Off-Road Tire Size Converter & Gear Ratio Calculator

Convert metric tire sizes to imperial off-road dimensions (e.g., 33x12.50). Calculate ground clearance gains and find the optimal gear ratio for larger tires.

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Category Car Calculators

Metric Tire Input

/ R

Example: 285 / 75 R 16

Drivetrain Details (Optional)

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About

Upgrading to larger tires is the most common modification for off-road enthusiasts looking to improve ground clearance and traction. However, metric tire sizes (like 285/75R16) can be confusing when comparing them to the traditional imperial notation (like 33x11.50) used in the 4x4 community.

This tool acts as a bridge between these two systems, converting your metric measurements into height and width in inches. More importantly, it calculates the mechanical impact of your upgrade. Installing significantly larger tires without re-gearing your differentials puts immense stress on your transmission and reduces torque, making the vehicle feel sluggish. By analyzing your factory gear ratio against the new tire diameter, this calculator suggests the optimal new gear ratio to restore factory performance and fuel economy.

off-road tire converter gear ratio calculator lift kit jeep tires 4x4

Formulas

To convert metric dimensions to imperial height in inches:

Hin = (Widthmm × Aspect ÷ 1270) + Rim

To calculate the effective new gear ratio required to match stock torque:

GRnew = GRold × HnewHold

Reference Data

Metric SizeImperial ApproxHeight (in)Width (in)Common Use
265/75R1632x10.5031.610.4Stock / Mild Lift
285/75R1633x11.5032.811.2Most Popular 33"
315/70R1735x12.5034.412.4Aggressive 4x4
255/85R1633x10.0033.110.0"Pizza Cutters"
285/70R1733x11.5032.711.2Modern Stock Upgrades
305/70R1633x12.0032.812.0Wide 33"
315/75R1635x12.5034.612.4True 35"
37x12.50R1737x12.5037.012.5Rock Crawling
40x13.50R1740x13.5040.013.5Extreme Builds

Frequently Asked Questions

A 'Pizza Cutter' refers to a tall, skinny tire (e.g., 255/85R16). In many off-road situations like mud or snow, a narrower tire cuts through the soft top layer to find traction on the hard surface below, whereas a wide tire might 'float' on top and spin.
If you increase tire diameter by more than 2-3 inches, you will likely notice a significant loss in power and fuel economy. If your transmission constantly hunts for gears on the highway, it's time to re-gear.
It means the driveshaft must rotate 4.10 times to turn the wheels once. Higher numbers (e.g., 4.88, 5.13) provide more torque and are better for larger tires but reduce top speed.
Rarely. Most vehicles require at least a 2.5-inch to 4-inch suspension lift and possibly fender trimming to fit 35-inch tires without rubbing during turns or suspension compression.