Tire Basics

Learning Adams/Tire

Adams/TireUse and Understanding of Adams/Tire

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Use and Understanding of Adams/Tire

How to Use Adams/TireThe Tire Basic help section provides overview material for using Adams/Tire to add tires to a mechanical system model. It assumes that you know how to run Adams/Car, Adams/Solver, Adams/View, or Adams/Chassis. It also assumes that you have a moderate level of tire-modeling proficiency

You use Adams/Tire to simulate tires according to your analysis requirements. You can create your own tire models or you can use the tire models that come with Adams/Tire. The following describes how you use Adams/Tire. For more about how you can create your own tire models, see User-Written Tire/Road Models.

3Learning Adams/TireUse and Understanding of Adams/Tire

Adams/Tire Steps

To use Adams/Tire:

1. Define tires. How you define tires depends on the product you are using (Adams/Chassis, Adams/Car, or Adams/Solver). For more information on defining tires, see Defining Tires.

Regardless of the product you use, the product creates an Adams dataset (.adm), which contains the necessary statements that represent the tires in your Adams model, as well as other elements of the vehicle, such as the wheel, suspension, and landing gear strut. The primary statement for each tire is a GFORCE that applies the tire force to the wheel in your suspension.


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2. Reference an existing tire property file from:

• Adams/Tire (/install_dir/solver/atire)

• Tire manufacturers or testing companies.

• Files that you create. For example, you can create your own tire property file for simple kinds of tire models, such as the Fiala model.

You can find examples of tire property files for all tire models in the Adams installation directory at:

install_dir/solver/atire

where install_dir/ is the path to the installation directory for Adams/Tire.

3. Reference an existing road property file.

You can find an example road property file for a flat road in the Adams installation directory:

install_dir/solver/atire/mdi_2d_flat.rdf

where install_dir/ is the path to the installation directory for Adams/Tire.

4. Run a simulation of your model.

You can run a simulation using Adams/Car’s version of Adams/Solver (you do not need an Adams/Car license) or you can create an Adams/Solver user library and then run your simulation using this library and Adams/Solver. For more information, see Performing Simulations.

5. View the results of the simulation in a postprocessor, such as Adams/PostProcessor.

Understanding Adams/Tire ProcessesWhen you add tires to your Adams model, three processes occur:

• Adams/Solver invokes Adams/Tire.

• Adams/Tire determines the tire and road model to use.

• Adams/Tire performs any calculations the tire model requires.

5Learning Adams/TireUse and Understanding of Adams/Tire

Flow of Information in Adams/Tire

Invoking Adams/Tire

• When you perform an analysis, Adams/Solver investigates your .adm file to find elements that represent a tire. For example, it looks for a GFORCE with the necessary parameters to define the force to the wheel in your suspension. When it finds these parameters, it invokes Adams/Tire.

• Adams/Solver obtains the names of the tire property file (.tir) and road property file (.rdf) from the STRING statements in the .adm file.

Determining Tire and Road Model to Use

Inside Adams/Tire, the Tire Object Manager examines the tire property file to determine the tire model (for example, Fiala or Pacejka ‘89) to use and examines the road property file to determine the road model (for example, 2D or 3D) to use.

Performing Calculations

• The Tire Object Manager calls the selected tire model to calculate the tire forces and moments.

• The tire model reads the tire property file to obtain data for calculating the tire forces and moments. It then calls the road model to evaluate where the road is in relation to the tire.

• The road model reads the road property file to obtain data about the road.


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• The tire model returns the forces and moments to Adams/Solver.

• Adams/Solver applies the forces and moments to the wheel part.

7Learning Adams/TireDefining Tires

Defining Tires If you use Adams/Car or Adams/Chassis, typically the models you work with will already include tires (for example, the statements necessary to invoke Adams/Tire). Therefore, you do not need to add tires to your model. If you work with Adams/View, however, you will need to define the tires, and for Adams/Solver, add statements to your Adams model using Adams/View or a text editor. Learn how to work with:

• Adams/View

• Adams/Car

• Adams/Chassis

• Adams/Solver

• Defining Wheel Inertia

Defining Tires in Adams/CarAdams/Car includes a wheel-tire subsystem and template that you can use in any full-vehicle assembly. The wheel-tire subsystem includes all the elements necessary to start Adams/Tire. You can modify the wheel inertia and change the property files.

To modify tires in a subsystem:

1. Select the wheel/tire on the screen, right-click, and then select Modify.

Adams/TireDefining Tires

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The Modify Wheel dialog box appears with options that allow you to modify the tire property file and wheel inertia.

2. Change the values as desired, and then select OK. Learn about entering values in Create/Modify Wheel dialog box.

Defining Tires in Adams/ChassisAdams/Chassis includes wheels and tires in all body-tire subsystems.

To modify tires in Adams/Chassis:

1. In Build mode, in the treeview, select the wheel subsystem.

2. In the property editor, select the Tires tab.

The property editor displays options for changing the wheels and tires as shown below.

Note: You can also use the Display Tire Property File tool to display the tire property file in an Information window. You cannot, however, specify or display the road property file from this dialog box. In Adams/Car, you specify the road property file when you submit a full-vehicle analysis


Tires Tab in Adams/Chassis

3. Edit the wheels and tires, such as edit the tire property files and change the scaling coefficients. Learn About Tire Subsystems in Adams/Chassis.

Defining Tires in Adams/SolverIf you use Adams/Solver, you must add a set of statements to your Adams model for each tire as described in the table, Statements Needed for Adding Tires to Your Model. Once you have added these statements to your model, you change the tire or road property file by entering new file names in the STRING statements holding the file names. You can do this in your Adams/Solver dataset files (.adm) or from an Adams/Solver command file (.acf) using a STRING command. In an .acf file, the STRING command must appear before any simulation commands. For example:

test_rig.admmytestSTRING/99, STRING=/usr/mdi/solver/atire/mdi_fiala01.tirSIMULATE/STATICSIMULATE/DYNAMIC, DURATION=1.0,STEPS=50STOP

Learn more:

• Statements Needed for Defining Tires

• Example Dataset

Statements Needed for Defining Tires

For each tire you want to add to your model, you must create a set of statements in your model. This can be done using the dialog box in Adams/View (see Defining Tires in Adams/View) or manually using a text


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editor. For a car with four tires, you need four sets of statements. The table below describes the sets of statements. The table, MARKER Locations and Orientations, describes how to locate and orient the three MARKERs.

