Peak vs Sustained Torque: What Direct Drive Wheelbase Ratings Actually Mean

Peak torque is the most torque a direct drive wheelbase can produce for a brief moment. Sustained torque is the torque it can keep producing continuously without overheating. Peak figures cover short spikes such as kerb strikes and sudden corrections; sustained figures decide what the base can hold corner after corner over a long session. The same number in Nm therefore describes two different capabilities, and a torque figure on a spec sheet only becomes comparable once you know which one you are reading.

What Is Peak Torque in a Direct Drive Wheelbase?

Three constraints set a motor's peak torque:

• Supply limit. The drive electronics can only deliver so much current and the power supply so much power, and when the wheel spins fast, the voltage the motor itself generates leaves less room for current.

• Magnetic saturation. Past a certain point, extra current adds progressively less torque, so a small torque gain carries a large heat penalty.

• Thermal limit. Maximum current heats the windings quickly, so this level of output is only available in short bursts before the system has to back down.

In force feedback, those bursts are the abrupt events: a harsh kerb, a heavy suspension impact, a sudden correction to catch a sliding car. How long a base can stay at its peak depends on its design, so a peak figure on its own says little about what the base can hold.

What Is Sustained (Continuous) Torque?

Sustained torque, also called continuous torque, is a thermal rating: the torque a base can keep producing without its motor or drive electronics exceeding their temperature limits. The figure only holds for given conditions, such as the surrounding temperature and the cooling available. Copper loss rises with the square of the current, and the current is what makes the torque, so doubling the torque roughly quadruples the heat. The sustained rating is the highest torque at which that heat is shed as fast as it is produced without passing the limit. Hold more than that for long enough and thermal protection reduces the current, so the force feedback gets lighter. In a warmer room, the same base can hold less torque continuously.

MOZA rates its Ultra Series in sustained torque, from the MOZA R16 Ultra at 16 Nm through the MOZA R21 Ultra at 21 Nm to the MOZA R25 Ultra at 25 Nm. A flat-wire motor sits at the core of all three. It produces less heat at a given torque than a comparable round-wire motor and dissipates it more effectively (see Flat-Wire Motors Explained: What They Change in a Direct Drive Wheelbase).

Why Do Steady Loads Account for Most of the Heating?

Engineers size servomotors with the effective (RMS) torque of a duty cycle: the constant torque that would heat the motor as much as the real mix of loads. The effective level over a stint must stay within the sustained rating, and the highest instantaneous torque within the peak rating. Because heat accumulates over time, the steady loads held through corners account for most of the heating. A spike heats intensely while it lasts, but an isolated one is too short to add much. Frequent heavy impacts, on a bumpy track for example, do add to the effective load. Heavy steady loads come from high-downforce cars, fast sweeping corners and high overall force feedback strength, and session length extends the time the motor spends carrying them.

Through a long corner, the steering wheel sits at an almost constant angle, so the motor is nearly stationary while it delivers a steady torque. When a motor turns, the current rotates through its three phase windings and the heat is shared between them. Held still, the current stops rotating. Depending on the rotor position, one winding can then carry the full peak of the current continuously, with up to twice the copper loss it would have at the same torque while turning, even though the motor's total loss is unchanged. A steady load at a standstill can concentrate the heat in one winding, which makes holding a corner harder on that winding than the same torque delivered while the motor keeps turning.

How Do Peak and Sustained Torque Map onto Force Feedback?

The force feedback signal carries several layers at once. Cornering force and weight transfer create a steady, slowly changing load, kerbs and bumps add brief sharp events, and the road surface adds small, fast detail. Chassis movement and weight transfer sit at the low end of the spectrum, below about 15 Hz, while kerb strikes and road texture reach higher, and the force feedback equalizer in MOZA Pit House lets you adjust the balance between them by frequency.

The sustained rating has to carry the steady load for the whole session; the peak rating has to cover the sharp events added to it. Hit a kerb in the middle of a fast corner and its spike arrives on top of a cornering load the motor is already holding, so the headroom left above that load decides how much of the spike reaches your hands.

When the requested force exceeds what the base can deliver, the signal clips. While the output sits at its ceiling, any detail that would push it higher is flattened, and the wheel feels heavy but uninformative through that part of the corner.

Why Are Wheelbase Torque Ratings Hard to Compare?

Wheelbase makers do not share a common test method or label. A spec sheet may give a peak figure, a sustained figure or a figure with no peak or sustained label. A base rated at a given number in peak torque will generally hold less over a session than a base rated at that number in sustained torque.

MOZA's own lineup uses both conventions. Some bases carry peak ratings (the MOZA R9 V3 at 9 Nm, the MOZA R12 V2 at 12 Nm), while sustained torque is the basis of the Ultra Series figures above. The 12 Nm of the R12 V2 and the 16 Nm of the R16 Ultra therefore sit on different scales: the first is the most the base delivers momentarily, the second what it holds continuously. Compare peak with peak and sustained with sustained; when a figure carries no label, treat it as unknown rather than assuming it is sustained.

What Doesn't a Torque Rating Tell You About Feel?

A rating in Nm says nothing about how quickly a base reaches that torque or how cleanly it renders small changes. Those depend on the motor, the drive electronics, the force feedback algorithm and its tuning, and the mechanical design.

The force you feel also depends on the rim. Force at the rim equals torque divided by rim radius, so 10 Nm on a 300 mm wheel (150 mm radius) is about 67 N at the rim. A larger rim gives a lighter feel for the same torque.

A Moment Versus a Stint

A peak figure bounds what a base can deliver for an instant, load and spike together; a sustained figure bounds the load it can keep holding, stint after stint. Peak torque still matters for every sharp event, but a high peak figure is not enough on its own. What matters just as much is the ability to sustain strong torque for tens of minutes at a time, which is what the Ultra Series' sustained ratings describe.