Tire Development for rFactor 2

About Tire Development for rFactor 2

Tire development in rFactor 2 is the foundation of authentic driving feel and vehicle dynamics. Unlike most simulators that use simplified tire models, rFactor 2 employs a sophisticated physical tire model (PTM) that simulates real rubber behavior, construction properties, heat transfer, and wear characteristics. This creates the most realistic tire physics available in sim racing.

Understanding the relationship between rFactor 2's tire files is critical: TGM (Tire Geometry Model) files are the master files that control the actual grip feel and user experience. The TGM defines how the tire deforms, generates grip, heats up, and responds to driver inputs > everything that makes the car feel authentic to drive. TBC (Tire Brand) files, on the other hand, primarily handle AI behavior and visual aspects of the tire around the rim, with a few parameters that collaborate with the TGM to complete the tire system.

Professional racing teams rely on rFactor 2 mod development for setup development and driver training precisely because of this tire model fidelity. This guide covers TGM and TBC file creation, along with the pTool and tTool workflow needed to develop professional-grade tire physics.

TGM Files - The Master Grip Model

TGM (Tire Geometry Model) files are the master files for tire physics in rFactor 2. Everything you feel as a driver > grip levels, tire response, contact patch behavior, and how the tire loads and unloads > comes from the TGM file. This is where the actual physics simulation happens.

TGM files define the physical construction and structural behavior of the tire carcass. Unlike TBC files which handle AI and visuals, TGM files model how the tire deforms under load, how heat flows through the rubber layers, how the contact patch forms and changes shape, and ultimately how much grip the tire generates. These files are significantly more complex than TBC files and require specialized tools (tTool) to generate and validate.

The TGM contains pre-calculated lookup tables that rFactor 2 uses in real-time to determine tire behavior at any given combination of load, speed, temperature, and pressure. This is why the TGM is the master file > it controls the user experience completely.

TGM File Structure Overview

TGM files contain several major sections that work together to create the complete tire simulation:

• QuasiStaticAnalysis: Defines tire structure and testing parameters for pre-calculation
• Node Definitions: Geometric points defining tire shape, thickness, and material properties
• Realtime Parameters: The core grip physics values used during actual driving
• LookupData: Pre-calculated tire behavior tables (binary encrypted) generated by tTool

The Realtime section is where the magic happens > this contains the grip coefficients, rubber viscoelastic properties, and degradation curves that directly control how the tire feels and performs under the driver's control.

TBC Files - AI Behavior & Visual Properties

Important: TBC files primarily control AI behavior and visual tire appearance. While TBC files do contain some parameters that work with the TGM (like base dimensions and certain multipliers), the actual grip feel and user driving experience comes from the TGM file's Realtime section.

TBC (Tire Brand) files handle how the AI evaluates tire performance, how tires look visually around the rim, and some high-level properties like optimal temperature and pressure ranges. A single TBC file can contain multiple tire compounds (e.g., soft, medium, hard) for both front and rear axles.

Think of the TBC as the "wrapper" around the TGM > it tells the game which TGM file to use, provides AI with decision-making data, and defines some collaborative parameters, but the TGM is doing the heavy lifting for physics.

TBC File Structure Overview

The TBC file contains the following sections:

• SlipCurve Definitions: Normalized curves used by AI to evaluate tire behavior
• Compound Definitions: Separate entries for each tire compound with TGM references and AI parameters
• Visual & AI Properties: Dimensions, optimal temperatures, wear rates for AI strategy

SlipCurve Types

SlipCurves in TBC files are primarily used by the AI to understand tire behavior. These curves are normalized (peak value of 1.0) and tell the AI when the tire is at peak grip, over the limit, or understeering/oversteering:

• Lateral Curve: Defines grip during cornering (slip angle-based)
• Acceleration Curve: Defines grip during power application (slip ratio-based)
• Deceleration Curve: Defines grip during braking (slip ratio-based)

Step Value Importance

The Step value determines the slip value at which peak grip occurs. This is critical for realistic tire behavior:

• Lateral Step: Typically 0.004-0.010 (corresponding to 6-12 degrees slip angle)
• Longitudinal Step: Typically 0.003-0.005 (corresponding to 1.5-2.5% slip ratio)

Setting step values correctly ensures the tire reaches peak grip at realistic slip angles, which directly affects how the tire responds to driver inputs and how aligning torque (self-centering force) behaves.

