INSIDE THE CFD DEVELOPMENT OF THE RM A90/A91 SUPRA GT4+ AERO PACKAGE

CFD analysis and technical reporting by Ridgeline Motorsport Engineering.

Developing individual aero parts is not the same as engineering a complete aerodynamic system. For the Ridgeline Motorsport GT4+ program, the front splitter, rear wing, hood vent, canards, body, wheels, and underbody were evaluated as one complete Toyota A90/A91 Supra package.

The resulting full-vehicle CFD comparison shows how the GT4+ Base Package performs and how the EVO upgrades address splitter-edge leakage, rear-wing tip losses, and airflow approaching the wing.

Quick Answer

At the 120 mph V²-scaled reporting condition, the Toyota A90/A91 Supra GT4+ Base Package produces 384.5 lbf of net downforce, while the EVO Package produces 421.5 lbf—a gain of 37.0 lbf, or 9.6%. The largest device-level improvement occurs at the front splitter, where integrated load increases by 28.3%. These figures were normalized from matched 100 km/h full-vehicle CFD results and do not represent a separately solved 120 mph simulation.

What Is Included in Each Package?

Both configurations were developed as complete aero systems rather than collections of unrelated components. The EVO Package retains the four core Base components while adding three airflow-control upgrades.

GT4+ Base Package

The Base Package combines the GT4+ front splitter without EVO endplates, 1600 mm rear wing with flat endplates, recessed hood vent, and GT4+ canards.

GT4+ EVO Package

The EVO Package retains every Base component and adds contoured splitter endplates, 3D rear-wing endplates, and a centerline GT4+ roof fin. These upgrades target the splitter-edge leakage, wingtip pressure losses, and rear-window airflow behavior identified during development.

How Was the Supra GT4+ CFD Evaluated?

The full-vehicle assessment was completed in Simcenter STAR-CCM+ using scanned exterior geometry, a simplified engine bay, a k-epsilon turbulence model, a target y+ of approximately 30, and roughly 70 million cells. Both configurations were evaluated in a straight-line condition at 100 km/h, or 62.1 mph.

The solved forces were normalized to 120 mph using V² scaling only, with no additional performance multiplier. This preserves the aerodynamic coefficients, relative Base-to-EVO changes, and lift-to-drag relationships from the original simulation.

The 120 mph figures are therefore normalized reporting values rather than a separate 120 mph CFD solution. Ride height, pitch, yaw, steering angle, tire wake, vehicle setup, and track conditions can affect real-world results.

GT4+ Base Package CFD Results

At the 120 mph V²-scaled reporting condition, the Base Package generates 384.5 lbf of net downforce with 265.8 lbf of total drag, producing an overall whole-vehicle lift-to-drag ratio of approximately 1.45. The full-vehicle rear-wing evaluation was completed at a 0-degree geometric angle of attack, representing the most common real-world setup.

Front Splitter Performance

The Base front splitter produces 179.8 lbf of integrated splitter load for 33.6 lbf of drag, corresponding to a lift-to-drag ratio of approximately 5.35.

Because the Ridgeline Motorsport splitter is a molded component rather than a universal flat panel, its diffuser geometry and local transitions can be developed as one integrated system. The CFD shows a stable low-pressure region beneath the front of the vehicle and broadly uniform surface flow across the splitter assembly.

The Base analysis also reveals local pressure equalization and airflow spill near the non-EVO splitter shoulder. This reduces the load retained at the outer section and directly informed the shape of the EVO endplates.

1600 mm Rear-Wing Performance

In the Base full-vehicle configuration, the 1600 mm rear wing produces 230.5 lbf of integrated load for 33.0 lbf of drag, giving the wing a lift-to-drag ratio of 6.98.

The underside maintains a strong and broadly even suction field, while the top surface remains positively loaded. Flow across the mainplane stays broadly attached, and the swan-neck supports create minimal disturbance.

The A90/A91 Supra roof and rear glass provide relatively clean approach flow to the wing. The primary local losses appear near the trailing edge and flat endplates, where pressure leakage and tip-vortex formation reduce effective outboard loading.

The GT4+ rear wing provides five adjustment positions from 0 to 6 degrees in 1.5-degree increments. For the best aerodynamic efficiency, Ridgeline Motorsport recommends running 3 degrees or less unless the vehicle setup requires additional rear load.

The following force-curve data is based on CFD analysis of the rear wing alone rather than a full-vehicle simulation.

