Tire Gear Ratio Calculator
Calculate effective gear ratio changes when changing tire sizes.
inches
Original tire overall diameter
inches
New tire overall diameter
Your current differential gear ratio
Effective Ratio = Current Ratio x (Original Tire Diameter / New Tire Diameter)
Example: Going from 28 inch to 33 inch tires with 3.73 ratio -> Effective ratio becomes 3.16, ideal new ratio is 4.40 (closest: 4.30)
Why do I need to change gears with bigger tires?
Larger tires effectively lower your gear ratio, reducing acceleration and increasing engine strain. Re-gearing restores original performance characteristics.
How do bigger tires affect my speedometer?
Bigger tires cause speedometer to read slower than actual speed. Example: 10% larger tires mean you're going 55 mph when speedo shows 50.
What's the formula for effective gear ratio?
Effective Ratio = Current Ratio x (Original Tire Diameter / New Tire Diameter)
📐 Formula
Effective Ratio = Current Ratio x (Original Tire Diameter / New Tire Diameter)
📝 Example Calculation
Example: Going from 28 inch to 33 inch tires with 3.73 ratio -> Effective ratio becomes 3.16, ideal new ratio is 4.40 (closest: 4.30)
❓ Frequently Asked Questions
Why do I need to change gears with bigger tires?▼
Larger tires effectively lower your gear ratio, reducing acceleration and increasing engine strain. Re-gearing restores original performance characteristics.
How do bigger tires affect my speedometer?▼
Bigger tires cause speedometer to read slower than actual speed. Example: 10% larger tires mean you're going 55 mph when speedo shows 50.
What's the formula for effective gear ratio?▼
Effective Ratio = Current Ratio x (Original Tire Diameter / New Tire Diameter)