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Performance vs. torque

What the hell does the papers for our new electric car say, 28 kW? This can not be true. According to the brochure, we were promised 150, which corresponds to an impressive 204 hp.

Fraud, reversal of the purchase contract? But that won't do any good unless we go back to the good old combustion engine. Doubts also arise as to whether the acceleration that is noticeable in the car and demonstrated to all passengers would be possible with just 28 kW.

That's just 38 hp, a little less than a 1300 VW Beetle had. And the certainly didn't accelerate that quickly. But the number is written there. A reason to notice the surroundings, because after a slash '30 min' appears.

So the law requires that the performance entered here must be maintained for at least half an hour. Yes, but why doesn't anyone notice that the car is weaker than a VW Beetle under constant use?

Now just ask yourself how you used to determine whether your car had the minimum performance documented in the documents, based on the acceleration? No, it was only really measurable at the top speed.

If you took it seriously, once on the motorway and then back again and deducted the advance from the speedometer. If you have taken it exactly, once on the highway there and then back again and subtracted the fast reading from the speedometer. Anyone who did this early enough on his/her new car, but after the break-in period, was then able to document any loss of performance later.

But see, that's exactly what's no longer possible these days, because almost all electric cars are limited. You can't tell from the acceleration anyway because an electric motor has completely different characteristics. Even with the same performance, it would easily outpace a Beetle. deducted from the speedometer.

Because of course a maximum is mentioned with the value documented in the papers. It's like the charging curve, where what's around it is actually more important than the peak value achieved over a short period of time.

Viewed from the outside, the electric motor is just as much a driver as the combustion engine. It just has two special features: it usually doesn't have a gearbox and it makes a huge drive from zero speed, which is completely different from the combustion engine, which, no matter how it is designed, has to build up torque first.

Not only does its torque curve start from 0 Nm, it only does so from idle speed at the earliest. A combustion engine therefore needs a gearbox so that it can always be operated in its highest torque or most powerful speed range, for example. However, this also applies to the possibility of driving it to save fuel.

It is no coincidence that a combustion engine has to be started by an electric motor and then usually has to be brought to at least 2000 rpm to drive. And if it's not a diesel or a large-volume petrol engine, it still needs more rpm, for example to get into the more powerful range.

This is foreign to the engine in a purely electric car. It is practically the starter, just much stronger. That's what makes it so practical when the traffic light turns green, no engine start as if the engine had been switched off by start-stop, for example. The engine itself has the high torque. It does not have to be produced by a shorter gear ratio.

But the electric car must also have some kind of overall gear ratio. According to the diagram above, it's best that everything happens between 0 and 4500 rpm. If we take our Kona and let it reach a speed of 170 km/h, then with 215/55 R 17 the wheel radius is 0.335 m and the wheel speed is 1,350 rpm. So the total gear ratio would be 3.33.

But the engineers at Hyundai gave him a ratio of around 8:1. Obviously, a kind of mean has to be found when it comes to electric cars. In practice, an electric motor is not constantly rotated between 0 and 4500 rpm, although we don't even know whether the torque curve in the Kona doesn't drop even earlier than in the BMW iX3.

And why? Because its performance is only increasing up to 4,500 rpm, which would have a significantly negative effect on acceleration despite the high torque of the electric motor. Porsche seems to be so dependent on good values that they installed a two-speed gearbox with a very reduced first gear on the rear engine of the Taycan. With electric cars, there is also a compromise in the design of the gear ratio.

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