One number, then everything around it.

It depends what you want from the car. Most everyday hatches, sedans and SUVs sit between 75 and 110 kW per tonne, which feels adequate. Hot hatches are around 150–200 kW/t, serious sports cars 200–275 kW/t, and supercars beyond that. Above about 150 kW/t, the tyres rather than the engine start to limit how quickly the car can accelerate and stop.

Divide peak power in kilowatts by the car's mass in tonnes. A 195 kW car weighing 1,430 kg makes 195 ÷ 1.43 = 136 kW per tonne. To convert horsepower to kilowatts, multiply by 0.7457; for metric PS, multiply by 0.7355.

Only the unit of power. One kilowatt is 1.341 mechanical horsepower, so 136 kW per tonne is 183 hp per tonne. American sources often flip the ratio to pounds per horsepower, where lower is quicker: 136 kW/t is about 12 lb/hp.

Tyres respond to force, and force scales with how much power is pushing how much mass. A 150 kW, 2.1-tonne ute and a 150 kW, 1.1-tonne roadster load their tyres very differently under acceleration, and the lighter car will explore the limits of its tyres far more often. The ratio captures that in one number.

Yes, for traction off the line and out of slow corners, especially on two-wheel-drive cars. Add torque under Fine-tune and ratio will flag it when torque per tonne is high enough that the tyres, not the engine, limit acceleration. Power still sets the category, because sustained power is what builds heat and wear.

You can buy a less performance-focused category, but not a worse tyre. Wet braking matters in every car, and it varies enormously between tyres within the same category. A good touring tyre often out-brakes a cheap performance tyre in the rain.

The load index estimate assumes a laden car (400 kg for a car, 500 kg for an SUV, 1,000 kg for a ute) with 58% on the heavier axle, then picks the smallest index that covers one tyre on that axle. The speed rating is the lowest symbol that covers the top speed you enter, or the minimum typical for the tier. Both are sanity checks. Your placard is the legal minimum and is usually higher.

Roughly ±10%. It is an empirical curve fitted to published times, adjusted for driven wheels and EV launch, and capped by traction for very powerful cars. Gearing, launch control and the tyres themselves move real times either way.

They are typical manufacturer figures for a common variant, and kerb weights vary by market, trim and options. If you know your exact numbers, type them in: the preset switches to 'edited' and everything recalculates.

Avoid it on the same axle, always. Across axles it is legal in most places but changes the balance of the car, so keep the grippier pair on the rear. On all-wheel drive, keep all four matched.