Understanding Slip Curves: Narrow vs Wide Grip Windows

The width of the grip window is critical for realistic tire behavior. A narrow optimal grip window (where the curve peaks sharply and drops off quickly) creates precise, controllable tire behavior that rewards proper driving technique. A wide grip window creates forgiving but unrealistic "drifting" behavior where the tire maintains high grip across a broad slip range.

Tire Compound Settings

Each compound in a TBC file represents a specific tire with its own TGM reference and AI-relevant properties. The most critical parameter in each compound definition is the TGM file reference > this links to the master physics file that controls the actual driving feel.

Key Compound Parameters

Critical Parameters Explained

TGM Reference - The Most Important Parameter

TGM="filename.tgm": This links to the Tire Geometry Model file that controls the actual driving physics. Everything the driver feels comes from this TGM file. If you want to change how the tire grips, responds, or feels, you modify the TGM file, not the TBC.

Grip Coefficients - AI Reference Values

DryLatLong=(lateral, longitudinal): These values are primarily used by the AI to understand relative grip levels between different compounds. While they do provide some high-level scaling, the actual grip curves come from the TGM's Realtime section. Think of these as "AI hints" rather than the primary grip source.

WetLatLong=(lateral, longitudinal): Similar to DryLatLong but for wet conditions. The AI uses these to decide pit strategy and pace management in the rain.

Physical Dimensions - Visual & AI

Radius=0.3185: Outer radius of the tire in meters > used for visual representation and AI calculations

Width=0.26: Tire width in meters (primarily affects visual skid marks and tire appearance around the rim)

Rim=(diameter, spring_rate, damper, sparks_velocity): Rim specifications for visual bottoming out behavior and AI damage assessment

Spring and Damping - Collaborative Parameters

SpringBase=180000: Base spring rate of the tire structure. This is one of the few TBC parameters that collaborates with the TGM to affect actual driving physics, influencing tire compliance.

SpringkPa=0: Additional spring rate per kPa of inflation pressure. Usually set to 0 for modern racing tires.

Damper=780: Damping rate > another collaborative parameter that works with the TGM to affect tire response.

Load Sensitivity - AI Strategy Parameter

LoadSensLat=(-4.2e-5, 0.41, 20000): Primarily used by AI to understand how the tire performs under different loads. The actual load sensitivity physics comes from the TGM file's Realtime section.

Peak Slip Values

LatPeak=(0.101, 0.139, 7800): Lateral slip peak at zero load, peak at maximum load, and the load value. These values determine how the slip curve's peak shifts with load changes.

LongPeak=(0.101, 0.102, 7100): Longitudinal slip peak with same parameter structure. Notice the smaller range compared to lateral - this is typical for tire behavior.

Thermal Properties - AI Temperature Management

Temperatures=(90.0, 20.0): Optimum operating temperature and starting temperature. Used by AI for pace management and tire strategy decisions.

Heating=(0.37, 0.0037): Heat generation parameters. The actual thermal model physics comes from the TGM.

Transfer=(0.00616, 0.00205, 0.000092): Heat transfer rates used by AI to estimate cooling.

Pressure Effects - AI Pressure Management

OptimumPressure=(152.0, 0.0060): Optimal pressure values used by AI for setup decisions.

GripTempPress=(0.60, 0.40, 0.50): AI parameters for understanding grip loss when temperature or pressure is non-optimal.

Wear Properties - AI Tire Strategy

WearRate=0.7202e-7: Base wear rate used by AI to calculate pit stop strategy and tire life.

WearGrip1 and WearGrip2: Arrays defining how AI should expect grip to change as tires wear. The actual wear physics comes from the TGM file's degradation parameters.

Tire Structure & Testing Parameters

The QuasiStaticAnalysis (QSA) section defines how tTool should test and model the tire's structural behavior before generating the lookup tables used in real-time simulation.

Key QSA Parameters

• NumLayers=2: Number of tire layers (must be 2 for current rFactor 2 implementation)
• NumSections=132: Radial divisions around the tire. More sections = more accuracy but higher computational cost. Minimum 2, recommended 132.
• RimVolume=0.01589: Air volume of the wheel rim in cubic meters, used to calculate actual tire internal volume
• GaugePressure=0: Test pressure in Pascals for QSA calculations. Multiple pressure values can be defined for multi-pressure testing.
• CarcassTemperature: Multiple temperature values (in Kelvin) at which tire behavior is calculated. Typically includes cold (273K), operating (353K), and hot (423K) temperatures.
• RotationSquared: Rotation speed in (rad/sec); for centrifugal force testing. Multiple values capture behavior from stationary to high speed.
• NumNodes=49: Number of nodes defining the tire profile. Minimum 31 suggested, 41-49 recommended for accurate results.

