Multi-Speed EV Transmissions Target Range and Torque Gaps in Class 8
Sigma's multi-speed gearbox aims to solve single-speed EV drivetrain limits in heavy-duty applications. Hybrid concepts promise 30% fuel savings in same footprint.
Can a multi-speed transmission fix Class 8 EV range and torque problems?
Yes, according to Sigma, which is developing multi-speed transmissions for battery-electric commercial vehicles. The company's approach addresses two persistent single-speed drivetrain weaknesses: insufficient torque at low speeds and poor efficiency at highway cruise. After years of OEMs assuming EVs would eliminate transmissions entirely, the market may be returning to geared solutions executed for electric motors instead of diesel.
Sigma's immediate focus is commercial EVs where high torque demands and challenging duty cycles expose single-speed limitations. A single-speed reduction gear optimizes for either launch torque or highway efficiency, not both. Multi-speed gearboxes let the motor operate in its most efficient RPM band across a wider speed range, potentially extending range without adding battery capacity or improving acceleration without upsizing the motor.
What about hybrid drivetrains?
Sigma also sees multi-speed transmissions enabling future hybrid systems for long-haul trucking. The company described concepts that combine downsized diesel engines, multiple electric motors, and Sigma's transmission technology into hybrid powertrains capable of all-electric urban operation and diesel-powered highway cruising.
"A properly designed hybrid system could deliver 30% fuel savings while fitting into the same space as an existing transmission," said Kimes, a Sigma representative.
The 30% fuel-savings claim assumes a hybrid configuration, not a pure EV. No fleet validation or third-party test data was provided. The "same space" reference means the hybrid drivetrain would occupy the transmission tunnel footprint in a conventional Class 8 tractor, simplifying integration for OEMs and reducing chassis redesign costs.
Why single-speed drivetrains dominate Class 8 EVs today
Most Class 8 battery-electric tractors on the market use single-speed reduction gears because electric motors produce peak torque from zero RPM, eliminating the need for multi-speed gearboxes in light-duty applications. That advantage erodes in heavy-duty vocational and regional-haul duty cycles where gross vehicle weight exceeds 60,000 pounds and grade performance matters.
A single-speed drivetrain optimized for 65-mph highway cruise sacrifices low-speed torque multiplication, forcing the motor to work harder at launch and on grades. A single-speed drivetrain optimized for launch torque runs the motor at inefficient RPM at highway speed, draining the battery faster. Multi-speed gearboxes let the motor stay in its efficiency sweet spot across both conditions, potentially extending range by 10% to 15% without adding battery weight or cost. Sigma did not provide specific efficiency-gain figures for its transmission.
What this means for Class 8 EV adoption
If multi-speed transmissions deliver measurable range gains or torque improvements without adding prohibitive cost or weight, they could address two barriers to Class 8 EV adoption: insufficient range for regional haul and poor performance in hilly terrain or heavy vocational work. The technology also creates a path for hybrid drivetrains that combine diesel and electric power, potentially offering better economics than pure battery-electric for long-haul applications where charging infrastructure remains sparse.
No pricing, weight, or production timeline was disclosed for Sigma's transmission. The company did not name any OEM partners or pilot fleets. Until multi-speed EV transmissions appear in production trucks with published TCO data, the technology remains a development-stage solution to a real problem: single-speed drivetrains work well enough in medium-duty delivery and transit, but struggle in the duty cycles that matter most to Class 8 fleets.
