Geometry and arithmetic for vehicles: tire and wheel fitment, gearing and speed, engine displacement and compression, power, fuel economy and cost.
Vehicle calculations that are geometry or arithmetic, worked in the open: what a tire size change does to diameter, speedometer and gearing; whether a wheel’s offset will fit; an engine’s displacement and compression ratio from its dimensions; horsepower from torque; fuel economy in every unit and what a trip or a year of driving costs. Nothing here is a manufacturer’s rating or a rule of thumb — the figures you enter are the vehicle’s, and the pages say what they do not decide.
Backspacing from width and offset, how far a new wheel’s inner and outer faces move (clearance and poke), and the bolt circle from the stud spacing.
You get: The inner and outer change in millimetres when you swap wheels, both wheels’ backspacing, and the PCD measured from adjacent studs — geometry only, no fitment promise.
Open Wheel Offset & FitmentTire diameter, sidewall, circumference and revs per mile from the size marking; compare two sizes for diameter change, ride height and speedometer error.
You get: Both tires’ geometry side by side, the percent change in overall diameter, the change in ride height, and the true speed when the speedometer shows a given figure.
Open Tire Size & ComparisonStatic compression ratio from bore, stroke, chamber volume, head gasket, deck clearance and piston dish or dome — every volume shown, nothing assumed.
You get: The swept and clearance volumes of one cylinder, the static ratio they give, the total displacement, and how a gasket, deck or dome change moves the ratio.
Open Compression RatioEngine displacement from bore, stroke and cylinders in cc, litres and cubic inches — or the bore or stroke that gives a target capacity; bore/stroke ratio.
You get: Per-cylinder and total displacement in cc, L and in³ with exact conversion, the bore-to-stroke ratio, and the dimension needed to reach a target displacement.
Open Engine DisplacementPower from torque and rpm, or torque from power, in hp, PS, kW, lbf·ft and N·m with exact NIST factors — the 5,252 relation worked in the open.
You get: The matching power and torque at your rpm in every customary unit, from either one, with the conversion factors stated.
Open Horsepower, Torque & kWInjector flow for a target horsepower from the BSFC you enter, injector count and the duty you allow; flow at another pressure; cc/min at your fuel density.
You get: Total fuel flow and the static flow each injector must deliver, in lb/h and cc/min, plus what a rated injector flows at your pressure and the duty it would run.
Open Injector SizingRoad speed at any rpm in every gear from tire diameter, gear ratios and final drive; rpm at a speed; the final drive that restores gearing after a tire change.
You get: A per-gear table of overall ratio, speed at your rpm and rpm at your speed, km/h per 1,000 rpm, and the corrected final drive for a new tire size.
Open Gear Ratio, RPM & SpeedFuel economy from a fill-up (distance and fuel in any unit) and any figure converted between L/100 km, km/L, mpg (US) and mpg (UK) with exact factors.
You get: One economy figure in all four units at once, from a trip or from a value you already have, with the US/UK gallon difference made explicit.
Open Fuel Economy & ConverterFuel needed and its cost for a trip from distance, consumption in any unit and pump price; round trip, split between people, and per week, month and year.
You get: Litres and cost for the journey, per person and per km or mile, and what the trip costs monthly and yearly when it repeats.
Open Fuel & Trip CostCost of running a vehicle per mile or km from your own yearly figures: fuel, depreciation, insurance, tax, maintenance, parking and finance; nothing estimated.
You get: The yearly total and its per-km, per-mile and per-day figure, with each cost line’s share, so you can see what actually drives the number.
Open Cost per Mile