Statements Needed for Adding Tires to Your Model

Statement types: Purpose in dataset:

MARKER (3) • Wheel center marker - Identify the wheel part, the wheel center location and orientation, and the location for applying tire force movements. Use as the GFORCE I marker.

• Road floating marker - Identify the road part to the GFORCE for applying reaction forces. Use as the GFORCE JFLOAT marker.

• Road reference marker - Identify the origin and orientation of the road. Use as the GFORCE RM marker.

You must locate and orient the MARKER statements as described in MARKER Locations and Orientations.

GFORCE (1) Apply the tire force and moments to the wheel part.

DIFF (2) Integrate internal tire states for lag effects.

REQUEST (Up to 11) Output tire kinematics and forces (longitudinal slip, slip angle, camber angle, contact patch forces, and moments). For more information, see Performing Simulations and Viewing Results.

STRING (5) Identify the tire property file, road property file, and other miscellaneous information.

Note: The STRING for "contact type" is required for Adams to correctly create the STI tire, but it does not change the contact method, which is based entirely on the road model.

ARRAY (1) Holds the IDs of the GFORCE, DIFF, and STRING statements.


MARKER Locations and Orientations

Example Dataset

This section gives you an example dataset fragment that includes a complete set of statements for a single tire. The example is based on the following assumptions:

• PART/21 is the wheel and PART/99 is ground.

• The orientations assume that the ground part's x-axis points towards the rear of the vehicle, the y-axis points towards the right side of the vehicle, and the z-axis points upward.

! adams_view_name='wheel_center_marker'MARKER/1, PART=21, QP = 0,0,0, REU = 180D, 0D, 0D !

adams_view_name='road_floating_marker'MARKER/2

Marker statements required in dataset: Location and orientation:

Wheel center marker Because the tire applies forces to the wheel center marker, you must define the wheel center so that it belongs to the wheel part and is located at the wheel center. You orient the wheel center as follows:

• x-axis lies in the wheel plane and points in the forward direction of the wheel.

• y-axis lies along the wheel's spin axis and points towards the left side of the vehicle.

• z-axis lies in the wheel plane and points upward.

Road floating marker The tire applies the reaction forces to the road floating marker. The road floating marker must belong to the road part, usually ground, and must be defined as FLOATING. Because the marker floats, you do not enter a location or orientation.

Road reference marker The road reference marker gives the location and orientation of the road. You define the road reference marker so that it belongs to the road part, usually ground. In addition, the road reference marker’s z-axis must be directed upward, meaning the z-axis is parallel to, but points in the opposite direction of, the gravity vector.

Locations of the points on the road contained in the road property file are given relative to this marker. Generally, the road reference marker should be located on the road surface and below the wheel center by approximately the static loaded radius of the tire.


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, PART = 99, FLOATING !

adams_view_name='road_reference_marker'MARKER/3, PART = 99 ! adams_view_name='tire_forces'GFORCE/1, I = 1, JFLOAT = 2, RM = 3, FUNCTION = USER(900,1,100)/, ROUTINE=abgTire::gfo900 !

adams_view_name='tire_force_dif1'DIFF/2, IC = 0, FUNCTION = USER(900,1,100)/, ROUTINE=abgTire::dif900 !

adams_view_name='tire_force_dif2'DIFF/3, IC = 0, FUNCTION = USER(900,1,100)/, ROUTINE=abgTire::dif900 !Map for GFORCE/DIFF USER Functions:!-----------------------------------!par(1): dispatcher branch for tire request (always 900).!par(2): tire GFORCE statement id.!par(3): tire ARRAY statement id. !

adams_view_name='tire_input_array'ARRAY/100,IC,SIZE=9,NUM= 2, 3, 1, 99, 100, 101, 102, 103, 0!array[ 1] : 1st DIFF statement id!array[ 2] : 2nd DIFF statement id!array[ 3] : side flag (0 left, 1 right)!array[ 4] : tire_minor_role STRING id!array[ 5] : tire_property_file STRING id!array[ 6] : simulation_type STRING id!array[ 7] : road_property_file STRING id!array[ 8] : road_contact_type STRING id!array[ 9] : RIGID_WHEEL Radius (SUSPENSION analysis tire only) !

adams_view_name='tire_rolling_states'REQUEST/1,, FUNCTION = USER(902,1,1) !

adams_view_name='tire_kinematic_states_ISO'REQUEST/2,, FUNCTION = USER(902,2,1)!


adams_view_name='tire_forces_contact_patch_ISO'REQUEST/3,, FUNCTION = USER(902,3,1) !Map for REQUEST USER Functions:!-------------------------------!par(1) = branch for tire request (always 902).!par(2) = reqtyp = {1,2,3,4,5,6,7.8.9.10,11}!par(3) = tire GFORCE statement id.!String Statements Description of use:!------------------!! adams_view_name='tire_minor_role'! Used by Adams/Car to determine minor role (for example, FRONT or REAR).STRING/99,S=front

! adams_view_name='tire_property_file'! Used by TYRxxx routines. Name of tire property file including

full path that! contains tire data or 'RIGID_WHEEL' for use in a suspension

analysis.STRING/100,S=mdi_tire01.tir

!adams_view_name='simulation_type'

! Used by Adams/Car to determine analysis to be performed one of'VEHICLE_HANDLING_DYNAMIC'or 'SUSPENSION'STRING/101,S=VEHICLE_HANDLING_DYNAMIC

!adams_view_name='road_property_file'

! Used by ARCxxx routines. Name of road property file including full path that

! contains road data or 'BEDPLATE' for a flat, rigid road used! with suspension analysis.

