Gearbox: totally unnecessary.

[Jhenson29]

So time will tell with next generation Taycan. And I would not think 70 kgis something to sneeze at.

Keep in mind that 70kg is the entire gear box. If you remove the two-speed gearbox, you’ll have to replace it with a single speed, which will still have weight.
There will be some weight savings, but not 70kg. That’s why I said assume half, just to throw a number out there, so I was saying 35kg, not 70kg.

And I don’t think either weight has much impact in the context of a 0-60 acceleration as the OP asked about, at least not relative to how changing to a single speed gearing with the current motors would affect it.

So, in the context of the question, I do sneeze at it. It is covered in my snot. ?

And separately, once you start adding HP, some if not all of that weight saving may return with potentially heavier or more motors and gearboxes. The extra HP will overcome it and then some just fine, but you may not end up with an overall lighter car.

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[logic]

EV's can solve the problem of having torque at both low and high speed by using two different kind of motors in an all-wheel-drive setup.
Typically a motor at the rear optimised for low speeds and a motor at the front for high speed torque. I understood this is also what Tesla is doing.

I also understood that Tesla used the front motor for higher speeds (bigger gearing). A very simple solution to the problem, BUT, dynamically speaking, I can't help but think it has to be a nightmare? At lower speeds the rear motor would overcome the front, which is totally fine - dynamically speaking-. However, at higher speeds, the front motor will overpower the rear, in essence, the rear bias will shift towards FWD bias, yikes! Nothing you and I would consider much of a problem, but we're talking Porsche here. // could be one of many reasons why Porsche went for the gearbox? (with no other solutions in sight, back then).

 

[Jhenson29]

@Scandinavian I checked out your link. I’m just not as quick to dismiss there being a two-speed gearbox in the Taycan for a while. I don’t guarantee it. I just think it could still go either way.

But I do guarantee that if we see it change to a single speed gearbox, it comes with a significant increase in HP.

 

[JimBob]

So, the two speed gearbox is required then?
No. The alternative is more HP*. But that's basically it. You can maybe sacrifice some top end speed if you don't feel ~150-160mph is necessary, but not nearly enough. Not unless all you want is the first gear top speed which is lower than the speed limits of some US highways.

I think this is the most likely way that Porsche will go. More horsepower with a two speed gearbox.

 

[Dee]

I think most people are familiar with this:

Notice how the 1st gear wheel torque follows the 2nd gear wheel torque in the constant HP region (around the upshift).

We can extend this further to arbitrary gear ratios.

The below graph shows a constant HP torque curve in red.
The X axis is mph.
I've marked the Y axis in gear ratio.

From there. You can draw a straight line out to the constant HP curve and that will be the motor torque curve (the straight line until the constant HP torque curve, and it follows the constant HP torque curve from there).

I've put two lines on here. One for 1st gear (purple) and one for 2nd gear (orange).
But you could put a line on there at any gear ratio and see the expected torque curve.

So, the actual torque curves are like this:

Now, the other thing to consider though is the maximum motor speed.
I've added another green, dashed line here for that.

Wherever the straight line from the gear ratio intersects the green line, that's the maximum speed for that gear ratio.

So, our torque curves will actually stop at those maximum speeds here:

And we're left with the following two final torque curves within the motor's speed range for each gear:

So, it is as @JimBob quoted from Jalopnik.
First gear for for low end acceleration.
Second gear is for top end speed.

Neither gear can do the other anywhere near as well.
And anything in-between will be a compromise of both.

So.......

Does the two-speed gearbox improve performance?
For a given motor power and within the limits of traction, YES.
Inarguably.
There's no debate to be had on that point.

Could they have done as well or better with a single speed gearbox?
Changing nothing else, no. There is no way a single speed gearbox would have been better. You are either sacrificing significant top end speed, significant acceleration, or both.

But what about the weight reduction of a single speed gearbox?
The weight for the whole gearbox is quoted at 70kg. Assume half that goes away with changing to a single speed gearbox. The weight difference is honestly negligible.

It’s less than the difference between me or my wife driving.
It's 1.5% of the mass of the Turbo S.

