
The Porsche Taycan's Two-Speed Gearbox - jbredeche
https://www.wired.com/story/electric-car-two-speed-transmission-gearbox/
======
compiler-guy
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 will end up being the wrong
solution.

But it can't be so obvious that random Joe-and-Jane HackerNews know the answer
off the top of their heads and Porsche doesn't after all the resources it has
spent to figure out the problem.

~~~
ztjio
So, I'll just hop in here and lay out the spoiler.

There is a major performance difference in the Taycan, it's endurance, and
it's highly likely this transmission is a key element to achieving it.

For those that don't know, Tesla's cars can not keep their maximum performance
up for a very long time. The battery gets hot and lowers power output until it
cools back down. The Taycan, while not having as impressive max specs or range
(and some serious questionability about the charging claims) _CAN_ keep its
maximum performance indefinitely. At least through a full discharge of the
battery pack, but, also after a recharge it can keep going and they
demonstrated this recently with a 24 hour marathon test drive stopping only to
charge it.

So, without really getting into all the weird perception based arguments,
there is clearly a difference in performance and the transmission may be
critical to it.

~~~
zaroth
This is more of a function of battery chemistry on the S/X - the Model 3 does
not have the same power restriction under load.

~~~
reitzensteinm
Which makes Elon's promise of sending the Model S round the ring a bit
confusing.

Presumably it would be a suicide run to match the Taycan, which to my
understanding would involve modifications and not be eligible for the same
category.

Either it was an idle boast, or we're about to see the launch of the 21700
Model S.

~~~
ztjio
Once around the ring is not an issue. It's a day at the track that's a
problem, not one lap. And not an issue at all if you're fine with waiting
periodically while the battery temp comes back to optimal.

~~~
maigret
Do you have data for a Tesla completing a single Nurburgring lap at full
speed? AFAIK they failed each time so far
[https://insideevs.com/news/323053/tesla-model-s-fails-to-
lap...](https://insideevs.com/news/323053/tesla-model-s-fails-to-lap-
nurburgring-under-full-power-video/)

------
gleglegle
It's a little surprising that even with a two-speed Gearbox the Taycan has
neither better range nor low range 0-60 acceleration than the Tesla P100D
(which has the same size battery). Obviously spec comparisons aren't the whole
story and the handling and high-range acceleration may be better on the
Taycan. Looking forward to seeing more comparisons and already glad to see
more EV models in this category.

Edited incorrect comment about top speed.

~~~
dragontamer
> It's a little surprising that even with a two-speed Gearbox the Taycan has
> neither better range nor low range 0-60 acceleration than the Tesla P100D
> (which has the same size battery).

0-60 times probably don't matter on the track. Its probably more important to
optimize the 60 to 120mph time, which is where the torque of a (single gear)
electric motor begins to taper off. I bet that Taycan has superior
60-to-120mph times than any gearbox-free design, which would lead to superior
track performance. Especially on a track as big as Nurburgring.

Even on highway driving, 0-60 times kind of don't matter as much as 30-60
times. (Aka: merging into a highway). The only reason to push 0-60 times is
for drag-racing really.

~~~
newnewpdro
> The only reason to push 0-60 times is for drag-racing really.

Wat? Most people care about accelerating from a standstill to the average
legal speed limits.

0-60 captures that perfectly. It's incredibly relevant to the general public's
driving patterns.

~~~
Ididntdothis
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.

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

~~~
dragontamer
Leaving all the other cars next to you in the dust is quite antisocial
behavior actually.

For the most part, I want to accelerate with everyone else when that green
light goes off (except for Trucks: I wanna leave Trucks in the dust and get
away from them ASAP). The 30mph to 60mph acceleration of off-ramp into freeway
cruising speed however, is pretty important. A lot of things are going on when
I merge onto a freeway, so I'd like to make sure I can accelerate in an
adequate amount of time: to the point where I've (occasionally) downshift to
2nd, even in standard traffic, to get to 60mph asap.

~~~
Zanni
Serious question: how is this antisocial behavior? I understand wanting to
stick with the flow of traffic when you're part of the pack, but if you're in
front of the pack, what's the advantage (to anyone) of hanging back?

~~~
dragontamer
1\. By accelerating dramatically off the line, you're telling the other cars
that they are driving too slowly.

2\. Alternatively: you may be sending a signal that you want to drag-race with
someone. And nobody likes it when drag-racers start playing on public roads.
Keep that stuff off the streets and on the track only.

Now sure, if the cars next to me are driving slowly, I'll leave them in the
dust. But its not something I'll do on every green-light, and its something
I'd do only if they're going exceptionally slowly (ex: driving 40mph in a
60mph zone)

Those are the two signals I perceive whenever someone accelerates strongly off
of a green light: either #1, or #2, depending on context. There's certainly a
time to signal #1, but its a relatively rare event.