STRING/102,S=example_2d_flat.rdf ! adams_view_name='road_contact_type'! handling/durability !STRING/103, STRING =handling

Defining Tires in Adams/ViewAdams/View provides a dialog box that introduces a tire-wheel assembly in your model. You can also use the dialog box to create a road.


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• Creating a Tire-Wheel Assembly

• Creating a Road

Creating a Tire-Wheel Assembly

To create a tire-wheel assembly in Adams/View:

1. Do one of the following:

• From the Create Forces Palette and Tool Stack, select the Tire tool.

• From the Build menu, point to Forces, and then select Special Force: Tire.


The Create Wheel and Tire dialog box appears with options that allow you to introduce the wheel inertia, tire property file, and side of the vehicle.

2. Enter the values as desired to define the tire, and then select OK. Learn more with Create/Modify Wheel and Tire dialog box help.

Creating a Road

If your model includes tires, you must specify a road because each tire must reference a road. The road determines the surface friction, bumps, and other inputs to tires.


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To create the road:

1. Display the Create Wheel and Tire dialog box as explained in step 1 above.

2. Right-click the Road text box, point to vpg_road, and then select Create.

The Create Road dialog box appears.

3. Enter the values as desired, and then select OK. Learn more about the values with Create/Modify Road dialog box help..

Defining Wheel InertiaThe input values for the wheel part inertia are different depending on the tire model you are using. There are differences among the tire models in the Adams/Tire Handling Module, including Adams/Tire Motorcycle Tire, and FTire, as explained in the next sections:

• Adams/Tire Handling and Motorcycle Modules

• Adams/Tire FTire

Note: This dialog box generates a tire interface based on the general-state equation subroutine. A more simple interface is shown in Defining Tires Using Adams/Solver.


Adams/Tire Handling and Motorcycle Modules

For tire models in the Adams/Tire Handling Module and the Pacejka Motorcycle Tire model, the inertia given for the wheel part must be equal to the total inertia of the tire and the rim.

Adams/Tire FTire

In FTire, a part of the tire can move with respect to the rim. Therefore, the tire mass and moments of inertia have to be split into two parts: a part that is moving with the rim (wheel part) and a part that is moving with the tire itself. This subdivision is performed during preprocessing of the tire property (.tir) file. When a simulation begins with FTire, the following lines appear in the .msg file:

CTI: add the following mass properties to the rim in your MBS modelCTI: (the 'rim-fixed' tire parts which are not accounted for in FTire):

The inertia data printed after this message has to be added to the rim inertia and used to defined the wheel part inertia. Modification of the wheel part is not done automatically.

Adams/TireSimulations and Results

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Simulations and Results

Performing SimulationsOnce you have incorporated the required statements for modeling a tire into your dataset, you can submit the dataset for simulation. If you have Adams/Car installed, you can submit your dataset to the Adams/Car version of Adams/Solver, or you can create an Adams/Solver user library and then run your simulation using this library and standard Adams/Solver.

To submit your dataset to the Adams/Car version of Adams/Solver, do one of the following:

In a command window, submit your dataset for simulation using the following commands:

• For UNIX, enter:

mdadams2010 -c acar ru-solver• For Windows, enter:

mdadams2010 acar ru-solver• On Windows, from the Start menu, point to Programs, point to MSC.Software, point to MD

Adams 2010, point to ACar, and then select Adams - Car (solver).

• On UNIX, from the Adams Toolbar, right-click the Adams/Car tool, and then select Adams/Car - Solver.

To create an Adams/Solver user library:

1. Copy the file install_dir/solver/atire/atire.f to your local directory.

2. Using atire.f, create a user Adams/Solver library:

a. In a command window, enter the command, where mysol.dll is the name of the library:

• For UNIX, enter:

mdadams2010 -c cr-user n atire.f -n mysol.dll exit

• For Windows, enter:

mdadams2010 cr-user n atire.f -n mysol.dll exit

b. On Windows, from the Start button, point to Programs, point to MSC.Software, point to MD Adams 2010, point to ASolver, and then select Create Custom Solver. Follow the menu selections to create a private or site library. For more information see Creating User Libraries.

Note: You can also set the Adams/Car tool on the Adams Toolbar to automatically run Adams/Car with Adams/Solver. For more on the Adams Toolbar see Configuring Adams.

../adams_configure/master.htm

19Learning Adams/TireSimulations and Results

c. On UNIX, from the Adams Toolbar, right-click the Adams/Solver tool, point to New, and then select Adams/Solver User Library. Enter the parameters to define how to create the library. For more information see Creating User Libraries in Running and Configuring Adams.

To submit your dataset to Adams/Solver using your Adams/Solver user library:

• In a command window, submit your dataset for simulation using the following command (assuming your library was mysol):

a. For UNIX, enter:

mdadams2010 -c ru-user i mysol

b. For Windows, enter:

mdadams2010 -c ru-user i mysol

• On Windows, from the Start menu, point to Programs, point to MSC.Software, point to MD Adams 2010, point to ASolver, and then select Run Custom Solver. Enter the name of the library you want to run.

• On UNIX, from the Adams Toolbar, right-click the Adams/Solver tool, point to Select Library, and then select a library, such as mysol.

Outputting ResultsIf you combine requests with a USER function, you can output tire results to the request (.req) and results (.res) files. The form of the request statement is:

REQUEST/id, FUNCTION = USER(902, REQTYP, TIR_ID)/, ROUTINE = abgTire::req902

where:

• 902 - Branch flag for tire request subroutine.

• REQTYP - Integer code fixing the information output to the request file. Valid values are {1,2,3,4,5,6,7,8,9,10,11}. The output for each value of REQTYP is described in the table, Tire Outputs.