And acceleration equals force / mass, so you are not going to see big gains here.

So, the two speed gearbox is required then?
No. The alternative is more HP*. But that's basically it. You can maybe sacrifice some top end speed if you don't feel ~150-160mph is necessary, but not nearly enough. Not unless all you want is the first gear top speed which is lower than the speed limits of some US highways.

*or significantly less weight, but I don't see that happening anytime soon.


-------------
note: I just plugged in approximate values for the curves, so exact points maybe slightly off, but the relationships stand. I don't need any messages about how a top speed in the graph is 3 mph off or something.
-------------

Maybe I wasn't clear making my point.
I was only taking about performance, 0-60, as Porsche is all about performance.

When you want to increase performance you have two options:
1. More hp.
2. A Gearbox (to overcome the shortcomings of a motor).

Tesla did #1.
Advantage: relatively simple and straight forward.
Disadvantage: running out of rpm/power at higher rpm.

Porsche did #2.
Advantage: more torque and better use in every gear.
Disadvantage: complex design and you need a clutch.

But Tesla and Porsche are both as quick so the advantage of having a gearbox isn't that clear imho.

My point is: if the gear ratio was like 1:18 or even higher (instead of 1:15) the Taycan was much quicker than a Tesla and the gearbox would have made more sense.
Now it's just about the same.
Again, I'm not talking about topspeed or efficiency.
I hope you now see what I mean: there was just so much more potential in this set-up with a gearbox...

Anyway, thx for that excellent torque curve explanation. ??

 

[f1eng]

I was only taking about performance, 0-60, as Porsche is all about performance.

Yes but 0-60 is only a tiny part of the performance and Porsches are sold worldwide and it is other aspects of the performance which are important in my country and most of the others I have visited.
Drag racing is not an international sport

 

[Dee]

Yes but 0-60 is only a tiny part of the performance and Porsches are sold worldwide and it is other aspects of the performance which are important in my country and most of the others I have visited.
Drag racing is not an international sport

Of course but it does say something about what a car is capable of, also about picking up speed corner-out.
Sure, chassis set-up and handling are a big part of it's performance as well.
I'm just trying to explain my point about the "conservative" gear ratio of the gearbox in conjunction with the way Tesla does things.

PS Drag racing IS an international sport, I've seen it happen at every single traffic light I visit! ?

 

[f1eng]

Of course but it does say something about what a car is capable of, also about picking up speed corner-out.
Sure, chassis set-up and handling are a big part of it's performance as well.
I'm just trying to explain my point about the "conservative" gear ratio of the gearbox in conjunction with the way Tesla does things.

PS Drag racing IS an international sport, I've seen it happen at every single traffic light I visit! ?

I have never had a drag race, there are almost no traffic lights around here and the few there are don’t have several lanes going the same way so no car pulling up along side to “race”.
The only time I have done maximum acceleration from a standing start was when i was competing in sprints and hillclimbs 50 years ago.

I think Porsche and Tesla took a different set of decisions on the load cycle they designed their cars for thats all, and FWIW I am very much with Porsche on it, not Tesla.

Mind you my career was designing and running Formula 1 racing cars so my priorities will be unusual.

 

[Dee]

Mind you my career was designing and running Formula 1 racing cars so my priorities will be unusual

We talked about Benetton and Jos Verstappen, remember?
Still, driving on the road is different than on a circuit so I always keep that in mind when I see your replies, don't worry. ?
On the other hand, it's great to see your pov nevertheless, love it. ?

 

[bosbruce]

So the Taycan has a 2-speed gearbox.
As we all know, a gearbox is to overcome the shortcomings of an engine/motor.
So why did Porsche make a gearbox as electric motors really don't need a gearbox after all due to their power and torquecurve.
I guess it was to defeat Tesla but in the end it isn't that quick after all, still ridiculously quick though...

So, my conclusion is that it only added extra weight and that has killed the extra performance (and efficiency) which I think was the whole concept of adding a gearbox: to improve performance.

What Porsche should've done is raise the ratio more cuz only then it would benefit the performance (if you wear proper shoes that is).
I'm talking 0-60 times here.
Ok, you'll loose some topspeed but still it would make much more sense.