~~~
velp
If you take someone accelerating quickly from a light as a signal that you're
driving too slowly, you probably drive too slowly. I don't think its a signal
at all - and who really cares if it is?

------
phkahler
Aside from not providing much of any performance benefit, this will introduce
difficulty coordinating regenerative braking through the shift point.

One of my former employers had a group trying really hard to make a 2-speed
for EVs make sense. It just doesn't. If there is an efficiency gain, it's
probably better to throw the extra money and weight into the motor. An
exception _might_ be if you want to cruise at 120+ mph for long distances, but
that's not realistic.

~~~
youeseh
Which part of cruising at 120+ mph for long distances is not realistic?

~~~
sdfswfsafaswf
1\. outside Germany, cops 2\. power scales as v^3 destroying range.

~~~
Gibbon1
We shouldn't lose sight of #3.

3\. This is a toy we're talking about here.

------
AgloeDreams
As I understand it, this gearbox type is key on Porche's intent to make it
able to maintain performance over use rather than overheat, notably it
improves acceleration and efficiency at high speed. I would expect the Taycan
to use less energy to maintain 150mph.

~~~
nraynaud
don't you have a ton of cooling air at 150mph?

~~~
AgloeDreams
It's about efficiency at various speeds, plus having to intake more air to
cool more things increases drag, the best way to improve cooling performance
is to improve power use in the first place.

------
nickhalfasleep
In dual-motor (front, rear) Tesla vehicles, each motor is on a different gear
ratio for optimal power bands.

~~~
adrianmonk
I wonder if this is part of why their dual-motor models get better range. I
could see it being better for regenerative braking, too.

~~~
adrr
Not sure on the S or X but my model 3 AWD has less range than RWD. AWD is
quicker by 10%.

~~~
driverdan
AWD adds more weight and drive train losses.

~~~
STRML
This is only true on the Model 3. Indeed, on the S, the dual-motor variants
were _more_ efficient due to different gearing. It is still unclear the
community why the 3 dual motor variants are as much as 10% less efficient. It
is not totally accounted for by weight, and the extra induction motor should
be capable of torque sleep.

------
aidenn0
FWIW the original Tesla roadster was also a 2 speed, but they dropped the
gearing as soon as they could meet their original top-speed without it.

~~~
rconti
Yeah, and it was apparently prone to breaking (I learned this from Googling
just now). I was pretty sure I drove a 2-speed Roadster back in the day, but
wanted to confirm that actually made it to production -- it did. (The
Roadsters I drove were Tesla-owned but I'm pretty sure they were full
production models).

The more things change, the more they stay the same. I remember Tesla being
laughed at for this whole overpriced roadster thing, then because their
transmissions were breaking, then because the 'fix' was to produce a
"crippled" 1-speed car because they couldn't figure out how to make a
transmission that didn't break.

And now, 10 years later, I own a 1-speed one, and, miraculously, the whole
thing works on a real sedan, not just a kit car.

------
jaclaz
Once upon a time there were cars with a "normal" 4 speed (+reverse) gearbox
and an added "overdrive" box (that if I recall correctly could only be used in
3rd and 4th gear), surely there were a few Triumph's and some Volvo station
wagons, they had a button/switch on the gear stick that activated it
electrically.

[https://en.wikipedia.org/wiki/Overdrive_(mechanics)](https://en.wikipedia.org/wiki/Overdrive_\(mechanics\))

This device (with all the possible evolutions in these 30 or 40 years) sounds
a lot like this "overdrive" box.

~~~
kwhitefoot
Loads of cars had an overdrive and it made a significant difference to fuel
economy at high speed.

I think the difference here is that the Taycan has a kind of automatic gearbox
that can operate while under hard acceleration whereas, as far as I remember,
you only pushed the overdrive button when you had reached cruising speed.

~~~
jaclaz
Yes, that is part of the evolutions I mentioned, what I meant essentially was
saying that a two speed gearbox (electrically/hydraulically operated) reminds
me more an overdrive box (which is actually a two speed gearbox
electrically/hydraulically operated) than an actual 4/5/6 speed manual or
automatic gearbox.