• TIR_ID - Tire GFORCE statement ID.

For information on the axis systems and sign conventions for these outputs, see About Axis Systems and Sign Conventions.

Note: On Windows, you can now enter the FORTRAN file directly without first compiling it.

Note: You can also set the AdamsAdams/Solver tool on the Adams Toolbar to automatically run with your user library. For more on the Adams Toolbar, see Running and Configuring Adams.


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Example of a request in a dataset.

Tire Outputs

Output:REQTYP Request: Component definitions:

Tire rolling states 1 x = rolling radius

y = (rad/sec)

z = free (rad/sec)

is the actual angular velocity about the wheel's axis, while free is the velocity of the wheel's axle center divided by

the radius to the instantaneous center of rotation. The difference between the two is, therefore, a measure of the slip when the vehicle is accelerating or decelerating.

Tire kinematic properties in TYDEX-W axis (ISO) system.

2 x = longitudinal slip (%)

y = lateral slip angle (degrees)

z = inclination angle (degrees)

Tire contact patch forces in TYDEX-W axis (ISO) system

3 x = longitudinal force (model units)

y = lateral force (model units)

z = vertical force (model units)

r1 = residual overturning moment (model units)

r2 = rolling resistance moment (model units)

r3 = aligning moment (model units)

Tire contact patch forces in SAE axis system




r1 = residual overturning moment (model units)



21Learning Adams/TireSimulations and Results

Tire kinematic properties in SAE axis system

5 x = longitudinal slip (%)

y = lateral slip angle (radians)

z = inclination angle (radians)

Forces at hub, in TYDEX-C axis system




r1 = overturning moment (model units)



Miscellaneous tire states #1

7 x = longitudinal lag (du/dt)*

y = lateral lag (du/dt)*

z = longitudinal coefficient of friction

r1 = lateral coefficient of friction

r2 = FXMAX = DX + SVX (peak from Pacejka + vertical shift)

r3 = FYMAX = DY + SVY (peak from Pacejka + vertical shift)


8 x = pneumatic trail *

y = residual aligning moment at contact patch in ISO

z = FX moment arm*

r1= longitudinal relaxation length*

r2 = lateral relaxation length*

r3 = gyroscopic moment*


9 x = inclination angle induced side force*

y = surface friction



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14 x = distance traveled*

y = effective plane height*

z = effective plane angle*

r1= effective plane curvature*

r2 = contact length*

Contact patch locations (the contact patch location along the plane of the tire in the GFORCE reference marker’s coordinate system.)

10 x = road contact point X location

y = road contact point Y location

z = road contact point Z location

r1 = tire radial penetration into the road surface

r2 = tire radial penetration velocity into the road surface

Hub and wheel velocities 11 x = hub longitudinal velocity in wheel carrier (TYDEX-C) axis system

y = tire longitudinal velocity at the contact patch in the contact patch axis system

z = tire lateral velocity at the contact patch in the contact patch axis system


23Learning Adams/TireAbout Axis Systems and Sign Conventions

About Axis Systems and Sign ConventionsThe following sections describe the tire axis systems and the sign conventions for tire kinematic and force outputs.

• Tire Axis Systems

• About Tire Kinematic and Force Outputs

• Sign Conventions for Tire Outputs

Tire Axis SystemsThe following sections describe the ISO coordinate systems to which Adams/Tire conforms. The ISO coordinates are shown as follows:

• ISO-C (TYDEX C) Axis System

• ISO-W (TYDEX W) Contact-Patch Axis System

• Road Reference Marker Axis System

ISO-C (TYDEX C) Axis System

The TYDEX STI specifies the use of the ISO-C axis system for calculating translational and rotational velocities, and for outputting the force and torque at the tire hub.

The properties of the ISO-C axis system are:

• The origin of the ISO-C axis system lies at the wheel center.

• The + x-axis is parallel to the road and lies in the wheel plane.

• The + y-axis is normal to the wheel plane and, therefore, parallel to the wheel’s spin axis.

• The + z-axis lies in the wheel plane and is perpendicular to x and y (such as z = x x y).

Adams/TireAbout Axis Systems and Sign Conventions

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TYDEX-C Axis System Used in Adams/Tire

ISO-W (TYDEX W) Contact-Patch Axis System

The properties of the ISO-W (TYDEX W) axis system are:

• The origin of the ISO-W contact-patch system lies in the local road plane at the tire contact point.

• The + x-axis lies in the local road plane along the intersection of the wheel plane and the local road plane.

• The + z-axis is perpendicular (normal) to the local road plane and points upward.

• The + y-axis lies in the local road plane and is perpendicular to the + x-axis and + z-axis (such as y = z x x).


TYDEX W-Axis System Used in Adams/Tire

Road Reference Marker Axis System

The road reference marker axis system is the underlying coordinate system that Adams/Tire uses internally. For example, the tire translational displacement and local road normal for a three-dimensional road are expressed in the axis system of the road reference marker.

The properties of the reference marker axis system are:

• The GFORCE reference marker defines the axis system.

• The + z-axis points upward.

About Tire Kinematic and Force OutputsAdams/Tire calculates the kinematic quantities of slip angle, inclination angle, and longitudinal slip. These are based on the location, orientation, and velocity of the tire relative to the road. In turn, Adams/Tire calculates the forces and moments of the tire using the tire kinematics as inputs to the tire mode you select.

Sign Conventions for Tire OutputsThe table below, Conventions for Naming Variables, and the figure, ISO Coordinate System, show the sign conventions for tire kinematic and force outputs.

Adams/TireAbout Axis Systems and Sign Conventions

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Conventions for Naming Variables

Variable name and abbreviation: Description:

Slip angle The angle formed between the direction of travel (velocity) of the center of the tire contact patch and the ISO-W: x-axis. If the wheel-travel direction has a component in the ISO-W: +y direction, a is positive. This produces a negative lateral force (Fy). Note that the steer angle, or the vehicle attitude angle, plays no part in defining the slip angle.

