How IMSA’s new torque sensors are changing the balance of performance game 

Balance of performance (BoP) has often been a taboo discussion in sportscar racing because everyone wants to find an advantage over their competition and be able to use it. But new technology arriving in the paddock could make those debates a thing of the past. 

Sportscar racing regulations in WEC and IMSA are unique based on the fact that to keep racing competitive, they opt to “balance” the performance between almost a dozen different engine types for a given class. In the past, this was done through methods ranging from data collected from manufacturers to analyzing data collected by engine dyno tests. This year, IMSA aims to better equalize their Grand Touring (GT)-class cars by introduction of torque sensors for the 2025 season.

2023 brought about the first iteration of these torque sensors with the debut of the Grand Touring Prototype (GTP) class in IMSA. These hybrid prototypes, as part of their “spec” series, required a method to measure the combined torque produced by their internal combustion engines (manufacturer-provided) and electric motors (spec). To achieve these measurements, it made sense to measure the torque (power output) at the driveshaft for a realistic output figure. That system appears to have worked out well in the GTP class as balance of performance discussions seem to be much less common among members of the paddock and even in media coverage than what we’ve seen in previous iterations of IMSA’s top class.

A successful implementation of torque sensors on prototypes eventually led to their appearance on the WEC’s GT cars in its LMGT3 class for the 2024 season. Its success paved the way for the same sensors to make their way to the GTD and GTD Pro in IMSA.

Before that, IMSA based their initial powertrain settings on manufacturer baseline engine data, IMSA’s own engine dyno test data, and anything that would be provided by the GT3 homologation authority — which decides what componentry is required to make a GT3 vehicle compatible to compete in the sportscar series. Once a car would hit the track they would then monitor and regulate the engine output using things like boost pressures, intake air restrictor sizing, ignition angle, air-fuel ratio, fuel capacity, and data based on IMSA powertrain modeling.

How it works

IMSA’s driveshaft-mounted torque sensors aim to reduce some of those requirements and even eliminate things like engine dyno testing when possible, by measuring power output directly at the driveshafts in what would most commonly be phrased as “power at the wheels.” The MagCanica UHA (Ultra High Accuracy) Driveshaft Torque Sensors are small cylinders that mount onto the driveshafts that lead from the transaxle to the wheel hub. These torque sensors require specialized driveshafts with a raised lip in order to locate the sensors in place along with a secondary securement method such as a small strut rod in order to prevent the sensor from spinning on the driveshaft.

Photo by: MagCanica

Photo by: MagCanica

Once a car is moving, the driveshaft produces a magnetic field which is detected by the torque sensor surrounding it. That magnetic field is converted to measurable voltage which corresponds to a given torque figure. Once the voltage is recorded it is then transmitted over the car’s data network to IMSA’s data logger where the torque is calculated in real time based on that torque sensor data along with things like wheel speed.

This data is interpreted by IMSA and from there the sanctioning body can set baseline power levels — equalizing the eleven manufacturers that currently compete in the GT classes sporting everything from turbocharged V6 engines to naturally aspirated V8s. The torque sensors also allow IMSA to monitor data throughout the race and enforce penalties if a car exceeds the controlled powertrain parameters outlined in the rules.

The data transmitter that sends torque information to IMSA, in the No. 14 Vasser Sullivan Racing Lexus GTD Pro car.

Photo by: Lalita Chemello

The torque sensors basically act like a portable dyno and not only measure peak torque but can draw a curve of a car’s torque band that IMSA is regulating. If a car exceeds the regulatory curve at any point in time, a warning or penalty may be issued. And these little instruments are so sensitive, in fact, that drivers have had to adapt to this new regulatory environment and drive more careful on curbing because some impacts can cause blips on the torque sensor readout which could lead to a warning or penalty.

Ten of the eleven manufacturers competing in the IMSA WeatherTech Sportscar Championship have had some previous experience with these sensors as they’ve already completed a season in WEC on GT cars and had some of the bugs worked out when it comes to interfacing with the individual car computers. Mercedes-Benz, who had not participated in WEC last year, is the only manufacturer that is learning the system here for the first time.

IMSA is very strict on keeping the sensors accurate. Even outside racing conditions it requires mechanics to complete a spin test multiple times during an event in order to verify that the sensors are reading correctly. During these tests they move the sensor around the driveshaft in both directions and the resulting data is then submitted to IMSA officials for comparison to their baseline data set.

Sports car racing might not be the final frontier for these torque sensors. If the sensors are successful for the GT cars in IMSA then we are likely to see them tested in NASCAR as that series looks to change its engine formula in the future. These sensors could then provide a pathway for allowing engines outside of the current strict V8 parameters to compete but keep competition even across the field, making the series more welcoming to new, future manufacturers. With that in mind, all eyes will be on this weekend’s Rolex 24 to see how the new sensors work and how the latest balance of performance requirements play out.