Specifications
Tyre sizes and speedometer error, horsepower from torque, and speed, distance and time.
Tire Size Calculator
Overall diameter and sidewall from a tyre size such as 225/45R17, and how a different size changes the diameter, what the speedometer reads and the odometer.
Horsepower Calculator
Horsepower and kilowatts from torque and engine speed, or an estimate from quarter-mile trap speed or time, with power at the wheels and power to weight.
Speed, Distance and Time Calculator
Speed, distance or time from the other two, the true average speed over several legs of a journey, and the time a faster speed really saves.
Three pieces of physics that come up around cars. A tyre's overall diameter follows from its size code, the rim diameter plus two sidewalls, and fitting a different size changes what the speedometer reads: a larger tyre makes it read low. Horsepower from torque is torque times engine speed, and the familiar 5,252 is where the two numbers meet, 33,000 divided by two pi. Speed, distance and time are one formula three ways, with one trap worth knowing: the average speed over a journey is total distance over total time, lower than the average of the speeds. None of these pages makes a fitment or safety claim.