Inclination angle

The angle formed between the ISO-W: x-z plane and the wheel plane. If the wheel plane has a component lying in the direction of ISO-W, the inclination angle is positive.

Longitudinal slip (Wactual-

Wfree)/Wfree

The ratio of the longitudinal-slip velocity of the contact patch to the longitudinal velocity of the wheel. The longitudinal slip is positive during acceleration of a moving tire and negative during braking. Longitudinal slip is limited to the range -1 to +1.

Longitudinal force at contact patch

Fx The x-component of the force exerted by the road or tire.

Lateral force at contact patch

Fy The y-component of the force exerted by the road or tire. Lateral force may be produced by one or any combination of the following: slip angle, inclination angle, conicity, or plysteer.

Normal force at contact patch

Fz The z-component of the force exerted by the road or tire. The direction of this force is up.

Overturning moment at contact patch

Mx The moment of the forces at the contact patch acting on the tire by the road with respect to the ISO-W: x-axis.

Rolling resistance moment

My The moment of the forces at the contact patch acting on the tire by the road with respect to the y-axis.

Aligning moment

Mz The moment of the forces at the contact patch acting on the tire by the road with respect to the z-axis.

Spin axis Spin Axis The axis about which the wheel rotates. Perpendicular to the wheel plane, not necessarily about the ISO-C: y-axis (only if inclination angle is zero).

The central plane of the tire and wheel

Wheel plane The wheel plane is normal to the wheel spin axis.


ISO Coordinate System

Wheel heading along road

ISO W:X This is not the same as the direction in which the wheel is traveling. If the tire reverses its direction, the axis system flips 180 degrees about the z'-axis.

Direction to the left along the road

ISO W:Y The direction to the left along ground as viewed from behind a forward rolling tire. Expressed as right-hand orthogonal to the definitions of x' and z' (such as y = Z x X).

Z-coordinate ISO W:Z Perpendicular to the road in the neighborhood of the origin of the tire axis system in a positive (downward) direction. (If the road is flat and in the x-y plane, this is negative global z.)

Variable name and abbreviation: Description:

Adams/TireUnits Supported in Tire Property Files

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Units Supported in Tire Property Files

Tire Property FileA tire property file specifies what kind of tire model Adams/Tire should use. The tire property file contains the data that defines the tire's force and moment characteristics. The amount and kind of data varies according to the type of tire model you use. A STRING statement in the Adams dataset holds the name of the tire property file.

Road Property FileA road property file contains data that defines the road surface and coefficient of friction. The road can be flat or have a three-dimensional surface represented as triangular patches. A STRING statement in the Adams dataset provides the name of the road property file.

UnitsThe following tables list the valid choices for the parameters in the UNITS section of a tire property file. Note the following:

• You must enter the choices in single quotes, such as 'METER' for meter.

• The choices are case-insensitive. Therefore, 'MeTeR,' 'meter,' and 'METER' are all equivalent.

• The strings are limited to 12 characters and the minimum abbreviation is shown in the tables. So, for example, 'millisecond' is valid and is interpreted as 'MILLI.’

Length Units

Note: For some tire models, the [UNITS] section is not applied consistently to all tire parameters. The exceptions are the Magic Formula coefficients for the Pacejka ‘89 and ‘94 model and spline data for the 521 model, where the unit conversion factors have to be defined explicitly.

The unit: Can be abbreviated:

Kilometers 'KM'

Meters 'METER'

Centimeters 'CM'

Millimeters 'MM'

Miles 'MILE'

Feet 'FOOT'

Inches 'IN'

29Learning Adams/TireUnits Supported in Tire Property Files

Time Units

Angle Units

Mass Units

Force Units


Milliseconds 'MILLI'

Seconds 'SEC'

Minutes 'MIN'

Hours 'HOUR'

The units: Can be abbreviated:

Degrees 'DEG'

Radians 'RAD'


Kilograms 'KG'

Grams 'GRAM'

Pound-Mass 'POUND_MASS'

Kilo-Pound-Mass 'KPOUND_MASS'

Slugs 'SLUG'

Ounce-mass OUNCE_MASS'


Kilograms-Force ‘KG_FORCE'

Newtons 'NEWTON' or 'N'

Kilo-Newtons 'KNEWTON' or 'KN'

Pounds-force 'POUND_FORCE'

Kilo-Pound-Force 'KPOUND_FORCE'

Dynes (gram-cm/sec2) ‘DYNE'

Ounce-force 'OUNCE_FORCE'

Adams/TirePAC2002 Tire Data and Fitting Tool (TDFT)

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PAC2002 Tire Data and Fitting Tool (TDFT)The PAC2002 Tire Data and Fitting Tool (TDFT) calculates PAC2002 tire model parameters out of tire measurement data or virtual test data for steady-state pure and combined slip conditions including the possibility to visualize/modify tire characteristics.

Tires added to the Tire Data Tool can be saved to a tire database file. This file stores all data used for the tire parameter identification and tire characteristic visualization. Each tire in the tire database can be exported to a PAC2002 tire property file that can be used with Adams/Tire.

In addition:

• The Tire Data and Fitting Tool offers you the possibility to switch to the PAC2002 tire model by using virtual tire test data from another tire model. Virtual test data may be generated using the Adams/Car Tire Testrig.

• The Tire Data and Fitting Tool offers the user the possibility to modify the tire characteristics and to create a new tire property file.

• Same PAC2002 tire model is used for both tire parameter identification and Adams simulation.

A scheme of the Tire Data and Fitting Tool or Tyre Data and Fitting Tool is shown below.

