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It's all about the assumptions, but here's one guess:
From the main D intro thread, post #522:
About time to unveil the D and something else - Page 53
S85D performance estimate
Estimated performance and torque curves for a Tesla S AWD.
This assumes Tesla will use the current S motor and transaxle for the rear and the motor and transaxle they build for the Toyota RAV4 for the front axle.
This is the arrangement shown for the bare chassis picture of the Model X.
Source Tesla Motors Inc (TSLA): The 3 Tesla Secrets - Seeking Alpha
From the main D intro thread, post #522:
About time to unveil the D and something else - Page 53
Gizmotoy
Active Member
There was a lot of really impressive analysis done. I'll try to dig up the thread, but it's pretty old.
Essentially the conclusions were: S60 = battery limited, S85 = inverter limited, P85 = battery limited.
That's not to say an AWD couldn't see substantial 0-60 improvements even if it doesn't have more power: getting 4k+ pounds moving is hard, and the P85 is traction-limited at launch. You could easily shave a chunk of time off that with better grip. I doubt a 1 second improvement as noted above, but certainly a half second seems easily-attainable (and note current P85s post numbers closer to 3.9s, not 4.2s).
Sub 4 seconds would be sick. I can see 1/2 second improvement and would gladly pay a premium for it. Be interesting to see what happens. There is all this talk about demand from cold weather areas but I'm sure Tesla is expecting demand from more than just areas that get snow.
The 911 4S and 911 S only differ by 0.1 second in the 0-60. Same engine, with power distributed to 4 wheels instead of 2 wheels, doesn't make much difference.
Why would we expect a substantial improvement in P85 0-60 with the same total power driving 4 wheels instead of 2 wheels when it makes only a very small improvement in the 911 S?
Why would we expect a substantial improvement in P85 0-60 with the same total power driving 4 wheels instead of 2 wheels when it makes only a very small improvement in the 911 S?
R²B
All Star
It is more power though right? Two drive units implies more total power output. It's like if the 911 went with 2 engines (front and back) each being fed from the same gas tank.
Raffy.Roma
Rome (Italy)
Because the electric AWD System is better than the ICE AWD System. With the electric AWD System you have two motors applying the torque in an independent way to the front and the rear wheels.
On the contrary in the case of the ICE AWD System you have only one motor applying the torque to both axes. I would say that in this case the torque applied by the single motor is "shared" between the two axes.
Raffy.Roma
Rome (Italy)
IMO we cannot answer to this question for the time being. It maybe that Tesla is using two smaller motors for the P85D and that there is no problem coming from the battery limit. Let's wait till to the event of Oct 9th (but I know that some people cannot wait for the event
).Even if they're right that the P85 has reached the maximum power the battery is capable of, the AWD version will have more power below 43 mph.
Remember the characteristic behavior of synchronous AC drive motors: they operate at a fixed torque limited by current flow in the motor until they reach the peak power that the system can handle, then at nearly peak power thereafter (slowly dropping as RPMs rise.)
In the S60 and P85, that transition happens at 43 mph. (The S85 is more like 55 mph.) The notional AWD car could deliver more torque until it reaches the power limit even if Tesla can't find any more power in the battery - and delivering more acceleration at low speeds would have a substantial effect on 0-60 times.
Walter
gocken2
Model S: P6931
There have been several assumptions on this forum that seem to turn into fact. The battery limit is one of those. It is not fact. Batteries don't have a set limit. They have a limit over a time period. If you reduce the time period of a constant current draw then you can increase the current without harming the battery life. If you sacrifice some battery life you can also increase the current.
Granted. However, that's at the cell level. One of the most common problems (though still fairly rare) seems to be a failure of the high voltage contactors in the battery - the famous clunk on hard acceleration that's followed by no power and a battery replacement.
I haven't quite decided from the limited information available whether it's related to the small 12V battery and DC-DC converter being overwhelmed or if it is just the limitations of the contactors themselves.
Either way, it is one of a set of pack level power/current limitations that can't be exceeded by merely accepting a shorter service life - the wires and contacts and contactors and fuses all have explicit current limits and exceeding them will cause failures.
(Having said that, I have no idea how close to the limits on those components the car is currently - just that the limits are out there somewhere.)
Walter
Raffy.Roma
Rome (Italy)
The fun is that many people on TMC cannot wait for the event. (You didn't report all the original sentence).
You know, I've wondered about this as well. Maybe you can answer a couple questions I have.
1. When I go out to the car in the morning and open the door I hear a click-click. Is that the battery contact engaging? People have reported failed main packs before presumably because the contactor got "stuck." This happens while parked.
2. If the answer to 1 is yes, then I don't see why heavy acceleration has any effect on the contactor itself. So when the car is driving the contactor is presumably already engaged. It seems that it would be a fuse rather than a contactor that would blow out under high current load.
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