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Comment by stcredzero | Hacker News Reader

I wonder how well a special version of the Tesla Model S would do on the Top Gear track, if it reduced its battery weight to the point where it could just barely complete the course? The battery weight is its biggest problem as a track car.

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The trouble is that battery capacity and power output are greatly related. That's why this new P100D is faster than the P90D, and why Tesla's slowest offerings are also those with the smallest batteries. For a given battery, you can extract X% of its capacity per minute without significantly damaging it, where X depends on chemistry, temperature, and what you consider to be "significant." If you add capacity, X remains the same, so the absolute power you can extract goes up.

From what I hear, cooling is its biggest problem as a track car. The cooling system is sized for highway cruising, not track driving, so it overheats and limits power after a while.

How about specialized Tesla racing battery packs using super-capacitors and equipped with a cooling system? (Using the whole aluminum underside of the battery pack as a radiator.)

I'm not sure how supercapacitors do on energy density right now, but a better cooling system certainly sounds good. It would be interesting to see what the Electric GT people are doing. They're going to be racing P85+s next year, and I imagine it would be boring to the viewers if the cars limited power due to overheating during the race.

I would love it if they would do another roadster (or coupe) like this.

The Telsa also is really only fast from 0-60 or maybe 0-100. I've ridden around my local race track in one with tires squealing the whole way and while it was ridiculous off the line (I say that as the owner of a 600+ hp car), it's acceleration dropped off greatly the faster you went.

Depends on the track of course, but cars on Laguna Seca rarely go above 100mph.

https://www.youtube.com/watch?v=la6BZ89Z6bs

Sure, the CTS-V starts at 120mph, but as soon as the turns start up its difficult for the driver to get the speed up. A lot of turns are taken at 40mph or slower, and accelerating back up to ~100mph is something the Tesla is very good at.

I don't think the Tesla's top-speed issues are a problem. Its more about the weight and its poor skid-pad that is keeping it off the track. And of course, that electric-battery heating issue.

> cars on Laguna Seca rarely go above 100mph

Depends heavily on the car: https://youtu.be/pXP3Eij2GGA (same driver as your video)

Anyway, this was around Portland International Raceway and your car has to be pretty dang slow to not break 100 MPH on both the front straight and the back straight there.

Sub 1:30 on Laguna Seca? That's pretty darn good.

> your car has to be pretty dang slow to not break 100 MPH on both the front straight and the back straight there.

That's true. By "rarely", I mean maybe three or so of the straights. Although I guess that's a very poor definition of "rarely"...

A smaller battery would be limited to a lower output power (as max battery power is defined as a function of battery capacity), so reducing the battery size would make it slower. The fastest it could be would be for most of the mass of the car to be battery, at which point it could theoretically have 5000+ horsepower, although there are practical limitations of course of transmitting that to the road.

I think the biggest problem Model S has as a track car is that it is a luxury four door sedan.

The WHOLE point is this ton of bricks luxury four door can accelerate like no bodies business, faster than most track cars. Not that the Model S/X is a track car.

Interesting idea, why not make the battery in segments and removable. Weight affects range too, so why not make the battery as 4 segments, and if you're just going to have a 30 minute daily commute, you could take out 3 segments and have enough range while saving weight, and the environment. If you want to go for a weekend trip you'd plug in the other segments.

Obviously it'd be a bit of a nuisance and probably the segment that is always in the car will die first, because it'll have the most cycles. Unless the software controls which segments you can remove and do some wear-levelling.

The battery is already removable. I could see a Tesla battery swap machine at a track with lightweight "track batteries."

you need the larger pack size to deliver enough current to do 0-60 in 2.5 seconds.

Just don't ask how it would perform in a 10 mile race ;-)

spoiler alert: the software throttles the top speed down aggressively as the battery heats up, which it will do very quickly while accelerating rapidly.

I haven't kept up with it (I'd assume someone has more recent data/times), but I know older version's of the S had trouble doing full laps of Laguna Seca and the Nürburgring due to heat. Is that still the case?

Look at Formula E. They last 20 minutes or so.

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