Cars & Driving
Twenty tools for running costs, fuel, tyres and what a car is actually worth. Every one of them works on numbers you can read off the car, the pump or the paperwork — and none of them tells you a figure your handbook is the authority on.
20 tools in Cars & Driving
- Car Depreciation CalculatorWhat a car is worth after N years at a decline rate you set, and the cost per year of simply owning it.
- Car Loan Early PayoffWhat paying extra each month removes from a car loan, and the month the balance finally drops below what the car is worth.
- EV Charging Cost CalculatorCost to add a given range at home or public rates, including the energy lost to charging that never reaches the battery.
- EV vs Petrol Running CostPence or cents per mile for each, over a year of your own driving, on the electricity and fuel prices you actually pay.
- Fuel Economy CalculatorMiles per gallon or litres per 100 km from a tank and a trip, with the US and imperial gallon kept apart because they are not the same size.
- Two-Stroke Fuel Mix RatioOil to add to a given volume of petrol at a ratio your engine manual specifies, in millilitres and fluid ounces.
- Insurance Excess CalculatorWhether a higher excess is worth the lower premium, and how many claim-free years it takes before it has paid for itself.
- Car Lease vs Buy ComparisonLeasing against buying over the same period, counting the deposit, the payments and what you still own at the end.
- Maintenance Interval TrackerSeveral service items with different intervals, showing which comes due first and how far each has left to run.
- Oil Change Interval PlannerWhen the next service falls due by mileage or by months, from the interval your manual gives rather than any figure we invent.
- Total Cost of Car OwnershipEverything a car costs in a year once fuel, insurance, servicing, tax and the value it quietly loses are added together.
- Parking Cost CalculatorDaily, monthly and yearly parking compared, including the days you do not park, so a season ticket is judged on real usage.
- Road Trip Fuel PlannerFuel needed and what it will cost for a journey, split leg by leg, using the consumption figure your own car actually returns.
- Service Cost TrackerServicing and repairs logged over the years you have owned a car, as a yearly average and a running total.
- Speedometer Error CalculatorWhat a tyre size change does to an indicated speed, and the true speed behind a given reading on the dial.
- Trailer Weight DistributionWhere a load sits over a trailer axle and what that does to the nose weight, explained rather than approved.
- Tyre Pressure ConverterConvert between psi, bar and kilopascals. A conversion only, never a recommendation about what any tyre should run at.
- Tyre Size ComparisonTwo tyre sizes compared on rolling diameter, and the percentage change that follows through to your speedometer.
- Car Value by MileageHow far above or below average mileage moves a valuation, using the adjustment per thousand miles that your own market data gives.
- Wheel Offset CalculatorHow a change of width or offset moves a wheel inward and outward, in millimetres, at each edge.
The rule this whole category is built on
A car tool that guesses is dangerous in a way a mortgage calculator is not. Get an interval, a pressure or a load figure wrong in the generous direction and the consequence is mechanical rather than financial, so the standard here is strict: if the correct number depends on your specific engine, tyre or vehicle, this site asks you for it instead of inventing an average.
That is why the oil change planner does not suggest how often to change oil — the right interval spans roughly five thousand miles to twenty thousand across ordinary road cars, depending on the engine, the approved oil specification and how it is driven. You open the handbook and type in what it says; the planner then does the fiddly part, which is tracking a distance limit and a months limit at once and telling you which you will meet first.
The tyre pressure converter is the same principle in one line. It converts between psi, bar and kilopascals and never recommends a pressure. The trailer weight distribution tool explains what moving a load over an axle does to the nose weight, and approves nothing. The speedometer tool quotes no legal tolerance at all, because that figure differs by country and is periodically revised, and anyone quoting you one without naming the regulation is guessing.
Costs, and the ones people leave out
Half the category is money. Fuel, charging, insurance excess, parking, servicing, depreciation, finance — and the reason there are so many separate tools is that the expensive item is nearly always the one nobody added up.
Depreciation is the classic. It is usually the single largest cost of owning a car and it never appears on a statement, so it is invisible next to a fuel bill a tenth its size. The total cost of ownership tool exists to put it back in the same column as everything else, and the lease-against-buy comparison exists because the two options hide their costs in different places — one in a monthly figure, the other in a resale value years away.
On the fuel side the trap is definitional rather than psychological. A US gallon and an imperial gallon differ by twenty per cent, so the same consumption produces two very different miles-per-gallon figures, and every tool here that touches a gallon states which one it means.
Wheels and tyres, where a small change is not a small change
Four tools deal with fitment, and they are grouped because a change to one of the numbers moves all the others. A taller tyre raises the rolling diameter, which changes the distance covered per wheel revolution, which changes what the speedometer reads and what the odometer records — and it spends the built-in margin that makes an instrument read high, pushing it towards under-reading.
A wider wheel or a different offset moves the wheel inward and outward at each edge by an amount you can calculate in millimetres, which is the difference between a fitment that clears and one that fouls a strut. The tools give you those millimetres. Whether the result clears on your car is a question about your car.
Where to start, by what you are trying to settle
- Fuel Economy Calculator
- What the car actually returns, from a fill and an odometer reading.
- Total Cost of Car Ownership
- Everything in one column, including the depreciation nobody bills you for.
- EV vs Petrol Running Cost
- Comparing the two on your own electricity and fuel prices rather than on a headline.
- Tyre Size Comparison
- Two tyre sizes on rolling diameter, and the percentage change that follows.
- Oil Change Interval Planner
- Your handbook’s distance and months limits, tracked together.
- Car Value by Mileage
- What the odometer reading does to what the car is worth.
Three things drivers ask these tools
Why will none of these tell me my tyre pressure?
Because the correct pressure is a property of your vehicle and its load, published by the manufacturer on a placard in the door shut or filler flap and in the handbook. A number from a website is a number for somebody else’s car. The converter exists for the genuinely useful case: your gauge reads in one unit and the placard is printed in another.
How much of what a car costs am I actually seeing?
Usually the fuel and the insurance, because those arrive as bills. Depreciation, tyres, servicing and the interest inside a finance payment tend to be absorbed without ever being counted, and together they routinely exceed the fuel. Putting them in one place is the entire purpose of the ownership cost tool.
Is a speedometer reading high a fault?
No — reading a little high is the intended behaviour, and the margin is there by regulation. What matters is the direction of any change you make: a taller tyre eats into that margin, and the direction the rules do not permit is under-reading. No tolerance figure is quoted anywhere on this site, because it varies by jurisdiction and gets revised.