[giobox]

I wonder if the tri-motor CT models will be able to simulate a locked rear diff, much like the quad motor rivian models can simulate a locked diff front and rear thanks to being able to adjust torque to all four wheels individually. Only the rear axle of the CT would presumably be able to do this due to the tri-motor layout, unless they resort to the individual wheel braking like they've done on their road cars to simulate diff features. A rear only lock is still a useful offroading feature.

From what I've read, it doesn't sound like the quad motor "virtual" locked diff feature on the Rivian trucks works as well as a proper locking diff - its close but still slips occasionally. If I recall correctly their cheaper dual motor models don't have the feature either.

I imagine eventually the quad motor "virtual" locking diff solutions will probably get reasonably good, if Tesla decide to do a quad motor CT later.

[SigmundA]

I posted below but you cannot fully simulate a locker with independent motors. The quad motor Rivian is actually inferior to the dual motor for rock crawling due to this.

The quad motor Rivian produces 908 lbs/ft of torque which means each motor produces 908/4 = 227 lbs/ft. It has a single speed gear ratio of 12.6:1 meaning each wheel can get a maximum of 227 * 12.6 = 2860.2 lbs/ft wheel torque.

The dual motor Rivian produces 829 lbs/ft of torque which means each motor produces 829/2 = 414.5 lbs/ft. It has has a single speed gear ratio of 13.7:1 (11:1 front) in the rear meaning each rear wheel can get a maximum of 414.5 * 13.7 = 5678.65 lbs/ft wheel torque (4559.5 front) with brake locking diff.

Contrast this with a Jeep Wrangler which can put out 20,000 to 30,000 lbs/ft of torque to any single wheel through its torque converter, transmission, transfer case and axle gearing which can be over 100:1 in gear ratio and single ICE.

There are videos of Rivian's stalling rock crawling that are no issue for an old Jeep with weak engine due to lack of torque to the wheels. EV's will need lockers and probably at least two speed transmission to compete here, or they will need way oversized quad motors to make enough low speed torque without the gearing and lockers.

[brucethemoose2]

Quad motor is even better than a locking diff if all the motors are modulated right.

I dunno what Rivian does, but I saw that Rimac does 1 motor per wheel, and each motor madly modulates itself during launch control to stop its wheel from slipping... Perfect, maximum torque, all the time.

[giobox]

There's still some slip though in all these virtual solutions - a wheel has to start slipping for the software to notice and modulation to kick in. With a real locking diff, it's physically impossible for one wheel to spin faster than the other. For sure they can likely modulate the wheel torque quickly though to get the wheels back to the same rotation speed.

[brucethemoose2]

In theory, the system can just monitor rotation and "lock" the wheels together with torque as a goal of the system, instead of trying to detect when the tires are slipping.

As a bonus, a computer is smart enough to spin the tires at slightly different rates when turning, instead of dragging them along like a locked diff.

[lolbase]

I believe that Rivian offers a quad-motor option, and a standard dual-motor with an open-diff that uses the brakes to try to compensate (similar to a typical AWD system).