gear: 3.91
Speed at 3000 RPM: 60 MPH
FAQs
What is vehicle speed?
In this tire speed calculator, we will show you how to find your vehicle speed in seconds. Vehicle speed tells you how fast your vehicle is moving in miles per hour.
What is tire circumference?
Tire circumference is the distance around your tire. We will also help you understand why it matters in calculating your speed.
How does RPM affect speed?
RPM is the engine speed in revolutions per minute. Higher RPM usually means your vehicle goes faster. This calculator makes it easy to see that.
Why do we use 336 in the formula?
336 is the magic number that converts inches per minute into miles per hour. Don’t worry, the calculator does it for you!