31Learning Adams/TirePAC2002 Tire Data and Fitting Tool (TDFT)

Following Sections explain how to:

1. Create a measurement input data file for the tire parameter identification process:

2. Perform PAC2002 tire parameter identification:

3. Verification of calculated tire parameters versus measurement data:

4. Plotting tire characteristics:

1. Create a measurement input data file for the tire parameter identification process:

This Section explains how to create a measurement/virtual data input file. The TDFT uses the following 3 keys to identify pure and combined slip measurement data in the measurement data file:

1. [FX_PURE] - Pure longitudinal slip (kappa) versus longitudinal force (Fx) data.

2. [FYMZ_PURE] - Pure lateral slip (alpha) versus lateral force (Fy) and/or self-aligning torque (Mz) data.

3. [FXYMZ_COMBINED] - Combined longitudinal and lateral slip versus longitudinal, lateral and self-aligning torque data.

An example measurement data file containing measurement data for both pure and combined slip conditions 'fm_data_example_tdft.txt' can be found in following directory <adams_install>/acar/shared_car_database.cdb/tires.tbl.

Following Figures show some typical tire characteristics expressed in ISO coordinates and also show the sign convention used in the TDFT for longitudinal, lateral force and self-aligning torque. The curves are created using the example measurement data file ‘fm_data_example_tdft.txt’.

Note: It is important that measurement data is expressed in ISO coordinates. (See also Axis Systems and Slip Definitions in PAC2002 Tire Model.).


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Figure 1 Pure slip condition: longitudinal slip (kappa) versus longitudinal force (Fx).

Figure 2 Pure slip condition: lateral slip (alpha) versus lateral force (Fy).


Figure 3 Pure slip condition: lateral slip (alpha) versus self-aligning torque (Mz).

Each measurement/virtual input data file must consist of 7 columns:

1. Lateral Slip (alpha)

2. Longitudinal Slip (kappa)

3. Inclination Angle (camber)

4. Vertical Load (fz)

5. Longitudinal Force (fx)

6. Lateral Force (fy)

7. Self-Aligning Torque (mz)

which must be placed in Sections starting with [FX_PURE] for pure longitudinal slip data, [FYMZ_PURE] for pure lateral slip data and [FXYMZ_COMBINED] for combined slip data.

See also fm_data_example_tdft.txt for an example:

[FX_PURE]

{ alpha kappa camber fz fx fy mz }

0.0000000e+000 -1.0000000e+000 0.0000000e+000 2.0000000e+003 -1.8423142e+003 0.0000000e+000 0.0000000e+000

0.0000000e+000 -9.9900000e-001 0.0000000e+000 2.0000000e+003 -1.8423986e+003 0.0000000e+000 0.0000000e+0000.0000000e+000 -9.9800000e-001 0.0000000e+000 2.0000000e+003 -1.8424832e+003 0.0000000e+000 0.0000000e+000

…

The order of the measurement/virtual data signals must be specified. It is possible to do this for each measurement/virtual data Section by adding Section [FX_PURE_SIGNALS],


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[FYMZ_PURE_SIGNALS] or [FXYMZ_COMBINED_SIGNALS] before each measurement/virtual data Section, for example.

$---------------------------------------------------------------units[FX_PURE_SIGNALS]ALPHA = 1KAPPA = 2CAMBER = 3FZ = 4FX = 5FY = 6MZ = 7$----------------------------------------------------------------fx_pure[FX_PURE]{ alpha kappa camber fz fx fy mz }

0.0000000e+000 -1.0000000e+000 0.0000000e+000 2.0000000e+003 -1.8423142e+003 0.0000000e+000 0.0000000e+000

0.0000000e+000 -9.9900000e-001 0.0000000e+000 2.0000000e+003 -1.8423986e+003 0.0000000e+000 0.0000000e+000

0.0000000e+000 -9.9800000e-001 0.0000000e+000 2.0000000e+003 -1.8424832e+003 0.0000000e+000 0.0000000e+000

It is also possible to define a Section [SIGNALS] that specifies the order of the measurement data/virtual data signals for all measurement/virtual data Sections, for example.

$----------------------------------------------------------------units[SIGNALS]ALPHA = 1KAPPA = 2CAMBER = 3FZ = 4FX = 5FY = 6MZ = 7

If the Section [SIGNALS] is present, the Sections [FX_PURE_SIGNALS], [FYMZ_PURE_SIGNALS] and [FXYMZ_COMBINED_SIGNALS] will be ignored.

2. Perform PAC2002 tire parameter identification:

This Section explains how to add measurement data to a tire and how to perform the PAC2002 tire parameter identification by means of an example.

To start the PAC2002 Tire Data and Fitting Tool in Adams/Car:

1. From the Simulate menu, point to Component Analysis, and then select PAC2002 Tire Data and Fitting Tool…

Note: It is not necessary to store all data in a single file. Multiple measurement data files can be used as input to the TDFT.


Figure 4 PAC2002 Tire Data and Fitting Tool (TDFT)

2. Create an empty tire by selecting File -> Create New Tire Property (default values) from the menu bar (see red arrow in Figure 4). Default values are specified in <adams_install>/acar/shared_car_database.cdb/tires.tbl/tdft_template.tir

It is also possible to use an existing PAC2002 tire property file as a base for the tire identification process to add new and/or overwrite existing tire parameters. To import a tire property file, select File -> Open Tire Property and Add to Tire Database… from the menu bar.

Note: You set the environment variable TDFT_TEMPLATE_PATH to overwrite the default location of tdft_template.tir (which is the Adams/Car Shared Tires Database).


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Figure 5 PAC2002 TDFT; Create an empty tire

3. It is important to verify that following parameters are specified because these parameters are used in the PAC2002 tire model to make the tire parameters dimensionless:

Under entry Vertical in the left column (see red arrow in Figure 5): FNOMIN ($Nominal wheel load)

Under entry Dimension in the left column (see red arrow in Figure 5): UNLOADED RADIUS ($Free tire radius)


4. Select the tire by clicking on the top of the tire data column (1). Click on the Tire Fit button (see red arrow in Figure 6) in the PAC2002 Tire Data and Fitting Tool or select Run -> Tire Fit from the menu bar to start the Tire Fit Tool.

