Struct SurfaceProperties

Namespace

LibreRally.Vehicle.Physics

Assembly

LibreRally.dll

Physics properties for a driving surface. These values scale the tyre model's grip envelope and energy dissipation.

Surface friction is decomposed into two texture-scale contributions following The Contact Patch, C1603:

• FrictionCoefficient: overall peak µ multiplier relative to the tyre model's internal reference surface. Values near 1.0 are neutral; rally asphalt may be slightly above 1.0. This is the combined result of microtexture and macrotexture contributions.
• Microtexture: adhesion-dominant grip from sub-0.5 mm asperity peaks (0–1 scale). Provides dry and light-wet grip. Polished surfaces have low microtexture. Reference: The Contact Patch, C1603, §Microtexture.
• Macrotexture: hysteresis grip and water-evacuation capacity from 0.5–20 mm scale aggregate texture (0–1 scale). High macrotexture drains water from the contact patch, delaying hydroplaning onset. Reference: The Contact Patch, C1603, §Macro-texture.
• WaterDepth: surface water film thickness (m). Zero for dry surfaces. Values above ~0.0025 m (2.5 mm) trigger hydroplaning risk at speed. Reference: The Contact Patch, C1603, §Aqua-planing.
• RollingResistance: rolling-resistance force coefficient (N per N of load).
• SlipStiffnessScale: scales the tyre's pure-slip stiffness and brush stiffness. Lower values make loose surfaces feel compliant rather than like low-grip asphalt.
• RelaxationLengthScale: scales carcass relaxation lengths. Higher values delay force buildup on deformable or rough surfaces.
• PeakSlipRatioScale: scales the longitudinal slip ratio at which peak traction occurs. Higher values allow more wheelspin before the tyre saturates.
• DeformationFactor: how much the surface deforms under load (0 = rigid, 1 = fully deformable). Affects longitudinal slip behaviour — deformable surfaces tolerate higher slip before saturation.
• NoiseFactor: road roughness amplitude (0 = smooth, 1 = very rough). Drives deterministic per-frame micro-variation in grip based on road-surface power spectral density, giving the feel of aggregate texture at the contact patch. Reference: The Contact Patch, C1603, §Power spectral density curves.

public readonly struct SurfaceProperties

Inherited Members

ValueType.Equals(object)

ValueType.GetHashCode()

ValueType.ToString()

object.Equals(object, object)

object.GetType()

object.ReferenceEquals(object, object)

Properties

DeformationFactor

Deformation factor (0 = rigid, 1 = fully deformable).

public float DeformationFactor { get; init; }

Property Value

float

FrictionCoefficient

Peak friction multiplier relative to the tyre model's internal reference surface.

public float FrictionCoefficient { get; init; }

Property Value

float

Macrotexture

Macrotexture level (0–1). Represents 0.5–20 mm aggregate texture depth. High macrotexture provides hysteresis grip and drains water from the contact patch. Positive texture (surface dressing) ≈ 0.9; polished concrete ≈ 0.2. Reference: The Contact Patch, C1603, §Macro-texture.

public float Macrotexture { get; init; }

Property Value

float

Microtexture

Microtexture level (0–1). Represents sub-0.5 mm asperity peaks that provide adhesion grip. Higher values = grittier surface = better dry and light-wet grip. Fresh calcined bauxite ≈ 1.0; polished stone ≈ 0.3. Reference: The Contact Patch, C1603, §Microtexture.

public float Microtexture { get; init; }

Property Value

float

NoiseFactor

Road roughness amplitude (0 = smooth, 1 = very rough).

public float NoiseFactor { get; init; }

Property Value

float

PeakSlipRatioScale

Scale factor for the longitudinal slip ratio at peak traction. Higher values allow more wheelspin before reaching peak force.

public float PeakSlipRatioScale { get; init; }

Property Value

float

RelaxationLengthScale

Relaxation-length scale applied before tyre carcass and operating-point modifiers. Higher values delay force buildup across the contact patch on loose or rough surfaces.

public float RelaxationLengthScale { get; init; }

Property Value

float

RollingResistance

Rolling-resistance force coefficient (N per N of load).

public float RollingResistance { get; init; }

Property Value

float

SlipStiffnessScale

Slip-stiffness scale applied to the tyre force-curve slope and brush stiffness. Dry asphalt ≈ 1.0, gravel ≈ 0.5, snow ≈ 0.3.

public float SlipStiffnessScale { get; init; }

Property Value

float

WaterDepth

Surface water film thickness (m). Zero for dry conditions. Light rain ≈ 0.0005 m, moderate ≈ 0.001 m, heavy ≈ 0.003 m. Hydroplaning onset ≈ 0.0025 m at highway speeds. Reference: The Contact Patch, C1603, §Aqua-planing.

public float WaterDepth { get; init; }

Property Value

float

Methods

ForType(SurfaceType)

Returns the default SurfaceProperties for the given surfaceType. Values are tuned for rally driving conditions. Friction coefficients calibrated from The Contact Patch, C1603, Table 1: dry tarmac 0.8–1.0, wet 0.2–0.65, icy 0.15. Microtexture/macrotexture values represent typical UK road aggregate.

public static SurfaceProperties ForType(SurfaceType surfaceType)

Parameters

surfaceType SurfaceType

Surface type to resolve.

Returns

SurfaceProperties

The default physics properties for the requested surface type.

Lerp(in SurfaceProperties, in SurfaceProperties, float)

Linearly interpolates two surface property sets for contact blending.

public static SurfaceProperties Lerp(in SurfaceProperties a, in SurfaceProperties b, float t)

Parameters

a SurfaceProperties

Primary surface properties.

b SurfaceProperties

Secondary surface properties.

t float

Blend factor in the range [0, 1].

Returns

SurfaceProperties

The blended surface properties.