[DiabloD3]

Disclaimer: IANAL, but also asked that question once in my youth, and went digging for the answer.

They technically don't in a meaningful sense.

What they do is make a car that has high torque and can accelerate 0-60 mph as quickly as possible. This has the unwanted side effect of also being able to still continue accelerating quickly past the target zone (<= 85mph). Some street legal cars have governors because of how exceptional their acceleration is.

The acceleration in cars are designed around pretty much one extra horrible edge case: accelerating up to freeway speeds, up an onramp that is entirely too steep (yet legally designed), from a standstill (ie, gridlock conditions), while also carrying max cargo capacity. Cars must be able to do this to be considered safe by any meaningful definition.

Also, there are no laws against going fast. The laws are purely against the law on public roads, as per the posted limit; there are many private racetracks that are completely legal. Not all countries even have limits comparable to America's, so being able to safely go 100+ mph is worth it if you were to, say, drive on the German Autobahn.

[lldbg]

A bit of a pet-peeve of mine, but it is the power that makes the car accelerate, not torque. With gearing, any value of torque is possible at the wheels, but not for any given speed. A car with 300 Nm of torque but 100 kW of power will never accelerate faster than the same car, but with less Nm and say 150 kW of power. Gearing is suitably chosen according to power production, not torque. The answer to the question "At what RPM will I accelerate the fastest, for a given speed" is always the RPM at which peak power is produced - which may or may not be avaliable because of gearing, but usually you can come pretty close since the power curve is somewhat flat around a region of RPM. Typically.

[ce4]

Exactly. E.g. Diesel engines have a much lower maximum rpm limit (4.5-5.5k rpms) so they need to deliver that amount of power by delivering more torque at lower RPMs when compared to comparably powered petrol engines.

And electric car motors can draw almost maximum Amperes at very low rpms, hence the insane numbers of torque for electric cars

[giantg2]

"Some street legal cars have governors because of how exceptional their acceleration is."

Most manufacturer limits on top speed are tied to the vehicle tire speed rating (usually somewhere around 92-116mph). There are a few that are sort of an industry standard cutoff for 'safety', like 300kpm (I think) on sport bikes.

[majewsky]

> the German Autobahn

Since this meme comes up a lot: About two thirds of the Autobahn network do have speed limits, ranging between 80-130 km/h (50-80 mph). In fact, one of the arguments for a general 130 km/h speed limit is that it would reduce the rate of speed limit changes, thus making traffic flow smoother overall.