Automotive calculators cover the two sides of car ownership — what it costs and what it does. Fuel economy, finance payments and lease-versus-buy comparisons on one side; tyre sizing, horsepower estimates and quarter-mile times on the other. Useful whether you are negotiating at a dealership or setting up a track day car.
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Fuel cost per distance is straightforward — distance divided by economy, multiplied by price per unit — but it understates real cost per mile. Depreciation is usually the largest single expense in the first years of ownership, followed by insurance, tyres, servicing and finance interest. A more efficient car that costs considerably more to buy can take years to repay the difference in fuel alone.
Economy figures also depend on conditions. Official ratings are measured on standard cycles; short urban trips, roof boxes, low tyre pressure and cold weather all push real consumption above the sticker figure, often by 10 to 20%.
A car loan is an amortising loan like any other, so the monthly payment depends on principal, rate and term. Longer terms make almost any car look affordable while increasing total interest and the period spent owing more than the car is worth. A lease payment is built differently: it covers the expected depreciation over the term plus a rent charge on the capital, which is why lease payments are lower but leave no equity.
The honest lease-versus-buy comparison is total cost over the same period including the vehicle's residual value, not a monthly payment side by side.
Tyre size codes encode width in millimetres, aspect ratio as a percentage of that width, and rim diameter in inches, so changing any one figure changes rolling circumference — and with it speedometer accuracy and gearing feel. Keeping overall diameter within roughly 3% of standard is the usual guidance.
Performance estimates such as quarter-mile time from power and weight come from empirical trap-speed formulas fitted to real runs. They are good for comparing setups but real times depend heavily on traction, gearing, driver and air conditions.
Official figures come from standardised test cycles that under-represent short cold trips, hard acceleration, high motorway speeds and accessory load. A 10 to 20% shortfall in everyday driving is normal, and more in winter or heavy city use.
Leasing usually has a lower monthly payment because you only pay for depreciation during the term, but you own nothing at the end. Over a long ownership horizon, buying and keeping a car past the loan term is generally cheaper per year.
Yes. The speedometer is calibrated to the original rolling circumference, so a larger overall diameter makes the car travel further per revolution and read low. Keeping the new size within about 3% of the original diameter keeps the error negligible.
They use empirical formulas based on power-to-weight ratios and typically land within a few tenths for well-set-up cars. Traction, gearing, altitude and driver skill can easily shift a real run beyond that range.