What are your thoughts about the advantage of a gearbox in the Taycan?

I agree with many other comments here... Basically Porsche needed to do it to momentarily beat Tesla Performance S in the 0-60 and 1/4 mile races until the Plaid came out and to compensate for low torque and high RPM power degradation. (Aside Tesla had 2 speed in their original roadster but decided to junk that allegedly due to cost and reliability issues)... Also, Porsche is still heavily focussed (including top performance models) in ICE powered cars hence didn't have the R&D cash/time/motivation to put a better rear motor in the Taycan. IMO it is also that the gear shift offers a kick in the pants bit of fun that makes the car unique. My 4S is still sitting at the dock or I'd have a more informed opinion of living with it but I found my test drive of a Turbo a bit more fun and also a bit more jarring because of the shifting.

The anemic Taycan rear motor, enabled to continue being used because of this gear shift, is the reason I went with a 4S when I would otherwise have gone with a RWD Taycan to save weight and complexity and improve handling/range... But I could not envision owning a so-called performance EV that takes more than 5 seconds to get to 60 mph given my old Tesla 3 did it in 3.6 seconds. If Porsche were all-in on electrification they would have put in a far more capable rear motor (or 2 like the plaid) not requiring a gear shift by now. Hopefully they'll do so right after I sell my Taycan 4S but not before...

 

[JimBob]

Porsche has several cars with a different gear set up so the argument is more complicated.

The Taycan has 2 gears
Formula E has 5 gears
MIssion R (concept for Cayman?) has 1 gear

Reasons for this:

The Taycan is heavy so short of more horsepower, it needs a second gear to get both acceleration and high speed.

Formula E doesn't need to worry about costs and wants to maximize torque at each RPM

Mission R is a light weight car so a high RPM electric motor is sufficient

@Dee may want to trade his Taycan for an electric Cayman when it comes out.

 

[Jhenson29]

If Porsche were all-in on electrification they would have put in a far more capable rear motor (or 2 like the plaid) not requiring a gearbox by now.

Just to be clear, a single speed gearbox is still a gearbox.

 

[Jhenson29]

My point is: if the gear ratio was like 1:18 or even higher (instead of 1:15) the Taycan was much quicker than a Tesla and the gearbox would have made more sense.

I think if all you care about is 0-60 and literally nothing else, you gear the motor in for max speed at 60mph, which is (I think) around 1:21.

 

[bosbruce]

Just to be clear, a single speed gearbox is still a gearbox.

Just to be clear, a single speed gearbox is still a gearbox.

Caught me... I mentioned Gear Shift 3-4 times but mistakenly put "Gearbox" in there once, now fixed that .... Long and short of it, if Porsche were laser focused on their EVs becoming their top performance vehicles they would have engineered a better rear motor and not used the "these are the parts we have available, here's how we shoehorn them in to make something that meets our requirements" approach of an anemic rear motor boosted by a 2 speed transmission... Maybe that will happen in an upcoming model or model refresh as it is clear that electric motors can be made to generate plenty of low end torque and high RPM power to handle amazing 0-60 and 200+ mph speeds (see Plaid ... maybe Plaid motors won't be reliable past 150 mph so maybe a bit more work still to be done).

 

[Archimedes]

Caught me... I mentioned Gear Shift 3-4 times but mistakenly put "Gearbox" in there once, now fixed that .... Long and short of it, if Porsche were laser focused on their EVs becoming their top performance vehicles they would have engineered a better rear motor and not used the "these are the parts we have available, here's how we shoehorn them in to make something that meets our requirements" approach of an anemic rear motor boosted by a 2 speed transmission... Maybe that will happen in an upcoming model or model refresh as it is clear that electric motors can be made to generate plenty of low end torque and high RPM power to handle amazing 0-60 and 200+ mph speeds (see Plaid ... maybe Plaid motors won't be reliable past 150 mph so maybe a bit more work still to be done).

You should say that the Porsche rear motor sucks a few more times. I don’t think you’ve made your trolling point yet…

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