Node Definitions

Each node defines a point along the tire's cross-section profile with geometric and material properties:

• Geometry=(X, Y, thickness): Position (X=radial distance, Y=lateral offset) and thickness of this section
• BulkMaterial=(temp, density, Young's modulus, Poisson's ratio, compression multiplier, specific heat, thermal conductivity): Material properties at specified temperature. Multiple temperature entries define how material properties change with heat.
• TreadDepth=0.0024: Thickness of tread rubber in meters. Thicker tread reduces tire stiffness and can affect grip.
• RingAndRim=(ring_fraction, spring_rate): Connection to rigid ring/rim structure
• PlyParams=(angle, thickness, connection_flags): Tire ply (internal fabric layer) properties

Realtime Grip Parameters - The Core of User Experience

This is the most important section of the TGM file. The Realtime parameters directly control the grip feel, tire response, and driving characteristics that you experience during simulation. While the QSA section defines the tire's structure for pre-calculation, these Realtime values are what rFactor 2 uses every single frame to determine how much grip the tire generates.

When you feel the tire start to slide, when you sense the grip limit, when the tire overheats and loses performance > all of this comes from the Realtime section of the TGM file.

Base Grip Coefficients

StaticBaseCoefficient - Overall Grip Level

What it does: Controls overall grip level when the tire is not sliding. This is the foundation of tire grip > everything builds on this value.

Real example: Changing from 3.64 to 3.39 (reduction of 0.25)

• Result: Reduced "front bite" on initial turn-in
• Driver feedback: "Less pointy front, more realistic initial grip"
• Use case: When car has too much grip on turn-in compared to real life

SlidingBaseCoefficient - Sliding Grip

What it does: Controls grip level when the tire is actively sliding beyond peak slip angle.

Real example: Changing from 2.63 to 2.45 (reduction of 0.18)

• Result: More progressive sliding, harder to recover from slides
• Driver feedback: "Front gets more lazy after peak, closer to reality"
• Use case: Making sliding more challenging and realistic

Diffusive Adhesion - Grip Curve Sharpness

StaticDiffusiveAdhesion - Peak Grip Sharpness

What it does: Controls how sharp the grip peak is. Higher third value = sharper peak and more sudden falloff.

Real example: Changing third value from 0.80 to 0.90

• Result: Sharper grip falloff after optimal slip angle
• Driver feedback: "More snappy behavior, less forgiving"
• Use case: Creating more precise, less forgiving tire characteristics (narrow grip window)

SlidingDiffusiveAdhesion - Sliding Curve Sharpness

What it does: Controls sliding grip curve sharpness and speed sensitivity.

Real example: Changing second value from 3600 to 6600

• Result: Different sliding behavior at various speeds
• Driver feedback: "Better sliding characteristics at higher speeds"
• Use case: Fine-tuning how tire behaves when sliding at different velocities

Temperature Behavior - Critical for Realism

What it does: Defines grip vs temperature relationship across the entire operating range.

• 273K (0 °C): 0.6 = 60% grip when cold
• 378K (105 °C): 1.0 = 100% grip at optimal temperature
• 428K (155 °C): 0.7 = 70% grip when overheated

Real example: Changing to (257, 0.65, 366, 1.2, 518, 0.3)

• Result: Peak at 93 °C instead of 105 °C, much harsher overheating penalty (30% vs 70% grip when hot)
• Driver feedback: "Front becomes lazy when overheated, forces thermal management"
• Use case: Creating realistic temperature windows and harsh penalties for overdriving

Tire Wear and Degradation

AbrasionVolumePerUnitEnergy - Physical Wear Rate

What it does: Controls how much rubber physically wears away per unit of friction energy. This array has up to 32 values for different temperature-corrected conditions.

Real example: Halving all values (e.g., 3.26e-10 > 1.63e-10)

• Result: Doubled tire lifetime from 15 to 30+ laps
• Driver feedback: "Tires last much longer, more realistic stint length"
• Use case: Adjusting tire life for different race formats (sprint vs endurance)

DegradationPerUnitHistory - Thermal Degradation

What it does: Controls grip loss from accumulated heat damage over time. Even if the tire isn't worn physically, heat cycles cause chemical degradation.