The actual use of the old overdrive was to lower revs of the engine (please
read as save fuel) at a given speed, or (I know, not the actual intended use)
to increase top speed, which is exactly what the new Taycan gearbox seemingly
is used for (automatically, not manually, of course).

I remember a diesel Volvo station wagon (must have been a volvo 240 or 244)
where in order to overtake someone at 120-130 kmh, the procedure was:

1) turn A/C off

2) accelerate as much as possible in 4th gear

3) push the override button

that gave just a little more speed.

------
mprovost
Interesting fact about ZF: it was founded in 1915 to make gearboxes for
zeppelins.

~~~
johnvanommen
TIL:

 _" ZF Friedrichshafen is more than 90% owned by the Zeppelin Foundation,
which is largely controlled by the town of Friedrichshafen."_

------
elihu
Seems logical. I think most manufacturers have just decided that they'd rather
use an over-sized motor than deal with a transmission, but if you're willing
to tolerate a more complicated drive-train you get more usable power with less
weight.

Using a transmission might get weird if you have multiple motors, though. For
instance, it would be odd to have the front wheels in one gear and the rear
wheels in a different gear, or the right rear wheel in a different gear than
the left rear wheel.

~~~
jameskilton
From what I've read, the AWD versions of the Model 3 (possibly others)
actually do this (different ratios in the front and back). As the article
says, Tesla had a hard time building a transmission that wouldn't tear itself
apart under the torque of the electric motors.

So, they put the front and back motors at different ratios. The back motor is
used at lower speeds, and the front motor kicks in at higher speeds.

~~~
rconti
I'm not sure about the higher speeds vs lower speeds thing. Anyway, Tesla
knows the gear ratios in both units, they can apply power as necessary to get
the exact torque split the computer wants.

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p1mrx
> comes mated to a motor with a maximum power rating of 140 kW

Is that a typo? The Chevy Bolt and Hyundai Kona both have 150 kW motors, and
Teslas start above 200 kW.

~~~
STRML
They don't have any actual inside information about the Taycan, so they switch
to talking about the ZF transmission.

------
userbinator
Many years ago I remember reading about EV conversions, and besides direct
drive or keeping the existing multispeed (manual) transmission, one of the
other relatively popular options was a Chevrolet Powerglide with the torque
converter removed. This is a two-speed automatic from the 1950s that's known
for being simple and very strong, and remains quite popular for drag racing. I
suspect its popularity for EV conversions also arises from being able to
handle the huge amount of torque an electric motor can exert, and the better
performance of 2 speeds, so it's interesting to see Porsche also choosing a
2-speed auto for its EV.

------
woodandsteel
According to the article, two-speed transmissions can increase range about 5%.
That is important because batteries are so expensive.

However, battery prices are falling rapidly. They dropped 35% in 2018 alone.
That being the case, I am guessing most ev manufacturers will stick with
single-speed powertrains, and focus their technological efforts elsewhere.

------
ravedave5
Porsche has to have reasons for using a gearbox but I don't think this article
espouses them. The points they hit on are where Tesla's as good or better, so
there must be other good reasons.

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mywittyname
I'm surprised ZF/Porsche didn't turn this into an eCVT, as an eCVT (a la
Prius) has probably the same complexity, but with the added benefit of having
more ratios. I suspect it would also reduce shock loads on the transmission as
a result of shifting.

I wish the article would have gone into this, because I suspect Porsche said
no more for marketing reasons rather than technical ones, as CVTs are
universally hated in car performance circles.

~~~
efraim
A CVT can't handle as much torque as a gear-based transmission.

~~~
mywittyname
CVT != eCVT

An eCVT is a planetary gearbox which uses a pair of electric motors to control
the rotational speed of the ring and planetary gears to achieve an overall
gear ratio anywhere between a minimum and maximum ratio.

It's largely the same thing as what this two-speed gearbox is, but it
leverages electric motors to provide a smooth transition between two ratios,
instead of using (presumably) a set of clutches and auxiliary gears to select
one of two fixed ratios.

This is why this question jumped out at me immediately. On the surface, they
are going with a really, really archaic, complex design over a more simple,
all-electric design which is ideally suited for their application.

I can't help but think ZF started with an eCVT, then retrofited it back to
being a two-speed. They must have had a good reason for this. And I wonder if
it's a patent/license issue, or if there's some technical reason this wouldn't
work. And I'm disappointed the article doesn't go into details on this.

