# Forums

## Does a Model X (85 kWh) with a dual motor have a smaller range than a Model X (85 kWh) with a single motor?

Suppose we have the following situation.

There is a 1,000 km long straight road of good quality (specially good for fast driving, like a race track) with no hills, or stoplights or any other obstructions. The weather is fine and there is no traffic at all. And we have two Tesla Model X cars (both have a 100% full charged 85 kWh battery), 1 is red and has 1 motor, and the other is blue and has a dual motor. Both start at the same time and drive side by side at the same speed (200 km/hr), and the cruise control keeps them at that speed until the battery will have gone fully empty (0%). There are no pit-stops or anything. Both cars have only the driver sitting in them. Both cars are equally equiped, and have the same tyres, etc.

My questions are:
1) Does the single motor of the red Tesla Model X have to work "harder", compared to the two separate motors of the blue Tesla Model X? Regarding that both cars are driving at the same speed of 200 km/hr.

2) Do the two separate motors in the blue Tesla Model X have to work equally "hard"? Or is there a difference between the two separate motors?

3) Do the two separate motors in the blue Tesla Model X always work together from the start, or will the second motor be turned on only at a certain speed?

4) Will the total distance of the journey of both cars be the same (when the battery finally is empty), or will 1 of the cars stop earlier than the other?

5) Can we say something about how long the total distance (separately) of the journey of both cars will be in km?

Brian H | 30 januari 2013

1) Yes; both the mass and air resistance of the X are higher. More energy will be used.
4) The X will travel a shorter distance.
5) TM hasn't released any stats for such a high speed.

Benz | 30 januari 2013

@Brian H
Both cars are the same Tesla Model X. One is red with 1 motor, and the other is bleu with a dual motor. So, why would there be any difference in mass and air resistance?

And which Tesla Model X car will travel a shorter distance? Red or Blue?

And what about my question number 2 and 3?

Benz | 31 januari 2013

By the way, both of these Model X cars are not the Performance or the Signature models, they are just the standard production cars with the largest battery pack available (85kWh).

Timo | 31 januari 2013

Dual motor one is heavier so if motor efficiencies are same then it doesn't get quite as far, but OTOH your set speed is very high which means that single motor one probably is at it's limit, while dual motor one has still some way to go before it hits the same limit (probably) so it might have better motor efficiency.

Benz | 31 januari 2013

@ Timo
I do not quite understand what you mean. When comparing the cars please use their color, as that would be easier (for me) to understand. And what is "OTOH"?

Both Model X cars have exactly the same electric motors. The red Model X car has got 1 single electric motor (between the rear wheels). And the second car, which is the blue Model X car, has got a dual electric motor, 1 between the rear wheels and 1 between the front wheels.

Timo | 31 januari 2013

OTOH = On The Other Hand. Common internet acronym. IMO = In My Opinion (sometimes with "Humble" IMHO), AFAIK = As Far As I Know, IIRC = If I Recall Correctly and so on and so on.

Replace "dual motor" with blue and single motor with red in my message.

Benz | 31 januari 2013

@ Timo

OK, thanks for the explanation regarding the acronyms.

And you have raised a good point about the limited top speed of the red Model X with the single electric motor.

Has Tesla Motors already unveiled what the top speed is of a Tesla Model X with a 85 kWh battery pack, and with a single (standard)electric motor between the rear wheels? Is it even possible to drive this car at a speed of 200 km/hr? That just might not be the case with this Model X car, I am afraid?

The top speed of the (standard production) Model S is 200 km/hr.
The top speed of the Performance Model S is 212 km/hr.

The Model S really has got a very low drag figure (0.24 I believe). The shape of the Model X is obviously not as aerodynamic as the Model S. That is for sure, so that would mean that the top speed that I have used in the situation that I have described is too optimistic and certainly not correct. That must be the conclusion now. Therefore I shall have to change that. I think that a top speed of 160 km/hr should be very well possible with the standard production Model X with a 85 kWh battery pack, and with a single (standard) electric motor between the rear wheels. Do you agree on this?

Brian H | 31 januari 2013

Sorry, confused myself by thinking one was an S and one was an X, hence the air resistance comment.

I think top speed will be almost the same as the S, but the battery will have to supply more power to achieve it.

Timo | 31 januari 2013

I believe top speed is actually RPM-limited, not power-limited, so Model X could have higher or lower top speed depending of what TM decides to do with reduction gear(s). Even at 125mph air drag+rolling resistance is still not as high as max power from the single motor but power actually drops at higher RPM. Weakening low speed acceleration should give you higher top speed. Kind of driving in second gear instead of first gear situation.

With two motors (with enough power from the battery) you can have same or slightly higher acceleration with much higher top speed, because those motors need to work half as hard to get same total torque as single motor, and as such can have much lower reduction gears.

Benz | 1 februari 2013

@ Timo

Thanks. I think this is the answer to my first question:

"With two motors (with enough power from the battery) you can have same or slightly higher acceleration with much higher top speed, because those motors need to work half as hard to get same total torque as single motor, and as such can have much lower reduction gears."

It sounds very logical to me, but can anyone else confirm this?

Jorg | 13 oktober 2015

What will happen is that the motors, run at that speed, need to generate quite a lot of torque, and they can't do it for very long. Tesla's control electronics will sense the overheating and reduce your speed.

With the dual-motor configuration, the heat is split across two motors, so the dual-motor car will be able to maintain the high speed for a little longer than the other one.

(Unless the battery gets too hot first, in which case both cars are likely to hit the limit at about the same time.)

vandacca | 14 oktober 2015

Can anyone say for certain that the two motors are geared slightly differently? For example, the rear motor is most efficient in the 0-60mph range and the front motor is geared to be most efficient in the 60-100mph range. That way, they can choose the motor that's most efficient for the speed.

I know with the Roadster, they tried for the longest time to get a 2-speed transmission to maximize motor efficiency. They just couldn't build or find a reliable transmission to make it work, so they gave up. Having 2 motors seems like an obvious way to create a 2-speed transmission.

georgehawley.fl.us | 14 oktober 2015

Reading between the lines of JB's blog post: "Q: Which drive unit is able to sleep, front or rear?
With the P85D we put the large, rear, drive unit to sleep while cruising. We choose to sleep the rear unit since the new generation small front drive unit is actually more efficient at converting battery DC electricity into mechanical shaft power. So we benefit from using the small, front drive unit more of the time when it can provide all of the torque requested. In the 85D both drive units are the same and we can sleep either unit, front or rear to best optimize efficiency."
I conclude that the gear ratios are the same. If so, there is a small savings accrued by using both drive units because internal losses are cut in half due to spilitting the total current in two. Internal dissipation is proportional to the square of the current. 1/4 + 1/4 = 1/2 but it is one half of maybe 5-6% (my guess) so you save maybe 2-3 % so that an S85 D gets maybe 5-8 mile more per kWh with 2 motors running than with one.

Tâm | 14 oktober 2015

@Benz

In general, All-Wheel-Drive in ICE would sip more fuel, thus you get less range than 2-wheel-drive.

It's opposite in Tesla. Dual Motors can be finetuned by computer to be more efficient than Single Motor can be and thus, you get more range.

One of those tricks is sleep mode which is explained above by georgehawley.fl.us .