Real example: Changing second value from 0.98 to 0.99 (slower degradation)

• Result: Tires maintain grip longer when operating at high temperatures
• Driver feedback: "Less grip drop-off after several hot laps"
• Use case: Balancing thermal management difficulty vs drivability

Pressure Sensitivity

What it does: Controls optimal tire pressure and how sensitive grip is to pressure changes.

Real example: Changing from (-40, 1.13e7, 5e5, 1) to (-25, 8e6, 5e5, 1)

• Result: Moves optimal pressure from 1.5 bar to 1.9 bar
• Driver feedback: "Need higher pressure for best grip, more realistic for this tire"
• Use case: Matching real-world optimal tire pressures for specific compounds

Sliding Behavior Curves

SlidingAdhesionCurve - Sliding Speed vs Grip

What it does: Controls grip at different sliding speeds. Format is pairs of (sliding_speed, grip_multiplier).

Real example: Changing to (-7.2, 0.35, -4.2, 1.6, -1.2, 0.18)

• Result: Less grip when sliding, more difficult to catch slides
• Driver feedback: "More challenging to recover from mistakes"
• Use case: Making tire behavior more demanding and realistic

Micro and Macro Deformation Curves

What they do: Fine-tune sliding behavior at different deformation scales. Micro affects small-scale rubber flex, macro affects large-scale contact patch deformation.

Real example: Reducing all grip multiplier values by 0.05-0.1

• Result: More progressive sliding, less sudden grip loss
• Driver feedback: "Sliding feels more natural and controllable"
• Use case: Balancing challenge vs drivability for different skill levels

Longitudinal Grip (Braking/Acceleration)

What it does: Controls how longitudinal forces (braking, acceleration) distribute across the contact patch.

Real example: Changing from 0.5 to 0.4

• Result: More forward slip under braking, less aggressive ABS intervention
• Driver feedback: "ABS feels less intrusive, more realistic braking feel"
• Use case: Adjusting braking characteristics and ABS behavior to match real car

Key Development Principles from Real Experience

Additional Realtime Parameters

• TemporaryBristleSpring=(lat, vert, long): Spring rates for tire "bristles" that model rubber deformation
• TemporaryBristleDamper=(lat, vert, long): Damping for bristle deformation
• WLFParameters=(glass_transition_temp, C1, C2, C3): Williams-Landel-Ferry equation for rubber viscoelastic behavior
• GrooveEffects: Track groove/roughness influence on grip components
• DampnessEffects: Wet track effects (negative values reduce grip)
• MarbleEffectOnEffectiveLoad: Grip reduction when driving on rubber marbles
• DegradationPerWearFraction: Grip degradation based on wear percentage

tTool Workflow - Generating the Master Physics Lookup Table

tTool is where professional tire physics comes to life. This tool takes your TGM file's parameters and generates a comprehensive lookup table through extensive automated testing. This process takes approximately 2 hours on a fast computer to run 590+ individual tests, calculating tire behavior at every combination of load, speed, temperature, pressure, and slip conditions. This lookup table is what enables rFactor 2 to simulate incredibly sophisticated tire behavior in real-time.

1

Prepare Your Working Directory

Before launching tTool, create a dedicated working directory: DRIVE:\SteamLibrary\steamapps\common\rFactor 2\pTool

Start with a good candidate TGM file. Professional tire development works best by starting with a validated TGM file from a similar tire (same size category, similar compound) and tweaking parameters from there. Creating TGM files from scratch rarely works well > it's better to have a solid foundation and iterate.

Place your candidate TGM file in this folder. Use proper tire naming conventions based on real-world specifications:

• Example: Dry_260-650-R18-SOFT.tgm
• Format: Condition_Width-Diameter-RimSize-Compound.tgm
• Source: Base dimensions on actual tire specs from PDFs or race team data

For this tutorial, we'll use Dry_260-650-R18-SOFT.tgm as our example file in the pTool folder.

2

Launch rFactor 2 with tTool

In Steam Library, right-click rFactor 2 -> Properties -> General -> Launch Options

Add the launch parameter: +tTool

Launch rFactor 2. Instead of the normal game launcher, you'll see the tTool green GUI interface. This is your tire physics development environment.

3

Load Your TGM File in tTool

In the tTool green GUI, scroll down until you see the I/O menu section. You'll find:

• File Name: Shows "something.tgm" by default
• Load File button
• Save File button

Manual entry required: Copy and paste your TGM filename (Dry_260-650-R18-SOFT.tgm) into the File Name field in the GUI, then click Load File.

Once loaded, the right side of the tTool interface will display a pink cross-section shape showing your tire's geometry profile. This confirms the TGM file is loaded correctly.

