EVwire brief: Tesla redesigned the Semi’s drivetrain to make it lighter, more efficient, more reliable, and cheaper to produce than the system used in the truck’s earlier iterations. This was highlighted by Tesla VP of Vehicle Engineering Lars Moravy and Semi Program Lead Dan Priestley, who walked through the changes during the Semi's rollout event.
One of the biggest changes is the move from a Plaid carbon-fiber-sleeved rotor to a steel-caged rotor. Tesla said the new design improves efficiency, reliability, and mass while making the motor cheaper and easier to manufacture.
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The updated drive axle also uses a bar-wound stator, a technology already developed for Tesla’s automotive products and shared with the Cybertruck. Tesla said the changes reduced the drive axle’s weight by about 80 kilograms (176 pounds) while improving reliability.
The company also simplified the drivetrain’s lubrication system. The original Semi drive axle used three separate oils for the motor, gearbox, and hubs. The new version eliminates oil from the hub entirely and uses a single common oil for the motor and gearbox.
Tesla said the integrated hub improves reliability and reduces rolling resistance, while the shared motor and gearbox oil is designed to last more than 250,000 miles.
“Occasionally, we get a little too far out there. And we ended up with three oils in the first round of the truck. We had a motor oil, we had a gear oil, and we had a hub oil. And we've changed that. Now we have on the hub side fully integrated so fully integrated hub and no oil whatsoever, which is more reliable and lower rolling resistance. And then we've gone on the gearbox and motor to one common oil thanks to our lubricants team who really came through there.”
Tesla frames both changes as extensions of the same parts-reduction philosophy that also shaped Semi's steer-by-wire steering system.
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Context:
Tesla's Semi Factory was already showing signs of scale before the rollout event. Recent drone footage caught a row of customer-branded trucks waiting on the lot, with badges from PepsiCo, US Foods, Einride, LTS, Nevoya, OK Produce, ABF Freight, DHL, WattEV, IMC Logistics and HMD.
The timing lined up with two other announcements. ZET SCALE locked in a 2,500-truck electric Class 8 order two days before the event, naming Tesla as its primary OEM across 10 freight hubs, while Forum Mobility unveiled four new California charging depots adding 30 MW of capacity, three with public Megachargers. Forum Mobility also noted that over 330 Tesla Semis already have fleet offtake contracted at its FM Santa Fe depot in Rancho Dominguez.
Source: Tesla Semi on X
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