Why MPG and L/100 km do not scale linearly
MPG (miles per gallon) and L/100 km are reciprocals of each other: one is distance per fuel, the other is fuel per distance. Doubling MPG halves L/100 km, butimproving MPG by 10 has very different real-world meaning at 20 vs 50 MPG. European countries use L/100 km because it is linear in fuel saved.
US vs UK gallons
A US gallon is 3.785 L; an imperial (UK) gallon is 4.546 L — about 20% larger. So the same car achieves about 20% more "MPG" on the UK scale. 30 US MPG ≈ 36 UK MPG ≈ 7.84 L/100 km.
Torque
1 N·m = 0.7376 lb·ft. A car spec sheet listing 300 N·m of torque is roughly 221 lb·ft. Use the converter for any number, including the tiny torque values used for bicycle bolts.
Tire sizes
A tire stamped 225/45 R 17 is 225 mm wide, has a sidewall that is 45% of the width (101 mm), and fits a 17-inch (432 mm) wheel. The overall diameter is 632 mm. Going up one rim size with a lower profile keeps overall diameter close — that is how OEMs offer optional wheel sizes.