Introduction to Tire Modeling
Tires are critical elements to modeling a vehicle’s interaction with a road, with some tire models better suited to specific simulation domains.
- Vehicle Dynamics
- Simulations run over smooth long-wave roads with low frequency inputs where the vehicle response to steering, brake and throttle input is of interest.
- Vehicle Ride Comfort
- Simulations run over non-smooth roads to assess the occupant comfort.
- Vehicle Durability
- Simulations run over rough roads to obtain the peak loads and/or load histories for use as inputs for predicting the fatigue life of vehicle components.
- Vehicle on Soft-Soil
- Simulations run over soft-soil terrains to capture the vehicle performance and dynamic behavior of the tires on compressible surfaces.
MotionSolve and MotionView
interface with the following tire models:
| Altair Fiala | CDTIRE | FTIRE | MF-Tyre | MF-SWIFT | PM Flex Tire | Altair Soft Soil | |
|---|---|---|---|---|---|---|---|
| Author | Altair | Fraunhofer Institute | Cosin Scientific Software | Siemens | Siemens | Pratt Miller | Aristotle University of Thessaloniki/Altair |
| Model Type | Enhanced Fiala | Flexible Ring | Flexible Ring | Pacejka Magic Formula | Pacejka Magic Formula | Finite Element Model | Enhanced Fiala with the Bekker, Wong and Janosi empirical equations |
| Application(s) | Vehicle Dynamics | Vehicle Dynamics Vehicle Ride Comfort Vehicle Durability |
Vehicle Dynamics Vehicle Ride Comfort Vehicle Durability |
Vehicle Dynamics | Vehicle Dynamics Vehicle Ride Comfort Vehicle Durability |
Vehicle on Soft-Soil | Vehicle on Soft-Soil |
| Licensing | No additional license required | Requires purchase of a license available from Altair or Fraunhofer | Requires purchase of a license available from Cosin | No additional purchase required | Requires purchase of a license available from Siemens | Requires license access to the Altair Partner Alliance program | No additional license required |
| Installation | No additional installation required | License purchased from Altair: No additional installation required License purchased from Fraunhofer: Must install License Server and License |
Must install:
|
No additional installation required | Must install:
|
Must install: | No additional installation required |
| Tire Data | Requires physical tire testing with subsequent parameter fitting | Requires physical tire testing with subsequent parameter fitting | Requires physical tire testing with subsequent parameter fitting | Requires physical tire testing with subsequent parameter fitting | Requires physical tire testing with subsequent parameter fitting | Requires Tire CAD and material properties Requires the soil representation in Altair EDEM |
Requires the tire basic parameters and soft soil characterization Altair Soft Soil parameters (Soft Soil Tire Model) |
| Contact Type | Point Follower or Elliptical Cams | Discritized tire patch with brush type contact | Discritized tire patch contact with bushing elements | Point Follower | Elliptical Cams or Rigid Ring | Discrete Element Method particles to Finite Element mesh | Point Follower or Elliptical Cams |
| Road Types | Altair Roads (Altair Road Modeling) 3D Curved Regular Grid (OpenCRG) |
2D Analytical and Stochastic Road 3D Curved Regular Grid (OpenCRG) 3D Master and Micro Patches |
2D Analytical and Stochastic Road 3D Curved Regular Grid (OpenCRG) 3D Regular Grid Road (RGR) |
Altair Roads (Altair Road Modeling) 3D Curved Regular Grid (OpenCRG) |
Altair Roads (Altair Road Modeling) 3D Curved Regular Grid (OpenCRG) |
EDEM Bulk Material | Regular Grid Roads for soft-soil (Soft Soil Tire Model) 3D Curved Regular Grid (OpenCRG) |
Note: Altair does not provide the physical tire testing and parameters
fitting for the tire data file. However, several third-party tire testing facilities
provides such services, including the tire vendors listed in the table.
How to Select the Tire Model
Altair Motion Solutions provides the interface with low and high frequency range tire
models to enable all types of analysis required for vehicle design and evaluation. The
necessary fidelity of a tire model dependents on the application and the frequency range
that needs to be captured. For example, vehicle dynamics evaluations with low frequency
inputs can be conducted with low fidelity tire models that consists of a single point
contact. On the other hand, ride comfort analysis have to capture high frequency inputs
coming from irregular roads, such as Belgian blocks, and need to rely on higher fidelity
tire models with discretized contact patches. The representation of tire model during the
virtual development processes differs significantly, more requirements and better modeling
of certain effects increase not only the computational effort, but also the amount and
quality of model parameters needed. Most often parameters set for the models must be
measured and identified, and dependent on the model, they may only be valid for a certain
tire pressure and temperature. Below are short descriptions of supported tire types that
will guide you on your next model selection:
- Mathematical and Empirical tire models
- In these models the tire and rim are represented as one single rigid body in which the tire-road forces are dependent on the position and velocity of a single point of interaction in the road surface. The Fiala and Pacejka Magic Formula are based on this approach differing however in how they expressed the nonlinear behavior of the tire forces, for example the degressive characteristic of side forces as a function of lateral slip. The mathematical and empirical tire models are recommended for vehicle dynamics applications where the road surface is assumed to be smooth with low frequencies range of 1-2Hz. The enhanced version of the Fiala model introduces a Cam-Contact method where multiple point contacts allow the tire to capture different road obstacles, such as pothole, bumps, and curbs, being suitable for basic durability analysis.
- Rigid ring tire models
- The rigid ring tire model is described by the MF-SWIFT model, in which the wheel is characterized as a rigid rim and the tire as 6DOF rigid ring connected with elastic elements to the rim representing the tire rubber. With this implementation the fundamental modes of a pneumatic tire could be observed in the model, for example the oscillations of the ring with respect to the rim.
- Flexible ring tire models
- The flexible ring approach, implemented by FTire and CDTire, builds on top of the previous model by defining the tire-road contact surface in a greater detail providing a pressure distribution between the rubber and the road. Consequently, they are suitable for rough roads and often used for studying comfort effects. Since the air in the tire is also modeled, they can be used to simulate temperature effects and the impact of a pressure loss. This class of models are able to cover a frequency range of up to 300 Hz.
- Finite Element tire models
- The Finite-Element tire models are represented as elastic bodies covering in detail the rim, rubber and cleats, belt fabric and steel threads, and the air in the tire. Such models are very complex for vehicle simulations, however they are useful for the development of the tire itself.
- Soft-soil capable tire models
- This class of tire models do not assume the road as rigid but models the interaction of the tire with soft-soil terrain. The terrain can be represented either by empirical formulations or discretized methods, such as Discrete Element Method (DEM). Empirical formulations have a lower computational cost being suitable for quick studies and vehicle optimization. The soft-soil representation using DEM considers the characterization of terrain’s complexity using granular materials which provides more realistic results by including influence of tire tread, better representation of the bulldozing effect, and better representation of soil morphology, with the price of a larger computational cost.