Figure 6 PAC2002 TDFT; Starting PAC2002 Tire Fit


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Figure 7 PAC2002 TDFT; PAC2002 Tire Fit

5. Figure 7 shows the Tire Fitting Tool. Clicking on the available entries to the left, start values and lower/upper boundaries for each parameter of the identification process are shown and may be modified, see Figure 8.

Default values are specified in <adams_install>/acar/shared_car_database.cdb/tires.tbl/tdft_template.tir.

Figure 8 PAC2002 TDFT; start values and lower/upper bounderies


6. Select Add Measurements (see red arrow in Figure 9) and add the measurement data files to the Measurement File(s) Table. See <adams_install>/acar/shared_car_database.cdb/tires.tbl/fm_data_example_tdft.txt for an example measurement data file containing steady-state force and moment measurement data for pure and combined slip conditions.

Figure 9 PAC2002 TDFT; start values and lower/upper bounderies

7. If measurement data for both pure and combined slip conditions is available, select Characteristic = All under Fitting Parameters and click on Start. Now, all tire characteristics will be fitted in following order:

a. Fx_pure

b. Fy_pure

c. Mz_pure

d. Fx_combined

e. Fy_combined

f. Mz_combined

It is also possible to fit each tire characteristic separately if not all measurement data is available. Select the desired Characteristic under Fitting Parameters.

Force/Moment expressions for the combined slip conditions are based on the expressions for the pure slip conditions. Therefore, the force and/or moment for pure slip conditions need to be fitted first before fitting the combined slip conditions.


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8. The next step will be to verify the calculated tire parameters versus measurement data and to generate a tire property file which will be discussed in next Section.

3. Verification of calculated tire parameters versus measurement data:

In this Section you'll learn how to verify the resulting tire model parameters by graphically comparing measurement/virtual test data to the PAC2002 model.

Note: • Fy (and Fx in case of combined slip conditions) needs to be fitted before Mz because the Mz formulation depends on the lateral force Fy.

• The .log files in the working directory show the result of the tire identification process. The fit error (=100*sqrt(((measurement data)^2 - (model data)^2)/(measurement_data)^2) ) and variations of each tire parameter are shown.

• The X[0], X[1], X[2], etc are the tire parameters that are identified and could be seen in the log file generated in your working directory. For instance, if you perform a tire fit for the FX_PURE coefficients then following parameters are being identified (see also pac2002_205_55R16_tdft.tir, Section Longitudinal_Coefficients):

PCX1 = 1.3178 $Shape factor Cfx for longitudinal forcePDX1 = 1.0455 $Longitudinal friction Mux at FznomPDX2 = 0.063954 $Variation of friction Mux with loadPDX3 = 0 $Variation of friction Mux with camberPEX1 = 0.15798 $Longitudinal curvature Efx at Fznom PEX2 = 0.41141 $Variation of curvature Efx with load PEX3 = 0.1487 $Variation of curvature Efx with load squared PEX4 = 3.0004 $Factor in curvature Efx while driving PKX1 = 23.181 $Longitudinal slip stiffness Kfx/Fz at Fznom PKX2 = -0.037391 $Variation of slip stiffness Kfx/Fz with load PKX3 = 0.80348 $Exponent in slip stiffness Kfx/Fz with load PHX1 = -0.00058264 $Horizontal shift Shx at Fznom PHX2 = -0.0037992 $Variation of shift Shx with load PVX1 = 0.045118 $Vertical shift Svx/Fz at Fznom PVX2 = 0.058244 $Variation of shift Svx/Fz with load PTX1 = 0.85683 $Relaxation length SigKap0/Fz at Fznom PTX2 = 0.00011176 $Variation of SigKap0/Fz with load PTX3 = -1.3131 $Variation of SigKap0/Fz with exponent of load PTX4 = 0.1

You can find these parameters under the entry Longitudinal in the left column of the PAC2002 Tire Fit Tool as well. Please note that both pure and combined slip parameters are shown. The order of the parameters logged in the log file is the same as in the Longitudinal entry of the PAC2002 Tire Fit Tool. This is also applicable for other tire characteristics.


Force/Moment characteristics are by default created using the embedded plotter and can be exported to Adams/Postprocessor by selecting Plot -> Adams/PPT under Plot Parameters.

Select Settings -> Plot Units… to change the default plot units (SI).

1. Select Measurement Data = Yes under Plot Parameters, see Figure 10.

This means that measurement data (as added to the tire for the tire parameter identification process) is plotted against PAC2002 model data. Longitudinal (kappa), lateral (alpha) slip data, inclination angle (camber) and vertical tire load (Fz) extracted from the measurement data files will be used as input to the PAC2002 tire model and the resulting forces/moment will be plotted against measured forces/moment.

2. Select Slip Condition = Pure under Plot Parameters, see Figure 9.

Set Slip Condition to Pure to plot pure slip tire characteristics (that is, only braking/traction or only cornering) or set Slip Condition to Combined to plot combined slip tire characteristics (that is, cornering while braking/driving).

3. Select X-axis = Longitudinal Slip and select Y-axis = Fx to plot the longitudinal slip-force characteristic versus measurement data for pure slip conditions.

4. Click on Tire Plot in the Main GUI (see red arrow in Figure 9) or select Run - > Tire Plot from the menu bar to plot the PAC2002 tire model results versus measurement data. Plots are by default created using the embedded plotter.

Click on Clear Tire Plot(s) or select Run -> Clear Tire Plot(s) to remove the plots from the embedded plot window.

Figure 11 shows the resulting longitudinal slip-force characteristic versus measurement data for pure slip conditions using Adams/Postprocessor.


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Figure 10 PAC2002 TDFT; Plotting Results


Figure 11 Longitudinal slip-force characteristic versus measurement data for pure slip conditions using Adams/Postprocessor

5. Table 1 provides more information about selections for Slip Condition, X-axis and Y-axis for plotting of the tire model results versus measurement data for pure and combined slip conditions.

