Gear Ratio Calculator

Preserve the stock-vs-new tire gearing calculation while adding drivetrain speed/RPM context and a reusable per-gear table.

Tire-change effective gearing

Preserve the familiar stock-versus-new tire calculation, then use the drivetrain section to see what that gearing means at the road.

Stock tire

New tire

Stock axle ratio

A tire-diameter change alters effective gearing but does not literally change the differential gears. Real loaded rolling diameter can differ from nominal tire geometry.

Speed per gear RPM ↔ speed Gear ratio Speedometer error Tire size

Effective ratio result

—Effective axle ratio

—Axle ratio to restore stock

—Diameter change

—RPM change at same road speed

——

Road-speed check

Transmission gear

Engine RPM

Road speed to compare

Automotive tolerance cluster

Calculate the nominal spec, then expose how real-world input spread can move it

Vehicle calculations are often exact only on paper. This cluster keeps the base result while making rolling radius, gearing, wheel measurements and performance-input sensitivity visible.

Tire size Gear ratio Speedometer

All 23 automotive tools

RPM ↔ SpeedRolling diameter + ratio spread → calibration envelope Engine DisplacementBore/stroke spread → swept-volume envelope Wheel BackspacingWidth/flange/input spread → backspacing envelope Wheel OffsetWidth/offset spread → inner/poke envelope Power-to-WeightPower/mass spread → ratio sensitivity Speed Per GearTire/gearing/redline spread → per-gear envelope Tire ComparisonReal rolling diameter → speedometer envelope Tire SidewallWidth/aspect spread → sidewall/diameter envelope

Compound gear-train speed & torque solver

Multiply stage ratios, include per-mesh efficiency, and solve output RPM and torque across a compound train rather than stopping at a single pair.

Stages (driver:driven)Input RPMInput torque (N·m)Efficiency / mesh (%)

—Total ratio

—Output RPM

—Output torque

—Rotation

Ready.

Check tire, gear, and speed assumptions

Road speed, engine RPM, tire circumference, transmission ratio and final drive describe the same geometric drivetrain relationship. WebToolArc keeps those assumptions visible and links tire-size changes to the speed/RPM consequences instead of hiding everything behind one unexplained number.

Real-world boundary

These are theoretical geometry calculations, not vehicle fitment or safe-speed recommendations. Loaded tire radius, pressure, wear, wheel/tire construction, tire growth, clutch or torque-converter slip, drivetrain losses, electronic calibration and vehicle-specific clearances can change real measurements. Confirm safety-critical fitment and calibration with vehicle/tire/wheel manufacturer data or a qualified professional.