------
Whatarethese
Currently there is no reason to put transmissions into EV's. More money should
be put into the improvement of electric motors and battery tech. People care
about range and reliability. While acceleration is awesome, Tesla can already
achieve sub 2.5s 0-60 which is more than most anyone can handle. Adding a
transmission to an EV just adds one more thing to fail and replace fluid every
few years.

~~~
compiler-guy
Are saying that Porsche--which is spending billions of dollars on the Taycan
and its transmission--is doing this for no good reason?

"People care about range and reliability."\--Certainly some, perhaps most
people, do. And Tesla serves that market very well.

But that isn't Porsche's market. Porsche's target market cares a lot about
handling, and performance in track-like conditions.

~~~
Dylan16807
> 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.

~~~
GhostVII
In what way is "better on track" a bad reason? Lots of cars have features
which are only really useful on a track, are all of these cars needlessly
complex?

~~~
Dylan16807
A lot of people would say yes, and I would not call them objectively wrong to
have that opinion.

------
rukuu001
I'm amazed they spent all that R&D loot and then called it 'Taycan' \- I can't
decide if it sounds more like 'toucan' or 'trashcan'.

FWIW the Wikipedia article[0] on the car has this to say about the name:

> The name Taycan, roughly translates from Turkish as "lively young horse" in
> reference to the steed of the Stuttgart coat of arms on the Porsche crest.

[0]
[https://en.wikipedia.org/wiki/Porsche_Taycan](https://en.wikipedia.org/wiki/Porsche_Taycan)

------
baybal2
Direct drive BLDCs have enough torque to drive anything under 1t.

A split torque design doubles that to 2t.

Tiny Chinese EVs have no problems with autobahn speeds for any amount of time.

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nraynaud
just to be sure: should I be in awe in front of a 2 speeds automotive gearbox
from a 100 years old manufacturer?

it's been a few minutes and I still don't feel the tingling.

------
FullyFunctional
What a load of bullshit. The article is making a merit out of a clutch to
cover for their failing. I had to stop reading after ridiculous statements
like “that 5 percent range improvement can save significant money as battery
capacity” - riiiight it can save ... 5%. I’d rather pay more for the battery
and save of the maintenance down the road. Serious Wired, how much did they
pay you for this?

------
kazinator
> _Multispeed transmissions must be robust to deal with the massive amounts of
> torque that electric motors can generate in a very short period of time,
> says Shashank Sripad, a mechanical engineer also from Carnegie Mellon._

Put a manual clutch on it; problem solved. Manual boxes can be built strong.

Then make it at least a 3 speed so there is a decent H pattern there from the
stick user's perspective, and so that the ratio isn't so large (it's like
around 2X change¹, supposedly! That means the motor's RPM has to drop by by
half on upshift and double on downshift.)

3 speeds could use a 1.44 step.

    
    
       1 3
       | |
       +--
       |  \
       2  R = V/I
    
    

\---

1\. Source: this article claims the gears are 16:1 and 8.05:1.
[https://jalopnik.com/an-extremely-detailed-look-at-the-
porsc...](https://jalopnik.com/an-extremely-detailed-look-at-the-porsche-
taycans-engin-1837802533)

~~~
GhostVII
If you put a manual gearbox in it, I bet a single bad shift would tear it
apart with all that torque at low RPM. Also would probably kill the clutch
unless you are a really good driver, and it is hard to shift when you can't
hear the engine RPM.

And I don't think manual gearboxes are any stronger than a well built
automatic but I have nothing to back that up except intuition.

~~~
kazinator
> _it is hard to shift when you can 't hear the engine RPM._

A third-rate hardware tinkerer could come up with a circuit that makes a
motorboating sound from a speaker at the engine RPM. That could be heard just
during shifting activity, like when the clutch is out.

> _Also would probably kill the clutch._

It would require a special clutch design. The clutch is not needed when
starting, of course, because since the motor can generate torque right from
zero RPM, the transmission can be engaged. A clutch mechanism needed when
changing gears due to the mismatch in speeds that needs to be bridged. The
existing two-speeder must have something serving as a clutch, just not a
manually operated one.

Speaking at torque at zero RPM; can't that be modulated down somehow? Surely
there must be some way of managing the motor to bring in torque gently. This
must be happening already, right? I mean, electric cars don't burn rubber each
time they get moving.

> _I don 't think manual gearboxes are any stronger than a well built
> automatic_

That's easy; just define the requirements for "well built" so that it is so,
and don't care about weight, size, and other things. The automatic
transmission from a bus is probably stronger than the manual in an econobox
car.

