What is the torque on traverse wheels?
The torque on traverse wheels is not a fixed value. It depends on the engine’s output, the transmission and final-drive gear ratios, drivetrain efficiency, and how the system splits torque across axles and wheels under current traction. In practice, you compute it from the engine torque multiplied by the effective gear ratio and efficiency, then account for how the diff distributes torque to the driven wheels.
Defining traverse wheels and drive layouts
Traverse wheels refer to the driven wheels in a vehicle—typically the front pair in front‑wheel drive, the rear pair in rear‑wheel drive, or multiple axles in all‑wheel drive or four‑wheel drive. This distinction matters because only the traverse wheels receive torque from the engine through the drivetrain, while non‑driven wheels may merely roll.
Key factors that determine torque on traverse wheels
Understanding the main factors helps explain why the torque can vary from moment to moment.
- Engine torque and total gear reduction: T_axle = T_engine × gear_ratio × drivetrain_efficiency. This sets the torque available at the driven axle(s).
- Drivetrain configuration: Front‑wheel drive, rear‑wheel drive, and all‑wheel drive determine how torque is distributed between axles and wheels via differentials and center couplings.
- Differentials and traction conditions: Open differentials tend to send more torque to the wheel with better grip; locked or limited‑slip differentials can force a more even or biased distribution.
- Traction at each wheel: Slippage or loss of grip reduces the effective road torque; torque at the wheel hub can exceed the tractive force if slip occurs.
- Dynamic effects: Braking, steering, weight transfer, and electronic stability/traction control alter instantaneous torque distribution among wheels and axes.
These factors collectively determine the torque actually acting at each traverse wheel at any moment.
How torque is split across wheels (simple cases)
Use this guide to understand straightforward cases with open diffs and equal traction, and then consider more complex systems with limited-slip or torque-vectoring controls.
- Single driven axle with open differential and equal traction: T_wheel1 = T_wheel2 = T_axle/2.
- Single driven axle with unequal traction (one wheel slipping): The non‑slipping wheel receives more of T_axle up to the available torque and the limits of traction.
- All‑wheel drive with a center differential (open): T_front and T_rear are split according to the center diff, often near 50/50 at rest but varying with speed, load, and traction.
- Limited‑slip or torque‑vectoring differentials: The system can bias torque toward the wheel with better grip within the overall torque budget.
In all these simple cases, the total torque delivered by the engine, after gear reduction and efficiency losses, is allocated among axles and then among wheels according to the differential behavior and traction.
Worked example
Consider a front‑wheel‑drive car with engine torque of 320 Nm at the crank, an overall gear ratio of 3.5 (including final drive), and drivetrain efficiency of 0.92. The torque at the driven axle is T_axle = 320 × 3.5 × 0.92 ≈ 1030 Nm. If the front axle has an open differential and both front wheels have similar traction, each wheel initially receives about 515 Nm. If one front wheel loses traction, the other wheel can take most of the axle torque, subject to the differential and electronic controls.
Summary
Torque on traverse wheels is not a universal constant. It arises from the engine’s torque, through gearing and efficiency, and is distributed to the driven wheels by the drivetrain’s diff mechanism under real‑world traction conditions. The exact values vary with drive layout (FWD, RWD, AWD), gear selection, speed, weight transfer, and electronic controls.
