The Toyota A90/A91 Supra is a strong aerodynamic platform, but making individual aero parts is not the same as developing a complete aero system. With the RM GT4+ program, our goal was to understand how the front splitter, rear wing, hood vent, canards, body, wheels, and underbody interact as one vehicle - then use that information to define a clear development path from the Base Package to the GT4+ EVO Package.

The result is not simply more downforce. It is a matched package built around measurable load, usable aerodynamic balance, and transparent reporting.

KEY RESULT:  At the 120 mph V^2-scaled reporting condition, the Base Package produces 384.5 lbf of net downforce, while the EVO Package increases that figure to 421.5 lbf - a gain of 37.0 lbf, or 9.6%.

What Is Included in Each Package?

GT4+ Base Package

The Base Package contains four core aerodynamic components: the RM GT4+ front splitter without EVO endplates, the 1600mm GT4+ rear wing with flat endplates, the recessed GT4+ hood vent, and the GT4+ canards. Together, these parts establish the complete street-and-track foundation of the system.

GT4+ EVO Package

The EVO Package includes every Base Package component and adds three airflow-control upgrades: contoured EVO splitter endplates, 3D rear-wing endplates, and the centerline roof fin. These parts were developed around the specific losses identified in the Base Package CFD, particularly outer-edge pressure leakage at the splitter and three-dimensional leakage at the rear-wing tips.

How the CFD Was 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. The model was evaluated in a straight-line condition at 100 km/h (62.1 mph).

To make the results easier to compare with common aftermarket aero figures, the solved forces were normalized to 120 mph using V-squared scaling only. No additional performance multiplier was applied. This preserves the aerodynamic coefficients, the relative Base-to-EVO gains, and the lift-to-drag relationships from the original simulation.

This also means the 120 mph figures are a normalized reporting condition, not a separate 120 mph CFD solution or a substitute for track correlation. Ride height, pitch, yaw, steering angle, tire wake, and real surface conditions can all affect the final on-track result.

GT4+ Base Package: The Aerodynamic Foundation

At the 120 mph V^2-scaled reporting condition, the Base Package generates 384.5 lbf of net downforce with 265.8 lbf of total drag, producing an overall lift-to-drag ratio of approximately 1.45. The full-vehicle rear-wing evaluation was performed 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 an L/D of approximately 5.35. Because the RM splitter is a molded component rather than a universal flat panel, the diffuser geometry and local transitions can be developed as one system. The CFD shows a stable low-pressure region beneath the front of the car and broadly uniform surface flow across the splitter assembly.

The Base analysis also revealed the next area to address: the non-EVO outer edge allows local pressure equalization and spill near the splitter shoulder. This reduces the amount of load retained at the outer section and directly informed the shape of the EVO endplates.

1600mm Rear-Wing Performance

In the Base full-vehicle configuration, the 1600mm rear wing produces 230.5 lbf of integrated load for 33.0 lbf of drag, giving a rear-wing L/D 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 roof and rear glass provide a relatively clean approach flow to the wing. The primary local losses appear near the trailing edge and at the flat endplates, where pressure leakage and tip-vortex formation reduce effective outboard loading.

The GT4+ wing provides five adjustment positions from 0 to 6 degrees in 1.5-degree increments. For the best aerodynamic efficiency, RM recommends running 3 degrees or less unless the vehicle setup requires additional rear load. Below data is based on CFD analysis of the rear wing alone, rather than data from a full-vehicle simulation.

Recessed Hood Vent

The recessed RM 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 opening. RM track testing has also shown practical heat-extraction benefits, although the current CFD report does not assign a separate cooling-performance number to the vent.

From Base to EVO: What Changed?

The EVO configuration was evaluated under the same matched conditions as the Base Package. At the 120 mph V^2-scaled reporting condition, net downforce rises from 384.5 to 421.5 lbf, while total drag rises from 265.8 to 290.5 lbf. This represents a 9.6% gain in net downforce and a 9.3% increase in drag, with whole-vehicle L/D remaining approximately 1.45.

Metric	Base	EVO	Change
Net downforce	384.5 lbf	421.5 lbf	+37.0 lbf / +9.6%
Total drag	265.8 lbf	290.5 lbf	+24.7 lbf / +9.3%
Splitter load	179.8 lbf	230.7 lbf	+50.9 lbf / +28.3%
Splitter drag	33.6 lbf	36.1 lbf	+2.5 lbf / +7.3%
Rear-wing load	230.5 lbf	248.6 lbf	+18.1 lbf / +7.9%
Rear-wing drag	33.0 lbf	34.9 lbf	+1.9 lbf / +5.7%

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

EVO Splitter Endplates: The Largest Device-Level Gain

The largest integrated device-level improvement appears at the front splitter. 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 L/D improves from 5.35 to 6.39, a 19.4% efficiency gain.

The pressure and velocity fields are consistent with stronger outer-edge sealing. The contoured EVO endplates reduce lateral pressure equalization, help retain the low-pressure region near the outer edge, and support the molded diffuser geometry near the front-wheel area. Because the EVO configuration includes concurrent hardware changes, the result is reported for the integrated splitter assembly rather than as an isolated endplate-only figure.

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. That is a 7.9% gain in rear load for a 5.7% drag increase, improving rear-wing L/D 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. Local suction beneath the wingtip and coherent near-wall streamlines support improved pressure retention and reduced pressure equalization. These results reflect the complete EVO system; the individual contribution of the endplates was not separated 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 ahead of the wing. Positioned along the vehicle centerline, the GT4+ roof fin is designed to organize the roof flow and limit lateral crossflow as air approaches the rear-wing system.

Its main expected benefit is under yaw, where the incoming flow is no longer perfectly aligned with the vehicle. Because the present full-vehicle analysis is a straight-line case, yaw robustness remains a design target to be validated through additional CFD and track correlation rather than a separately quantified claim in this report.

What the Results Mean for Setup

The EVO Package adds useful front and rear load without reducing the overall whole-vehicle aerodynamic efficiency measured in the matched CFD comparison. Its largest gain occurs at the front splitter, so the added front load should be balanced through rear-wing angle, ride height, alignment, spring and damper settings, and chassis tuning.

A Note on the 12-Degree Comparison Estimate

The information packet includes a nominal 12-degree rear-wing estimate intended only to align with a published competitor test configuration. That setting was not independently solved as a full-vehicle CFD case. For that reason, the core performance discussion in this article is based on the solved 0-degree full-vehicle rear-wing configuration and the matched Base-versus-EVO comparison.

The GT4+ Development Path

The Base Package establishes a capable aerodynamic foundation for the A90/A91 Supra. The EVO Package then uses the CFD findings to address the most visible local losses: splitter-edge leakage, wingtip pressure equalization, and consistency of the flow approaching the rear wing.

At the 120 mph V^2-scaled reporting condition, EVO increases net downforce by 9.6%, raises integrated splitter load by 28.3%, and increases rear-wing load by 7.9%, while maintaining an overall whole-vehicle L/D of approximately 1.45. More importantly, the changes follow a clear engineering logic: identify the loss, develop the hardware around it, and compare the result under the same conditions.

FINAL TAKEAWAY  The RM A90/A91 Supra GT4+ EVO Package delivers its largest device-level gain at the front splitter, adds usable rear-wing load, and preserves whole-vehicle aerodynamic efficiency in the matched CFD comparison.

CFD is a development tool, not the finish line. Additional yaw analysis, setup sweeps, and on-track correlation remain part of the validation process as RM continues developing the GT4+ platform.