Axle
Automotive calculators
Engine speed from a tire and a gear, compression from the chamber stack, injector and turbo sizing from horsepower, the driven gear a cable speedometer needs, a quarter-mile estimate, a 0-60 estimate, a power-to-weight ratio, and torque at one RPM.
Gear Ratio Calculator
Gear ratio calculator. Ring and pinion, and engine RPM at a road speed for a tire size and a transmission gear.
Compression Ratio Calculator
Compression ratio calculator. Static CR from bore, stroke, chamber, piston, gasket, and deck, plus dynamic CR at intake-valve closing.
Wheel Offset Calculator
Wheel offset calculator comparing an old and a new wheel. Width, offset, backspace, poke, and inner clearance.
Tire Size Calculator
Tire size calculator comparing two sizes. Diameter, width, sidewall, revolutions per mile, and speedometer error.
Engine Displacement Calculator
Displacement calculator from bore, stroke, and cylinders. Cubic inches, cubic centimetres, and litres.
Fuel Injector Size Calculator
Fuel injector calculator for lb/hr and cc/min from horsepower, BSFC, and duty cycle, plus fuel-pressure correction and pulse-width duty. Sizing estimates only.
Turbo Size Calculator
Turbo size calculator for airflow, pressure ratio, and corrected lb/min by the published Garrett matching method. A blank grid for the turbo maker’s compressor map.
Speedometer Gear Calculator
Speedometer gear calculator for driven-gear teeth from tire diameter, axle ratio, and drive gear. Tooth lists come from published charts. Check the result against GPS.
Quarter-Mile Calculator
Quarter-mile calculator for elapsed time, trap speed, and horsepower. Hale’s 1986 constants and Fox’s 2001 constants, both labelled as estimates.
Power-to-Weight Ratio Calculator
Power-to-weight calculator for lb/hp, hp per ton, and W/kg. Vehicle weight and power, or a rider’s watts per kilogram. No training zones.
Torque and Horsepower Calculator
Torque calculator for horsepower at one RPM, torque from horsepower, a force and a lever arm, and lb-ft to N·m. Not a bolt-tightening tool.
0-60 Calculator
0-60 calculator from horsepower, weight, and drivetrain. A traction-and-power estimate, plus acceleration from a measured time. For comparison only.
How these calculators work
Tire diameter is the rim plus two sidewalls. Sidewall height is section width × aspect ratio, converted from millimetres. Engine RPM is road speed × axle ratio × transmission ratio × 336.14, divided by the diameter in inches. The 336.14 is 63,360 inches in a mile, divided by 60, divided by π. Ring teeth ÷ pinion teeth is the axle ratio when you have the gears in hand.
Static compression is (swept volume + chamber) ÷ chamber. The chamber here is the head volume, plus a dish or minus a dome, plus the gasket cylinder and the deck cylinder. Dynamic compression uses the same chamber and the stroke that remains when the intake valve closes. Wheel offset uses the usual 1 inch of flange: an 8-inch wheel at ET 0 has 4.5 inches of backspace. Positive offset moves the mounting face outward, which tucks the outer lip in and eats inner clearance. The tire comparison puts two molded sizes side by side, including revolutions per mile and the speedometer error. Displacement is bore, stroke, and cylinder count into cubic inches, cc, and litres.
Injector size is horsepower times a brake specific fuel consumption, divided by the injector count and the duty cycle, then converted between lb/hr and cc/min with the fuel density. It is a sizing estimate. A tune and a wideband confirm it. Turbo airflow is horsepower times the air-fuel ratio times BSFC, divided by 60. Manifold pressure, pressure ratio, and corrected airflow follow the matching method Garrett published. The grid is blank so the points can be compared with the compressor map from the turbo maker. Speedometer driven teeth are output-shaft revolutions times the drive teeth, divided by the speedometer’s revolutions per mile. Tooth counts this page will accept or reject come from the cited gear charts. A GPS check after the swap is the confirmation.
The quarter-mile calculator is Hale’s 1986 pair and Fox’s 2001 pair. Elapsed time and trap speed come from the cube root of pounds per horsepower, and the same constants run backwards to a horsepower estimate. Both are estimates. Weight includes the driver. Horsepower is at the clutch, not at the wheels. The 0-60 page is a separate estimate from traction and power, not those quarter-mile constants.
Power-to-weight is total weight divided by mechanical horsepower, with the metric forms beside it. A rider mode divides watts by kilograms and does not assign a training zone. Torque and horsepower use 33,000 ÷ 2π and 60,000 ÷ 2π. A force and a lever are physics torque, not a bolt spec.