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Comment by msk-lywenn | Hacker News Reader

Funny that it packs 3000hp while the Chiron « only » needs 1600hp to achieve mostly the same speed.

At that speed the limiting factor likely moves from raw power output to things like cornering ability on the track, grip of the tires, aerodynamics, downforce, driver skill, mechanical linkages, etc.

There's a reason why all the world's land speed records since the 1930s [1] get set at the Bonneville Salt Flats or similar flat desert terrain. FWIW, the speed listed in this article was exceeded in 1937. The hard part is not necessarily going fast, it's going fast in a street-legal vehicle.

[1] https://en.wikipedia.org/wiki/List_of_land_speed_records

For a top speed run, cornering ability is next to useless. You need grip to put down the power and be stable at speed, the corners taken for top speed runs are fairly wide. The bigger issue here is for how long can a BEV sustain max power output - it can deplete its battery in 2 minutes. EVs also can only produce top power whilst battery is at top voltage, since draining it drops voltage, max power drops with charge levels. The tyre grip itself is fine, the issue is tyre durability - they can usually last less than 20 minutes at top speed.

It is an impressive feat of engineering to get to a vmax record in a BEV.

I'll need evidence of "Top power at Top Voltage." Since so little capacity is at that part of the curve, It'd make sense to design around (as in avoid, not feature) it rather than use it.

I suspect theres inductance and capacitance enough that even if the motors can't handle the voltage, it can be "clipped" until the pack comes down. (Especially since fmu these are 3phase AC motors, the motor driver is already regulating voltage and current to produce whatever the optimal waveform is)

Well you can see reports of people drag stripping teslas, and comparing speeds at 100 vs 90 vs 50% charge. Whatever the reason, you do slow down.

Apples to broccoli comparison. Besides what I mentioned being optional (I'm sure it has downsides, probably cost), comparing road legal cars with a supercar is... interesting.

You don't need a Tesla to figure this out, my toy RC monster truck does the same thing.

You don't need to design around it - it is not like you can use top power for 100% of the time in most EVs anyway, and there's no good reason to restrict it such that the vehicle can operate at a limited max power for longer. ICE cars also reach top power only in a given RPM range, so it still is a curve, albeit turbo cars can flatten the curve quite a bit.

There was quite an interesting youtube from Engineering Explained speculating it had enough power to do 400 mph. There may have been other constraints limiting things like the tyres being safe and apparently the battery only has capacity for 2 mins at full power, plus bits may overheat and the like.

(https://youtu.be/z6q7du1q2U8)

It's also interesting that the fastest time on the Nürburgring at 5 min 19 was from a Porsche hybrid with 900 hp, a fair bit quicker than the BYD which took 6:59 I think. The Porsche had a lot more downforce than the BYD.

> 5 min 19 was from a Porsche hybrid with 900 hp

You're talking about the non-production Porsche 919 Hybrid Evo race car. A Corvette ZR1X did 6:49 with a third of the HP

Yeah, the weight and battery are the limiting factors. Their battery tech is impressive though.

>the battery only has capacity for 2 mins at full power

"The tires on the Veyron can only last 15 minutes at top speed, but that's ok because the fuel tank only has capacity for 7 minutes at top speed." (From memory, IIRC, Top Gear on the Veyron)

https://youtu.be/jk1t6S737Cs?t=393

> the tires will only last for about 15 minutes but it's okay because the fuel runs out in 12 minutes

I watched a video of the speed test a few days ago and it looked like the BYD car was still accelerating when the top speed was reached, such that it could have gone faster than the record they were aiming for—there was a speed curve and it wasn't plateauing. Of course there are lots of possible reasons why the car couldn't have managed a higher speed, but I wonder if it's like incredibly tall skyscrapers having secretly validated a taller version in the wind tunnel so they can change plans if competition catches up during construction.

Tyres are almost certainly the limiting factor here; also I forget how close to the (admittedly banked) turn it was when it hit its top speed.

The best batteries have like 40 times less energy density than engines running on oil derivatives. Even considering that electrical engines are 90% efficient while combustion engines get like 25% efficiency, that still leaves the factor of 10 for energy density. That implies much bigger weight. And to compensate the engines must be more powerful.

Head to head, the Chiron SS would probably smoke this car at the top end, heat is a way more difficult problem to deal with for EVs than ICEs.

Well, power at top speed will probably be similar, they don't seem to be too different aerodynamically (maybe the Bugatti has got the edge there, but still, won't be a 2x difference).

The question is also how much power the battery can continuously output, if it's the 3000hp for 15 seconds that won't be of much use for a max speed test.

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