Table 1 Input selection for plotting of tire model results versus measurement data.

6. To generate a tire property file, select Save Tire property file (see red arrow in Figure 11) or select File -> Save Tire Property File from the menu bar.

Note: Only the X-axis, Y-axis and Slip Condition need to be selected if Measurement Data is set to Yes. The other options do not have any effect as input data is taken from the measurement data files.

Fx_pure Fy_pure Mz_pure Fx_combined Fy_combined Mz_combined

Slip Condition

Pure Pure Pure Combined Combined Combined

X-axis Long. Slip Lat. Slip Angle Lat. Slip Angle Long. Slip Long. Slip Long. Slip

Y-axis Fx Fy Mz Fx Fy Mz


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Figure 12 PAC2002 TDFT: Save Tire Property File

7. To save the database, that is, calculated tire parameters for a tire, loaded tires and references to measurement data files, select Save Tire Database (see red arrow in Figure 13) or select File -> Save Tire Database from the menu bar. Tire Database files can be loaded by clicking on Open Tire Database which is located next to the Save Tire Database button.


Figure 13 PAC2002 TDFT; Save/Open Tire Database

4. Plotting tire characteristics:

This Section explains how to plot tire characteristics by means of an example (longitudinal slip-force characteristic) by evaluating the PAC2002 tire model for a given set of input data.

1. Open Tire Property File <adams_install>/acar/shared_car_database.cdb/tires.tbl/pac2002_205_55R16_tdft in the PAC2002 Tire Data and Fitting Tool and select the tire by clicking on the first column (1).


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Figure 14 PAC2002 TDFT; Plot Parameters

2. Set Measurement Data = No under the Plot Parameters, see Figure 15. This means that measurement data (added in Tire Fit) is not used for plotting but only input data entered in the Plot Parameters is used to evaluate the PAC2002 tire model.

3. Set Slip Condition = pure to plot pure slip tire characteristics (that is, braking/traction without cornering and vice versa).

To plot tire characteristics for combined slip conditions, set Slip Condition = combined (that is, cornering while braking/driving).


4. Set X-axis = Longitudinal Slip and set Y-axis = Fx for plotting the longitudinal slip along the X-axis and longitudinal force along the Y-axis.

5. Set Sweep = Longitudinal Slip. The Sweep variable is varied along each curve.

Input data for Longitudinal Slip can be entered in the Longitudinal Slip input field. Enter -1:0.01:1 to specify a range of values from -1 to 1 using a 0.01 step size.

Other possible input data formats:

0.0 - single values

1,2,3 - values separated by a comma

6. Set Independent = Vertical Load. The independent variable is constant for each curve. Input data as shown in Figure 15 will produce 3 curves, one for each vertical load (2000, 4000 and 6000 N.). Input data for the Vertical Load can be entered in the Vertical Load input field, see Figure 13. Enter: 2000, 4000, 6000.

7. Data for remaining fields must also be entered as this is input to the PAC2002 tire model.

Set Lateral Slip Angle = 0.0.

Set Inclination Angle = 0.0.

For a pure longitudinal slip-force characteristic, the lateral slip will not be used and vice versa. However, it is recommend to use a single value (for instance 0) for the fields that are not used in order not to evaluate unnecessary data points and not to increase calculation time.

8. Click on Tire Plot or select Run -> Tire Plot from the menu bar. You can either use the embedded plotter or Adams/Postprocessor. Figure 15 shows the longitudinal slip-force tire characteristic for pure slip conditions using Adams/Postprocessor.

Figure 15 Pure slip condition: longitudinal slip (kappa) versus longitudinal force (Fx).


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More examples of typical tire characteristics are shown below:

Measurement Data: NoSlip Condition: PureX-axis: Lateral Slip AngleY-axis: FySweep: Lateral Slip AngleIndependent: Vertical Load

Vertical Load: 2000, 4000, 6000Longitudinal Slip: 0.0Lateral Slip Angle: -0.2:0.002:0.2Inclination Angle: 0.0

Figure 16 slip condition: lateral slip (alpha) versus lateral force (Fy).

Measurement Data: NoSlip Condition: PureX-axis: Lateral Slip AngleY-axis: Mz


Sweep: Lateral Slip AngleIndependent: Vertical Load

Vertical Load: 2000, 4000, 6000Longitudinal Slip: 0.0Lateral Slip Angle: -0.2:0.002:0.2Inclination Angle: 0.0

Figure 17 Pure slip condition: lateral slip (alpha) versus self-aligning torque (Mz).

Measurement Data: NoSlip Condition: CombinedX-axis: FxY-axis: FySweep: Longitudinal SlipIndependent: Lateral Slip Angle


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Vertical Load: 2000, 4000, 6000Longitudinal Slip: -1.0:0.01:1.0Lateral Slip Angle: -0.2:0.002:0.2Inclination Angle: 0.0

Figure 18 Combined slip condition: Longitudinal force versus lateral force.

Tire Test Data

High quality of tire test data is the basis of the tire parameter identification. To ensure good tire model results, tire testing should be performed under realistic tire operating conditions.

An example of a PAC2002 conventional Force and Moment test program is given in following table:

Slip condition Vertical load [N]

Slip angle [deg]

Inclination angle [deg]

Long. Slip [-]

Pure lateral slip Fz1, Fz2, Fz3 -12 - +12 -5, 0, 5 deg Free rolling


More information about the tire test data required to calculate PAC2002 tire parameters can be found in Knowledge Base article 1-KB12543.

Pure longitudinal Slip Fz1, Fz2, Fz3 0 0 - 100% - 0 - 100%

Combined slip Fz1, Fz2, Fz3 -1, 1, 3, 5, 8 -5, 0, 5 deg - 100% - 0 - 100%

Slip condition Vertical load [N]

Slip angle [deg]

Inclination angle [deg]

Long. Slip [-]


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