Axle

Automotive calculators

Engine speed from a tire and a gear, compression from the chamber stack, and how a new wheel changes clearance.

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.

Which calculator?

What RPM is this gear at this speed?

Gear Ratio Calculator

Gear ratio calculator. Ring and pinion, and engine RPM at a road speed for a tire size and a transmission gear.

What is the static compression ratio?

Compression Ratio Calculator

Compression ratio calculator. Static CR from bore, stroke, chamber, piston, gasket, and deck, plus dynamic CR at intake-valve closing.

Does the new wheel stick out farther?

Wheel Offset Calculator

Wheel offset calculator comparing an old and a new wheel. Width, offset, backspace, poke, and inner clearance.

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