The Porsche Taycan's Two-Speed Gearbox • Hacker News Board

Re: The Porsche Taycan's Two-Speed Gearbox

#211

Post by Dylan16807 » Sat, Sep 07, 2019, 7:59 PM UTC

compiler-guy wrote: post #203

Dylan16807 wrote: post #156

Earlier quoted context omitted.

> Are saying that Porsche--which is spending billions of dollars on the Taycan and its transmission--is doing this for no good reason? Yes, they are. They are saying that "better on a track" is a bad reason, and "it makes more money" is a bad reason. That is not a claim that Porsche is incorrectly engineering to reach their goal, or doing anything unprofitable. It's an opinion.

That's a different opinion than the one being expressed and therefore the I'm discussing. The argument I'm talking about is the one which claims, "There is no advantage to a two-speed transmission". You seem to be saying that the advantages of such a transmission are bad reasons to build it. But those are different arguments.

> the one which claims, "There is no advantage to a two-speed transmission"

The post does not say those words.

The discussion of how Tesla can "already" achieve a fast 0-60 is a pretty clear acknowledgement that the number can be improved. But there's "no reason" because it's already so good, and there are important downsides.

That's all paraphrasing the post itself. It is not the blatantly false technical argument that you imagine.

And the post I made earlier was not a novel argument. It was taking "no [good] reason" and using that to classify a couple obvious "reasons" as not good. A very small logical step.

Re: The Porsche Taycan's Two-Speed Gearbox

#212

Post by lazyjones » Sat, Sep 07, 2019, 8:31 PM UTC

compiler-guy wrote: post #109

The level of hubris here is pretty high. "No reason"? "No performance benefit"? Porsche is spending billions of dollars to bring a very high performance track-focused sports-sedan to the market. Hundreds of extremely good engineers are getting paid millions of dollars to figure this problem out. I'm sure the transmission is a giant set of engineering tradeoffs (what project isn't), and maybe it won't work out and wil…

> Porsche is spending billions of dollars to bring a very high performance track-focused sports-sedan to the market. Hundreds of extremely good engineers are getting paid millions of dollars to figure this problem out.

And yet their car is only about as fast as a FWD 300HP Renault Megane RS on the Nurburgring.

Re: The Porsche Taycan's Two-Speed Gearbox

#213

Post by kenhwang » Sat, Sep 07, 2019, 10:21 PM UTC

giobox wrote: post #189

kenhwang wrote: post #134

Earlier quoted context omitted.

The Taycan currently only comes with two brake options: carbon surface coated brakes or full carbon ceramic brakes.

Porsche have said in many interviews the coating is for cosmetics rather than performance. Like most electric cars, when driving “normally” you don’t really ever touch the brakes as the energy regen that kicks in when you step off the accelerator pedal slows the car down so effectively. Porsche were worried the discs would develop unsightly surface corrosion from lack of use for some drivers - the coating keeps them…

Primarily for cosmetics since it generates much less brake dust, but it's also has a shorter stopping distance due to increased coefficient of friction from increased contact area and seems to be more resistant to fade.

https://thebrakereport.com/porsche-surface-coated-brake-pscb...

Re: The Porsche Taycan's Two-Speed Gearbox

#214

Post by kenhwang » Sat, Sep 07, 2019, 10:40 PM UTC

compiler-guy wrote: post #205

giobox wrote: post #189

Earlier quoted context omitted.

Porsche have said in many interviews the coating is for cosmetics rather than performance. Like most electric cars, when driving “normally” you don’t really ever touch the brakes as the energy regen that kicks in when you step off the accelerator pedal slows the car down so effectively. Porsche were worried the discs would develop unsightly surface corrosion from lack of use for some drivers - the coating keeps them…

The Taycan freewheels when you take your foot off the accelerator and only regenerates when you hit the brakes. This is quite different than most other electric cars.

That's just a default configuration difference. You can configure it to do lift-off regen if you like. There's also a camera based auto-regen mode that can switch between coasting and regen based on the distance to the car in front.

Philosophically, Porsche believes it's easier to drive a car fast when one pedal is solely responsible for accelerating and one for braking. Having the throttle be responsible for acceleration and light braking makes it difficult to modulate speed consistently. You can even see the philosophy at work on their gasoline cars, in Sport+ mode the anti-lag system pretty much removes engine braking.