4

Activate Physics Calculations

At the full top of the tTool GUI menu, locate and activate "Run Physics". This enables the physics calculation engine.

5

Configure and Start Automated Testing

At the full bottom of the tTool GUI, locate the automated testing controls:

• Check the "Run Automated" checkbox
• The system will run 590 tests (or more if configured)
• Time requirement: Approximately 2 hours on a fast computer

Start the automated test sequence. You'll see the Automated Test Index incrementing as tTool progresses through each test. The system tests every combination of conditions to build the complete physics lookup table.

Important: The visual interface may continue showing activity even after reaching the 590 test target. Wait until all calculations fully complete before proceeding.

6

Save the Calculated TGM File

Critical final step: Once all 590+ tests complete, return to the I/O menu and click "Save File". This writes the newly calculated lookup table into your TGM file.

After saving, close tTool. In your pTool folder, you'll now find:

• Your fresh Dry_260-650-R18-SOFT.tgm with complete physics calculations
• A backup of the original (.tgm.bak)
• The [LookupData] section now contains thousands of lines of calculated physics data

7

Integration and Validation

Transfer your calculated TGM file from the pTool folder to your mod's tire directory. Link it in your TBC file using: TGM="Dry_260-650-R18-SOFT.tgm"

This is where the real work begins. Testing the car in-game, recording MoTeC telemetry data, and iteratively tweaking tire parameters until achieving realistic results can take days of dedicated work.

Best Practices for Tire Development

Research Requirements

Accurate tire modeling requires real-world data. For professional-grade results, you need:

• Tire Specifications: Exact dimensions (width, aspect ratio, diameter), construction type (radial vs bias), load ratings
• Compound Information: Treadwear rating, temperature rating, traction rating (UTQG data for road tires)
• Performance Testing Data: Skidpad G-force results, slalom times, braking distances - these provide grip coefficient baselines
• Thermal Characteristics: Operating temperature ranges, optimal pressure ranges
• Construction Details: Sidewall stiffness, tread depth, internal structure if available

Validation Methods

After creating tire files, validation is essential:

• Real-World Lap Time Comparison: Compare simulation lap times to real track data with the same vehicle
• Telemetry Analysis: Match tire temperature buildup, pressure changes, and wear rates to real data
• Driver Feedback: Professional drivers can identify unrealistic tire behavior quickly
• Cross-Vehicle Testing: Same tires should behave consistently across different vehicles
• Temperature Sensitivity Testing: Verify that cold tires have less grip and that tires overheat under abuse

Common Pitfalls

Avoid these frequent mistakes in tire development:

1. Incorrect Step Values

Setting slip curve step values too high or too low results in unrealistic peak slip angles. This makes the tire either too forgiving (peak too late) or too snappy (peak too early). Always research real tire behavior for your specific compound type.

2. Focusing on TBC Instead of TGM

The most common mistake is spending too much time adjusting TBC values trying to fix grip feel. Remember: the TGM controls grip, not the TBC. If the tire doesn't feel right to drive, you need to adjust the TGM's Realtime section, not the TBC's DryLatLong values.

3. Unrealistic Load Sensitivity

Real tires lose grip efficiency as load increases. If load sensitivity isn't properly configured, the tire may gain grip linearly with weight transfer, which is incorrect.

4. Ignoring Temperature Effects

Tires must perform poorly when cold and degrade when overheated. Grip should peak in a realistic temperature window (typically 20-30 °C range depending on compound).

5. Excessive Wear Rates

While racing tires do wear quickly, exaggerated wear rates make stint length predictions impossible. Match wear rates to real-world tire life data.

6. Copy-Paste Without Understanding

Every tire is unique. Copying another tire's values and only changing the name will produce unrealistic results. Each parameter should be researched and justified.

Professional Development Workflow

For teams using tire development for competitive advantage:

1. Data Collection: Gather all available technical data about the real tire
2. Initial Implementation: Create basic TBC/TGM files with conservative estimates
3. Baseline Testing: Run extensive in-sim testing to establish baseline behavior
4. Iterative Refinement: Adjust parameters based on testing feedback, one variable at a time
5. Validation: Compare to real-world data; adjust until correlation is acceptable
6. Multi-Compound Development: Once base compound is validated, create variants (soft/hard) from the validated baseline
7. Documentation: Record all parameter choices and justifications for future reference

Common Tire Development Issues & Solutions

These are real-world problems encountered during tire development with technical solutions based on professional experience: