Lotus 23B Mod

This is the tbc file for the BMW Sauber F1 2006. TBC files are text files and may be viewed and edited in any decent text editor or even Notepad.

I have added comments about new or uprated statement lines which have been found in tbc files released since the '06 BMW F1, and they are placed where they appear in the files concerned.

The original is shown in regular text. My comments are in bold.

Top of File
// Tire brand found in *.hdv files refer to file name.
"//" symbols are used to delimit comments in the original file and in other physics files. All characters after // and before the next Carriage Return are ignored by the game

// Slip curves do not represent the coefficient of grip. Instead they represent
// the reaction to the current slip. Regardless of the peak value in this curve,
// it will be automatically normalized to have a peak of 1.0.

// The peak of the slip curve is dynamically adjusted to higher or lower slip
// values based on current load and speed. The second value of "SpeedEffects"
// is an equivalency value for load and speed. To calculate the slip peak, we
// use the following input which is a combination of load and speed:
// <load/speed combination> = <load> + (<speed> * <equivalency>)
// Obviously a larger equivalency value will make speed a more dominant factor
// in the calculation of the peak. See the SpeedEffects, LatPeak, and
// LongPeak tire parameters for more info.

// Slip curve data points are connected using a cubic spline, so there is no
// need to use a massive amount of data points unless the curve is really busy.

// Lateral slip angles are normalized so that you need to take the sine of the
// angle to get the slip. For example, 12 degrees is a slip of 0.208 and vice
// versa. Longitudinal slip ratios closely match the SAE definition.

// All curves should probably go out to at least a slip of 2.0, even the lateral
// and braking curves. Although locking up your brakes is a slip of 1.0, there
// are situations where you can spin your wheels in the opposite direction of
// your velocity (like shifting into reverse while moving forwards).

// Note that the initial slope of the curve may have an effect on how some
// features behave, such as traction control, ABS, skids, and tire smoke.

// The "DropoffFunction" is a new feature (new in rF) in the [SLIPCURVE] section. It
// describes how the slip curve dropoff is affected when the peak of the
// slip curve changes. The peak of the slip curve may move to a smaller
// or larger slip when load or speed changes. When this happens, the
// slip curve is stretched or shrunk to match. The DropoffFunction parameter
// allows you to affect the behavior beyond the peak when this happens:
// -1.0 = dropoff occurs faster when peak increases
// 0.0 = dropoff curve does NOT change shape when the peak changes
// 1.0 = dropoff curve is stretched or shrunk with the rest of the curve,
// which means the dropoff may feel more gradual as the peak increases.
// This is the default.

[SLIPCURVE]
Name="LatSlip"
Note that the name of the curve is enclosed in double-quotes/inverted commas/rabbit's ears, and the same applies further down where the curve is called for use.

Step=0.009000 // Slip step
DropoffFunction=-0.10 // See explanation above
Data:
0.000000 0.174836 0.349483 0.518060 0.668882 0.790665 0.878928 0.936783 0.971287 0.989751
0.997978 1.000000 0.999632 0.998538 0.996690 0.994069 0.990622 0.986566 0.982162 0.977223
0.972191 0.967169 0.962158 0.957368 0.952395 0.947268 0.942100 0.937138 0.932347 0.927646
0.923216 0.918857 0.914620 0.909990 0.905347 0.900211 0.894754 0.888562 0.881919 0.874943
0.867751 0.860449 0.853111 0.845815 0.838611 0.831522 0.824611 0.817849 0.811257 0.804850
0.798539 0.792387 0.786377 0.780673 0.775277 0.770211 0.765415 0.760879 0.756604 0.752550
0.748670 0.744944 0.741404 0.737984 0.734717 0.731545 0.728464 0.725526 0.722667 0.719902
0.717246 0.714664 0.712174 0.709790 0.707439 0.705187 0.703003 0.700892 0.698841 0.696828
0.694901 0.693027 0.691223 0.689478 0.687770 0.686107 0.684496 0.682947 0.681417 0.679925
0.678489 0.677069 0.675672 0.674308 0.672985 0.671663 0.670389 0.669153 0.667905 0.666712
0.665554 0.664420 0.663300 0.662203 0.661157 0.660122 0.659088 0.658104 0.657138 0.656191
0.655272 0.654370 0.653475 0.652626 0.651793 0.650965 0.650161 0.649373 0.648597 0.647836
0.647068 0.646312 0.645579 0.644848 0.644128 0.643430 0.642753 0.642067 0.641411 0.640745
0.640110 0.639464 0.638837 0.638220 0.637611 0.637022 0.636430 0.635857 0.635295 0.634733
0.634179 0.633635 0.633100 0.632573 0.632055 0.631545 0.631044 0.630550 0.630065 0.629587
0.629116 0.628654 0.628198 0.627749 0.627307 0.626873 0.626445 0.626023 0.625608 0.625199
0.624797 0.624401 0.624011 0.623626 0.623248 0.622876 0.622509 0.622147 0.621792 0.621441
0.621096 0.620756 0.620422 0.620092 0.619768 0.619448 0.619133 0.618823 0.618518 0.618218
0.617922 0.617631 0.617344 0.617061 0.616783 0.616511 0.616241 0.615976 0.615716 0.615459
0.615206 0.614958 0.614714 0.614474 0.614237 0.614005 0.613776 0.613552 0.613330 0.613114
0.612900 0.612690 0.612484 0.612282 0.612082 0.611887 0.611695 0.611507 0.611322 0.611141
0.610963 0.610788 0.610617 0.610449 0.610281 0.610118 0.609957 0.609799 0.609647 0.609496
0.609346 0.609199 0.609051 0.608909 0.608766 0.608626 0.608491 0.608363 0.608238 0.608115
0.608000 0.607887 0.607788 0.607697 0.607612 0.607534 0.607500

The strings of numbers above is a sequence of values that go to make a column in a table. In the tbc file they are arranged in 23 lines of 10 values, plus another seven values. The Slip Step is used to increment the value that each number is when matched up with in the table so you get something like this -

The first column is the step number. The second is the step value and the third is the slip value. There will be further posts in this thread which discusses slip curves in more detail.

-----1----------0--------------0.000000
-----2----------0.009----------0.174836
-----3----------0.018----------0.349483
-----4----------0.027----------0.518060
-----5----------0.036----------0.668882
-----6----------0.045----------0.790665
-----7----------0.054----------0.878928
-----8----------0.063----------0.936783
-----9----------0.072----------0.971287
----10----------0.081----------0.989751

and so on going down to 237 values. Plot that with the slip value on the Y axis and you get a chart like those in post #9 and following.

rF can handle multiple examples of these tables of slip values and this example file has three, each one having a separate name. They are called by the LatCurve, BrakingCurve and TractiveCurve statements in each of the compound types below.

These tables describe the type of behaviour of the tire as the the forces build up to and beyond the breakaway point where gripping gives way to sliding. Since forces and the response of the tire to them may not be equal in all directions, it could be quite useful to employ three curves.

[SLIPCURVE]
Name="AccelSlip"
Step=0.009000 // Slip step
DropoffFunction=0.8 // See explanation above
Data:

Table removed for clarity

[SLIPCURVE]
Name="DecelSlip"
Step=0.009000 // Slip step
DropoffFunction=0.0 // See explanation above
Data:

Table removed for clarity

// Note that the dry and wet performance numbers are NOT relative.
// They will still be scaled by the terrain dry/wet values in terrain.tdf.
// For example, if normal pavement has the scaling parameters dry=1.0 and wet=0.8,
// and a rain tire has scaling parameters of dry=1.30 and wet=1.35,
// then the overall grip in the dry will be (1.0 * 1.30) = 1.30,
// while the overall grip in the wet will be (0.8 * 1.35) = 1.08.

// FYI - we may add "Compound" to each name in order to translate it,
// because these names are not necessarily unique to tire compounds.

[COMPOUND]

At the time of writing rF did not support wet weather, so there is no requirement for wet compounds with defined names. Compound names in rF are free. The only requirement I know of is that they are unique within the file. Compounds are called from the hdv by number, with the first compound in the file being zero.

Name="Super Soft"
Note that the name of the compound is enclosed in double-quotes/inverted commas/rabbit's ears. Compounds are called from the hdv by number starting from 0 (zero). The name is displayed in the garage without the quotes. Names without quotes still work.

FRONT: // Arguments: ALL, FRONT, REAR, LEFT, RIGHT, FRONTLEFT, FRONTRIGHT, REARLEFT, REARRIGHT
Defines to which tyre position(s) the following parameters apply. All possible combinations are available.

DryLatLong=(2.2687702619, 2.3799400047) // Lateral/longitudinal coefficients in dry weather
Maximum Coefficients of Friction (CoF) for this compound on dry pavement in the lateral and longitudinal directions. Note that in simple terms, grip is coeficient times vertical load on the tyre.

Formula tires supplied by ISI have tires have about 5% more longitudinal than lateral grip while the longitudinal grip coefficient of other car types are about the same as their lateral grip coefficient.

rF does not use width to recalculate grip or apportion it between front and rear. Any actual differences in static no-load grip between front and back tyres are input directly as Dry or Wet Lat values in each compound. Please note that the LoadSens parameter further down defines the change in grip with load on the tyres and can play a part in managing actual grip levels.

WetLatLong=(0.920, 0.932) // Lateral/longitudinal coefficients in wet weather
I guess this is a placemaker since there is no current support for wet tracks.

Radius=0.327 // Radius of tire
Outside rolling radius, stationary. Feeds into the distance the car travels per 1000 rpm, so contributes to overall gearing and hence possibly top speed. Also defines the size of the tire on the car as seen on-screen. If the car floats in the air or has part of the tyres underground then there is a mismatch between the size of the tyres in this file and the size defined in the graphics.

RadiusRPM=1.722e-6 // Increased radius per unit RPM
How fast the radius grows with rotational speed of the wheel.

Width=0.340 // Width of tire
Used as input to the width of skid marks. No effect on grip.

Rim=(0.166, 750000.0, 7500.0, 3.0) // Rim radius, spring rate, damper rate, minimum velocity to produce sparks
Defines the wheel rim size and the physical characteristics as a sprung damped body. Presumably used to model what happens when a tire comes off a wheel - say after a blowout or other catastrophic failure. Velocity is in m/s.

This line is not compulsory and appears in only some of the ISI tire files.

SpringBase=50460.0 // Base spring rate with no pressure
SpringkPa=1200.00 // Spring rate per unit pressure
Defines how springy the tire is and relates to elasticity and deformation of the tyre under load. Analogous to load bearing capacity as it relates to tire heating. Does not affect grip. First parameter is the springyness of the carcass of the tire at zero inflation and the second is the springyness of the air inside which increases with inflation. The total value is the sum of the two.

The total of (SpringBase plus SpringKpa * tire pressure) may be several times larger than the base. For a typical F1 front tire, the inflation contribution is 160,000 while the base is 50,500, which is about 3.1:1.

This springiness is a measure of the tire's load-bearing capacity and is expressed in N/m. It also has an effect on the calculations about generation of heat, as a tire with low springyness for the load on it will compress and flex more and so get hotter at the same settings for heating and dissipation.

Low springyness will also reduce the rolling rotation of the tyre due to compression, affecting the overall gearing - the tyre runs a bit flat.

The ratio of SpringBase to SpringkPa affects the way in which the tire responds to changes in pressure. Please also see AirTreadRate.

This tyre is compressed by about 5.6mm by the weight of the car.

Damper=521.4 // Damping rate of tire
It was during the 60's that people discovered that tires with high hysteresis had more grip than tires with low hysteresis, particularly in the wet. Hysteresis is the amount of internal absorption of energy when a tire is flexed. So I presume that high values of damper translate into increased rolling resistance and to build up of heat. Todays road tire technology permits high hysteresis with low rolling resistance.

SpeedEffects=(267.5, 18.5) // Speed at which grip drops to half (m/s, 0.0 to disable), speed load equivalency (see above)
Described in the preamble at the beginning of the file. Permits management of the relative importance of load and speed on grip

The first parameter effects grip as follows. If the speed across the ground is equal to the first parameter, then the grip is halved compared with grip at zero speed. At 2:1, grip is reduced to 1/3rd, at 3:1, it is reduced to 1/4, and so on. At slower speeds, the grip is reduced to 3/4 at a speed of 1/3rd of the first parameter. Obviously, as speed increases, grip eventually approaches zero..

LoadSensLat=( -3.88e-6, 0.365, 23350) // Load sensitivity for lateral grip (initial slope, final grip multiplier, final load)
LoadSensLong=(-3.86e-6, 0.435, 23350) // Load sensitivity for longitudinal grip (initial slope, final grip multiplier, final load)
Defines the effect of vertical load on tyre grip.

rF permits differing LoadSens values to be applied to lateral and to longitudinal forces. A simpler version is supported as an alternative, in which case there is a single line like -

LoadSens=( -3.88e-6, 0.365, 23350) // Load sensitivity for lateral grip (initial slope, final grip multiplier, final load)

Load sensitivity is a multiplying factor from 0.0 to 1.0 to be applied to the grip defined in DryLatLong and the like. At zero load, the multiplier is assumed to be 1.0. The initial slope, final grip multiplier and final load then provide a total of 4 pieces of information, for which you can solve for the unknowns in the following cubic equation:

Grip multiplier = a*t^3 + b*t^2 + c*t + d

where t = current load as a fraction of final load, or (current load / final load).

Any load greater than the "final load" returns a grip multiplier of "final grip".

In that equation, d is 1.0 and c is the initial slope, so you really only need to solve for a and b.

The form of that equation used by ISI is

mult = ((2 + LSFL*LSIS - 2*LSFM) / LSFL^3)* Fz^3 + ((3 * LSFM - 3 - 2 * LSFL * LSIS) / LSFL^2) * Fz^2 + LSIS*Fz + 1

where:
LSIS = LoadSensInitialSlope - first parameter
LSFM = LoadSensFinalMultiplier - second parameter
LSFL = LoadSensFinalLoad - third parameter
Fz = NormalLoad on the tyre - in Newtons

Thanks to Kangaloosh and ISI for the above explanations - better than me guessing at it.

In general, larger tyres and tyres for heavier cars would have smaller Initial Slopes so the grip falls off more slowly, and higher Final Loads so there is more headroom. Typical Final Load values are around 10 times the static load on the tyre or more.

Tyre designers have the option of using LoadSens to manage the difference in grip found for tyres of different sizes - notionally, larger tyres have slower fall-off with load than smaller tyres and this results in higher grip for the wider tyre at the same load, or the same grip at a higher load. Alternately the extra grip can be factored into DryLatLong, or one can have a bit each way.

In rF, inappropriate LoadSens values may cause the car to feel like it is driving on ice. This can happen, for instance, when a tyre for a light car is applied to a heavy car. In general terms, if you wish to duplicate behaviour, the 1st parameter decreases with increases in the mass of the car while the 3rd parameter increases as the mass of the car goes up.


LatPeak=( 0.0817, 0.233, 13825.0) // Slip range where lateral peak force occurs depending on load
LongPeak=(0.0937, 0.247, 13850.0) // Slip range where longitudinal peak force occurs depending on load
Defines the effect of load on the peak slip range.

LatPeak defines a curve where the load on the tire is along the x-axis and the y-axis is the sine of the slip angle where peak forces occur.

The slip curve data at the top of the file gives the shape of the slip curve. The LatPeak and LongPeak parameters shrink and stretches those curves along the horizontal axis according to the load on the tire.

LatPeak and LongPeak define where the peak of the curve should be in terms of slip angle/ratio. What we use as slip "angle" is really a lateral slip ratio. Take the sin(slip-angle) to find the lateral slip ratio. Between a load of zero and the load specified as the third parameter, the peak ratio follows half of a sine wave smoothly between the two values (starts level and ends level). Beyond the specified max load, the peak stays constant at the second ratio.

At zero load, the sine of this slip angle is 0.0817, so the slip angle at which maximum lateral force is generated is 4.7 deg. At a load on the tire of 13825 N, from the third value, the sine of the slip angle is then the second value, or 0.233, so the angle is 13.5 deg.

13825 N is 9-10 g so that is probably outside the active range for a car, even with with downforce, except for very vigorous changing states of motion such as impacts.

The first value dictates how sharp and grippy the tire feels, or in tire technology terms, the "stiffness". Low values mean a tire which responds rapidly to applied side forces, as you might expect from a racing tire. Higher values up to 0.15 and maybe higher mean a tire which feels like it was built for comfort, not handling, or possibly a cross-ply tyre. It will be looser, less precise and less demanding.

LatCurve="LatSlip" // Slip angle curve (data uses normalized angle)
BrakingCurve="DecelSlip" // Slip ratio curve under braking
TractiveCurve="AccelSlip" // Slip ratio curve under acceleration
Define the slip curve table names used for each axis. Note that as standard practise the name of the curve is enclosed in double-quotes/inverted commas/rabbit's ears as it was when named, although it will still work without the quotes. CarFactory (v1.82) analysis does not read the slip curve names unless they are in quotes.

CamberLatLong=(2.70, 0.125, 0.560) // Peak camber angle, lateral gain at peak, longitudinal loss at 90 degrees
Defines what happens when camber is set in the hdv. The first value is the upper limit for camber (in degrees) that gives a change in CoF. The second value is the fraction of additional lateral grip gained at that camber value. It follows one quarter of a sine wave up to the peak angle (starts with a slope, ends level), then it is just a linear drop-off after that. The 3rd value is the loss of longitudinal grip because a cambered wheel is not flat on the road, also at the max camber value. The loss of longitudinal grip is linear with camber angle. These are relatively weak representations of what truly happens with camber.

Note that negative camber increases grip in the direction towards the centreline of the car.

Camber will affect total heat generated and temperature distribution across a tire. Negative camber will increase relative grip at that end of the car at the expense of both local heating and added wear at the inside edge of the tire.

The first parameter is a matter for the designer of the tire - at some point the tire stops responding to camber changes. The second and third parameters should relate to the design and purpose of the tyre.

RollingResistance=3172.0 // Resistance torque (Nm) per unit deflection (m) on ground
The amount of effort to roll the tire along the road. Part of the acceleration and top speed equations. Feeds into heat build-up equation, as do the Heating and Transfer parameters, as well as contributing to the mechanical drag of the car.

Also related to relative width front and back.

PneumaticTrail=6.00e-7 // Pneumatic trail per unit load (m/N), adjusted based on slip
Pneumatic trail is the distance by which the cornering force of the tire trails the sideways force at the axle. This distance produces a moment or torque, which is the cornering force multiplied by that distance. The moment provides the self-aligning torque which loads up the steering when cornering and tends to realign the road wheel with the direction of straight travel. Presumably the "load" above is the vertical force on the tyre and depends on mass and downforce.

In reality Pneumatic Trail is responsible for generating one of the self-aligning torques which cause the steering to feel like it loads up as cornering rate increase - others are from caster and mechanical trail. Self-aligning torque from pneumatic trail rises to a maximum at about half the maximum slip angle, and then falls away. My observation is the the tyres for the standard ISI cars do not exploit pneumatic trail to the full extent that they could, to the detriment of handling and feel and the way they work with RealFeel.

The pneumatic trail calculation is based on an estimate of what fraction of the tire contact is actually sliding. This estimate is done by comparing the current point on the slip curve with an extension of the initial slip curve slope. For example if you drove a straight line from the origin along the initial slip curve slope, you might get a value of say, 3.0 near the peak slip angle. Since the grip multiplier at peak slip is 1.0, then the estimate is that 2/3 of the contact patch is sliding. Not perfectly realistic, but it could be made to be close with the right inputs.

Based on the numbers for this car, a 600kg F1 car with 3g of downforce would generate about 3.5mm of pneumatic trail. References suggest that this is too small by a factor of 10x or more, although the value may be particular to F1 tyres as they are quite specialised.

HeatBasePeak=(0.16, 0.05) // Base peak slip to compute friction heat, fraction of base to use (0.0=use dynamic peak slip only)
Permits a base friction heating load from Sliding to be defined at no slip.

This line is not compulsory and appears in only some of the ISI tire files.

Heating=( 4.9833e-1, 10.683e-3) // Heat caused by (rolling, friction)
The first Heating parameter creates heat linearly with rolling speed and vertical tire deflection. Rolling speed depends on tyre radius so if you change a tyre's diameter then the rolling heat will need to be changed as well to retain the same degree of heating. Tyre deflection depends on pressure, of course, so less pressure builds up more heat.

The second Heating parameter compares the current slip value to either the realtime peak slip (which changes with load using LatPeak and LongPeak), or a constant peak slip, or a combination of those two depending on the values in HeatBasePeak. Adjusting these is usually done through trial and error

Transfer=(7.30e-3, 4.00e-3, 1.40e-4) // Heat transfer to (road, static air, moving air)
Similarly.