Re: The Porsche Taycan's Two-Speed Gearbox

#215

Post by kenhwang » Sat, Sep 07, 2019, 11:14 PM UTC

elihu wrote: post #174

adrianN wrote: post #164

Earlier quoted context omitted.

It's also unclear to me why a gearbox alone would give you longer sustained maximum power.

Most electric motors are most efficient and can generate the most power within a certain RPM range. (It's a lot wider than gas engines, but beyond a certain speed the torque falls off.) If you can drive at high speeds at a more efficient motor RPM, then that's less excess heat for the motor and inverter to deal with, and less current draw from the batteries.

Electric motors are pretty much opposite of gasoline engines. Motors have peak torque at 0-2krpm and it drops off rapidly after that. Gasoline cars tend to hit peak torque near the end of their rpm range (ignoring turbos that can change that in any number of ways).

From what I can see, most electric motors are tuned to have peak efficiency at ~5krpm which is conveniently around freeway driving speeds.

Re: The Porsche Taycan's Two-Speed Gearbox

#216

Post by natch » Sun, Sep 08, 2019, 1:01 AM UTC

newnewpdro wrote: post #50

Ididntdothis wrote: post #47

Earlier quoted context omitted.

People rarely do a full power 0-60 with a car that can do it under 5 seconds. More likely they go from 30-60 or similar.

When a car does it silently without being overtly antisocial they do it far more often.

John Carmack among others agrees with you about Tesla acceleration not being antisocial. Here he is talking about it (timestamp in link takes you to the right part of the video):

https://youtu.be/Ua-ikbZVofc?t=674

Re: The Porsche Taycan's Two-Speed Gearbox

#217

Post by CamperBob2 » Sun, Sep 08, 2019, 8:51 AM UTC

dghughes wrote: post #158

leetcrew wrote: post #94

Earlier quoted context omitted.

if you accelerate quickly to the legal limit and others take it as an invitation to drive recklessly, that sounds an awful lot like their own problem. I agree with your other comments about driving in traffic. avoiding large speed differentials when you are surrounded by other cars is very much your responsibility.

> avoiding large speed differentials That would be (or should be) the entire point of a posted speed limit, go with the flow. There should also be a lower speed limit. On roads I would bet many crashes occur due to the difference in speed between vehicles. Speeding motorcycles, slow trucks, fast sports cars, all of which would be around vehicles of moderate speed. The reaction time for the faster vehicle driver is di…

That would be (or should be) the entire point of a posted speed limit, go with the flow. There should also be a lower speed limit.

You can't have both. Suggest doing some Googling for a topic called the "85th percentile rule."

Re: The Porsche Taycan's Two-Speed Gearbox

#218

Post by cat199 » Wed, Sep 11, 2019, 12:54 AM UTC

whalesalad wrote: post #129

cat199 wrote: post #125

Earlier quoted context omitted.

someone this close minded would likely not be considering electric in the first place (and would probably whine about porches being mostly v6 and not v8/10/12)

Close minded? Huh. You won’t find a CVT in anything but a budget economy vehicle. If you want performance, you don’t want a CVT. If you want to prioritize efficiency over everything else (including reliability), a CVT is fine.

yes - close minded.

if you want performance - you want performance however you get it.

if someone makes a performant cvt, you want that. if they don't, you dont.

someone bound up in performance==x will not buy 'y', period.

Re: The Porsche Taycan's Two-Speed Gearbox

#219

Post by eigenloss » Thu, Sep 12, 2019, 3:05 AM UTC

kenhwang wrote: post #215

elihu wrote: post #174

Earlier quoted context omitted.

Most electric motors are most efficient and can generate the most power within a certain RPM range. (It's a lot wider than gas engines, but beyond a certain speed the torque falls off.) If you can drive at high speeds at a more efficient motor RPM, then that's less excess heat for the motor and inverter to deal with, and less current draw from the batteries.

Electric motors are pretty much opposite of gasoline engines. Motors have peak torque at 0-2krpm and it drops off rapidly after that. Gasoline cars tend to hit peak torque near the end of their rpm range (ignoring turbos that can change that in any number of ways). From what I can see, most electric motors are tuned to have peak efficiency at ~5krpm which is conveniently around freeway driving speeds.

One might even imagine they were engineered to be optimally efficient at freeway driving speeds! :D