5 ms·

If your velocity is over 400 kph and you just slam on the brakes and keep them on 100% until the car stops, does that not just totally destroy the brakes, maybe

If your velocity is over 400 kph and you just slam on the brakes and keep them on 100% until the car stops, does that not just totally destroy the brakes, maybe even melting them? (The kinetic energy of a 2300 kg object moving at 410 kph is over 50 gigawatt-hours) Edit: I made a typo in wolfram alpha :]

doikor 3y ago
That is why they make the brakes out of fancy carbon ceramics. You can still burn them but not in a single 400kph to 0. They do kinda suck when driving slowly as they only really work well when hot but electric cars can just brake with the engines at those speeds to make up for it. Though they are used in combustion engine sports cars too so it is not that bad. Just need to warm them up like tires when driving hard on a race track. For sports cars carbon ceramic brakes also have the massive advantage that they do not fade with heat like traditional brakes.
- bitexploder 3y ago
  Most modern sports cars with proper brake fluid (higher boiling point) and some heat management have no problems with brake fade in steel discs. Many that track their GT3 / GT3 RS (Porsche 911) prefer steel discs due to the maintenance cost of carbon ceramic and properly designed steel discs perform just the same as carbon ceramics because the brake fade isn’t a big problem, even in a pretty extreme application like this. Not sure if the Rimac really needs anything otherwise as well. Plus, it has regen braking and a crazy cooling system to help there. Parents math was off about the amount of energy also. My car has carbon ceramic brakes (GT3). Two reasons: don’t need to be warmed up for full stopping power and way less brake dust. That is the only advantages in practice. On the track warming the brakes up is easy.
smcameron 3y ago
> over 50 gigawatt-hours That can't be right. 2300 kg * sqr(410000/3600) * 0.5 = 14893006.000 Joules 14893006J * 0.000277778 = 4136.9 watt hours Edit: out of curiousity, in order to have a kinetic energy of 50GWh, it would need a speed of 1424260 km/h (884994 mph)
- redox99 3y ago
  Yeah, it's quite clearly wrong when you realize that the batteries would never be able to deliver 50GWh in the first place.
  - smcameron 3y ago
    And if they could, in order to charge it up, the battery would have to consume the entire output of the world's largest power station, the Three Gorges Dam, for more than two hours. (Three Gorges Dam outputs 22.5GW
    - dsr_ 3y ago
      And would need about 750,000 of the best Level 3 DC fast chargers connected simultaneously. And 0.01% inefficiency in transfer would melt the car (and the road, and...)
  - adrianN 3y ago
    The video shows max power of around 1.3MW for like 10s. That's enough to get the right ballpark for the kinetic energy.
- shric 3y ago
  Maybe the GP assumed 410km/sec instead of 410kph.
  - deleted 3y ago
    [deleted]
- bombcar 3y ago
  I did based on 88 gigawatts being enough to send the vehicle backwards through time.
  - kcplate 3y ago
    Great Scott!
culopatin 3y ago
That would mean that the batteries have that capacity too, I don’t think your math is right.

doikor 3y ago

That is why they make the brakes out of fancy carbon ceramics. You can still burn them but not in a single 400kph to 0. They do kinda suck when driving slowly as they only really work well when hot but electric cars can just brake with the engines at those speeds to make up for it. Though they are used in combustion engine sports cars too so it is not that bad. Just need to warm them up like tires when driving hard on a race track. For sports cars carbon ceramic brakes also have the massive advantage that they do not fade with heat like traditional brakes.

bitexploder 3y ago
Most modern sports cars with proper brake fluid (higher boiling point) and some heat management have no problems with brake fade in steel discs. Many that track their GT3 / GT3 RS (Porsche 911) prefer steel discs due to the maintenance cost of carbon ceramic and properly designed steel discs perform just the same as carbon ceramics because the brake fade isn’t a big problem, even in a pretty extreme application like this. Not sure if the Rimac really needs anything otherwise as well. Plus, it has regen braking and a crazy cooling system to help there. Parents math was off about the amount of energy also. My car has carbon ceramic brakes (GT3). Two reasons: don’t need to be warmed up for full stopping power and way less brake dust. That is the only advantages in practice. On the track warming the brakes up is easy.

smcameron 3y ago

> over 50 gigawatt-hours That can't be right. 2300 kg * sqr(410000/3600) * 0.5 = 14893006.000 Joules 14893006J * 0.000277778 = 4136.9 watt hours Edit: out of curiousity, in order to have a kinetic energy of 50GWh, it would need a speed of 1424260 km/h (884994 mph)

redox99 3y ago
Yeah, it's quite clearly wrong when you realize that the batteries would never be able to deliver 50GWh in the first place.
- smcameron 3y ago
  And if they could, in order to charge it up, the battery would have to consume the entire output of the world's largest power station, the Three Gorges Dam, for more than two hours. (Three Gorges Dam outputs 22.5GW
  - dsr_ 3y ago
    And would need about 750,000 of the best Level 3 DC fast chargers connected simultaneously. And 0.01% inefficiency in transfer would melt the car (and the road, and...)
- adrianN 3y ago
  The video shows max power of around 1.3MW for like 10s. That's enough to get the right ballpark for the kinetic energy.
shric 3y ago
Maybe the GP assumed 410km/sec instead of 410kph.
- deleted 3y ago
  [deleted]
bombcar 3y ago
I did based on 88 gigawatts being enough to send the vehicle backwards through time.
- kcplate 3y ago
  Great Scott!

culopatin 3y ago

That would mean that the batteries have that capacity too, I don’t think your math is right.