HeatDistrib=(25.00, 163.0) // (Max camber angle, max off-pressure) that affects heat distribution (higher number -> less temperature difference)
Determines how much of the heat goes to the left, center, and right side of the tread based on how much current camber and pressure there is compared to the values given here.

The words suggest that higher values reduce the actual temperature difference that results from these conditions. The values in this file are quite large - about 5-8 times max camber and twice a typical pressure value.

AirTreadRate=0.011 // Heat transfer between tread and inside air
Trials suggest that this factor permits management of heat distribution across the tire. For a given tyre, any increase in weight supported causes the outside edges of the tyre to heat in preference to the middle. This can be addressed in part by increasing the pressure in the tyre. Alternatively, the tyre will heat more evenly if this parameter is increased in line with the increase in weight supported. Trial also suggest that wide tyres need higher values than relatively narrower tyres, for the same weight.

WearRate=9.720e-7 // Wear rate constant
WearGrip1=(0.989,0.981,0.9745,0.9715,0.969,0.967,0 .9 655,0.9645) // Grip at 6/13/19/25/31/38/44/50% wear (defaults to 0.980->0.844), grip is 1.0 at 0% wear
WearGrip2=(0.964,0.9638,0.963,0.961,0.9535,0.936,0 .8 50,0.775) // Grip at 56/63/69/75/81/88/94/100% wear (defaults to 0.824->0.688), tire bursts at 100% wear
Permits detailed mapping of the relationship between grip and wear over the life of the tire by modifying the internal defaults.

These lines are optional and the internal defaults will apply if they are omitted. At the time of writing they are found in the tire files for formula cars. A short one-line version using the label "WearGrip" is found in some but not all other ISI tire files.

Softness=0.66 // Softness is now just for AI strategic use
Not sure what the AI do that is strategic, although a lot of their tactics are rubbish...

AIGripMult=1.021 // Grip multiplier for AI vehicles (due to tire model simplification)
Enables control over difference between the player and AI cars for overall grip and F/R balance. Typically AI cars oversteer compared with player cars using the same physics, but less than they used to in F1C. F1 values are 1.021 front and 1.032 rear. Others may differ. Cars with little or no downforce or which respond more slowly than Formula cars and/or cars with predominant oversteer characteristics may need the value for the rear tires increased to enable the AI to stay on the track through S-bends.

AIPeakSlip=0.07 // Simple peak slip angle for AI vehicles
Analogous to the first value for LatPeak and used by the AI to define peak slip.

AITireModel=0.3 // 0.0 = original AI tire model in terms of slip, 1.0 = more similar to player tire model
This line is an overide for the AI Tire Model line in the plr file. The default line in that file is -
AI Tire Model="0.40000" // 0.0 = use AI peak slip, 1.0 = use player's dynamic slip, or a blend between the two (can be overrode in TBC with AITireModel)

The line is optional in the tbc and appears in only some of the ISI tire files. The tyre model defaults to the original behaviour in its absence.

AIWear=3.888e-7 // AI wear rate constant

Temperatures=(104.0, 75.0) // Optimum operating temperature for peak forces (Celsius), starting temperature
Defines the best operating tire temperature and the start temperature for the session.

OptimumPressure=(60.5, 0.0221) // Base pressure to remain flat on ground at zero deflection, and multiplier by load to stay flat on ground
First value defines the pressure for a properly formed tire with no load applied. The second value is the kpa/N of applied load required to maintain that shape. So a 1000kg car, with 50:50 weight distribution, would have 2452 N force on each tire. That requires 2452 x 0.0221 or 54 kpa to maintain the tire shape - so the loaded tire pressure would be 114.5 kpa. This compares with the value from the hdv of 132 kpa.

GripTempPress=(2.524, 1.323, 0.845) // Grip effects of being below temp, above temp, and off-pressure (higher number -> faster grip dropoff)
Some numeric (fudge?) factors which are used to change the grip when the tire is, respectively, too cold, too hot and off-pressure. The smaller the number, the less the effect.

//
REAR:
Same again at the back

Repeated for each compound
[COMPOUND]
Name="Soft"
...

more compounds


Currently there are no rules about compounds and weather, so number and names of compounds are a free choice.