Recessed Hood Vent

The recessed GT4+ hood vent and its upstream Gurney flap are positioned within a local low-pressure region over the hood. This placement promotes the extraction of hot, high-pressure engine-bay air rather than relying only on the size of the vent opening.

Ridgeline Motorsport track testing has shown practical heat-extraction benefits, although the current CFD report does not assign a separate cooling-performance figure to the vent.

Base vs. EVO CFD Results

Under the same matched conditions, the EVO Package increases net downforce from 384.5 to 421.5 lbf and total drag from 265.8 to 290.5 lbf. This represents a 9.6% increase in net downforce and a 9.3% increase in drag, while the whole-vehicle lift-to-drag ratio remains approximately 1.45.

Technical note: Component values represent selected surface-force groups and are not intended to add directly to whole-vehicle net downforce. The body, wheels, underbody, and interaction effects contribute to the remaining aerodynamic balance.

EVO Splitter Endplates: The Largest Device-Level Gain

Splitter load increases from 179.8 to 230.7 lbf—a gain of 50.9 lbf, or 28.3%—while splitter drag increases by only 2.5 lbf. As a result, splitter lift-to-drag ratio improves from 5.35 to 6.39, representing a 19.4% gain in aerodynamic efficiency.

The pressure and velocity fields are consistent with stronger outer-edge sealing. The contoured EVO endplates reduce lateral pressure equalization, retain more of the low-pressure region near the splitter edge, and support the molded diffuser geometry near the front wheels.

Because the EVO configuration includes multiple concurrent hardware changes, these figures represent the integrated splitter assembly rather than the isolated contribution of the endplates.

3D Rear-Wing Endplates: Better Pressure Retention

In the complete EVO configuration, rear-wing load increases from 230.5 to 248.6 lbf, while rear-wing drag rises from 33.0 to 34.9 lbf. This represents a 7.9% increase in rear load for a 5.7% increase in drag, improving rear-wing lift-to-drag ratio from 6.98 to 7.12.

The contoured 3D endplates help retain the pressure difference at the wingtip and keep more of the outboard mainplane aerodynamically loaded. The reported result reflects the complete EVO configuration; the contribution of the endplates was not isolated from roof-fin and package-interaction effects.

Roof Fin: Organizing the Approach Flow

The surface-relative-velocity field identifies a lower-velocity boundary-layer region over the rear glass. Positioned along the vehicle centerline, the GT4+ roof fin is designed to organize the flow approaching the rear wing and limit lateral crossflow.

Its primary expected benefit occurs under yaw. Because the current analysis uses a straight-line condition, that benefit remains a development target rather than a separately quantified claim.

What Do the CFD Results Mean for Vehicle Setup?

The EVO Package increases front and rear load without reducing the whole-vehicle aerodynamic efficiency measured in the matched comparison. Because its largest gain occurs at the splitter, the additional front load should be balanced through rear-wing angle, ride height, suspension settings, alignment, and the wider chassis setup.

The appropriate balance will depend on vehicle weight, tires, suspension configuration, driver preference, circuit layout, and operating speed.

CFD Limitations and the 12-Degree Estimate

The development information includes a nominal 12-degree rear-wing estimate intended only to align with a published competitor test configuration. Because that setting was not independently solved as a full-vehicle CFD case, the primary results in this article use the solved 0-degree configuration and matched Base-versus-EVO comparison.

Additional yaw analysis, setup sweeps, and on-track correlation remain part of the GT4+ validation process.

Final Takeaway

The GT4+ Base Package establishes the aerodynamic foundation for the Toyota A90/A91 Supra, while the EVO Package targets the losses identified around the splitter edge, rear-wing tips, and airflow approaching the wing.

Under matched CFD conditions, the EVO configuration increases net downforce by 9.6%, with its largest device-level gain occurring at the front splitter, while maintaining an overall whole-vehicle lift-to-drag ratio of approximately 1.45.

The development process remains ongoing. Additional simulation, vehicle setup work, and on-track correlation will continue to refine the GT4+ platform.

Explore the Toyota A90/A91 Supra GT4+ System

Explore the complete Toyota A90/A91 Supra aero collection, including the GT4+ splitter system, canards, 1600 mm rear wing, hood vent, and RS roof fin.

For the real-world development background behind the package, see Tim’s Toyota A90 Supra GT4+ development car and its track-focused aero configuration.