LMDh: The First Pass of a Full Overhaul

This important update brings the LMDh class to the new standards set in Update 2.1 with the GT3 and GT4 classes, and marks Phase One with this initial focus tackling the most urgent issues, as well as improving the driving experience and laying the foundations for deeper development in future updates.

Before getting into the details, there is one important note to do with setups: While your old setups will still work with this update, you will likely experience changes in handling and performance with your old setups. Therefore, we strongly recommend starting from the new default setups or using newly updated setups available from the ModHub.

Now with that out of the way, here’s what’s changed.

ICE: Smoother, More Responsive, More Predictable

The internal combustion engine simulation in LMDh class has received a substantial first round of work.

ICE inertia has been improved, along with throttle response and engine braking. Steady-throttle behaviour while driving has also been revised to eliminate the oscillations that could previously appear under constant throttle, with some oscillation potentially still present at idle.

We have fixed the major ICE oscillations that could occur when the front MGU deployed power in LMDh machinery, while the ICE now responds more cleanly to MGU deployment overall.

This remains an area of active development, but the first pass should already deliver a considerably more stable and natural relationship between combustion and electric power.

Power delivery has also been reworked around the Balance of Performance rules.

The ICE now respects its prescribed BoP power limitation throughout the rev range, with the system deliberately attempting to apply that limitation as smoothly as possible rather than simply cutting or shifting power delivery.

Interaction between the combustion engine and the hybrid system has also been improved.

Brake-by-Wire and Regeneration

The hybrid braking systems have received equally important changes.

ABS assist now works in both Safe Regen and Full Regen modes and is compatible with any level of regeneration being produced by the MGU.

Brake-by-wire functionality has also been improved with the result that, as MGU regenerates and vehicle speed and aerodynamic downforce change, the brake balance now changes dynamically in real time to compensate.

That behaviour reflects the way these systems operate under real regulations, where the relationship between friction braking and regenerative braking cannot simply remain fixed as the car’s operating conditions change.

The improved brake-by-wire system also remains compatible with ABS assist for players who choose to use it.

Regeneration itself is now also considerably more intelligent. MGU regeneration varies with speed and therefore with the changing aerodynamic load on the car. This helps prevent the unusual axle lockups that could previously occur under regeneration—particularly at the rear axle in LMDh machinery and the front axle in LMH machinery.

Regeneration also now responds to lateral G. If the driver is asking the tyres for a significant amount of cornering grip, for example, regenerative braking is adjusted to avoid unnecessarily destabilising the car.

The aim is for regen to behave as part of the overall vehicle dynamics rather than operating independently of what the tyres, brakes and aero are doing.

First Iteration of the New Tyre Model: 3 Compounds

LMDh also receives the first iteration of a new tyre model. There are now three compounds to choose from, but the differences between them are not primarily about creating large steps in outright grip.

Instead, the compounds vary mainly through internal heat generation and tyre pressure behaviour. Grip differences remain—as in the real world—relatively small.

The intention is for compound choice to become more relevant according to ambient temperature and track temperature, making tyre selection more about putting the tyre into the correct operating range than simply choosing the “compound with the most grip”.

This is the beginning of that work rather than the destination, and further compound development is already under development.

A New Aero Foundation

The aero model has also received its first overhaul. The cars now demonstrate greater pitch sensitivity, meaning changes in the attitude of the car have a more significant effect on aerodynamic behaviour.

The model also accounts for the 4:1 aerodynamic efficiency limitation defined by the regulations. What does this mean? Run the car too low, for example, and aerodynamic performance can now deteriorate through low-ride-height stalling, rather than “lower ride height automatically meaning better performance”.

The effect of the cars’ vertical fins under yaw is also now represented.

Together, these changes create a much more dynamic aero platform—one that asks the driver and setup engineer to think about how the car moves rather than simply where it sits at one static ride height.

Chassis and Suspension

The chassis and suspension models have received their own first round of improvements alongside the tyre and aero work.

Updates include improved:

• Centre of gravity

• Vehicle inertias

• Suspension geometry

• Setup limits

Again, this is the first iteration of the new approach. The intention is to eventually move beyond a broad class-wide solution and develop more individual behaviour for the different LMDh and LMH cars.

What Comes Next

This update is the first pass, not the finished overhaul. There is already more work in development across virtually every part of the LMDh and LMH simulation.

Future development includes more precise ICE BoP power limitation, with the goal of reducing oscillation to an absolute minimum—or eliminating it entirely. Turbo boost control will be improved. Throttle control will be improved. Fuel consumption and overall energy control will be improved. And the interaction and deployment strategy between the ICE and MGU will continue to be refined.

The three tyre compounds will also receive further work. Aero development will increasingly move toward different, car-specific aerodynamic models rather than a single broad class treatment. And the same is planned for the chassis and suspension systems, with individual models assigned and developed for each car.

And there is more beyond that still to come.

Let’s Go!

This first update is about getting the fundamentals into a stronger place: fixing the major issues, improving the interaction between combustion power, hybrid deployment, regeneration and braking, and introducing the first versions of the new tyre, aerodynamic, chassis and suspension models.

From here, those systems can become progressively more detailed—and progressively more specific to each prototype. For now, start with the new default setup, get some laps in, and discover how the new foundation feels.