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Comment by djrogers | Hacker News Reader

> From what I keep hearing, current EV acceleration is limited by the battery discharge rates

Acceleration today is mostly limited by available traction. It's not at all clear that a liveable car could get appreciably faster acceleration than we have today without a breakthrough in tire technology.

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The new Tesla roadster coming soon(TM) does 0-60 mph in 1.9 seconds, and the quarter mile in 8.8, which is staggeringly fast even by ultra car standards. People that spend years and hundreds of thousands of dollars on their dedicated drag car never get that fast. I don't believe there's ever been a production car that runs in the nine second range, let alone into the eights.

I believe with EVs, traction is not as much of an issue because the computer can adjust the torque output 1000 times per second, unlike an Internal Combustion Engine which takes eons to react and change it's power output. Obviously off the line it is, but certain as you get moving more you can dump a lot of torque into sticky rubber.

Tesla are having a "battery day" soon, and I for one suspect their new batteries (maybe just for the new Roadster, maybe for all their cars) will be some kind of hybrid capacitor, or at least have some of their capacity does that way.

Nobody needs this performance in everyday life.

That's right, nobody really needs this, but the point of the Roadster V2 isn't to satisfy a need, it's to eradicate the perception that gasoline cars are better performing. By building a supercar that will humiliate all the Porsches and Ferraris, with no hope of gasoline cars remotely in the same price range ever being able to compete (unless they go hybrid?), Tesla will catch a lot of press. A new generation of kids will grow up with the clear perception that electric cars are superior technology. They will have Tesla Roaster posters on their walls instead of gasoline cars. The roaster is very much an expensive PR piece, but it will change the world and accelerate the transition to renewable energy in a meaningful way. Perception counts.

> Tesla Roaster posters

Now I'm wondering what Elon will name his coffee roasting company.

Zapped Beans?

> The new Tesla roadster coming soon(TM) does 0-60 mph in 1.9 seconds

Except it hasn't, because the production version does not exist. I don't even think the 1.9 second claim has been verified for the prototype.

AFAIK, usually Tesla reports performance numbers conservatively. For example production version of Model Y has longer range than what it was announced to have. Why would this be any different?

Hans (the lead designer) has been quoted a few times saying the production version will surpass the stated figures in every way.

I'm extremely excited, but as you said, it's still ~9 months away from being sold.

Yep, and why every supercar's 0-60 time is limited to about ~2.6s these days. Also why tesla is claiming to be able to achieve <2.6s only with the cold gas thruster "SpaceX" package, they're no longer solely relying on the tire traction.

No, tesla s with ludicrous mode is doing 0-60 in 2.28 today. The new roadster is aiming for 1.9 and probably less with the SpaceX package.

The exact number wasn't really the point + elon has a history of releasing high performance spec's before the actual technology is ready. Maybe they have special tires in the works, but the rubber that's on the market today can't do that

Can't the tires just continue to get wider and wider until the rear tires are even about 4 ft wide?

That should provide lots of traction.

But friction is dependent on the pressure between the contact patches. More area of contact reduces the pressure per unit of area. So you’d need more pressure on said tires without augmenting mass (because then you’d need yet more friction to accelerate that mass, that’s why wings are a thing, more pressure on the tires without adding mass that you’d have to turn accelerate.

Problem with wings is that they not only add drag but they are not affecting anything at launch. Maybe if you had a big electromagnet under the car and a steel path under the asphalt.

Just pack a giant fan onto it, kinda like an up-side-down hovercraft.

Why not going full hovercraft? Use the obsolete tire technology only for transition and slow speeds, thereby eliminating all that rubber dust!1!!

Some race cars [1] put fans under the cars, sucking upward. This effectively created a vacuum under the car and allowed it to stick to the road pretty well. It was more for cornering fast than straight-line acceleration. But modern race cars to use aerodynamic tricks to create downforce, but only to keep the car on the ground at high speeds.

1. https://jalopnik.com/brabham-bt46b-fan-car-making-lemonade-f...

But you won't be turning that car around any time soon. The Flintstones notwithstanding it isn't particularly clever to have your tires run the width of the car because the inner and outer radius during a turn will cause the tire to wear rapidly. You could cut the width-of-your-car tire into a lot of slices I guess but that would be mechanically quite complex and you'd still have to drive it somehow.

On the chance of non-sarcasm :)

You get into the limits of being able to transfer the rotation of the axle to the tire patch.

Mental picture time, if you will: 1. Axle spins, which rotates the metal wheel |> since the metal wheel is metal to metal with the axle, we will consider it to be one unit, even though technically, it is not

2. Metal wheel rotates the part of the tire near the rim |> There is only so much force which can be applied to join the tire's bead to the metal of the wheel. "Bead locking" can be done, but this is esoteric and, at least in the US, is mostly not legal for road-going vehicles. Also, the amount of space necessary for bead locking components is a complex challenge for the passenger car wheels, and is usually reserved to far larger wheels found in off-road-like vehicles.

3. The tire rim has to transmit the rotation to the tire contact patch, which happens via the tire sidewall. |> This sidewall has to stay flexible otherwise the ride would be nigh impossibly jarring. Check videos of sidewall flex of drag tires for a practical example of this, a-la https://youtu.be/rw3LE78gwhg

There are plenty of other things in play, top, but these are the big limiting factors.

that isn't how friction works really.

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